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3.25: Signs of evolutionary history - Biology

3.25: Signs of evolutionary history - Biology



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Evolution is an ongoing experiment in which random mutations are selected based on the effects of the resulting phenotypes on reproductive success. In any case, evolution is not a designed process that reflects a predetermined goal but involves responses to current constraints and opportunities - it is a type of tinkering in which selective and non-selective processes interact with pre-existing organismic behaviors and structures and is constrained by cost and benefits associated with various traits and their effects on reproductive success106. It is possible that the costs of a particular "imperfect" evolutionary design are offset by other advantages. For example, the small but significant possibility of death by choking may, in an evolutionary sense, be worth the ability to make more complex sounds (speech) involved in social communication107.

As a general rule, evolutionary processes generate structures and behaviors that are as good as they need to be for an organism to effectively exploit a specific set of environmental resources and to compete effectively with its neighbors, that is, to successfully occupy its niche. If being better than good enough does not enhance reproductive success, it cannot be selected for (at least via natural selection) and variations in that direction will be lost, particularly if they come at the expense of other important processes or abilities. In this context it is worth noting that we are always dealing with an organism throughout its life cycle. Different traits can have different values at different developmental stages. Being cute can have important survival benefits for a baby but be less useful in a corporate board room (although perhaps that is debatable). A trait that improves survival during early embryonic development or enhances reproductive success as a young adult can be selected for even, if it produces negative effects on older individuals. Moreover, since the probability of being dead (and so no longer reproductively active) increases with age, selection for traits that benefit the old will inevitably be weaker than selection for traits that benefit the young, although this trend can be modified in organisms in which the presence of the old can increase the survival and reproductive success of the young, for example through teaching and babysitting. Of course survival and fertility curves can change in response to changing environmental factors, which alter selective pressures. In fact, lifespan itself is a selected trait, since it is the population not the individual that evolves108.

We see the evidence for various compromises involved in evolutionary processes all around us. It explains the limitations of our senses, as well as our tendency to get backaches, need hip-replacements, and our susceptibility to diseases and aging109. For example, the design of our eyes leaves a blind spot in the retina. Complex eyes have arisen a number of times during the history of life, apparently independently, and not all have such a blind spot. We have adapted to this retinal blind spot through the use of saccadic eye movements because this is an evolutionarily easier fix to the problem than rebuilding the eye from scratch (which is essentially impossible). An "intelligently designed" human eye would presumably not have such an obvious design flaw, but because of the evolutionary path that led to the vertebrate eye, it may simply have been impossible to back up and fix this flaw. More to the point, since the vertebrate eye works very well, there is no reward in terms in reproductive success associated with removing the blind spot. This is a general rule: current organisms work, at least in the environment that shaped their evolution. Over time, organisms that diverge from the current optimal, however imperfect, solution will be at a selective disadvantage. The current vertebrate eye is maintained by stabilizing selection (as previously described). The eyes of different vertebrates differ in their acuity (basically how fine a pattern of objects they can resolve at what distance) and sensitivity (what levels and wavelengths of light they can perceive). Each species has eyes (and their connections to the brain) adapted for its ecological niche. For example, an eagle see details at a distance four to five times are far as the typical human; why, because such visual acuity is useful in terms of the eagle’s life-style, whereas such visual details could well be just a distraction for humans110.


3.25: Signs of evolutionary history - Biology

Fossils or organisms that show the intermediate states between an ancestral form and that of its descendants are referred to as transitional forms. There are numerous examples of transitional forms in the fossil record, providing an abundance of evidence for change over time.

Pakicetus (below left), is described as an early ancestor to modern whales. Although pakicetids were land mammals, it is clear that they are related to whales and dolphins based on a number of specializations of the ear, relating to hearing. The skull shown here displays nostrils at the front of the skull.

A skull of the gray whale that roams the seas today (below right) has its nostrils placed at the top of its skull. It would appear from these two specimens that the position of the nostril has changed over time and thus we would expect to see intermediate forms.

But, the standard diagram does clearly show transitional stages whereby the four-toed foot of Hyracotherium, otherwise known as Eohippus, became the single-toed foot of Equus. Fossils show that the transitional forms predicted by evolution did indeed exist.


Contents

Due to natural selection, people who lived in areas of intense sunlight developed dark skin colouration to protect against ultraviolet (UV) light, mainly to protect their body from folate depletion. Evolutionary pigmentation of the skin was caused by ultraviolet radiation of the sun. As hominids gradually lost their fur between 1.2 and 4 million years ago, to allow for better cooling through sweating, their naked and lightly-pigmented skin was exposed to sunlight. In the tropics, natural selection favoured dark-skinned human populations as high levels of skin pigmentation protected against the harmful effects of sunlight. Indigenous populations' skin reflectance (the amount of sunlight the skin reflects) and the actual UV radiation in a particular geographic area is highly correlated, which supports this idea. Genetic evidence also supports this notion, demonstrating that around 1.2 million years ago there was a strong evolutionary pressure which acted on the development of dark skin pigmentation in early members of the genus Homo. [24] The effect of sunlight on folic acid levels has been crucial in the development of dark skin. [3] [25]

The earliest primate ancestors of modern humans most likely had light skin, like our closest modern relative—the chimpanzee. [26] About 7 million years ago human and chimpanzee lineages diverged, and between 4.5 and 2 million years ago early humans moved out of rainforests to the savannas of East Africa. [22] [27] They not only had to cope with more intense sunlight but had to develop a better cooling system. It was harder to get food in the hot savannas and as mammalian brains are prone to overheating—5 or 6 °C rise in temperature can lead to heatstroke—there was a need for the development of better heat regulation. The solution was sweating and loss of body hair. [22]

Sweating dissipated heat through evaporation. Early humans, like chimpanzees now, had few sweat glands, and most of them were located in the palms of the hand and the soles of the feet. At times, individuals with more sweat glands were born. These humans could search for food and hunt for longer periods before being forced back to the shades. The more they could forage, the more and healthier offspring they could produce, and the higher the chance they had to pass on their genes for abundant sweat glands. With less hair, sweat could evaporate more easily and cool the bodies of humans faster. A few million years of evolution later, early humans had sparse body hair and more than 2 million sweat glands in their body. [22] [28] [29]

Hairless skin, however, is particularly vulnerable to be damaged by ultraviolet light and this proved to be a problem for humans living in areas of intense UV radiation, and the evolutionary result was the development of dark-coloured skin as a protection. Scientists have long assumed that humans evolved melanin in order to absorb or scatter harmful sun radiation. Some researchers assumed that melanin protects against skin cancer. While high UV radiation can cause skin cancer, the development of cancer usually occurs after child-bearing age. As natural selection favours individuals with traits of reproductive success, skin cancer had little effect on the evolution of dark skin. Previous hypotheses suggested that sunburned nipples impeded breastfeeding, but a slight tan is enough to protect mothers against this issue. [22] [30] [31] [32]

A 1978 study examined the effect of sunlight on folate—a vitamin B complex—levels. [ citation needed ] The study found that even short periods of intense sunlight are able to halve folate levels if someone has light skin. Low folate levels are correlated with neural tube defects, such as anencephaly and spina bifida. UV rays can strip away folate, which is important to the development of healthy foetuses. In these abnormalities children are born with an incomplete brain or spinal cord. Nina Jablonski, a professor of anthropology and expert on evolution of human skin coloration, [33] found several cases in which mothers' visits to tanning studios were connected to neural tube defects in early pregnancy. She also found that folate was crucial to sperm development some male contraception drugs are based on folate inhibition. It has been found that folate may have been the driving force behind the evolution of dark skin. [3] [20]

As humans dispersed from equatorial Africa to low UVR areas and higher altitudes sometime between 120,000 and 65,000 years ago, dark skin posed a disadvantage. [34] [35] Populations with light skin pigmentation evolved in climates of little sunlight. Light skin pigmentation protects against vitamin D deficiency. It is known that dark-skinned people who have moved to climates of limited sunlight can develop vitamin D-related conditions such as rickets, and different forms of cancer. [3] [36]

Earlier hypotheses Edit

The main other hypotheses that have been put forward through history to explain the evolution of dark skin coloration relate to increased mortality due to skin cancers, enhanced fitness as a result of protection against sunburns, and increasing benefits due to antibacterial properties of eumelanin. [3]

