What exactly makes us human?

What exactly makes us human? This is the jumping-off point for the debate 'Natural Selection in Humans: Understanding our adaptations', held jointly by B·Debate –an initiative of Biocat and the "la Caixa" Foundation– and the Institute of Evolutionary Biology, a joint research center of the CSIC and Pompeu Fabra University (UPF). On 17 and 18 July, top-notch international researchers will meet at Palau Macaya to try to understand the genetic basis of our uniqueness as human beings and the differences between large population groups.

There are characteristics that are unique to the human species. Some of them include language, cognitive capacities and walking upright. But what are the biological keys hidden behind these traits that make us human? All of these things that set our species apart are the result of natural selection over thousands of years.  

For example, the human and chimpanzee genomes are 99% directly comparable or alignable. Although 1% may seem very little, this percentage translates into at least 30 million genetic differences between the two species, and that is a very broad field of scientific study. Even between any two human beings there can be 3 million genetic differences.

The genetic alterations that make us human

Modern human beings appeared approximately 200,000 years ago in Africa, from where they spread to regions all over the planet, ranging from tropical to high-altitude locations to which the specific groups adapted over thousands of years. Scientists have described various evolutionary adaptations that define us as a species. But within those parameters, humans have different genetic variants that allow us to adapt to our environment. One example is found in people who live at high altitudes and can survive with less oxygen. Others include the populations with genes that make them resistant to certain diseases, like malaria (so far researchers have identified 8 different gene mutations that help us beat malaria) and the Inuit populations in Canada, Alaska and Greenland who have adapted to a high-fat diet because they mainly eat fish.

But these aren’t the only adaptive changes. Human beings are the only mammals that continue to drink animal milk as adults because we are able to break down lactose molecules and take advantage of its nutrients, above all the fats. This arose roughly 5,000 years ago and was maintained because it gave us a great selective advantage, for example at times when food is scarce.