Selfish Ape
The Selfish Ape: Human Nature and Our path to Extinction
FIVE
GESTATION
How We Are Born
Two hundred and fifty babies are born every minute. The frequency of the process argues against calling it a miracle, but the spellbinding sight of a newborn can excuse this sloppy expression and mothers deserve veneration for their pains. After nine months of concealed assembly, there it is, rubbery and glistening, leaving us awestruck by the workings of nature. And awesome they are. If the arrangement of your adult organs allows you to inhale and exhale, digest food and urinate, it is certain that the chemical reactions that criss-crossed your unfolding embryo performed greater magic than the wildest designs of a modern bioengineer.
Like other sexual animals, we begin as a merger of two types of cell. Lured by pulses of ovular perfume, hundreds of sperm cells thrash around the egg. One from the swarm nudges between the obstructing follicle cells, spits a drop of enzymes from its head to dissolve a path through the coat below and sticks to the egg membrane. Fertilization proceeds with the passage of the nucleus from the sperm into the egg. Within 24 hours, the fertilized egg divides in two. Subsequent divisions create a ball of cells and, when about thirty cells have formed, the congregation organizes itself into a fluid-filled sphere called the blastocyst. The structure of a blastocyst is as simple as a colony of pond algae.
Greater complexity begins to emerge when an inner mass of cells forms at one end of the blastocyst and the embryo is planted in the wall of the uterus. The blastocyst becomes a gastrula when the layout of the body is established. This part of the engineering operation begins with the formation of a groove on the side of the embryo that will become the back of the animal. The groove is part of an emerging structure called the primitive streak. This serves as an early guidance system to ensure that the head ends up at the opposite end of the animal from its anus – which has its advantages. The left and right side of the body are positioned on either side of the streak.
Gastrula formation is also associated with the formation of three distinct tissue layers. The outermost layer, called the ectoderm, forms the skin and the nervous system; the middle layer, or mesoderm, is the source of muscle and bone tissues, and the gut and lungs come from the inner endoderm. A rod called the notochord forms inside the gastrula as the tissue layers are laid out. (Later in development, this flexible stick is absorbed into the backbone with the formation of the bony vertebrae.) A flattened plate of cells develops at one end of the primitive streak, which elongates and folds in on itself to create a tube that houses the nerve cord, which will become the spinal cord, and the swellings that become the brain. The embryo is no bigger than a sesame seed at this time, long before the identity of the animal becomes obvious.
Although the anatomy of vertebrates – animals with backbones – is more complicated than the structure of worms and insects, there are many similarities in the construction process. Earthworms have obvious segments, evident as rings on the outside and repetitive body parts on the inside. Modifications to a standardized segment plan customize the body components from one segment to the next. In the worm nervous system, for example, a pair of brain swellings at the front end arise
from less conspicuous bulges that repeat along the nerve cord in the other segments. The same goes for insects. The bodies of the larva and adult honey bee are organized as a series of segments visible as the rings on the outer skeleton of the animal. Mouthparts and antennae are attached to the ones at the front end of the adult, with three pairs of legs further back. The segmented nature of vertebrates is less obvious, but is apparent in the stacking of vertebra along the spine. Each vertebra corresponds to a body segment, referred to as a somite in the embryo. There is a common body plan at work here, accommodating hundreds of vertebrae and ribs in snakes, and reduced to 33 vertebrae and a dozen ribs in us.
Every cell in an embryo contains the whole genome of the organ-ism. The reason that brain cells work differently from lung cells is that specialized subsets of genes are active in the two types of cell. As the embryo grows, Hox
genes turn developmental pathways on or off according to the functions of each body segment. Hox
genes are organized along the length of chromosomes in the order that they are expressed, beginning with the genes that affect the formation of the head, followed by other Hox
genes that control development towards the tail of the embryo. This arrangement of genes aids their expression in the correct segment-by-segment order. Errors are disastrous. Mutations in developmental genes in fruit flies swap their antennae with stumpy legs, warp their translucent wings and shrink their eyes to dots. The consequences of these mutations in vertebrate animals include abnormal limb development and disordered organs, facial deformities, cancer and hearing loss.