Darkly pigmented, eumelanin-rich skin protects against DNA damage caused by the sunlight. [37] This is associated with lower skin cancer rates among dark-skinned populations. [38] [39] [40] [41] [42] The presence of pheomelanin in light skin increases the oxidative stress in melanocytes, and this combined with the limited ability of pheomelanin to absorb UVR contributes to higher skin cancer rates among light-skinned individuals. [43] The damaging effect of UVR on DNA structure and the entailing elevated skin cancer risk is widely recognized. [24] [44] [45] [46] [47] However, these cancer types usually affect people at the end or after their reproductive career and could have not been the evolutionary reason behind the development of dark skin pigmentation. [24] [31] Of all the major skin cancer types, only malignant melanoma have a major effect in a person's reproductive age. The mortality rates of melanoma has been very low (less than 5 per 100,000) before the mid-20th century. It has been argued that the low melanoma mortality rates during reproductive age cannot be the principal reason behind the development of dark skin pigmentation. [32]

Studies have found that even serious sunburns could not affect sweat gland function and thermoregulation. There are no data or studies that support that sunburn can cause damage so serious it can affect reproductive success. [3]

Another group of hypotheses contended that dark skin pigmentation developed as antibacterial protection against tropical infectious diseases and parasites. Although it is true that eumelanin has antibacterial properties, its importance is secondary to 'physical adsorption' (physisorption) to protect against UVR-induced damage. This hypothesis is not consistent with the evidence that most of the hominid evolution took place in savanna environments and not in tropical rainforests. [48] Humans living in hot and sunny environments have darker skin than humans who live in wet and cloudy environments. [35] The antimicrobial hypothesis also does not explain why some populations (like the Inuit or Tibetans) who live far from the tropics and are exposed to high UVR have darker skin pigmentation than their surrounding populations. [3]

Dark-skinned humans have high amounts of melanin found in their skin. Melanin is derivative of the amino acid tyrosine. Eumelanin is the dominant form of melanin found in human skin. Eumelanin protects tissues and DNA from the radiation damage of UV light. Melanin is produced in specialized cells called melanocytes, which are found at the lowest level of the epidermis. [49] Melanin is produced inside small membrane-bound packages called melanosomes. People with naturally-occurring dark skin have melanosomes which are clumped, large and full of eumelanin. [50] [51] A four-fold difference in naturally-occurring dark skin gives seven- to eight-fold protection against DNA damage, [51] but even the darkest skin colour cannot protect against all damage to DNA. [3]

Dark skin offers great protection against UVR because of its eumelanin content, the UVR-absorbing capabilities of large melanosomes, and because eumelanin can be mobilized faster and brought to the surface of the skin from the depths of the epidermis. [3] For the same body region, light- and dark-skinned individuals have similar numbers of melanocytes (there is considerable variation between different body regions), but pigment-containing organelles, called melanosomes, are larger and more numerous in dark-skinned individuals. Keratocytes from dark skin cocultured with melanocytes give rise to a melanosome distribution pattern characteristic of dark skin. [52] [53] Melanosomes are not in aggregated state in darkly pigmented skin compared to lightly pigmented skin. Due to the heavily melanised melanosomes in darkly-pigmented skin, it can absorb more energy from UVR and thus offers better protection against sunburns and by absorption and dispersion UV rays. [24]

Darkly-pigmented skin protects against direct and indirect DNA damage. Photodegration occurs when melanin absorbs photons. Recent research suggest that the photoprotective effect of dark skin is increased by the fact that melanin can capture free radicals, such as hydrogen peroxide, which are created by the interaction of UVR and layers of the skin. [24] Heavily pigmented melanocytes have greater capacity to divide after ultraviolet irradiation, which suggests that they receive less damage to their DNA. [24] Despite this, medium-wave ultraviolet radiation (UVB) damages the immune system even in darker skinned individuals due to its effect on Langerhans cells. [24] The stratum corneum of people with dark or heavily tanned skin is more condensed and contains more cornified cell layers than in lightly-pigmented humans. These qualities of dark skin enhance the barrier protection function of the skin. [24]

Although darkly-pigmented skin absorbs about 30 to 40% more sunlight than lightly-pigmented skin, dark skin does not increase the body's internal heat intake in conditions of intense solar radiation. Solar radiation heats up the body's surface and not the interior. Furthermore, this amount of heat is negligible compared to the heat produced when muscles are actively used during exercise. Regardless of skin colour, humans have excellent capabilities to dissipate heat through sweating. [35] Half of the solar radiation reaching the Earth's surface is in the form of infrared light and is absorbed similarly regardless of skin coloration. [24]

In people with naturally occurring dark skin, the tanning occurs with the dramatic mobilization of melanin upward in the epidermis and continues with the increased production of melanin. This accounts for the fact that dark-skinned people get visibly darker after one or two weeks of sun exposure, and then lose their colour after months when they stay out of the sun. Darkly-pigmented people tend to exhibit fewer signs of aging in their skin than the lightly-pigmented because their dark skin protects them from most photoaging. [35]

Skin colour is a polygenic trait, which means that several different genes are involved in determining a specific phenotype. Many genes work together in complex, additive, and non-additive combinations to determine the skin colour of an individual. The skin colour variations are normally distributed from light to dark, as it is usual for polygenic traits. [54] [55]

Data collected from studies on MC1R gene has shown that there is a lack of diversity in dark-skinned African samples in the allele of the gene compared to non-African populations. This is remarkable given that the number of polymorphisms for almost all genes in the human gene pool is greater in African samples than in any other geographic region. So, while the MC1Rf gene does not significantly contribute to variation in skin colour around the world, the allele found in high levels in African populations probably protects against UV radiation and was probably important in the evolution of dark skin. [56] [57]

Skin colour seems to vary mostly due to variations in a number of genes of large effect as well as several other genes of small effect (TYR, TYRP1, OCA2, SLC45A2, SLC24A5, MC1R, KITLG and SLC24A4). This does not take into account the effects of epistasis, which would probably increase the number of related genes. [58] Variations in the SLC24A5 gene account for 20–25% of the variation between dark- and light-skinned populations of Africa, [59] and appear to have arisen as recently as within the last 10,000 years. [60] The Ala111Thr or rs1426654 polymorphism in the coding region of the SLC24A5 gene reaches fixation in Europe, and is also common among populations in North Africa, the Horn of Africa, West Asia, Central Asia and South Asia. [61] [62] [63]

Skin pigmentation is an evolutionary adaptation to various UVR levels around the world. As a consequence there are many health implications that are the product of population movements of humans of certain skin pigmentation to new environments with different levels of UVR. [3] Modern humans are often ignorant of their evolutionary history at their peril. [3] Cultural practices that increase problems of conditions among dark-skinned populations are traditional clothing and vitamin D-poor diet. [64]

Advantages in high sunlight Edit

Dark-pigmented people living in high sunlight environments are at an advantage due to the high amounts of melanin produced in their skin. The dark pigmentation protects from DNA damage and absorbs the right amounts of UV radiation needed by the body, as well as protects against folate depletion. Folate is a water-soluble vitamin B complex which naturally occurs in green, leafy vegetables, whole grains, and citrus fruits. Women need folate to maintain healthy eggs, for proper implantation of eggs, and for the normal development of placenta after fertilization. Folate is needed for normal sperm production in men. Furthermore, folate is essential for fetal growth, organ development, and neural tube development. Folate breaks down in high intensity UVR. [35] Dark-skinned women suffer the lowest level of neural tube defects. [35] [65] Folate plays an important role in DNA production and gene expression. It is essential for maintaining proper levels of amino acids which make up proteins. Folate is used in the formation of myelin, the sheath that covers nerve cells and makes it possible to send electrical signals quickly. Folate also plays an important role in the development of many neurotransmitters, e.g. serotonin which regulates appetite, sleep, and mood. Serum folate is broken down by UV radiation or alcohol consumption. [35] Because the skin is protected by the melanin, dark-pigmented people have a lower chance of developing skin cancer and conditions related to folate deficiency, such as neural tube defects. [3]

