Independent Perspective News

Alberto Kornblihtt. Molecular biologist, a professor in the UBA and a researcher from the CONICET.

The old argument on whether man descends from monkey is already solved. Man doesn't descend from monkey: he is one. More precisely, an African one, like chimpanzees and gorillas, but not an Asian one like orangutan.

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The decoding of several genomes, apart from the human, has revealed something unexpected regarding the relation between an organism's complexity and the number of its genes. For instance, yeasts (...) have 6.000 genes; the Drosophila melanogaster fly, some 14.000 genes; the microscopic worm Caenorhabditis elegans, some 19.000; and us, mice (and very probably all mammals), some 30.000 genes. These figures show clearly that it's not the number of genes what makes the difference between us and mice.

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Another of the genome study's surprises is that genetic variation among humans is far lesser than previously thought. DNA is formed by the series of four chemical bases or "letters", called adenine (A), cytosine (C), guanine (G) and thiamine (T). Any DNA segment represents a "text", whose information depends on the order of its bases. It's a text written in a four-letter alphabet. If we analyze the same DNA segment from hundreds of people of different origins, we'll find out that their sequence is very similar, and that they present an average of 3,7 changes between pairs of individuals every 10.000 read letters. This means that our genomes are approximately 99,9% identical to each other.

If we compare the same segment from tens of chimpanzees we'll find out that their variability is 3 to 4 times higher. That is to say, the scarce 150.000 chimpanzees that inhabit the African savannas and jungles and the zoos of the Earth are much more different to each other than the 6.000 million human beings on the planet. Again, the paradox can be explained: the changes in the letters of the DNA sequences accumulate as time goes by, and humans (no matter how many of us there are) are much younger as a species than chimpanzees.

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Comparisons between human DNA sequences show that only 10% of the existing variability can be attributed to the differences among the so-called "races". Genetic differences between pairs of individuals account for 90% of the existing variability. To put it simple terms, a European person, for instance, may share more variants of their DNA sequence with an Asian or an African than with another European of the same skin color. Two black Africans may be further apart from each other than any of them from a white person. This results, for instance, in the fact that many times histocompatibility between a black and a white person is higher than between two individuals of the same "race" and, as a consequence, a black person is often more apt as an organ donor for a white person than another white person.

Politically correct

Genetist Svante Paabo, from the Max Planck Institute of Evolutionary Anthropology of Leipzig, Germany, is the authority in compared genomics in humans and primates. His latest molecular data only confirm the fact that human races don't exist.

In an article recently published in the prestigious magazine Nature, Paabo says: "... (the so-called "races") are not characterized by fixed genetic differences. It's been proved that the pretensions regarding genetic differences among races stem from an insufficient sample. (...) Instead of thinking in terms of ''populations", ''ethnic groups'' or ''races'', we should more constructively consider each particular individual's genome as a mosaic of sequence variations...(where)...each of us contains a vast proportion of the variation found in our species..."

There's every sign that no "race" has the necessary degree of genetic homogeneity to allow us to take the inverted comas from the term.

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