While returning things this Christmastime, my wife and I began to discuss the number of young, unmarried mothers nowadays.
**Is there any evolutionary ideal age for a woman to become a mother? **We wonder if perhaps society’s norms are at odds with biology’s dictates.
In purely biological terms it’s probably fairly young, less than 20 years old. In the modern world, an older successful woman may be able to better provide for her child.
18, probably.
Also keep in mind that evolutionary ideal age for having a first child might not necessarily be ideal for the child itself. It might be ideal for subsequent children. If (completely made up numbers) women having first children at 13 average 4.3 offspring that go on to reproduce, while women having first children at 16 average 3.2 offspring that go on to reproduce for some reason, 13 is a more ideal age, even if it leads to less survival of the first child.
Certain health risks (including some birth defects) to both mother and baby are more common in teenagers than women over 18 or 19 for multiple reasons, one of them that many girls that age are still developing physically, and pelvises continue to grow into the early 20s (and with each pregnancy). But fertility begins to decline (slightly) at around 25 - and reduced fertility really just means your eggs aren’t quite as good anymore. So IMO 19 to the mid-20s is the prime biological time for women to be reproducing.
Actually IIRC, in a majority of more ‘primitive’ cultures studied over the years women marry between 17-25 and have their first child within a year or so. Marrying as soon as you get your period and having babies as a teenager is more of a modern phenomena, seen mostly in cultures with certain religious beliefs and overcrowding issues (unfortunately for girls some of these cultures are enormous, like the parts of India where child marriage and early childbirth is distressingly common, despite the government’s efforts to outlaw it due mostly to the high rates of death and injury).
I recall reading about a hypothesis quite a few years ago, that held that women are biochemically/hormonally built to have children quite young, while mechanically (ie, hip width and such) are better off having children later. A suggestion was made that if this could be proven, a hormone treatment artificially simulating the hormonal effects of pregnancy might provide girls with the (alleged) long term biochemical benefits of an early pregnancy, without the physical and social downsides. But medicine would have to be really certain it would work before such thing would be even tried.
ETA: Don’t most variants of the Pill simulate pregnancy?
It seems that most mammals will become fertile and commonly bear their first offspring while still technically physically immature; but this is much less of a problem for, say, chimpanzees (to say nothing of animals that have litters of multiple tiny babies) because of their pelvic structure and the comparatively tiny size of their infant’s heads.
It’s been reported that hunter-gatherer and pastorialist cultures tend to experience slightly delayed puberty (13-16 at menarche rather than 11-14 as in farming cultures/most of the developed world). What foods you eat, how much you eat, and your body fat levels have a big influence on both puberty and fertility, and those are things that have changed a shitload ever since agriculture came about.
If we’re talking about things from a purely evolutionary standpoint, if ~18-20 is the ideal age, then why have evolutionary pressures not delayed menarche until then? If girls become fertile at ~12-13, isn’t that because genes for fertility at that age have been succesfully handed down over many generations?
Late 20s, early 30s.
Do you have a cite, or at least a rationale, to support that?
Evolution is a lot more complex than sweat peas and ear lobes. A specific genotype will have several related phenotypical characteristics, some of which increase reproductive success and some of which do not.
Fertility does not directly equate to motherhood.
The most obvious possibility is that the human female reproductive tract undergoes additional development with exposure to the changing and increasing hormone levels. Much like human visual system continuing to develop after birth in response to visual stimuli.
Probably because infant mortality was historically so high that it made evolutionary sense for women to have babies both before and after the ideal age for it. It’s not like a modern woman who can typically expect any children she has to survive to adulthood and outlive her, and can therefore schedule her childbearing for (relative) convenience and safety. A woman in the old days pretty much had baby after baby in the hope that just a few would make it all the way to adulthood.
Why are you busting my balls on this? If you disagree, just say so. No, I’m not an obstetrician. Didn’t say I was.
Because this the forum for fact based claims, and extraordinary claims require extraordinary evidence.
You’ve offered no evidence, and your claim is contrary to conventional wisdom and established medical fact - women generally become less fertile as they move into their thirties.