Disadvantages in low sunlight Edit

Dark-skinned people living in low sunlight environments have been recorded to be very susceptible to vitamin D deficiency due to reduced vitamin D synthesis. A dark-skinned person requires about six times as much UVB than lightly-pigmented persons. This is not a problem near the equator however, it can be a problem at higher latitudes. [35] For humans with dark skin in climates of low UVR, it can take about two hours to produce the same amount of vitamin D as humans with light skin produce in 15 minutes. Dark-skinned people having a high body-mass index and not taking vitamin D supplements were associated with vitamin D deficiency. [66] [67] Vitamin D plays an important role in regulating the human immune system and chronic deficiencies in vitamin D can make humans susceptible to specific types of cancers and many kinds of infectious diseases. [35] [68] [69] Vitamin D deficiency increases the risk of developing tuberculosis five-fold and also contributes to the development of breast, prostate, and colorectal cancer. [70]

The most prevalent disease to follow vitamin D deficiency is rickets, the softening of bones in children potentially leading to fractures and deformity. Rickets is caused by reduced vitamin D synthesis that causes an absence of vitamin D, which then causes the dietary calcium to not be properly absorbed. This disease in the past was commonly found among dark-skinned Americans of the southern part of the United States who migrated north into low sunlight environments. The popularity of sugary drinks and decreased time spent outside have contributed to significant rise of developing rickets. Deformities of the female pelvis related to severe rickets impair normal childbirth, which leads to higher mortality of the infant, mother, or both.

Vitamin D deficiency is most common in regions with low sunlight, especially in the winter. [71] Chronic deficiencies in vitamin D may also be linked with breast, prostate, colon, ovarian, and possibly other types of cancers. [22] [72] [73] [74] The relationship between cardiovascular disease and vitamin D deficiency also suggest a link between health of cardiac and smooth muscle. [75] [76] Low vitamin D levels have also been linked to impaired immune system and brain functions. [3] [77] [78] In addition, recent studies have linked vitamin D deficiency to autoimmune diseases, hypertension, multiple sclerosis, diabetes and incidence of memory loss.

Outside the tropics UVR has to penetrate through a thicker layer of atmosphere, which results in most of the intermediate wavelength UVB reflected or destroyed en route because of this there is less potential for vitamin D biosynthesis in regions far from the equator. Higher amount of vitamin D intake for dark-skinned people living in regions with low levels of sunlight are advised by doctors to follow a vitamin D-rich diet or take vitamin D supplements, [22] [79] [80] [81] [82] [83] although there is recent evidence that dark-skinned individuals are able to process vitamin D more efficiently than lighter-skinned individuals so may have a lower threshold of sufficiency. [19]

There is a correlation between the geographic distribution of UV radiation (UVR) and the distribution of skin pigmentation around the world. Areas that have higher amounts of UVR have darker-skinned populations, generally located nearer the equator. Areas that are further away from the equator and generally closer to the poles have a lower concentration of UVR and contain lighter-skinned populations. This is the result of human evolution which contributed to variable melanin content in the skin to adapt to certain environments. A larger percentage of dark-skinned people are found in the Southern Hemisphere because latitudinal land mass distribution is disproportionate. [24] The present distribution of skin colour variation does not completely reflect the correlation of intense UVR and dark skin pigmentation due to mass migration and movement of peoples across continents in the recent past. [24] Dark-skinned populations inhabiting Africa, Australia, Melanesia, Papua New Guinea and South Asia all live in some of the areas with the highest UV radiation in the world, and have evolved very dark skin pigmentations as protection from the sun's harmful rays. [22] [24] Evolution has restricted humans with darker skin in tropical latitudes, especially in non-forested regions, where ultraviolet radiation from the sun is usually the most intense. Different dark-skinned populations are not necessarily closely related genetically. [84] Before the modern mass migration, it has been argued that the majority of dark-pigmented people lived within 20° of the equator. [85]

Natives of Buka and Bougainville at the northern Solomon Islands in Melanesia and the Chopi people of Mozambique in the southeast coast of Africa have darker skin than other surrounding populations. (The native people of Bougainville, Papua New Guinea, have some of the darkest skin pigmentation in the world.) Although these people are widely separated they share similar physical environments. In both regions, they experience very high UVR exposure from cloudless skies near the equator which is reflected from water or sand. Water reflects, depending on colour, about 10 to 30% of UVR that falls on it. [35] [86] People in these populations spend long hours fishing on the sea. Because it is impractical to wear extensive clothing in a watery environment, culture and technology does little to buffer UVR exposure. The skin takes a very large amount of ultraviolet radiation. These populations are probably near or at the maximum darkness that human skin can achieve. [35]

More recent research has found that human populations over the past 50,000 years have changed from dark-skinned to light-skinned and vice versa. Only 100–200 generations ago, the ancestors of most people living today likely also resided in a different place and had a different skin color. According to Nina Jablonski, darkly-pigmented modern populations in South India and Sri Lanka are an example of this, having re-darkened after their ancestors migrated down from areas much farther north. Scientists originally believed that such shifts in pigmentation occurred relatively slowly. However, researchers have since observed that changes in skin coloration can happen in as little as 100 generations (

2,500 years), with no intermarriage required. The speed of change is also affected by clothing, which tends to slow it down. [87]

Australia Edit

The Aborigines of Australia, as with all humans, are descendants of African migrants, and their ancestors may have been among the first major groups to leave Africa around 50,000 years ago. Despite early migrations, genetic evidence has pointed out that the indigenous peoples of Australia are genetically very dissimilar to the dark-skinned populations of Africa and that they are more closely related to Eurasian populations. [88]

The term black initially has been applied as a reference to the skin pigmentation of the aborigines of Australia today it has been embraced by aboriginal activists as a term for shared culture and identity, regardless of skin colour. [89] [90]

Melanesia Edit

Melanesia, a subregion of Oceania, whose name means "black islands", have several islands that are inhabited by people with dark skin pigmentation. The islands of Melanesia are located immediately north and northeast of Australia as well as east coast of Papua New Guinea. [91] The western end of Melanesia from New Guinea through the Solomon Islands were first colonized by humans about 40,000 to 29,000 years ago. [92] [93]

In the world, blond hair is exceptionally rare outside Europe and Southwest Asia, especially among dark-skinned populations. However, Melanesians are one of the dark-skinned human populations known to have naturally-occurring blond hair. [94] [95]

New Guinea Edit

The indigenous Papuan people of New Guinea have dark skin pigmentation and have inhabited the island for at least 40,000 years. Due to their similar phenotype and the location of New Guinea being in the migration route taken by Indigenous Australians, it was generally believed that Papuans and Aboriginal Australians shared a common origin. However, a 1999 study failed to find clear indications of a single shared genetic origin between the two populations, suggesting multiple waves of migration into Sahul with distinct ancestries. [96]

Sub-Saharan Africa Edit

Sub-Saharan Africa is the region in Africa situated south of the Sahara where a large number of dark-skinned populations live. [97] [98] Dark-skinned groups on the continent have the same receptor protein as Homo ergaster and Homo erectus had. [99] According to scientific studies, populations in Africa also have the highest skin colour diversity. [100] High levels of skin colour variation exists between different populations in Sub-Saharan Africa. These differences depend in part on general distance from the equator, illustrating the complex interactions of evolutionary forces which have contributed to the geographic distribution of skin color at any point of time. [35]

Due to frequently differing ancestry among dark-skinned populations, the presence of dark skin in general is not a reliable genetic marker, including among groups in Africa. For example, Wilson et al. (2001) found that most of their Ethiopian samples showed closer genetic affinities with lighter-skinned Armenians than with dark-skinned Bantu populations. [101] Mohamoud (2006) likewise observed that their Somali samples were genetically more similar to Arab populations than to other African populations. [102]

South Asia Edit

South Asia has some of the greatest skin color diversity outside of Africa. Skin color among South Indians, Sri Lankans, and Bangladeshis are on average darker than North Indians and Pakistanis. This is mainly because of the weather conditions in South Asia—higher UV indices are in the south. [103] Several genetic surveys of South Asian populations in different regions have found a weak negative correlation between social status and skin darkness, represented by the melanin index. A study of caste populations in the Gangetic Plain found an association between the proportion of dark skin and ranking in the caste hierarchy. Dalits had, on average, the darkest skin. [104] A pan-India study of Telugu and North Indian castes found a similar correlation between skin color and caste association, linked to the absence of the rs1426654-A variant of the SLC245-A gene, but are also linked to mutations overriding these variants. [105]