The study of developmental abnormalities is called teratology and the heartbreaking specimens of this science are displayed in jars in anatomy museums. Embryologists are enthusiastic about interfering
with the embryos of chickens and other animals, but our knowledge of human teratology relies on the analysis of natural programming errors like
Hox gene mutations. A fourteen-day rule allows research on human embryos before they form the primitive streak and the left–right and head–tail organization begins to emerge. Eggs fertilized in the lab and cultured in Petri dishes will develop normally for one week, producing a blastocyst that can take root in the uterus if it is transferred into a prospective mother. New culture methods have succeeded in allowing rather misshapen embryos to grow for thirteen days after fertilization. The promise of these techniques has led to calls to revise the current legislation, but there is significant opposition from ethicists.
After the formation of the neural tube, all vertebrate animals pass through a developmental stage in which they look surprisingly similar. Fish, amphibians, reptiles, birds and mammals appear quite fishy – like fatty seahorses. Decades before the publication of Darwin’s evolutionary theory, study of the fossil record had shown that fish had evolved before other vertebrates. This encouraged ideas about a clockwork procession of beasts onto the land, the rise of the dinosaurs, birds and, crucially, Victorian gentlemen. Belief in our creation as the high point of evolutionary progress also encouraged fears about a reversal in fortunes – the possibility of bestial relapse. Robert Louis Stevenson fed this disquiet in his novel The Strange Case of’ Dr Jekyll and Mr Hyde, published in 1886:
that insurgent . . . lay caged in his flesh, where he heard it mutter and felt it struggle to be born; and at every hour of weakness, and in the confidence of slumber, prevailed against him, and deposed him out of life.
Early embryologists thought that they could see evidence of evolutionary progress in the embryos of different species, and this led to the claim that all vertebrates passed through a fish stage of development. The resemblance is real, but the modern reading of embryos reveals patterns of common ancestry: we all evolved from the same ancient wormy ancestor. The facts show, then, that salmon pass through a stage of development in which they look like the embryos of cheetahs, eagles resemble frogs and so on.
Among the most prominent shared features of embryos in this phase of manufacture are the folds that develop below the head. These are called pharyngeal pouches. Slits develop from the folds between the pouches in fish and poke through to create gills. Gill slits do not form in land animals and, instead, the pouches become very important in the development of the body segments. Part of the middle ear and eardrum form in the uppermost of the pouches in mammals; the thymus gland, which makes the protective T cells of the immune system, develops in the third and fourth pouches. At the other end of the embryo, the growth of a tail bud adds to the features that make it difficult to tell embryonic lizards from zebra. The eyes, the heart and other organs, the gut and four limb buds are carved out at this time too. The heart begins to beat and the embryo begins to assume the form of the animal that will be born months later.
The way that the identity of different animals unfolds from the common plan of the embryo is overwhelmingly beautiful. Bat fingers elongate and stretch the wing skin between them; elephant noses and upper lips are joined into little trunks; giraffe embryos grow long necks and dainty hooves. Wave upon wave of gene expression results in the precision sculpture of each mammal in its womb. These defining modifications continue after birth and the skeletons of adult mammals
reveal how many of the seemingly profound differences between species arise from the shortening and lengthening of a common set of bones.8 Humans develop in less than half the time it takes to make an elephant. Small rodents are the swiftest of the assembly jobs among the mammals with placentas, with shrews escaping the womb in two weeks. Marsupials are born in as little as twelve days, but they are helpless pinkies, tiny as bees, and spend the next few weeks in their mother’s pouch.
