Why Condoms Should Have Killed Natural Selection, But Didn’t

Feb 06, 2015 at 7:46 AM ET

Most people think we’ve beaten evolution. Perhaps once, unfit people died while the fittest survived to propagate their stellar genes. But nowadays modern medicine cures the unhealthiest members of society, and widespread use of contraception means that even so-called “fit” people are having fewer kids than ever. By all accounts, modern proclivities should have shut down natural selection, once and for all.

And yet, according to a recent study, Darwinian evolution is alive and well.

Researchers examined 10,000 genealogical records dating back to the 1700s. They found that anywhere from 4 to 18 percent of the variation between individuals is still due to genetics, even in modern times. Humanity, according to the study, has evolved at roughly the same rate for three centuries.

From the paper:

We have shown that there is ample potential for a population that has gone through the demographic transition to respond to selection, despite claims that human cultural adaptations, including medical advances, have effectively halted natural selection…or that fertility is now culturally influenced to a degree where fitness no longer has a heritable basis.

Scientists aren’t sure why modern medicine and contraception haven’t stopped evolution in its tracks. One theory is that modern societies have more individual freedoms, so people can now marry whomever they choose. It is possible that this mixes up the gene pool in a way that favors evolution—compensating for what natural selection lost to prenatal care and condoms.