Americas Edit

Relatively dark skin remains among the Inuit and other Arctic populations. A combination of protein-heavy diets and summer snow reflection have been speculated as favouring the retention of pigmented skin. [3] [100] [25]

Earliest European colonial descriptions of North American populations include terms such as "brown", "tawny" or "olive", though some populations were also described as "light-skinned". [106] Most North American indigenous populations rank similar to African and Oceanian populations in regards to the presence of the allele Ala111. [107]

Native South Americans and Mesoamericans are also typically considered dark-skinned, ranking similarly to African and Oceanian populations in regards to Ala111 presence. [107] High ultraviolet radiation levels occur throughout the Andes region of Peru, Bolivia, Chile, and Argentina. [108]

Genetic tests show significant Australian influence, [109] theorizing that Amazonian Indians and Australians both diverged from a common ancestor. Scientists tested the ancient and present-day Genome-wide analysis of 49 Central and South Americans up to 11,000 years old from Belize, Brazil, Peru, and the Southern Cone (Chile and Argentina). [110]


The Institute for Creation Research

If Charles Darwin could see today's best examples of evolution, would he be elated or depressed?

The well-known British naturalist popularized the idea of "natural selection," speculating that life could originate from non-life through natural means rather than through a living Creator. But finding examples of natural selection in action has proved to be difficult, even for modern researchers. In the journal Science, Dolph Schluter of the University of British Columbia summarized the current status of natural selection studies--which he admitted have been few.

One problem with conducting a rigorous study of natural selection is that there are so many factors involved. Pinning down what environmental factor supposedly influenced which trait is very difficult, likely impossible. Difficulties like this have probably dissuaded a more serious study of natural selection, though there has been no lack of speculation for the past 150 years as to its possible and varied manifestations.

Examples of natural selection cited by Schluter include studies of threespine stickleback fish, varieties of which can live in fresh water or the ocean. He also listed walking stick insect varieties that prefer different host plants, marine snails that live in differing regions of the intertidal zone, and mosquito fish, which tend to adopt more streamlined shapes when living in the presence of predators. In each example, small changes occurred in some individuals, and these then tended to breed with one another.

Schluter concluded that "the discovery that reproductive isolation can be brought about by ecological adaptation in ordinary phenotypic [visible] traits bridges Darwin's science of speciation and our own." 1

However, maintaining that any such bridge exists between Darwinistic imaginings and scientific realities ignores at least two considerations.

First, these studies concluded that the alterations made to organisms were a result of the environment acting upon the organisms, making the assumption that the environment was the active agent and the organisms were passive. The research failed to rule out the opposite possibility--that the environment was passive and the organisms actively underwent changes.

A better description of what took place would be internal genetic selection, if the alterations observed were the result of well-planned internal capacities to "select" the best features. But this points to an original high-quality design, something that doubtless would not mesh well with a naturalistic philosophy that holds that life progressed from simple to ever-more-complex forms.

Second, what do these subtle changes to certain traits have to do with the overarching evolutionary myth of particles-to-people? Schluter listed the examples as instances of "speciation" because researchers observed that a new offshoot from an original population no longer prefers to interbreed with its ancestral population. But this kind of "speciation" has nothing to do with generating fundamentally different body plans, as would be required for the development of new kinds of organisms.

Instead, it has everything to do with confusing the issue by invoking different definitions of &ldquospecies&rdquo to suit various explanatory needs. Oddly, Schluter referred to &ldquoa revision of the notion of speciation itself&rdquo as a conceptual advance. 1 But if speciation is no longer to be described in terms of body form and plan, then it loses its relevance to the whole question of particles-to-people evolution.

What the science observes is two individuals (or populations) that no longer interbreed. In stark contrast, the story of evolution asserts that apes share a common ancestor with earthworms. How are these supposed to relate?

Subtle variations in stickleback fish bodies may only be demonstrations of well-designed internal capacities to generate variation. In any case, these mostly reversible trait permutations do not result in any change in basic body plan. The stickleback fishes are all still sticklebacks, the walking stick insects are still walking stick insects, etc. If Darwinian evolution is true, fundamental changes should be observable both in modern creatures and in fossils. They are not.

But if creation is true, then science should observe exactly what it does: designed capacities for variations to occur on well-constructed basic body plans. And this means that Darwin would undoubtedly be utterly disappointed in evolution's current "best" examples.

Image credit: Adrien Pinot

* Mr. Thomas is Science Writer at the Institute for Creation Research.


Eliciting care

However, more recent theoretical research suggests something more: humans, in particular, are likely to show compassion to those showing symptoms of illness or injury. There’s a reason, this thinking goes, why people tend to exclaim when in pain, rather than just silently pull away from whatever is hurting them, and why fevers are linked to sluggish behaviour.

Some psychologists argue that this is because immune responses are as much about communication as they are about self-maintenance. People who received care, over humanity’s history, probably tended to do better than those who tried to survive on their own.

In the broader evolutionary literature, researchers refer to these kinds of displays as “signals”. And like many of the innumerable signals we see across the natural world, immune-related signals can be used — or faked — to exploit the world around us, and each other. Some birds, for example, feign injury to distract predators from their nests rats suppress disease symptoms so that potential mates won’t ignore them.

A killdeer bird feigning injury.

We also see many illustrations of immune-signal use and misuse in human cultures. In The Adventure of the Dying Detective (1913), for example, Sherlock Holmes starves himself for three days to elicit a confession from a murder suspect. The suspect confesses only when he is convinced that his attempt to infect Holmes with a rare disease has been successful, misreading Holmes’s signs of illness.

This is an extreme example, but people feign signals of pain or illness all the time to avoid obligations, to elicit support from others, or even to avoid submitting an article by an agreed deadline. And this is an essential element of any signalling system. Once a signal, be it a wince or a jaundiced complexion, elicits a response from whoever sees it, that response will start to drive how and why the signal is used.

Even germs use — and abuse — immune signals for their own gain. In fact, some viruses actually hijack our own immune responses, such as coughs and sneezes, to pass themselves on to new hosts, using our own evolved functions to further their interests.

Other germs, like SARS-CoV-2 (the virus that causes COVID-19) and Yersinia pestis (the bacterium that causes plague), can prevent our signalling to others when we are sick and pass themselves on without anyone realising.

This perspective of immunity — one that takes into account biology, behaviour and the social effects of illness — paints a starkly different picture from the more traditional view of the immune system as a collection of biological and chemical defences against sickness. Germs use different strategies, just as animals do, to exploit immune signals for their own purposes. And perhaps that’s what has made asymptomatically transmitted COVID-19 so damaging: people can’t rely on reading other people’s immune signals to protect themselves.

Insofar as doctors can predict how a particular infection — whether SARS-CoV-2, influenza, malaria or the next pathogen with pandemic potential — will interact with a patient’s immune system, they’ll be better positioned to tailor treatments for it. Future research will help us sort through the germs that hijack our immune signals — or suppress them — for their own purposes.

Viewing immunity not just as biological, but as a broader signalling system, may help us to understand our complex relationships with pathogens more effectively.


DISCUSSION

The current study was designed to identify ‘the core principles of evolutionary medicine’, with the expectation that they will be useful to guide curricular development. These core principles could be especially useful for creating learning objectives for courses in evolutionary medicine in a way that aligns with national recommendations for teaching big ideas, and not isolated facts [ 1]. The principles elicited came from the evolutionary medicine community, and they represent ideas central to the field with broad applications. With this in mind, the core principles elicited here should not be interpreted as prescriptive, and should instead be thought of as a recipe for the development of learning objectives that encourages users to add or subtract core principles to their own needs. Similar to other efforts to present a set of core principles [ 45, 51, 52], the goal is to provide a resource for instructors, but not meant to constrain them. Further, as we highlighted, disagreements among panelists about some of the principles highlight that core ideas in this field will continue to evolve over-time.

