Whaddaya know, more quotes from Peter Watts’ Blindsight! They’ll be a weekly thing (every Monday) till I either get bored or run out of quotables. These are for the most part infodumps, which some people are curiously averse to; of course saying that infodumps “make for bad writing” and meaning it literally is just succumbing to the mind projection fallacy of confusing states of mind (valuations, uncertain knowledge etc) with states of reality.
As always, quotes may contain spoilers so if you hate spoilers stop reading now.
I had my own style, of course. I tried to be charming in my own peculiar way. Once, after one too many fights about honesty and emotional manipulation, I’d started to think maybe a touch of whimsy might smooth things over. I had come to suspect that Chelsea just didn’t understand sexual politics. Sure she’d edited brains for a living, but maybe she’d just memorized all that circuitry without giving any thought to how it had arisen in the first place, to the ultimate rules of natural selection that had shaped it. Maybe she honestly didn’t know that we were evolutionary enemies, that all relationships were doomed to failure. If I could slip that insight into her head— if I could charm my way past her defenses— maybe we’d be able to hold things together.
So I thought about it, and I came up with the perfect way to raise her awareness. I wrote her a bedtime story, a disarming blend of humor and affection, and I called it
The Book of Oogenesis
In the beginning were the gametes. And though there was sex, lo, there was no gender, and life was in balance.
And God said, “Let there be Sperm”: and some seeds did shrivel in size and grow cheap to make, and they did flood the market.
And God said, “Let there be Eggs”: and other seeds were afflicted by a plague of Sperm. And yea, few of them bore fruit, for Sperm brought no food for the zygote, and only the largest Eggs could make up the shortfall. And these grew yet larger in the fullness of time.
And God put the Eggs into a womb, and said, “Wait here: for thy bulk has made thee unwieldy, and Sperm must seek thee out in thy chambers. Henceforth shalt thou be fertilized internally.” And it was so.
And God said to the gametes, “The fruit of thy fusion may abide in any place and take any shape. It may breathe air or water or the sulphurous muck of hydrothermal vents. But do not forget my one commandment unto you, which has not changed from the beginning of time: spread thy genes.”
And thus did Sperm and Egg go into the world. And Sperm said, “I am cheap and plentiful, and if sowed abundantly I will surely fulfill God’s plan. I shall forever seek out new mates and then abandon them when they are with child, for there are many wombs and little time.”
But Egg said, “Lo, the burden of procreation weighs heavily upon me. I must carry flesh that is but half mine, gestate and feed it even when it leaves my chamber” (for by now many of Egg’s bodies were warm of blood, and furry besides). “I can have but few children, and must devote myself to those, and protect them at every turn. And I will make Sperm help me, for he got me into this. And though he doth struggle at my side, I shall not let him stray, nor lie with my competitors.”
And Sperm liked this not.
And God smiled, for Its commandment had put Sperm and Egg at war with each other, even unto the day they made themselves obsolete.
I brought her flowers one dusky Tuesday evening when the light was perfect. I pointed out the irony of that romantic old tradition— the severed genitalia of another species, offered as a precopulatory bribe—and then I recited my story just as we were about to fuck.
To this day, I still don’t know what went wrong.
The cool thing about reading this was that it immediately reminded me of this Quora answer by Suzanne Sadedin, who has a Ph.D. in zoology, to the question “what is the evolutionary benefit or purpose of having periods?”. (Cool trivia: it has over 9000 upvotes.) (Side note: teleological dressing again! Sometimes I’m tempted to ask whether people can reword their discourse on evolution to completely eliminate anything related to “purpose” – because purpose isn’t a necessary ingredient in the mechanism of evolution – just to see whether they really understand it.) Anyway:
The answer to this question is one of the most illuminating and disturbing stories in human evolutionary biology, and almost nobody knows about it. And so, O my friends, gather close, and hear the extraordinary tale of:
HOW THE WOMAN GOT HER PERIOD
Contrary to popular belief, most mammals do not menstruate. In fact, it’s a feature exclusive to the higher primates and certain bats*. What’s more, modern women menstruate vastly more than any other animal. And it’s bloody stupid (sorry). A shameful waste of nutrients, disabling, and a dead giveaway to any nearby predators. To understand why we do it, you must first understand that you have been lied to, throughout your life, about the most intimate relationship you will ever experience: the mother-fetus bond.
Isn’t pregnancy beautiful? Look at any book about it. There’s the future mother, one hand resting gently on her belly. Her eyes misty with love and wonder. You sense she will do anything to nurture and protect this baby. And when you flip open the book, you read about more about this glorious symbiosis, the absolute altruism of female physiology designing a perfect environment for the growth of her child.
If you’ve actually been pregnant, you might know that the real story has some wrinkles. Those moments of sheer unadulterated altruism exist, but they’re interspersed with weeks or months of overwhelming nausea, exhaustion, crippling backache, incontinence, blood pressure issues and anxiety that you’ll be among the 15% of women who experience life-threatening complications.
From the perspective of most mammals, this is just crazy. Most mammals sail through pregnancy quite cheerfully, dodging predators and catching prey, even if they’re delivering litters of 12. So what makes us so special? The answer lies in our bizarre placenta. In most mammals, the placenta, which is part of the fetus, just interfaces with the surface of the mother’s blood vessels, allowing nutrients to cross to the little darling. Marsupials don’t even let their fetuses get to the blood: they merely secrete a sort of milk through the uterine wall. Only a few mammalian groups, including primates and mice, have evolved what is known as a “hemochorial” placenta, and ours is possibly the nastiest of all.
