A Alaskan Tribal Council Chief Glen “Tiny” Fredricks donates some DNA to the Genographic Project, a global, five-year research initiative launched by National Geographic and IBM, will trace the migration history of the human species and determine how related every race is.
Credit: Adrian Coakley/National Geographic
BIRMINGHAM: Perhaps the global human diversity we see today is not related to genes much at all.
Modern humans evolved around 200,000 years ago. But how have we changed since then? Jay Stock, a biological anthropologist at the University of Cambridge built a compelling case for audiences at the British Science Festival this week in Birmingham.
"There's tremendous variation throughout our species," Stock said. Ranging from typically taller, long limbed people in the tropics, to shorter, stocky limbed Inuit in the Arctic Circle.
You are where you live
Geographic variation in humans and other animals is often linked to climate, particularly temperature. For example, cold induced vasodilation - a mechanism that reduces the chances of getting frostbite - is common in Inuit populations and absent in the tropics.
However, many of the variations between people aren't due to natural selection, but an illustration of how the same genes can be expressed differently in different environments. "Plasticity can block genetic adaptation by allowing us to be flexible enough within our lifespan," explained Stock.
For example, the anti-frostbite mechanism mentioned above also appears in North Sea fishermen because they have adapted to their job in adulthood, not because they have a specific set of genes. Even limb length has been shown to be a product of the environment in which we live, rather than the genes we carry.
Limb proportions change quickly
"There can be dramatic changes in limb proportions within a single generation in migrant populations, from Mexico to the United States," Stock quoted.
Despite Homo sapiens' flair for adaptability, there are some patterns across the world that do suggest modern evolution in action. In central Africa more people are heterozygous carriers of the sickle cell gene as it reduces the risks from malaria.
Humans have adapted to different levels of UV radiation, with darker skin in the tropics and lighter skin towards the poles. In populations with a long history of cattle herding, adults maintain the ability to drink and digest milk due to the possession of a particular gene, whereas many people across the globe do not.
Chimpanzees have greater diversity
Although humans have migrated to inhabit every corner of the planet, our genetic make up is still very similar. "There's more genetic diversity in small populations of chimpanzees than there is within our entire species," Stock explained.
However, this may change in the future. At present "...physiological plasticity buffers our biology from the natural environment. In the future we cannot accurately predict the stresses we will face," he explained. "The relative importance of natural selection in shaping our species might be weak at present, but it has the potential to become stronger again in the future."
Human diversity not that great
Yes, Epigenetics!
Gene Expression.