Although there have been previous efforts to delineate the important concepts in evolutionary medicine, our efforts represent the first systematic study to do so with the involvement of over 50 individuals. The list of core principles is generally consistent with those emphasized in previous articles based on less systematic methods [ 25, 29, 31, 53]. While these articles did not necessarily aim to define core principles with the same definition adopted here, or have a focus on being exhaustive, it is nonetheless instructive to examine the over-lap between list here and principles discussed in previous work. By doing so, we get some idea of the reliability of the results. Table 4 lists principles, learning goals, and suggested biomedical examples of evolutionary concepts as worded in previous articles. We denote in the table how these ideas over-lap with the core principles elicited here. While many of these are directly congruent with the core principles, others are more specific or even common misconceptions related to a core principle. We would argue that by the nature of our study design, the community of evolutionary medicine can have more confidence that our core principles are a consensus view. Thus, we hope that it can spur greater emphasis on these topics in evolutionary medicine courses so that there can be greater commonalities between evolutionary medicine courses taught by different instructors at different institutions.

Principles, learning goals, and concepts as described in previous articles about evolutionary medicine

Source . Concept . CCP . SMCP . CWSP .
Nesse et al. [ 29] Demonstrate an understanding of how natural selection shapes traits in organisms.X
Describe the differences between proximate and evolutionary explanations, and the two subtypes under each.X
Describe the mathematical formulations that describe the rate of change of an allele’s frequency under different strengths of selection, and the implications for hypotheses about the role of selection in accounting for differences among human populations. X
Explain how the comparative method and other strategies can be used to test evolutionary explanations.X
Be able to describe the role of tradeoffs in traits shaped by natural selection.X
Understand the core principles of behavioral ecology.
Describe phenomena explained by kin selection and inclusive fitness more generally. X
Understand sexual selection, and how it can shape sex differences.X
Gluckman et al. [ 53] We are now living in novel environments compared to those in which we evolved.X
Selection acts on fitness, not health or longevity.X
Our evolutionary history does not cause disease, but rather impacts on our risk of disease in particular environments. X
Antolin et al. [ 31] Genetic variation is the material for evolutionary processes. X
Common descent is a result of evolution.X
Adaptations within populations arise through the process of natural selection in particular environments.X
Phenotypic expression of traits often varies across a range of environmental conditions and provides a predictive framework for potential responses to selection.X
Life span evolves in the context of trade-offs between traits that influence fitness early versus later in life.X
Evolutionary rate is dependent on generation times. X
Humans have coevolved with a variety of commensal and pathogenic organismsX
Graves et al. [ 25] Adaptation/adaptive.X
Hygiene hypothesis. X
Life history theory.X
Microbiome.X
Mismatch.X
Natural selectionX
Race (biological and socially defined). X
Trade-offs.X
Source . Concept . CCP . SMCP . CWSP .
Nesse et al. [ 29] Demonstrate an understanding of how natural selection shapes traits in organisms.X
Describe the differences between proximate and evolutionary explanations, and the two subtypes under each.X
Describe the mathematical formulations that describe the rate of change of an allele’s frequency under different strengths of selection, and the implications for hypotheses about the role of selection in accounting for differences among human populations. X
Explain how the comparative method and other strategies can be used to test evolutionary explanations.X
Be able to describe the role of tradeoffs in traits shaped by natural selection.X
Understand the core principles of behavioral ecology.
Describe phenomena explained by kin selection and inclusive fitness more generally. X
Understand sexual selection, and how it can shape sex differences.X
Gluckman et al. [ 53] We are now living in novel environments compared to those in which we evolved.X
Selection acts on fitness, not health or longevity.X
Our evolutionary history does not cause disease, but rather impacts on our risk of disease in particular environments. X
Antolin et al. [ 31] Genetic variation is the material for evolutionary processes. X
Common descent is a result of evolution.X
Adaptations within populations arise through the process of natural selection in particular environments.X
Phenotypic expression of traits often varies across a range of environmental conditions and provides a predictive framework for potential responses to selection.X
Life span evolves in the context of trade-offs between traits that influence fitness early versus later in life.X
Evolutionary rate is dependent on generation times. X
Humans have coevolved with a variety of commensal and pathogenic organismsX
Graves et al. [ 25] Adaptation/adaptive.X
Hygiene hypothesis. X
Life history theory.X
Microbiome.X
Mismatch.X
Natural selectionX
Race (biological and socially defined). X
Trade-offs.X

CCP, Congruent with core principle SMCP, Specific manifestation of a core principle CWSP, Congruent with a sub principle.

Principles, learning goals, and concepts as described in previous articles about evolutionary medicine

Source . Concept . CCP . SMCP . CWSP .
Nesse et al. [ 29] Demonstrate an understanding of how natural selection shapes traits in organisms.X
Describe the differences between proximate and evolutionary explanations, and the two subtypes under each.X
Describe the mathematical formulations that describe the rate of change of an allele’s frequency under different strengths of selection, and the implications for hypotheses about the role of selection in accounting for differences among human populations. X
Explain how the comparative method and other strategies can be used to test evolutionary explanations.X
Be able to describe the role of tradeoffs in traits shaped by natural selection.X
Understand the core principles of behavioral ecology.
Describe phenomena explained by kin selection and inclusive fitness more generally. X
Understand sexual selection, and how it can shape sex differences.X
Gluckman et al. [ 53] We are now living in novel environments compared to those in which we evolved.X
Selection acts on fitness, not health or longevity.X
Our evolutionary history does not cause disease, but rather impacts on our risk of disease in particular environments. X
Antolin et al. [ 31] Genetic variation is the material for evolutionary processes. X
Common descent is a result of evolution.X
Adaptations within populations arise through the process of natural selection in particular environments.X
Phenotypic expression of traits often varies across a range of environmental conditions and provides a predictive framework for potential responses to selection.X
Life span evolves in the context of trade-offs between traits that influence fitness early versus later in life.X
Evolutionary rate is dependent on generation times. X
Humans have coevolved with a variety of commensal and pathogenic organismsX
Graves et al. [ 25] Adaptation/adaptive.X
Hygiene hypothesis. X
Life history theory.X
Microbiome.X
Mismatch.X
Natural selectionX
Race (biological and socially defined). X
Trade-offs.X
Source . Concept . CCP . SMCP . CWSP .
Nesse et al. [ 29] Demonstrate an understanding of how natural selection shapes traits in organisms.X
Describe the differences between proximate and evolutionary explanations, and the two subtypes under each.X
Describe the mathematical formulations that describe the rate of change of an allele’s frequency under different strengths of selection, and the implications for hypotheses about the role of selection in accounting for differences among human populations. X
Explain how the comparative method and other strategies can be used to test evolutionary explanations.X
Be able to describe the role of tradeoffs in traits shaped by natural selection.X
Understand the core principles of behavioral ecology.
Describe phenomena explained by kin selection and inclusive fitness more generally. X
Understand sexual selection, and how it can shape sex differences.X
Gluckman et al. [ 53] We are now living in novel environments compared to those in which we evolved.X
Selection acts on fitness, not health or longevity.X
Our evolutionary history does not cause disease, but rather impacts on our risk of disease in particular environments. X
Antolin et al. [ 31] Genetic variation is the material for evolutionary processes. X
Common descent is a result of evolution.X
Adaptations within populations arise through the process of natural selection in particular environments.X
Phenotypic expression of traits often varies across a range of environmental conditions and provides a predictive framework for potential responses to selection.X
Life span evolves in the context of trade-offs between traits that influence fitness early versus later in life.X
Evolutionary rate is dependent on generation times. X
Humans have coevolved with a variety of commensal and pathogenic organismsX
Graves et al. [ 25] Adaptation/adaptive.X
Hygiene hypothesis. X
Life history theory.X
Microbiome.X
Mismatch.X
Natural selectionX
Race (biological and socially defined). X
Trade-offs.X

CCP, Congruent with core principle SMCP, Specific manifestation of a core principle CWSP, Congruent with a sub principle.

