Not so old, not so diseased
Walter de La Mare was quite probably wrong when he wrote
Very old are we men
Our dreams are tales
Told in dim Eden
By Eve’s nightingales.
The human genome has been busy over the past 5,000 years. Human populations have grown exponentially, and new genetic mutations arise with each generation. Humans now have a vast abundance of rare genetic variants in the protein-encoding sections of the genome.
Researchers used deep sequencing to locate and date more than one million single-nucleotide variants — locations where a single letter of the DNA sequence is different from other individuals — in the genomes of 6,500 African and European Americans. The findings confirm their earlier work suggesting that the majority of variants, including potentially harmful ones, were picked up during the past 5,000–10,000 years. Researchers also saw the genetic stamp of the diverging migratory history of the two groups.
More broadly, the results suggest that humans are carrying around larger numbers of deleterious mutations than they did a few thousand years ago. But this doesn’t mean that humans now are more susceptible to disease, says Akey. Rather, it suggests that most diseases are caused by more than one variant, and that diseases could operate through different genetic pathways and mechanisms in different people.
The findings further undermine the idea that common diseases are caused by common variations, says Sarah Tishkoff, a geneticist at the University of Pennsylvania in Philadelphia. When genomics researchers first began looking at the genome for links to diseases, that was their assumption, but they quickly saw it fall short.
That’s a breathtaking finding: the human population has expanded so fast in the last few thousand years that natural selection hasn’t been able to cope up!