This article was originally published on The Conversation.
Popular wisdom and established evolutionary science hold that the sexes seek fundamentally different relationships: men want short-term, no-strings-attached relationships whereas women value longer-term, loyal partnerships.
The explanation generally comes down to biological differences between men and women. Because women invest more in reproduction than men do – think pregnancy, morning sickness and stretchmarks – being picky becomes important because choosing poorly can be costly, even devastating. However, for men, reproduction may only entail a brief sexual liaison and a bit of sperm – there are potentially no long-term costs. This calculus has been built into our psychology, many argue.
Think about it more carefully, though. Where do all the women sleeping with these guys come from? Shouldn’t it be difficult for men to find so many willing partners? As theorist Hanna Kokko noted, it takes two to tango.
If we go by the numbers, in a group with an equal number of both sexes, it is impossible, on average, for men to have more partners than women. So why do we expect male psychology to be so hellbent on one-night stands? And why, clearly in opposition to this notion, are many men often so devotedly paternal?
Here’s where an established body of literature in sociology and demography – called mating market theory (MMT) – can help out. According to MMT, relationship preferences are expected to follow not simply from these fixed biological propensities, but also to be heavily influenced by partner availability.
When Linda May went in to see her obstetrician during her first pregnancy, he told her she probably shouldn’t jump, run, or even walk. But May, an exercise physiologist who studies pregnant women and their babies, knew a thing or two about the positive ways that being active can help a mom-to-be’s health. Women who exercise with baby on board have been known to have, among other things, lower risks of gestational diabetes and pregnancy-induced high blood pressure than those who don’t.
Since then, May and other researchers have discovered even more ways that prenatal exercise benefits not only an expectant mother, but her growing baby, too—sometimes for years into the future—as attendees learned at last week’s Experimental Biology 2014 meeting in San Diego.
Decades ago, many more doctors gave similar advice to May’s obstetrician. Pregnancy was thought to be almost like an illness, a time when women needed to rest to protect themselves and their babies. In 1985, the American Congress of Obstetricians and Gynecologists came out with their first set of guidelines for exercise during pregnancy—guidelines, now considered conservative, that included suggestions like keeping strenuous activities to 15 minutes or less.
Since then, research has turned that idea on its head. Exercise is now thought to be—for most women with healthy pregnancies—a boon for the mother’s health, and for the baby she carries as well. Researchers are now starting to look even more closely at how exercise can influence a baby’s health in the womb and how these effects might translate into protection from future health problems.
Scientists have called the contraceptive pill one of the most important inventions of the twentieth century. Now, more than fifty years after the Pill was first released, contraception remains a woman’s world.
Sure, men can use condoms or have a vasectomy, but women have a much more dizzying array of options from which to choose. From pills to contraceptive vaginal rings to intrauterine devices and more, most scientists and pharmaceutical companies have focused their contraception efforts on women.
This isn’t necessarily a bad thing. Many reproductive health scientists say that we need more, not fewer, options for contraception. The problem is that virtually all contraception is being geared toward women. That’s largely because, historically, contraception was grouped in with the traditional female concerns of family and childbearing.
“There are a fair number of women who are dissatisfied with their current method of contraception,” said Michael O’Rand, a biologist and male contraception expert at the University of North Carolina at Chapel Hill.
Sophie Bushwick (Twitter, Tumblr) is a science journalist and podcaster, and is currently an intern at DISCOVERmagazine.com. She has written for Scientific American, io9, and DISCOVER, and has produced podcasts for 60-Second Science and Physics Central.
Human chromosomes (grey) capped by telomeres (white)
U.S. Department of Energy Human Genome Program
Renowned biologist Elizabeth Blackburn has said that when she was a young post-doc, “Telomeres just grabbed me and kept leading me on.” And lead her on they did—all the way to the Nobel Prize in Medicine in 2009. Telomeres are DNA sequences that continue to fascinate researchers and the public, partially because people with longer telomeres tend to live longer. So the recent finding that older men father offspring with unusually lengthy telomeres sounds like great news. Men of advanced age will give their children the gift of longer lives—right? But as is so often the case in biology, things aren’t that simple, and having an old father may not be an easy route to a long and healthy life.
Every time a piece of DNA gets copied, it can end up with errors in its sequence, or mutations. One of the most frequent changes is losing scraps of information from each end of the strand. Luckily, these strands are capped with telomeres, repeating sequences that do not code for any proteins and serve only to protect the rest of the DNA. Each time the DNA makes a copy, its telomeres get shorter, until these protective ends wear away to nothing. Without telomeres, the DNA cannot make any more copies, and the cell containing it will die.
But sperm are not subject to this telomere-shortening effect. In fact, the telomeres in sperm-producing stem cells not only resist degrading, they actually grow. This may be thanks to a high concentration of the telomere-repairing enzyme telomerase in the testicles; researchers are still uncertain. All they know is that the older the man, the longer the telomeres in his sperm will be.
Every few years it seems that the British biologist Steve Jones declares the death of evolution by natural selection in the human species. The logic here is simple even to a schoolboy: evolution requires variation in fitness, and with declining risk by death during our reproductive years humans have abolished the power of selection. But this confuses the symptom for the disease. Death is simply one way that natural selection can occur. Michelle Duggar has 19 children. The average American woman has around two by the end of her reproductive years. It doesn’t take a math whiz to figure out that Michelle Duggar is more “fit” in the evolutionary sense than the average bear. Even without high rates of death, some people have more children than other people, and if those people who have more children than those who do not are different from each other in inherited traits, evolution must occur. Q.E.D.
But you probably shouldn’t be convinced by logic alone. Science requires theory, experiment, and observation. (If you’re talking humans, you can remove the second from the list of possibilities: there are certain unavoidable ethical obstacles to experimenting on human evolution—plus we take far too long to reproduce.) But humans sometimes have something which bacteria can not boast: pedigrees! Not all humans, of course. Like most of the world’s population I don’t have much of a pedigree beyond my great-grandparents’ generation. But luckily for biologists, the Catholic Church has long taken a great interest in life events such as baptism, marriage, and death, and recorded this info parish by parish. With these basic variables, demographers can infer the the rough life histories of many local populations over the centuries. In many European nations, these databases can go more than 10 generations back. And some aspects of human evolution are revealed by these records.
What aspects am I talking about? Reproduction itself. Not only is variation in fitness one of the primary ways by which evolution occurs, but it is also a trait upon which evolution operates! How else are there rabbits which breed like…rabbits, and pandas…which don’t. There is often variation within species for the odds of multiple births, age at first reproduction, and lifespan, depending upon the differences in selection pressures over a population. And that seems to be exactly what occurs in human beings. There is interesting evidence for evolution of reproductive patterns from populations as diverse African pygmies and Finns, but more recently some researchers have been plumbing the depths of the records of the Roman Catholic Church in Quebec, and they’ve come back with gold.