Us lot, contemporary humans in a postindustrial society, we've got a welfare system, social security and even, in some countries, free health care. Premature babies survive, the wounded get better, the hungry get fed. We're shielded from the blind hand of natural selection, aren't we?

Biologists readily agree that natural selection in our cave-dwelling past shaped the animal that we are now. We evolved in prehistoric times and still carry evolutionary leftovers from those times. This accounts for some of the puzzling things about humans compared to other animals: our long maturation period and our small litter size, for example. What's more controversial is whether selection is still continuing. Have our genes not changed since we lived in Stone Age conditions, or is natural selection continuing on the current human population in the modern environment, with modern human culture?

It's continuing, according to new evidence from an international team of scientists. An epic three-year analysis of census data from women enrolled at the Australian Twin Registry suggests that, in the population studied, women are having their first child at earlier ages. What's startling for those who thought we were removed from the animal world is that the research shows that the move to an earlier age of reproduction is an inherited evolutionary change.