The price of human domestication

Civilization is overrated — and often confused with culture, whose development predates civilization by tens of thousands of years.

The popular view is that once we started ploughing fields and building cities, we could rise above the needs of mere survival and start cultivating our higher faculties through art and science, and that did indeed happen — for a privileged few. For the mass of humanity however, civilization turned people into a herded animal.

We didn’t just domesticate plants and livestock but also human populations. And it turns out that like every other kind of domestication, the conditions suited to mass reproduction also serve as breeding grounds for harmful mutations.

For humans the vast majority of harmful mutations have occurred in the last 5-10,000 years with the highest concentration among Europeans. In a world that’s more than 4 billion years old, humans have only existed for a fraction of that — roughly 200,000 years. In those 200,000 years of existence, not a lot is known about genetic mutation until we close in on the last 5 to 10 thousand years. It is within that time that researchers believe nearly 75 percent of gene mutations have occurred, making our DNA distinctly different now than it was way back when.

This finding has been calculated in new research from the University of Washington, published in this week’s issue of the journal Nature. The results, based on a genetic study of roughly 6,500 Americans (4,298 European-Americans and 2,217 African-Americans), were gleaned from studying 1 million single-letter variations in the human DNA code. These variations revealed that most of the mutations seen are of recent origin. And more than 86 percent of the harmful protein-coding mutations found occurred during the past 10 millennia. In all, about 14 percent of mutations identified were found to be harmful.

While the researchers found instances of harmful mutations, most were benign and had no effect on people, and a few more may even be beneficial. While each specific mutation is rare, the findings of the study suggest that the human population acquired abundance of single-nucleotide genetic variants in a relatively short time.

“Recent human history has profoundly shaped patterns of genetic variation present in contemporary populations,” study researcher Joshua Akey, of the University of Washington, told Business Insider in an email. “Our results suggest that ~90% of evolutionary deleterious variants arose in the last 200-400 generations.”

Akey said the expanding human growth in population has enabled DNA errors to occur more abruptly. He noted that people with European ancestry have shown the most of these new deleterious mutations because the population boom was more recent among Europeans, and natural selection has yet to remove them.

“There’s an enormous amount of recently arisen, rare mutations that’s directly attributable to the explosive population growth over the last two to four generations,” Akey told Business Week’s Elizabeth Lapatto in a phone interview.

The population of the planet has just soared beyond 7 billion, according to US Census Bureau data. That’s nearly triple the 1950 population of 2.5 billion. Such a rapid increase in population could allow unusual combinations of gene mutations to affect more people albeit remaining relatively rare, Akey said.

While some mutations are seen in the lettering of our genes, other mutations change the way the proteins made from those genes act. Some of these deleterious mutations can have negative impacts on humans’ ability to survive and reproduce, while others could be evolutionary fodder for improving the human race.

“Each generation, humanity incurs on the order of 10^11 new mutations,” Akey said. “The vast majority of these either have no phenotypic or functional consequences, or are deleterious. However, a small fraction are expected to be advantageous [sic].”

“What specific traits they may influence would just be pure speculation, but we can reasonably posit they exist and will be potential substrates for natural selection to act on in the future,” Akey wrote.

Akey added that as the population continues to balloon, so too will new mutations. The growing population makes it more likely that new mutations will be introduced, such as those linked to autism, leading to an increase in other diseases. [Continue reading…]

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