In terms of evolution, sex is the bottom line. No sex, no reproduction; no future genes, no evolution. Period.
Normally any species that has food, space, health, and peace tends to have lots and lots of sex, and the population expands accordingly, often quite fast. Antibiotic- resistant bacteria spread, lilies take over ponds, and rabbits overwhelm. It’s normal and natural, in times of plenty, to have a lot of Boogie Nights. Beating the odds of natural selection requires that your specific gene code survive, thrive, and spread. So the notion that significant numbers of successful subgroups of a powerful and dominant species may choose not to have kids at all is truly unusual. . . .
There are some very weird customs and habits out there in the animal world, but even within the context of really unusual behaviors, such as mating plugs that glue a squirrel’s vagina closed, Indian stick insects that copulate for ten weeks straight, a honeybee’s exploding testicles, fig wasps that decapitate their lovers, no species, except humans, systematically practices birth control, abstinence, or childlessness when surrounded by abundance. That is truly unusual and kinky.
Widespread birth control, which allows us to decide when we have children, and how many, seriously bends Darwin’s rules of evolution toward our wishes. So too does domestication/ urbanization. Not that you’d want to really chat about this with your kids, or parents for that matter, but think back to when you were sixteen. Perhaps you might have had just a little curiosity about, interest in, and, dare we say it, obsession with sex? Likely you indulged some of that curiosity, desire, and the occasional fantasy? Contrast this with today’s Japanese teenage sex habits.
According to the Japan Family Planning Association, 59 percent of women aged sixteen to nineteen have no interest in sex. Perhaps far more shocking is that reportedly 36 percent of teen guys, those growing packets of acne and testosterone, have no interest in sex either. This is not a new phenomenon; in part, it’s why the Japanese population is collapsing at such a rapid rate. The demographics are already so unbalanced that each month the police arrest more elderly shoplifters than teenage ones. By 2060, the Japanese population will likely be one- third of what it is today. (And speaking of strange imbalances, within the Japanese porn industry there are more than 10,000 female actresses and fewer than 100 males, leading one overworked male star to argue that his kind are now rarer than Bengal tigers.)
It’s not just Japan. Globally, there are fewer kids born, and to increasingly older parents. In many countries, next generations grow ever smaller. In the United States in the 1970s, one out of 10 U. S. women was childless. Now it’s two in 10. Only one in 100 women in 1970 had her first child after age thirty- five; today, eight in 100 do. This trend quickly cascades upward, generating ever-larger gaps between generations; in 1990, about 90 percent of women ages sixty to sixty- four had at least one grandkid. Today, fewer than 75 percent in this age range are grandmothers; soon it will be less than 50 percent. By 2025, Germany will likely have twice as many folks over 60 as under 10 years of age.
Prior to the mid-twentieth century, humans attempted to protect and pass on their genes in some most creative ways. They implemented grand societal plans, attempting to codify rules and norms for all. They individually carried out various experiments in dark bedrooms and closets. Many wished for long- term, stable love, but they also experimented, officially and unofficially, with arrangements between men and women, men and men, women and women, lovers, mistresses, friends with benefits, communes, grandfathering, co‑ops, male violence, coercion, polygamy, matriarchy . . . As Bernard Chapais comments in the journal Evolutionary Anthropology, “The human mating system is extremely flexible.” Indeed, it is. The sheer variety and breadth of options is breathtaking. Only 17 percent of human cultures are supposedly strictly monogamous (one partner for life, period). All other societies allow some within their borders to operate under very different, overlapping, sometimes quite contradictory laws, beliefs, and morals. But there have always been kids, lots and lots of kids, running around. That’s how we got to 7 billion souls on Earth today.
Sometimes populations decline because humans impose wars, privation, and extreme oppression on other humans. Russia is no stranger to depopulation. It occurred from 1917 to 1923 as the empire became the “People’s Paradise.” At least a further 2 percent of the entire country’s population was lost just from 1933 to 1934 as Stalin collectivized agriculture. World War II and its aftermath killed off a further 13 million. The irony is that the greatest driver of Russian depopulation hasn’t been death and despair. It’s been relative democracy and peace. No period of Russian depopulation has been as long and lasting as that which began with the dissolution of the USSR in 1992. In the final sixteen years of the Communist era, births in Russia exceeded deaths in Russia by 11. 4 million. But in the first sixteen years after glasnost and perestroika, deaths exceeded births by 12. 4 million.
Meanwhile, China, even as it reformed its economy and acquired wealth, enforced a one- child- per- couple law, resulting in an inverted population pyramid: eight great- grandparents relying for retirement on four grandparents who depend on two parents who had one child. But 8:4:2:1 is not a normal- looking population structure, and neither is it a structure that bodes well for future evolution. While initially one child per couple was a rational policy that cut down on explosive population growth and allowed decades of increasing productivity as the population rapidly matured, by 2012 these policies started to harm the labor force. For the first time, the absolute number of workers aged 15 to 60 declined 0.6 percent. And it will continue to do so, year after year, for the foreseeable future.
China recently slightly loosened its regulations— if both parents had themselves been only children, they could have two kids. But this change may be too little too late; young couples feel it is normal to be an only child and fear the coming burden of caring for aging parents. So China is beginning to follow the patterns of South Korea and Japan; in these countries it’s not legal restrictions on childbearing but rather expensive real estate, brutal education policies, lack of child- support networks, a desire for more personal freedom, and changing social norms that are rapidly shrinking overall populations. There may be a monetary or political logic to these choices as well, but this trend is not a natural Darwinian pattern. It’s unnatural selection that as nations get richer, more comfortable, more relatively open, less violent, and better at educating women (female literacy is a good predictor of birth rate), they also choose a massive decline in their current population.
