This story was originally written in Portuguese, and published to the website of Jornal O Globo, Brazil. It appears here with permission.
There is a well-established scientific consensus that the division of the human species into races makes no biological sense. “Race”, when we talk about Homo sapiens, is a social phenomenon – and one with very real social effects. We know, however, that many consensuses that are obvious to the scientific community are not always easy to convey.
Just look at the difficulty of explaining consensuses such as human-caused global warming and evolution. Perhaps the unreality of biological races is an even more complicated case – after all, people are culturally conditioned to take some differences in individual appearance as markers of “race.” But these markers are completely arbitrary; biologically, talking about the “white” (or black) race makes as much sense as referring to the “bald” (or hairy) race.
It doesn’t help, of course, when major universities try to use people’s appearance to decide whether or not they suffer from racism, misappropriating terms originated in biology, such as “phenotype.”
To make it perfectly clear how absurd the notion of “biological races” in humanity actually is, a group of researchers from the USA decided to use as an example a species in which talking about races does indeed make biological sense: dogs.
In a scientific article, the authors begin by showing that 27% of the genetic differences between dogs can be attributed to races. In humans, only 3-4% of genetic differences can be attributed to different populations of origin. Furthermore, in humans, the greatest genetic variation occurs within populations, and not between different populations; two people with the same skin tone from any African country probably have more DNA variations between them than if they were compared to people from another continent. And these differences are found in only 0.1% of the genome: we humans are 99.9% identical in DNA.
The opposite occurs in dogs. Breeds considered pure have very little internal genetic variation, but there are significant differences between breeds. In other words, dogs of the same breed are very similar to each other.
The authors also explain the difference between the pressures generated by natural selection in humans, and the artificial selection to which dogs have been subjected. In humans, no population has ever undergone complete genetic isolation. And even when selective pressures such as UV light incidence favoured different skin colors, or warmer or colder regions selected different body shapes, these selected characteristics are usually polygenic (involving many genes) and determined by different genes in different cases.
In other words, the same skin tone (or the same physiological characteristic, such as lactose intolerance) can be determined by different genes in different groups. The same characteristic, different genetic origins.
In dogs, most physical characteristics, such as color and height, are determined by a few genes, almost all known, and from the same origin. For example, the same mutant gene causes hairlessness in three different breeds, and can be traced back to one ancestor. There are only nine genes for coat pattern in dogs, five specifically for color. In humans, the authors cite more than 50 genes that influence skin pigmentation in the African continent alone.
This happens mainly because artificial selection allows the breeder to completely isolate one breed from another, preventing them from breeding “outside” the desired population. The breeder has total control over the “matrices”, those few animals that can produce offspring, keeping the breed pure. Some dogs have had more than 2,500 puppies. In humans, to this day, this radical isolation has never happened, as much as some fanatical racists have toyed with the idea. We are all mongrels, and that’s a good thing.
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