Darwin day lecture discusses skin tone

BY ALANNA KOEHLER ’15
Campus Life Editor

Nina G. Jablonski, professor of anthropology at Penn State University, delivered a presentation entitled “The Evolution of Human Skin Pigmentation by Natural Selection” at the 10th annual Darwin Day Lecture and Luncheon Friday in the Booth Ferris room of Steinman College Center.

This yearly event commemorates the Feb. 12 birthday of Charles Darwin, the man who laid the foundation of the controversial theory of evolution by natural selection with the 1859 publication of On the Origin of Species. The goal of the lecture is to provide an annual forum for students, faculty, and alumni to come together to ponder and discuss an interesting topic in evolutionary biology.

Jablonski was introduced by Dan Ardia, assistant professor of biology.

She immediately acknowledged the College’s reputation for having a distinguished body of evolutionary biologists and thinkers. Jablonski then turned her attention to the focal point of the afternoon: skin pigmentation.

“Human skin is remarkable of mammals,” Jablonski said. “We come in a variety of colors.”

Jablonski focused on the reasons for the evolution of this “gradient” of skin color, which is caused by different levels of melanin present in the skin. She also explained how this area of study is particularly difficult.

“Skin is rarely preserved,” Jablonski said. “We don’t have, for the most part, fossilized [human] skin.”

Instead, her research relies heavily on comparative anatomy and genetics to figure out what happened to human skin after the split that separated humans from their common ancestor, the chimpanzees.

“How did our bodies become mostly hairless and geographically varied in color?” she prompted.

She explained members of the early genus Homo who lived near the Equator had evolved mostly naked, melanin-rich skin.

The absence of hair allowed these humans to sweat, keeping them cool during physical exertion under the hot sun, and the dark pigmentation prevented burning and protected them from the harmful effects of ultraviolet radiation (UVR).

“Melanin is a superb natural sunscreen,” Jablonksi said.

UVR can cause damage to unprotected skin and can lead to different skin cancers due to damaged DNA. It can also affect folate metabolism; low folate levels can lead to birth defects due to slowed cell division and can also slow the rate of sperm production.

“When there is a lot of ultraviolet radiation, folate levels plummet,” Jablonski said.

However, there is one positive aspect of UVR. One form of UVR, classified as UVB, activates Vitamin D formation. Vitamin D is important to bones, muscles, and teeth, as well as the brain and immune system.

“Melanin competes with UVB photons,” Jablonski explained. While melanin can protect exposed skin, an overabundance of it can affect Vitamin D production.

“We can think of skin pigmentation as being really an evolutionary compromise of some sort,” Jablonski said.

For early humans living in the high-UV regions near the Equator, protection from UVR was more important than rapid production of Vitamin D. However, once humans started to disperse into different areas of the world, namely low-UV regions, high levels of melanin blocked too many UVB rays, preventing the adequate production of Vitamin D. This led to natural selection favoring less melanin pigmentation and, consequently, lighter skin tones in these areas. These “depigmented” people developed temporary pigmentation in response to harmful UV rays in the form of tanning.

Jablonski also pointed out while modern Eastern Europeans and Eastern Asians have similar depigmentation, they possess different genetic mutations that led to independent evolutions of the trait. Neanderthals also evolved depigmented skin, as shown by traces of their DNA. Neanderthal DNA looked similar to the DNA of Eastern Europeans when considering genes coding for pigmentation.

“Skin pigmentation basically goes it alone,” Jablonski said. “Skin color is a labile trait.”

These statements provide a powerful insight: “There are no natural accumulations of racial characteristics,” Jablonski said.

The genes that code for skin pigment act independently of genes that code for personality and other traits. This realization can serve as a tool in combatting racism and help to undo the “social reality” visually- oriented humans have created.

Jablonski’s work had another important implication as well, this time regarding skin cancer.

“[Today] we have the ability to disperse far away from our natal homelands,” Jablonski said. “We think that we’re the cat’s meow.”

She pointed out, however, humans are actually unprepared for this frequent voluntary (or involuntary) relocation.

When moving, either from low- UV environments to high-UV environments or vice versa, humans can suffer the consequences. Human skin with little melanin can become damaged by UVR, resulting in skin cancers. Increased human motility has led to an increase in all skin cancers, especially melanoma.

Vitamin D deficiency also continues to be a problem and not only for those with dark skin pigmentation living in or visiting low-UV environments. Modern people of various pigment gradients tend to spend much of their time indoors, away from the necessary UVB rays, and, when they do venture outdoors, they are more likely to slather on the sunscreen and wear concealing clothing.

Jablonski reiterated that protecting human skin from harmful UVR is, indeed, advised. However, humans still need some exposure to these rays in order to activate Vitamin D production. Vitamin D can also be supplemented with vitamins and by consuming fish such as mackerel, sardines, and cod.

Jablonski’s presentation was received with much applause and a number of curious questions from the audience. Her lecture not only commemorated the life of Darwin by taking an in depth look into one of the most visible products of evolution, but also touched on racism and important health implications.

alanna.koehler@fandm.edu

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