Defined partially by their explanatory breadth and importance to the field, core principles also provide a framework that can organize research. The framework of core principles provided here can help clarify connections between ongoing research that may be based on larger ideas, and not on topics or methodology. Organizing research by large ideas is not novel conference sessions have been organized on ideas such as life history theory and trade-offs. However, making the network of core principles more explicit can catalyze further connections between research that applies a shared principle without sharing topical focus or methods, and could expedite new and exciting research avenues.


Questions

Before and after every lecture, questions for further discussion and reflection were provided. Questions for lecture 1 and lecture 2 are given below:

Lec #1: Introduction - Rice: Chapter 1

  1. Why do organisms require evolutionary theory? What is it about organisms that requires an evolutionary accounting?
  2. Do all historical processes require a selectionist account?
  3. What are the major features of organic diversity?
  4. What other classes of objects, besides organisms, are conditioned by history?
  5. Describe the organization of morphospace. How is it clustered?
  6. How is individuality (variation within each type) like/unlike that found in minerals?
  7. What about the distribution of forms in morphospace encourages an historical explanation?
  8. Does perfection of organic design require evolutionary explanation?
  9. What is the principle of historical inference?
  10. How are the "quirks" within adaptations "signs of the past"?
  11. Distinguish transformational and variational evolution.
  12. How are changes in an ensemble different in biological evolution than in stellar evolution?
  13. Why is sieving useless without heritability of traits?

Gould, S. J. The Panda's Thumb: More Reflections in Natural History. Reissue ed. New York, NY: W.W. Norton and Company, 1992. ISBN: 9780393308198 .

Lec #2: Population Genetics - Rice: Chapter 1 and 2

  1. Describe the way variation, heritability and differential reproduction convert individual variation to population variation.
  2. Why does every population have differential reproduction? Does this always imply natural selection?
  3. How do we find out if variation is heritable? Why is this especially difficult with animal behavior?
  4. Are chromosome number and shape invariant in a population? (Discuss supernumerary chromosomes, inversion loops. )
  5. How much protein variation is there for sexually reproducing species? What are poly-morphic loci?
  6. How big does a population have to be to realize Hardy Weinberg assumptions?
  7. Contrast continuous and discrete population growth models.
  8. Compare fitness as defined in terms of contribution to the succeeding generation and fitness in terms of optimality.
  9. What are Mendel's laws? In what way are they laws?
  10. Is simple dominance common? Do all loci assort independently?
  11. Describe segregation distortion. How is the t-allele retained by the population?
  12. Define endogamy, planktonic mating, gene frequency (allele frequency), and gamete distribution.
  13. How do we move from phenotypic to genotypic frequency.
  14. Derive the Hardy-Weinberg equilibrium. What assumptions must be made?
  15. What does the following table illustrate? Focus on the assumptions that have to be made to apply this model.


  • Differential reproduction is not equivalent to natural selection.
  • Natural selection operating at various levels (e.g. group and kin selection with respect to altruism).
  • How does vegetative growth make the evaluation of fitness by "counting heads" difficult?
  • What are some causes of differential reproduction?
  • Discuss the fitness of phenotypic classes and the fitness of genotypic classes.

Binomial distribution can be found in any introductory statistics book, e.g.

Kachigan, S. K. Statistical Analysis. New York, NY: Radius Press, 1991, pp. 122-126. ISBN: 9780942154917 .

Dupré, John, ed. The Latest on the Best: Essays on Evolution and Optimality. Cambridge, MA: MIT Press, August 1987. ISBN: 9780262040907 .


Top 10 Signs Of Evolution In Modern Man

Through history, as natural selection played its part in the development of modern man, many of the useful functions and parts of the human body become unnecessary. What is most fascinating is that many of these parts of the body still remain in some form so we can see the progress of evolution. This list covers the ten most significant evolutionary changes that have taken place &ndash leaving signs behind them.

Humans get goose bumps when they are cold, frightened, angry, or in awe. Many other creatures get goose bumps for the same reason, for example this is why a cat or dog&rsquos hair stands on end and the cause behind a porcupine&rsquos quills raising. In cold situations, the rising hair traps air between the hairs and skin, creating insulation and warmth. In response to fear, goose bumps make an animal appear larger &ndash hopefully scaring away the enemy. Humans no longer benefit from goose bumps and they are simply left over from our past when we were not clothed and needed to scare our own natural enemies. Natural selection removed the thick hair but left behind the mechanism for controlling it.

Jacobson&rsquos organ is a fascinating part of animal anatomy and it tells us a lot about our own sexual history. The organ is in the nose and it is a special &ldquosmell&rdquo organ which detects pheromones (the chemical that triggers sexual desire, alarm, or information about food trails). It is this organ that allows some animals to track others for sex and to know of potential dangers. Humans are born with the Jacobson&rsquos organ, but in early development its abilities dwindle to a point that it is useless. Once upon a time, humans would have used this organ to locate mates when communication was not possible. Single&rsquos evenings, chat rooms, and bars have now taken its place in the process of human mate-seeking.

While many of the hangovers from our &ldquodevolved&rdquo past are visible or physical, this is not true for all. Humans have structures in their genetic make-up that were once used to produces enzymes to process vitamin C (it is called L-gulonolactone oxidase). Most other animals have this functioning DNA but at some point in our history, a mutation disbled the gene &ndash whilst leaving behind its remnants as junk DNA. This particular junk DNA indicates a common ancestry with other species on earth, so it is particularly interesting.

Also known as the extrinsic ear muscles, the auriculares muscles are used by animals to swivel and manipulate their ears (independently of their head) in order to focus their hearing on particular sounds. Humans still have the muscles that we would once have used for the very same reason &ndash but our muscles are now so feeble that all they can do is give our ears a little wiggle. The use of these muscles in cats is very visible (as they can nearly turn their ears completely backwards) &ndash particularly when they are stalking a bird and need to make the smallest movements possible so as to not frighten its future meal.

The plantaris muscle is used by animals in gripping and manipulating objects with their feet &ndash something you see with apes who seem to be able to use their feet as well as their hands. Humans have this muscle as well, but it is now so underdeveloped that it is often taken out by doctors when they need tissue for reconstruction in other parts of the body. The muscle is so unimportant to the human body that 9% of humans are now born without it.

Early humans ate a lot of plants &ndash and they needed to eat them quickly enough that they could eat a sufficient amount in one day to get all of the nutrients they needed. For this reason, we had an extra set of molars to make the larger mouth more productive. This was particularly essential as the body lacked the ability to sufficiently digest cellulose. As evolution made its selections, our diets changed, our jaws grew appropriately smaller, and our third molars became unnecessary. Some human populations have now all but completely stopped growing wisdom teeth, while others have almost 100% likelihood of developing them.

Life can get pretty deep. Turn off your brain for awhile and enjoy the 2001 film Evolution at Amazon.com!

If you watch a cat blink, you will see a white membrane cross its eye &ndash that is called its third eyelid. It is quite a rare thing in mammals, but common in birds, reptiles, and fish. Humans have a remnant (but non-working) third eyelid (you can see it in the picture above). It has become quite small in humans, but some populations have more visible portions than others. There is only one known species of primate that still has a functioning third eyelid, and that is the Calabar angwantibo (closely related to lorises) which lives in West Africa.

Darwin&rsquos point is found in the majority of mammals, and humans are no exception. It is most likely used to help focus sounds in animals, but it no longer has a function in humans. Only 10.4% of the human population still has this visible left-over mark of our past, but it is possible that a much larger number of people carry the gene that produces it as it does not always cause the ear tubercle to appear. The point (shown in the picture above) is a small thick nodule at the junction of the upper and middle sections of the ear.

The coccyx is the remnant of what was once a human tail. Over time we lost the need for a tail (as tree swinging was replaced by hanging out at the local water hole grunting neanderthal gossip), but we did not lose the need for the coccyx: it now functions as a support structure for various muscles and a support for a person when he sits down and leans back. The coccyx also supports the position of the anus.

The appendix has no known use in modern humans and is often removed when it becomes infected. While its original use is still speculated on, most scientists agree with Darwin&rsquos suggestion that it once helped to process the cellulose found in the leaf-rich diet that we once had. Over the course of evolution, as our diet has changed, the appendix became less useful. What is particularly interesting is that many evolutionary theorists believe that natural selection (while removing all of the abilities of the appendix) selects larger appendices because they are less likely to become inflamed and diseased. So unlike the little toe, which may eventually vanish and is equally useless, the appendix is likely to stay with us for a long time &ndash just hanging around doing nothing.


