Look Out, Darwin

Modern men and women have evolved from humans of historic ages. In the stone ages, muscular strength mattered, especially for men, who had to hunt for survival. This may have led to the differences in physical strength between men and women.  The slow but steady morphing of life forms, particularly via the process known as “natural selection” is not only easily apparent but also well established. Life forms that are suited to the environment multiply rapidly; those that are not die out. This process works for all life forms from microbes to humans.

Natural selection, also known as the “survival of the fittest” is a simple yet powerful maxim that explains much of the evolutionary processes that produce differences in races of a species. For example, humans have a range of skin color, quite correlated with their geographical origins. How did that happen?

Darker skin is much more tolerant of sunburn. A substance called melanin is the pigment that darkens the skin. Melanin is very effective in blocking out the sun’s ultraviolet radiation from damaging the cells of the skin. Ultraviolet (UV) light, surprisingly, has several effects on the human body. First, ultraviolet causes sunburn, which breaks down skin cells and forms painful lesions, eventually leading to melanoma—a particularly virulent form of cancer that can quickly spread to other parts of the body. Second, UV causes the skin to manufacture vitamin D, which is a particularly important vitamin. Third UV causes the folate level in the body to decrease—folate is a member of the vitamin B family.

Just these three effects of UV explain a range of selection phenomenon that leads to the panorama of skin color. People living in hot sunny climates do not fare well with fair skin. While fair skin leads to cancer and shortens lifespan, it does not fully explain why fair-skinned people did not reproduce well in warm climates. Therein comes the folate connection. Folate levels in blood cells are very necessary for healthy reproduction—women with folate deficiencies may produce babies with a variety of birth defects (such as spina-bifida an anencephaly).  Hence it is entirely likely that if there were fair-skinned humans in hot climates, they would tend not to reproduce well. Thus natural selection favored dark-skinned people over fair-skinned ones.

Dark skin, hence, should be suited to all climates. Why would then, in colder climates, dark skinned people not thrive as well as light skin people? The connection here is vitamin D. The melanin in dark skin absorbs UV, significantly decreasing production of vitamin D. Vitamin D is not something early humans ingested through food. The only natural food with vitamin D is fish, and fish was not a part of the diet of early humans. Deficiency of this key nutrient is the cause of rickets, a terrible condition afflicting children, which prevents afflicted people from reaching adulthood (hence, not multiply).

These simple factors also explain why people from the mountains in the tropical regions are fairer than people from the plains, but are not as fair as people from the northern latitudes. Though the mountains are cold, there is more UV there than the north, and the climate is often cloudy making the UV level lower than that of the plains. The connection of UV and skin color is only a part of the puzzle of human evolution. Many other aspects have shaped the way we are, including availability of food, environment and society.

That was then. Things are very different now. Light skinned people can thrive happily in hot climates thanks to clothing, indoor work areas, air conditioning and other niceties of life. Dark skinned people can thrive in cold countries, as vitamin D is added to food, and seafood is widely available even where there is no sea. People are no longer involved in hunting and gathering. Infant mortality is no longer the driving force behind natural selection. What does that mean for future evolutionary trends?

Many scientists are now proposing the idea that evolution for the human species is over, especially in the developed world. People do not face the hardships of life that were the selection factors for our forefathers. We do not have to hunt and live in caves. We do not have to fight with animals for survival. We do not face famines and epidemics. We do not starve. We do not die young, infant mortality is no longer the horror it was. A proponent of the “evolution is over”, theory is Stephen Jones of University College, London, and he says, “If you want to know what Utopia is like, just look around—this is it”.

What, then, is in the store for the future of humanity? That question is not only hard (if not impossible) to answer; the answers are filled with speculation and wild guesses. In the modern society, physical strength is no longer the attribute of success. Education and intellectual prowess is definitely the key the economic progress. However, economically advanced people have lower rates of fertility, they do not breed prolifically. This is the opposite of what it used to be—successful people had the largest families, endowing the offspring with the genes that led to the parent’s prowess.

Advances in genetic engineering may some day produce people with altered genes who live, healthfully, for a very long time. Hence if some people lived to be 150, it is entirely possible such people would have more children than those who lived to be 60. This may cause a trend towards the gene pool that favors longevity. Of course, this is heavily speculative.

At the present, evolution may have taken a setback. Natural selection, the cornerstone of evolution, is apparently not effective any more. Physically weak humans, do not die off, they live well and have families. Babies with no chances of survival a hundred years back, routinely grow up into productive adults. The range of medicines, particularly antibiotics have ceased the need for disease resistant humans. The effect of these advances in technology will definitely have an impact on the nature of humans to come, but what it would be is impossible to foretell.

Humans in older times did not travel. Communities were geographically clustered, giving rise to many different races and cultures. Today, travel and relocation is getting increasingly common. Men and women from different continents, routinely meet at colleges and pair up. The offspring inherits a diverse background. One theory says that the intermingling of races and societies will lead to a blending of the genes resulting in a uniformly “brown-skinned” human race and the old evolutionary forces that led to the range of skin colors may essentially disappear.

Such changes may even affect the physical and social conditioning of the sexes. Natural selection played a part in the physical superiority of men over women. Such forces do not exist any more; hence it is entirely likely that both sexes may become equal in physique. Overall physical prowess of humans have already diminished, we are far weaker than humans of 10,000 years back. Social roles of the sexes have undergone significant changes in the recent past. No longer is the man the sole breadwinner and no longer is the woman dependant on a man to provide her livelihood. Our children do not see the sharp divisions in gender roles while growing up, which were ingrained into the psyche of our grandparents. As the generations progress, it is not clear if there will exist any sexual differences in society.

An interesting fact is that the past 100 years have been the most tumultuously progressive times in human history. It took hundreds of thousands of years to transform humans from cave dwelling hunters to city dwelling social beings. It took many thousands of years for the basic systems of human existence to undergo transformation. It took unimaginable amounts of time to transition from the spear or the club as hunting instruments of choice to the invention of the gun. Yet, ever since man discovered technology, the roller coaster ride has kept on gathering speed. It took over 50 years since the invention of the internal combustion engine (1857) to the point ordinary citizens could think of having a car (Ford commercialized the car in 1908). But it took less than five years from the time the Internet went commercial to the point where almost everyone, almost worldwide use Email.

Evolution may have stopped or slowed in the developed world, but it definitely proceeds in the old fashioned way in much of the underdeveloped world. Another theory states that apes are immune to AIDS as they have developed this immunity. In many of the AIDS ravaged parts of the world, notably the interior of Africa, there is evidence that humans are developing immunity too. Hence it is not entirely unlikely that in centuries to come, humans from that part of the world will be wholly immune to AIDS (those that are not, will get eliminated from the gene pool).

It is probably terribly pretentious to think evolution for humans is over. The parameters have changed, and the future, as usual will be unpredictable.

Partha Dasgupta is on the faculty of the Computer Science and Engineering Department at Arizona State University in Tempe. His specializations are in the areas of Operating Systems, Cryptography and Networking. His homepage is at http://cactus.eas.asu.edu/partha