Genetics: Human Factors

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Genetics: Human Factors
Genetics: Human Factors

Human Factors

We share almost 99 percent of our genome with the chimpanzee. There is not much left for the human being. And yet a lot has happened in the human genome - some even recently.


Not so long ago, a split occurred in Africa that would have worldwide consequences: in the primate order, which had been relatively insignificant until then, one group stayed in the forests, while a second group preferred the open savannah. From the former emerged the species Pan troglodytes, i.e. the chimpanzee; the offshoots evolved into the species Homo sapiens-humans.

No one knows exactly when the event happened. The estimate is five million years – a blink of an eye for evolutionary biologists. So the new species had little time to genetically differentiate itself from its other primate relatives.

And so the result of the geneticists came as little surprise when they were able to present the completely deciphered genome of humans and chimpanzees: 98.8 percent of the genomes of the two species are congruent - only a tiny percent of its genome makes humans human.

In view of this fact, biologists are already calling for the historical systematic separation between the two genera Homo and Pan to be abandoned and both to be combined in a common genus. But of course humans differ from apes, and these differences must also be manifested genetically.

As early as 1975, the two American scientists Mary-Claire King and Allan Wilson suspected that the differences must not lie in the genes themselves, but rather in their control. The researchers working with Yoav Gilad from Yale University in New Haven [1] were looking for exactly these differences.

The scientists were less interested in the building blocks of DNA than in the product they read off, the messenger or mRNA, which contains the building instructions for the proteins. From a total of 1056 genes from the liver, they analyzed how much mRNA the cells produce in order to directly measure the activity of the genes. Five male individuals from each of four primate species – in addition to humans and chimpanzees, also orangutans (Pongo pygmaeus) and rhesus monkeys (Macaca mulatta) – donated their liver cells for this purpose.

The rapid evolution in transcription factors occurred only in humans

(Yoav Gilad) Over half of these genes were equally active in all four species. In other words, for 70 million years - since the first primates appeared - the activity of these genes has remained unchanged. However, the researchers found increased activity in the human genome in 14 genes and reduced activity in five genetic factors. And the particularly active genes are the interesting ones - after all, they are largely so-called transcription factors, which in turn control the reading of the genome.

"If we look at gene expression, we find only subtle changes over the 65 million years of evolution of rhesus monkeys, orangutans and chimpanzees," Gilad summarizes the result. "But over the next five million years of human evolution, rapid changes focused on a specific set of genes followed. The rapid evolution in transcription factors was unique to humans."

Obviously, the young species Homo sapiens felt compelled to adjust gene activity. Gilad sees changing eating habits as one reason for this change: "No other animal cooks. Perhaps cooking food changes something in the biochemical requirements to make nutrients available and to metabolize natural toxins in plant and animal foods."

But man's genetic evolution did not stop with his splitting off from his animal relatives. One percent of the genome is "typically human", a tenth of which - i.e. 0.1 percent - makes a person an individual. These tiny differences, which occur in all people apart from identical twins, sometimes involve just a single piece of DNA in a gene, called SNP (single nucleotide polymophism) by geneticists.

These one-base variations are often passed to the succeeding generation in clusters or haplotypes. The "HapMap" project - as a worthy successor to the human genome project - has dedicated itself to clarifying these individual differences.

This gave the researchers led by Benjamin Voight from the University of Chicago extensive data to analyze the genetic variations in recent human history. The scientists base their analysis on the genetic material of 209 people: 89 East Asians from Tokyo or Beijing, 60 Europeans and 60 representatives of the Yoruba from Nigeria [2].

Many of these variations seem particularly typical of the adaptation of modern humans

(Jonathan Pritchard) The comparison of around 800,000 SNPs revealed that evolution did not stand still: more than 700 human genes have probably only changed within the last 10,000 years - long after Homo sapiens left his native Africa set out to conquer the world.

The best-known example of this is probably the gene for the enzyme lactase: our hunting and gathering ancestors still lacked it. However, a random mutation made it possible for adults to also break down the milk sugar lactose - a crucial survival advantage for the early pastoral peoples of Europe and Asia. Today, about ninety percent of Europeans have this gene variant.

However, changes also occurred in other areas, for example in skin pigmentation - the researchers found five different genes here - in smell perception or in the metabolism of fats and alcohol.

"Many of these variations seem to be particularly typical of the adaptation of modern humans," explains working group leader Jonathan Pritchard, "such as skin pigmentation, which responds to changes in habitat, or metabolic genes such as lactase, which respond to changes in the Respond to agriculture."

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