IMHO is the forum for straight opinions. Though you’d do better even there if you’d back it up with arguments and information.
Thank you.
My hazing period should be over soon.
Paul in Qatar writes:
> . . . my wife and I began to discuss the number of young, unmarried mothers
> nowadays . . .
I’m not sure what you’re saying here. If you’re claiming that there are more teenage mothers today, your claim is exactly opposite the truth. The percentage of teenage women who have babies (in the U.S.) is the smallest that it’s been in something like fifty or sixty years, and that’s also approximately true in many other countries too.
I dunno, most 18 year-olds aren’t ready to be mothers. Most 18 year-olds are still in school, still getting themselves established in the world.
Recall reading about Samuel Pepys and his escapades. He became smitten with the girl(!) he married but decided that he would wait until she was 15 before they consumated the marriage.
OTOH, Captain Cook describes a ceremony in Hawaii where a girl of 10 or 12 was celebrating “the rites of Venus” in front of the audience, with a much older man, while being egged on with comments from the older women… King John (of Robin Hood fame) took up with a 13-year-old, as allegedly did Mohammed. And Loretta Lynn was married at 13 “…and a mother shortly after…”.
For all the discussion of “13”, remember that it’s good nutrition that allows the early development and early puberty that permits this sort of teen pregnancy. IIRC 15 used to be a more normal time for onset of fertility, suggesting 16 was the usual early time to give birth.
Also remember that an extended childhood is another modern invention, everyone had to earn their keep way back when. A woman reaching child-bearing age who did not have a husband was a burden on her family, unless there was enough housework to keep 2 women busy or some other productive job. Plus, she was no doubt in high demand by everyone looking for a wife. In societies that put a premium on purity (men being men, many did) the earlier she was unloaded the better.
Ah, how times have changed.
In terms of evolution, until some form of strict morals evolved, humans lived in groups or tribes and girls began reproducing as soon as they were physically able. So my guess is about 16 or so was the evolutionary ideal start. At that age, a female would be close to final full size and recently started ovulating, although she would have had the other physical attributes for a while.
I recall something I read about this that suggested women develope secondary sex characteristics - breasts, wide hips, etc. - before the onset of menstruation, thus ensuring they attracted a mate before they had to support a child; while males were the opposite, being able to produce sperm before they looked like full adults, in order to escape being singled out as rivals by bigger older males for a few extra years.
We as a species aren’t evolved to go to school. And going to school past the age of 18 is still something most humans on this planet do not do, and even in the US today, only about 30% of adults have completed a bachelor’s degree.
Besides, the OP was speculating on the physical childbearing prime years of a woman being at odds with the current social/economical take on when a woman “should” have children. Clearly the current mainstream middle-class view is mid-20s or so, or even later (as you suggest) into the early 30s for many upper middle class people who either treat their 20s as extended adolescence (“I only just got down with school at age 21 and deserve a decade of fun single time”). That is not what is being discussed here - not whether an 18 year old “should” get pregnant, or whether teenage pregnancy is more or less frequent now versus 20 or 50 or 150 or 1,000 or 10,000 years ago, but whether evolutionarily speaking that is when her body is best able to do so.
The answer depends on what is meant by “best” - as others have pointed out already: best for the child who will be born of the pregnancy, best for the mother’s health for the specific pregnancy, or best for the highest number of surviving adult children being born of the woman over her entire lifetime? That last measure is the real yardstick, evolutionarily speaking.
This study(PDF) suggests that the healthiest age range is between 20 and 34, saying that complications are actually more common in teenage mothers than mothers in their 20s.
However, that may be because of factors that aren’t biological (teens may be more reckless, or not realize they’re pregnant and drink and smoke throughout the first trimester).
When you’re talking fertility rates, clearly the young women have an edge. This study suggests that fertility starts to wane as early as 27. But that doesn’t really answer the question of when is the “best” time to get pregnant.
In this day and age, all other things being equal, I would guess that children who are born to mothers in their mid-20s probably have the best evolutionary edge. Still young enough to be producing eggs of good quality, but old enough to (probably) be more responsible than a 19-year-old mom.