Big Ideas Articles & More

Whether the display was sincere is not the issue here how we are affected by another’s predicament is. Empathy is second nature to us, so much so that anyone devoid of it strikes us as dangerous or mentally ill.

At the movies, we can’t help but get inside the skin of the characters on the screen. We despair when their gigantic ship sinks we exult when they finally stare into the eyes of a long-lost lover.

We are so used to empathy that we take it for granted, yet it is essential to human society as we know it. Our morality depends on it: How could anyone be expected to follow the golden rule without the capacity to mentally trade places with a fellow human being? It is logical to assume that this capacity came first, giving rise to the golden rule itself. The act of perspective-taking is summed up by one of the most enduring definitions of empathy that we have, formulated by Adam Smith as “changing places in fancy with the sufferer.”

An example of consolation among chimpanzees: A juvenile puts an arm around a screaming adult male, who has just been defeated in a fight with his rival. Consolation probably reflects empathy, as the objective of the consoler seems to be to alleviate the distress of the other. © Frans de Waal

Even Smith, the father of economics, best known for emphasizing self-interest as the lifeblood of human economy, understood that the concepts of self-interest and empathy don’t conflict. Empathy makes us reach out to others, first just emotionally, but later in life also by understanding their situation.

This capacity likely evolved because it served our ancestors’ survival in two ways. First, like every mammal, we need to be sensitive to the needs of our offspring. Second, our species depends on cooperation, which means that we do better if we are surrounded by healthy, capable group mates. Taking care of them is just a matter of enlightened self-interest.

It is hard to imagine that empathy—a characteristic so basic to the human species that it emerges early in life, and is accompanied by strong physiological reactions—came into existence only when our lineage split off from that of the apes. It must be far older than that. Examples of empathy in other animals would suggest a long evolutionary history to this capacity in humans.

Evolution rarely throws anything out. Instead, structures are transformed, modified, co-opted for other functions, or tweaked in another direction. The frontal fins of fish became the front limbs of land animals, which over time turned into hoofs, paws, wings, and hands. Occasionally, a structure loses all function and becomes superfluous, but this is a gradual process, and traits rarely disappear altogether. Thus, we find tiny vestiges of leg bones under the skin of whales and remnants of a pelvis in snakes.

Over the last several decades, we’ve seen increasing evidence of empathy in other species. One piece of evidence came unintentionally out of a study on human development. Carolyn Zahn-Waxler, a research psychologist at the National Institute of Mental Health, visited people’s homes to find out how young children respond to family members’ emotions. She instructed people to pretend to sob, cry, or choke, and found that some household pets seemed as worried as the children were by the feigned distress of the family members. The pets hovered nearby and put their heads in their owners’ laps.

But perhaps the most compelling evidence for the strength of animal empathy came from a group of psychiatrists led by Jules Masserman at Northwestern University. The researchers reported in 1964 in the American Journal of Psychiatry that rhesus monkeys refused to pull a chain that delivered food to themselves if doing so gave a shock to a companion. One monkey stopped pulling the chain for 12 days after witnessing another monkey receive a shock. Those primates were literally starving themselves to avoid shocking another animal.

Cognitive empathy, where one understands the other's situation, enables helping behavior that is tailed to the other's specific needs. In this case, a mother chimpanzee reaches to help her son out of a tree after he screamed and begged for her attention. © Frans de Waal

The anthropoid apes, our closest relatives, are even more remarkable. In 1925, Robert Yerkes reported how his bonobo, Prince Chim, was so extraordinarily concerned and protective toward his sickly chimpanzee companion, Panzee, that the scientific establishment might not accept his claims: “If I were to tell of his altruistic and obviously sympathetic behavior towards Panzee, I should be suspected of idealizing an ape.”

Nadia Ladygina-Kohts, a primatological pioneer, noticed similar empathic tendencies in her young chimpanzee, Joni, whom she raised at the beginning of the last century, in Moscow. Kohts, who analyzed Joni’s behavior in the minutest detail, discovered that the only way to get him off the roof of her house after an escape—much more effective than any reward or threat of punishment—was by arousing sympathy:

If I pretend to be crying, close my eyes and weep, Joni immediately stops his plays or any other activities, quickly runs over to me, all excited and shagged, from the most remote places in the house, such as the roof or the ceiling of his cage, from where I could not drive him down despite my persistent calls and entreaties. He hastily runs around me, as if looking for the offender looking at my face, he tenderly takes my chin in his palm, lightly touches my face with his finger, as though trying to understand what is happening, and turns around, clenching his toes into firm fists.

These observations suggest that apart from emotional connectedness, apes have an appreciation of the other’s situation and show a degree of perspective-taking. One striking report in this regard concerns a bonobo female named Kuni, who found a wounded bird in her enclosure at Twycross Zoo, in England. Kuni picked up the bird, and when her keeper urged her to let it go, she climbed to the highest point of the highest tree, carefully unfolded the bird’s wings and spread them wide open, one wing in each hand, before throwing it as hard as she could toward the barrier of the enclosure. When the bird fell short, Kuni climbed down and guarded it until the end of the day, when it flew to safety. Obviously, what Kuni did would have been inappropriate toward a member of her own species. Having seen birds in flight many times, she seemed to have a notion of what would be good for a bird, thus giving us an anthropoid illustration of Smith’s “changing places in fancy.”

This is not to say that all we have are anecdotes. Systematic studies have been conducted on so-called “consolation” behavior. Consolation is defined as friendly or reassuring behavior by a bystander toward a victim of aggression. For example, chimpanzee A attacks chimpanzee B, after which bystander C comes over and embraces or grooms B. Based on hundreds of such observations, we know that consolation occurs regularly and exceeds baseline levels of contact. In other words, it is a demonstrable tendency that probably reflects empathy, since the objective of the consoler seems to be to alleviate the distress of the other. In fact, the usual effect of this kind of behavior is that it stops screaming, yelping, and other signs of distress.

A bottom-up view of empathy

The above examples help explain why to the biologist, a Russian doll is such a satisfying plaything, especially if it has a historical dimension. I own a doll of Russian President Vladimir Putin, within whom we discover Yeltsin, Gorbachev, Brezhnev, Kruschev, Stalin, and Lenin, in that order. Finding a little Lenin and Stalin within Putin will hardly surprise most political analysts. The same is true for biological traits: The old always remains present in the new.

This is relevant to the debate about the origins of empathy, especially because of the tendency in some disciplines, such as psychology, to put human capacities on a pedestal. They essentially adopt a top-down approach that emphasizes the uniqueness of human language, consciousness, and cognition. But instead of trying to place empathy in the upper regions of human cognition, it is probably best to start out examining the simplest possible processes, some perhaps even at the cellular level. In fact, recent neuroscience research suggests that very basic processes do underlie empathy. Researchers at the University of Parma, in Italy, were the first to report that monkeys have special brain cells that become active not only if the monkey grasps an object with its hand but also if it merely watches another do the same. Since these cells are activated as much by doing as by seeing someone else do, they are known as mirror neurons, or “monkey see, monkey do” neurons.

It seems that developmentally and evolutionarily, advanced forms of empathy are preceded by and grow out of more elementary ones. Biologists prefer such bottom-up accounts. They always assume continuity between past and present, child and adult, human and animal, even between humans and the most primitive mammals.

So, how and why would this trait have evolved in humans and other species? Empathy probably evolved in the context of the parental care that characterizes all mammals. Signaling their state through smiling and crying, human infants urge their caregiver to take action. This also applies to other primates. The survival value of these interactions is evident from the case of a deaf female chimpanzee I have known named Krom, who gave birth to a succession of infants and had intense positive interest in them. But because she was deaf, she wouldn’t even notice her babies’ calls of distress if she sat down on them. Krom’s case illustrates that without the proper mechanism for understanding and responding to a child’s needs, a species will not survive.

During the 180 million years of mammalian evolution, females who responded to their offspring’s needs out-reproduced those who were cold and distant. Having descended from a long line of mothers who nursed, fed, cleaned, carried, comforted, and defended their young, we should not be surprised by gender differences in human empathy, such as those proposed to explain the disproportionate rate of boys affected by autism, which is marked by a lack of social communication skills.

