Anthropologist Henry Harpending is using microscopic scans of human chromosomes as peepholes to peer into humankind’s remote past — and its distant future.

The scans have thrown up insights into how genetic changes over thousands of years gave rise to light skins among Europeans, fuelled the expansion of Indo-Europeans into India, and are now turning some African populations resistant to malaria.

It’s the pace of such genetic changes that has stirred the scientific community. The study by Harpending at the University of Utah and his colleagues has shown that humans have evolved 100 times faster over the past 5,000 years than anytime before in human history.

“Human races are genetically diverging from each other, and the changes are different in different continents,” said Harpending. Some changes are apparent such as in skin, eye and hair colour, while others such as resistance to certain diseases remain hidden as subtle genetic variations.

Unchecked, Harpending said, such genetic divergence could even lead to the emergence of “new” species if the populations remain isolated sufficiently long enough.

“It seems to require something like one half to one million years of separation for large populations of mammals to become new species,” Harpending told KnowHow.

But Homo sapiens sapiens may not get a chance to branch out into Homo sapiens europiens, Homo sapiens asiensis or Homo sapiens africanus. (If they did, they would have probably got these names!)

Researchers believe globalisation and the mixing of populations is at work, countering the divergence. “There is so much migration now between continents and nations — millions of people a year — that they will become more homogeneous in the future,” said John Hawks, assistant professor of anthropology at the University of Wisconsin, Madison, and a research team member.

The study looked for evidence of natural selection — the evolution of favourable genetic mutations — during the past 40,000 years, by analysing DNA from 270 people representing European, African, Japanese and Chinese populations. The researchers specifically searched for single-point genetic variations called single nucleotide polymorphisms in chromosomes spreading through a significant proportion of populations. Over time, chromosomes randomly break and recombine to create new variants. If a favourable mutation appears, the number of copies of that chromosome will increase rapidly in the population because people with the mutation are more likely to survive and reproduce.

Scientists believe these genetic changes are primarily driven by population expansion and exposure to new environments and infections.

“Genes primarily involved in adaptation to different environments are favourably selected,” said Partha Majumder, head of the human genetics unit at the Indian Statistical Institute, Calcutta.

“Because of the adaptation and natural selection, human genome pools exposed to different conditions may have diverged more rapidly than what is expected by chance alone,” Majumder told KnowHow.

Mutations that favour light skin appeared among Europeans. Researchers believe light skin is needed in cold, dark climates to allow sunlight to synthesise vitamin D. When populations were exposed to new infections, genetic variations that protect against the diseases became favourable.

Genes that protect from malaria emerged in some African populations. Another gene named CCR5 originated about 4,000 years ago and now exists in about 10 per cent of the European population.

The CCR5 gene was discovered because it makes people resistant to HIV. But the researchers believe that its original value might have come from being able to obstruct the pathway for smallpox.

“Every mutation advantageous to people has a chance of being selected and driven towards fixation,” Hawks said. “Selection occurs because people carrying a gene are either more likely to survive long enough to have children or are more likely to have more of them,” Hawks told KnowHow.

Most mammals lose the enzyme to break down milk after they are weaned away, but Europeans and east Africans acquired it about 7,000 years ago. This was a new adaptation — directly linked to the domestication of animals and the use of milk as food. Harpending is now studying whether this mutation might have spurred the spread of the Indo-Europeans from central Asia to Europe and India 5,000 years ago.

He believes the ability to digest milk gave lactose-tolerant Indo-European speakers more energy, allowing them to conquer a large area.

While the study identified about 3,000 genes in each of the populations studied, the role of many genes is still unclear. “For many of these genes, we don’t know what the new version does better, but we can tell that they must have done something,” Hawks said.

Chinese and Japanese populations, for instance, have evolved genes that produce dry ear wax instead of the wet and sticky ear wax found in other populations. “The best guess about what these genes are doing is the suppression of odour,” said Harpending.

Harpending concedes that the findings are likely to become controversial as they deal with genetic differences between human populations.

“How the genetic differences will pan out is hard to predict,” Majumder said. But skin colour differences are already apparent, and specific populations might be more susceptible or protected from certain diseases.

“It worries me. There is a lot of racial and ethnic tension and such findings will not help address these issues. But we can’t censor scientific findings,” said Harpending.