Entire nations have decided, through the choices made sometimes by governments, sometimes by individual after individual, not to grow, not to reproduce, not to create more kids. We think this is normal. In the traditional terms of evolutionary biology, however, it’s just plain weird. And it is only one of the really strange trends going on in sex and mating that will change how many of us there are and whom we mate with, thus determining the genes of our descendants.
Perhaps the greatest irony in our recent sexual evolution is the profound change in the number of years in which we can reproduce, physiologically speaking. While the average age of conception has been rising and rising, the onset of puberty has been steadily falling. Since the 1750s the average age of male puberty has fallen 0.2 years per decade. Between the mid- nineteenth and mid- twentieth centuries, girls in the United States and several European countries began menstruating younger and younger. Every decade, the ability to reproduce comes 0.3 years earlier. In the United States, the average age of first menses dropped from seventeen to around thirteen between 1830 and 1962. The average U. S. boy begins to enter puberty at age ten. As we continue to alter our environment, our chemistry, our habits, and our hormones in unnatural ways, ever more girls and boys enter puberty while their birthdays are still in single digits.
At some point, we may consider whether to alter the most appropriately named KISS1 gene, which influences when puberty switches on or off. The point is, we have a choice. How we address this choice will influence our evolution.
Meanwhile, there is another major, and opposite, trend in the reproductive viability of men; in the United States and parts of Europe, male sperm count fell by up to 50 percent in the latter half of the twentieth century. In France, male sperm count fell 1.9 percent per year from 1989 to 2005. (So the rumor that men are ever more useless may be partly true?)
Today’s reproductive technologies and choices would bring some crimson to Darwin’s Victorian cheeks, but they would also fascinate him. As far as Darwin (and even your grandparents) knew, there was one, and only one, way to get pregnant. Today there are dozens. Start with the de‑linking of sex and birth. Historically, a couple would mate, and often less than a year later, a baby arrived. Now birth control allows far more choice of when to conceive. We have decoupled sex from time, and are stretching the calendar way, way out. None of our apelike human ancestors could reproduce outside the body, keep the embryos locked away inside frozen nitrogen far from home, and then implant the embryo inside a surrogate mother. No other mammal could freeze its eggs. But we can. Decoupling reproduction from age so you can have kids years, or decades, later? Nope, not on previous menus of sex acts either. And the oddest thing? We take it all for granted. Just before the birth of the first in vitro fertilized (IVF) baby, four of five Americans thought “test tube babies” were against God’s will. But within a month of Louise Brown’s July 1978 birth, an abstract procedure was transmogrified into a healthy, smiling baby. Suddenly more than 60 percent of those surveyed decided they were OK with IVF. Now it’s just part of the “natural” order of things, something to be discussed and thought about over a Starbucks latte with one’s partner.
Time of birth is ever further removed from “the act” by ever- evolving technologies; since the 1960s, millions of couples have benefited from an increasing variety of innovative ways to get pregnant.
Five percent of births are spurred on by fertility drugs. In 2012, about 1.5 percent of all births involved in vitro fertilization, in which hormone injections stimulate a woman’s ovaries to release multiple eggs, which are taken outside the body, put together with sperm from the woman’s male partner or a donor, and grown into minute embryos that are then transplanted back into the woman or a surrogate. The use of surrogates further allows a woman’s babies to be born years after she and her partner pass away; a baby can be born a year, five years, or 10 years after an egg or sperm leaves the body. Two parents or three, or four, is not the way Grandma did it.
And while we are on the topic of the elderly, chemicals have also radically changed sexual habits, and even parenthood, among this demographic. As the smart folks at Wired so aptly put it, “Yesterday’s drugs were about need, today’s are about desire.” While “overweight, depressed, bald, and impotent were merely descriptive terms, in today’s America they’re considered illnesses and are fought back with some $44 billion a year in direct medical expenses— fast approaching the $50 billion we spend battling cancer.” (By the way, this article was published in 2002.) As old folks sought and found better sex through chemistry, the widespread availability of Viagra, Cialis, and other erectile-promoting drugs led to some strange outcomes: The fastest-growing population for sexually transmitted disease? Not the inner cities, but old folks’ homes. It also led to some rather elderly fathers and mothers; Maria del Carmen Bousada was just about sixty- seven when she gave birth to twins. An unnatural trend that again promises nonconventional evolution opportunities. Women are supposedly born with all their eggs, whereas men continue to produce sperm throughout their lives. As men age, their sperm acquire mutations (accumulating about two per year). This means around 75 percent of the natural human rate of mutation has been driven by men. The older the man, the more mutations; fathers 30 to 34 years old increase the chances that their kids will have neural tube defects by 20 percent compared with 20- to 25-year--old dads. Fathers aged 50 and up have a 230 percent higher likelihood of engendering these, and many other types of birth defects. Aging parents drive a more rapid change of the human genome; they drive faster evolution.
Then there is the option of picking and choosing embryos outside the body based on the fitness of their DNA (pre- implantation diagnostics reveal chromosomal defects such as Tay-Sachs or Down syndrome). And we’re introducing new genes into embryos, or blocking some genes from expressing, pre- birth. And we’re operating on embryos. The list goes on and on. When a species takes such deliberate and clear technological control over its own reproduction, something very fundamental has changed. And of course we’re just getting started. The unnatural selection of future humans will be greatly augmented by nonrandom mutations arising from cloning, asexual reproduction, and edited copies of ourselves born decades in the future.
Reprinted from "Evolving Ourselves" by Juan Enriquez and Steve Gullans with permission of Current / Penguin, a member of Penguin Group (USA) LLC, A Penguin Random House Company. Copyright (c) Juan Enriquez and Steven Gullans, 2015. All rights reserved.