Empathy also plays a role in cooperation. One needs to pay close attention to the activities and goals of others to cooperate effectively. A lioness needs to notice quickly when other lionesses go into hunting mode, so that she can join them and contribute to the pride’s success. A male chimpanzee needs to pay attention to his buddy’s rivalries and skirmishes with others so that he can help out whenever needed, thus ensuring the political success of their partnership. Effective cooperation requires being exquisitely in tune with the emotional states and goals of others.

Within a bottom-up framework, the focus is not so much on the highest levels of empathy, but rather on its simplest forms, and how these combine with increased cognition to produce more complex forms of empathy. How did this transformation take place? The evolution of empathy runs from shared emotions and intentions between individuals to a greater self/other distinction—that is, an “unblurring” of the lines between individuals. As a result, one’s own experience is distinguished from that of another person, even though at the same time we are vicariously affected by the other’s. This process culminates in a cognitive appraisal of the other’s behavior and situation: We adopt the other’s perspective.

As in a Russian doll, however, the outer layers always contain an inner core. Instead of evolution having replaced simpler forms of empathy with more advanced ones, the latter are merely elaborations on the former and remain dependent on them. This also means that empathy comes naturally to us. It is not something we only learn later in life, or that is culturally constructed. At heart, it is a hard-wired response that we fine-tune and elaborate upon in the course of our lives, until it reaches a level at which it becomes such a complex response that it is hard to recognize its origin in simpler responses, such as body mimicry and emotional contagion. (See sidebar.)

Biology holds us “on a leash,” in the felicitous words of biologist Edward Wilson, and will let us stray only so far from who we are. We can design our life any way we want, but whether we will thrive depends on how well that life fits human predispositions.

I hesitate to predict what we humans can and can’t do, but we must consider our biological leash when deciding what kind of society we want to build, especially when it comes to goals like achieving universal human rights.

If we could manage to see people on other continents as part of us, drawing them into our circle of reciprocity and empathy, we would be building upon, rather than going against, our nature.

For instance, in 2004, the Israeli Minister of Justice caused political uproar for sympathizing with the enemy. Yosef Lapid questioned the Israeli army’s plans to demolish thousands of Palestinian homes in a zone along the Egyptian border. He had been touched by images on the evening news. “When I saw a picture on the TV of an old woman on all fours in the ruins of her home looking under some floor tiles for her medicines, I did think, ‘What would I say if it were my grandmother?’” he said. Lapid’s grandmother was a Holocaust victim.

This incident shows how a simple emotion can widen the definition of one’s group. Lapid had suddenly realized that Palestinians were part of his circle of concern, too. Empathy is the one weapon in the human repertoire that can rid us of the curse of xenophobia.

Empathy is fragile, though. Among our close animal relatives, it is switched on by events within their community, such as a youngster in distress, but it is just as easily switched off with regards to outsiders or members of other species, such as prey. The way a chimpanzee bashes in the skull of a live monkey by hitting it against a tree trunk is no advertisement for ape empathy. Bonobos are less brutal, but in their case, too, empathy needs to pass through several filters before it will be expressed. Often, the filters prevent expressions of empathy because no ape can afford feeling pity for all living things all the time. This applies equally to humans. Our evolutionary background makes it hard to identify with outsiders. We’ve evolved to hate our enemies, to ignore people we barely know, and to distrust anybody who doesn’t look like us. Even if we are largely cooperative within our communities, we become almost a different animal in our treatment of strangers. (See sidebar.)

This is the challenge of our time: globalization by a tribal species. In trying to structure the world such that it suits human nature, the point to keep in mind is that political ideologues by definition hold narrow views. They are blind to what they don’t wish to see. The possibility that empathy is part of our primate heritage ought to make us happy, but we are not in the habit of embracing our nature. When people kill each other, we call them “animals.” But when they give to the poor, we praise them for being “humane.” We like to claim the latter tendency for ourselves. Yet, it will be hard to come up with anything we like about ourselves that is not part of our evolutionary background. What we need, therefore, is a vision of human nature that encompasses all of our tendencies: the good, the bad, and the ugly.

Our best hope for transcending tribal differences is based on the moral emotions, because emotions defy ideology. In principle, empathy can override every rule about how to treat others. When Oskar Schindler kept Jews out of concentration camps during World War II, for example, he was under clear orders by his society on how to treat people, yet his feelings interfered.

Caring emotions may lead to subversive acts, such as the case of a prison guard who during wartime was directed to feed his charges only water and bread, but who occasionally sneaked in a hard-boiled egg. However small his gesture, it etched itself into the prisoners’ memories as a sign that not all of their enemies were monsters. And then there are the many acts of omission, such as when soldiers could have killed captives without negative repercussions but decided not to. In war, restraint can be a form of compassion.

Emotions trump rules. This is why, when speaking of moral role models, we talk of their hearts, not their brains (even if, as any neuroscientist will point out, the heart as the seat of emotions is an outdated notion). We rely more on what we feel than what we think when solving moral dilemmas.

It’s not that religion and culture don’t have a role to play, but the building blocks of morality clearly predate humanity. We recognize them in our primate relatives, with empathy being most conspicuous in the bonobo ape and reciprocity in the chimpanzee. Moral rules tell us when and how to apply our empathic tendencies, but the tendencies themselves have been in existence since time immemorial.


Evolutionary Dynamics of Pathoadaptation Revealed by Three Independent Acquisitions of the VirB/D4 Type IV Secretion System in Bartonella

The α-proteobacterial genus Bartonella comprises a group of ubiquitous mammalian pathogens that are studied as a model for the evolution of bacterial pathogenesis. Vast abundance of two particular phylogenetic lineages of Bartonella had been linked to enhanced host adaptability enabled by lineage-specific acquisition of a VirB/D4 type IV secretion system (T4SS) and parallel evolution of complex effector repertoires. However, the limited availability of genome sequences from one of those lineages as well as other, remote branches of Bartonella has so far hampered comprehensive understanding of how the VirB/D4 T4SS and its effectors called Beps have shaped Bartonella evolution. Here, we report the discovery of a third repertoire of Beps associated with the VirB/D4 T4SS of B. ancashensis, a novel human pathogen that lacks any signs of host adaptability and is only distantly related to the two species-rich lineages encoding a VirB/D4 T4SS. Furthermore, sequencing of ten new Bartonella isolates from under-sampled lineages enabled combined in silico analyses and wet lab experiments that suggest several parallel layers of functional diversification during evolution of the three Bep repertoires from a single ancestral effector. Our analyses show that the Beps of B. ancashensis share many features with the two other repertoires, but may represent a more ancestral state that has not yet unleashed the adaptive potential of such an effector set. We anticipate that the effectors of B. ancashensis will enable future studies to dissect the evolutionary history of Bartonella effectors and help unraveling the evolutionary forces underlying bacterial host adaptation.

Keywords: AMPylation bacterial effector filamentation induced by cAMP parallel evolution.

© The Author(s) 2017. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution.

Figures

Comprehensive phylogeny of the genus…

Comprehensive phylogeny of the genus Bartonella . Maximum likelihood phylogeny of Bartonella based…

The VirB/D4 T4SS of B.…

The VirB/D4 T4SS of B. ancashensis was acquired independently from its homologs in…

The phylogeny of Bartonella effectors…

The phylogeny of Bartonella effectors reveals that the repertoire of B. ancashensis evolved…

Domain architectures and tyrosine phosphorylation…

Domain architectures and tyrosine phosphorylation motifs of the three Bep repertoires. ( A…

FIC domains of B. ancashensis…

FIC domains of B. ancashensis Beps show strong signs of functional diversification. (…

FicA antitoxin homologs (BiaA) found…

FicA antitoxin homologs (BiaA) found at bep loci in all bartonellae. Alignment of…

BiaA-like modules of Bep3 and…

BiaA-like modules of Bep3 and Bep4 orthologs. BiaA modules were found in the…

The BatR/BatS two-component system controls…

The BatR/BatS two-component system controls all three instances of the VirB/D4 T4SS. (…


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