Inside the uterus we have a thick layer of endometrial tissue, which contains only tiny blood vessels. The endometrium seals off our main blood supply from the newly implanted embryo. The growing placenta literally burrows through this layer, rips into arterial walls and re-wires them to channel blood straight to the hungry embryo. It delves deep into the surrounding tissues, razes them and pumps the arteries full of hormones so they expand into the space created. It paralyzes these arteries so the mother cannot even constrict them.
What this means is that the growing fetus now has direct, unrestricted access to its mother’s blood supply. It can manufacture hormones and use them to manipulate her. It can, for instance, increase her blood sugar, dilate her arteries, and inflate her blood pressure to provide itself with more nutrients. And it does. Some fetal cells find their way through the placenta and into the mother’s bloodstream. They will grow in her blood and organs, and even in her brain, for the rest of her life, making her a genetic chimera**.
This might seem rather disrespectful. In fact, it’s sibling rivalry at its evolutionary best. You see, mother and fetus have quite distinct evolutionary interests. The mother ‘wants’ to dedicate approximately equal resources to all her surviving children, including possible future children, and none to those who will die. The fetus ‘wants’ to survive, and take as much as it can get. (The quotes are to indicate that this isn’t about what they consciously want, but about what evolution tends to optimize.)
There’s also a third player here – the father, whose interests align still less with the mother’s because her other offspring may not be his. Through a process called genomic imprinting, certain fetal genes inherited from the father can activate in the placenta. These genes ruthlessly promote the welfare of the offspring at the mother’s expense.
How did we come to acquire this ravenous hemochorial placenta which gives our fetuses and their fathers such unusual power? Whilst we can see some trend toward increasingly invasive placentae within primates, the full answer is lost in the mists of time. Uteri do not fossilize well.
The consequences, however, are clear. Normal mammalian pregnancy is a well-ordered affair because the mother is a despot. Her offspring live or die at her will; she controls their nutrient supply, and she can expel or reabsorb them any time. Human pregnancy, on the other hand, is run by committee – and not just any committee, but one whose members often have very different, competing interests and share only partial information. It’s a tug-of-war that not infrequently deteriorates to a tussle and, occasionally, to outright warfare. Many potentially lethal disorders, such as ectopic pregnancy, gestational diabetes, and pre-eclampsia can be traced to mis-steps in this intimate game.
What does all this have to do with menstruation? We’re getting there.
From a female perspective, pregnancy is always a huge investment. Even more so if her species has a hemochorial placenta. Once that placenta is in place, she not only loses full control of her own hormones, she also risks hemorrhage when it comes out. So it makes sense that females want to screen embryos very, very carefully. Going through pregnancy with a weak, inviable or even sub-par fetus isn’t worth it.
That’s where the endometrium comes in. You’ve probably read about how the endometrium is this snuggly, welcoming environment just waiting to enfold the delicate young embryo in its nurturing embrace. In fact, it’s quite the reverse. Researchers, bless their curious little hearts, have tried to implant embryos all over the bodies of mice. The single most difficult place for them to grow was – the endometrium.
Far from offering a nurturing embrace, the endometrium is a lethal testing-ground which only the toughest embryos survive. The longer the female can delay that placenta reaching her bloodstream, the longer she has to decide if she wants to dispose of this embryo without significant cost. The embryo, in contrast, wants to implant its placenta as quickly as possible, both to obtain access to its mother’s rich blood, and to increase her stake in its survival. For this reason, the endometrium got thicker and tougher – and the fetal placenta got correspondingly more aggressive.
But this development posed a further problem: what to do when the embryo died or was stuck half-alive in the uterus? The blood supply to the endometrial surface must be restricted, or the embryo would simply attach the placenta there. But restricting the blood supply makes the tissue weakly responsive to hormonal signals from the mother – and potentially more responsive to signals from nearby embryos, who naturally would like to persuade the endometrium to be more friendly. In addition, this makes it vulnerable to infection, especially when it already contains dead and dying tissues.
The solution, for higher primates, was to slough off the whole superficial endometrium – dying embryos and all – after every ovulation that didn’t result in a healthy pregnancy. It’s not exactly brilliant, but it works, and most importantly, it’s easily achieved by making some alterations to a chemical pathway normally used by the fetus during pregnancy. In other words, it’s just the kind of effect natural selection is renowned for: odd, hackish solutions that work to solve proximate problems. It’s not quite as bad as it seems, because in nature, women would experience periods quite rarely – probably no more than a few tens of times in their lives between lactational amenorrhea and pregnancies***.
We don’t really know how our hyper-aggressive placenta is linked to the other traits that combine to make humanity unique. But these traits did emerge together somehow, and that means in some sense the ancients were perhaps right. When we metaphorically ‘ate the fruit of knowledge’ – when we began our journey toward science and technology that would separate us from innocent animals and also lead to our peculiar sense of sexual morality – perhaps that was the same time the unique suffering of menstruation, pregnancy and childbirth was inflicted on women. All thanks to the evolution of the hemochorial placenta.