We’re All Cherry Cupcakes
by Kathleen Fuller, Ph.D.
As technology “shrinks” the world, we become more and more aware of the great diversity present in our world. Awareness of the reasons for and appreciation of this diversity are vitally important if we are to understand and effectively communicate with each other. However, it is also vitally important that our focus on diversity does not lead to divisiveness. Too much emphasis on our differences can lead us to forget our much more impressive underlying commonalities.
As a physical anthropologist, I am fascinated by the human organism. What makes us human? How are we similar to and different from other primates? Why do humans differ from each other? When did we become human? Who are we? Anything that concerns the physicality of being human falls within the purview of my field. It is, therefore, a most intriguing and absorbing field of study for those of us interested in knowing more about ourselves.
It is from the perspective of a physical anthropologist that I approach the issue of diversity. As a physical anthropologist, I know that humans are primates. Genetic analysis of the various primates has shown that we are most genetically similar to chimpanzees. Chimpanzees and humans are equally genetically distinct from gorillas and all other primates. In fact, approximately 99% of our genetic material is identical to that of chimpanzees. This leaves only 1% of our DNA with which to make us distinctively human. Of this 1%, probably only a tiny fraction is actually involved in the production of physical diversity. Genetically, we all have far more in common than we have differences.
One way to think of this is with the following very simple analogy. We are all cherry cupcakes, but some of us have green frosting with chocolate curls, some pink frosting with coconut flakes, some white frosting with confetti sprinkles, some chocolate fudge frosting, etc. The diversity is both visible and important: in part, it is the way in which we recognize and differentiate each other. However, the vast majority of what makes us human, the cherry cake, is held in common by all humans.
Besides allowing us to recognize each other, why do humans display so much physical diversity? In particular, given that it is our major method of classification, why are there so many shades of pigmentation? Variation in pigmentation is directly related to the need for past human populations, lacking our present technological sophistication, to adapt to varying latitudinal environments.
Human origin is in the equatorial zone of Africa. In these latitudes, UVB radiation is at its most intense. UVB radiation at the equator strikes the earth at a 90 degree angle, penetrating the ozone layer at its thinnest point. The only effective pre-technological protection against these cancer-causing rays was a heavy layer of melanin in the skin. While all humans have the same average number of melanocytes, these melanocytes are genetically programmed to produce different amounts of melanin in different individuals. The melanin layer diffuses the UVB radiation and prevents its penetration to the lower skin levels where it could cause cancer. Melanomas are rapid-spreading cancers which can kill within a few years of their occurrence. In order to survive in the equatorial zones, humans had to have very heavy pigmentation. Therefore, the first humans were heavily pigmented.
If the first humans were heavily pigmented, you may wonder why not all humans are still heavily pigmented. The reason for this also relates to UVB radiation. Curiously enough, the effects of UVB radiation are not all negative. In fact, all humans need to absorb some UVB radiation in the lowest layers of the skin in order to activate the hormonal cycle which controls bone growth and development. Without absorbing some UVB radiation, human bone growth is disrupted resulting in the skeletal abnormalities known as rickets.
While rickets, which primarily occurs during infancy, is not directly implicated in an individual’s death, it can cause a malformation of the ribs called “pigeon chest”. This malformation constricts the lungs and can lead to respiratory illnesses including pneumonia which can result in death. Rickets can also result in a compressed, flattened pelvis. The major growth of the pelvic blade (the ilium) is during infancy. If growth is disrupted, the ilium does not develop properly. While not as problematic for males, a compressed, flattened pelvis creates great difficulties for women during childbirth. Prior to the use of cesarean sections, these women and their fetuses would have been at high risk of death during childbirth.
UVB radiation is both a danger and a necessity. In the equatorial zones, the danger outweighs the necessity. But in equatorial zones UVB radiation is so intense that even with heavy pigmentation, some UVB radiation manages to penetrate to the lower skin levels so that bone growth is normal. However, as one moves out of the equatorial zones, UVB radiation rapidly decreases. The angle of the sun becomes more acute and it must penetrate an increasingly dense layer of ozone which is thickest over the poles. This means that the heavy pigmentation which is a necessity at the equator becomes a liability the further one moves into the higher latitudes. Rickets becomes a probability.
One of the ways to forestall the development of rickets is to have light pigmentation. The less melanin there is in the skin, the more UVB radiation that can penetrate to the lower skin layers. In the higher latitudes, prevention of rickets outweighs the possibility of developing skin cancer. Therefore, as one slowly travels from the equatorial regions towards the poles, skin pigmentation gradually, and imperceptibly, becomes lighter. There is no point at which there is a discrete change from one degree of pigmentation to the next. The variation is continuous and indivisible.
Skin pigmentation is a polygenic trait: one which is the result of the interaction of several genes with the environment and is continuously distributed. While we do not yet have a complete understanding of the genetics of pigmentation, it appears to be the result of the interaction of four to six different genes with the environment. Even heavily pigmented populations have variation in the degree of pigmentation. It is this inherent variation and its plasticity that has enabled humans to adapt to non-equatorial environments.
Variation, diversity, is an absolute necessity for the survival of the human species in differing environments. However, it must always be remembered that this diversity rests upon a massive, underlying genetic unity. We are all just cherry cupcakes with different frostings.
Kathleen Fuller, MA, PhD, Director of AnthroHealthTM, is a Biological Anthropologist with extensive knowledge of Human History and Human Biology.
Also by Kathleen Fuller, Ph.D.
- The Abolitionist Examiner: Diversity, Not Divisiveness
Copyright © 1996 Kathleen Fuller. All rights reserved.