Good news for future generations of career women: we are evolving to have more children later in life, according to a recent study.
Humankind has evolved more rapidly in the past 5,000 years, at a rate roughly 100 times higher than any other period of human evolution. And an author of the study predicts that this suggests humans will further evolve to have more children later in life.
Many people wait to have kids until they are in their late 30s to 40s
As a bonus, to help us stay fertile for longer, we will be troubled less by diseases such as type 2 diabetes and obesity that occur in middle age and beyond.
The claim counters a common theory that human evolution has slowed to a crawl or even stopped in modern humans, since in modern society the survivors no longer have to be the fittest, and is based on data from an international genetics project that can chart how evolution has shaped mankind over the past 40,000 years.
In a study published in the Proceedings of the National Academy of Sciences, a team led by University of Wisconsin-Madison anthropologist Prof John Hawks suggests that humans are in the evolutionary fast lane and many changes in our genes are driven by the dramatic rise in population, culture, changes in diet brought on by the advent of agriculture, and resistance to epidemic diseases that became major killers after the growth of human civilisations.
The findings may lead to a broad rethink of human evolution, Prof Hawks says: "We are more different genetically from people living 5,000 years ago than they were different from Neanderthals."
"In evolutionary terms, cultures that grow slowly are at a disadvantage, but the massive growth of human populations has led to far more genetic mutations," says Prof Hawks.
"And every mutation that is advantageous to people has a chance of being selected."
As for the next 5,000 years, he tells the Daily Telegraph that pressure to keep fertile for longer, so we delay having children, seems more important than living longer itself.
"This is always a tough question, because selection depends on the environment and our environment has been changing," he explains. "But there are basically two pathways for selection to affect a population - variation in mortality and fertility.
''Mortality variation has become very low in developed countries. Assuming that we manage to reduce malaria and other tropical diseases (and prevent a resurgence!), mortality selection will become less and less important.''
But several indications suggest that fertility selection is becoming stronger.
"The trend has been toward later reproduction," he says. "I have four kids, but my wife and I didn't start until we were in our late 20s. Many people wait to have kids until they are in their late 30s to 40s.
''But very few people lived into their 40's more than 50,000 years ago. That's a big biological change. So genes that impede fertility at later ages must be experiencing stronger and stronger selection pressure."
Equally, evolutionary pressure could help erase chronic diseases like obesity, cardiovascular disease, and type 2 diabetes, which can impede later fertility
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