Whale and dolphin development takes the prize for breathtaking embryological transformation, with the absorption of the hindlimb buds and flattening of the forelimbs into fins. When everything goes to plan, a sperm whale mother gives birth to a 1-ton, 4-m-long (13-ft) calf, which is nudged to the surface by other members of the pod to take its first breath of briny air. Sperm whale gestation lasts for four-teen to sixteen months, and the calf is nursed for two years. Hermann Melville described calves newborn and in utero
in Moby-Dick:
One of these little infants, that from certain queer tokens seemed hardly a day old, might have measured some fourteen feet in length, and some six feet in girth. He was a little frisky; though as yet his body seemed scarce yet recovered from that irksome position it had so lately occupied in the maternal reticule; where, tail to head, and all ready for the final spring, the unborn whale lies bent like a Tartar’s bow. The delicate side-fins, and the palms of his flukes, still freshly retained the plaited crumpled appearance of a baby’s ears newly arrived from foreign parts.
All mammals arrive from foreign parts and have no memory of those watery months. I was born five years before abortion was legalized in
the United Kingdom in 1967, and have good reason to believe that my biological mother would have opted for a termination had this been available. Vacuum aspiration would have sucked me into early oblivion and my adoptive parents would have been offered a different child. It is unsettling to consider this, but some objectivity changes the picture. The embryo that might have been terminated was not me; it was the seahorsey stage of a mammal that became me. If the abortion procedure had been carried out later in the pregnancy, the foetus would have looked a lot more like a new-born baby, but that would not have been me either; it would have been the foetal mammal that became me. A mammal is anticipated in the womb, but the individual – the person – does little to express itself until, like the whale, it takes its first breath.
Edmund Spenser offers a lyrical expression for the limits of this sort of counterfactual thinking in The Faerie Queene:
As when a ship, that flyes fayre under sayle,
And hidden rocke escaped hath unwares,
That lay in wait her wrack for to bewaile,
The Marriner yet halfe amazed stares
At peril past, and yet in doubt ne dares
To joye at his foolhappie oversight . . .
What was one of your hidden rocks? How about the time the side mirror of an accelerating bus whizzed by at head height the moment before you stepped off the curb? How lucky that a few seconds earlier you were distracted by a yellow moth fluttering behind the window of the sandwich shop and slowed your pace. Did the insect save your life, or should you thank the cleaner who did not bother to open the window? Life proceeds as a continuous stream of near misses and
then it stops. The possibility of an intentional abortion is an example of an early crossroad. But what if you had died during birth, your embryo had aborted spontaneously, your fertilized egg had failed to implant, or if your parents had not had sex on that seemingly consequential day? And, with all of the uncertainties of life, one of these early interruptions might even prove the best of all possible outcomes, saving a future family from losing a beloved parent when the side mirror of a bus did make contact.
Distressed by the unpleasant rules for mankind after the Fall, Adam questioned God’s motivation for his creation in Milton’s Paradise Lost:
Did I request thee, Maker, from my clay
To mould me Man, did I solicit thee
From darkness to promote me, or here place
In this delicious garden?
Mary Shelley used Adam’s plea to great effect as the opening epigraph of Frankenstein
(1818). Swept away by the furnace of his egotism, Victor Frankenstein had expected his monster to be grateful. At its best, life is a very surprising gift; at worst, an unwelcome burden. Considering the fortunes of my life, it would be difficult to regret being born. On the other hand, if ‘my’ fertilized egg had vanished I would not be here to express remorse and I would never have been known to the handful of people who lay some value in my respirations. The estimated number of induced abortions each year is 60 million. If abortion was eliminated, the annual growth of the global population would shift from a little above 1 per cent to 2 per cent. We can imagine a possible citizenry that would include individuals who did not make it beyond the womb and it would look very much like us – more of much
the same, with no change in the proportions of poets and fools.
For some opponents of abortion, the thought of all those prospective unborn babies is unbearable. Abortion looms large in their imagination and questions about abortion access dominate their choice of political candidates. Their interpretation of religious ethics may go further, forbidding any form of contraception. These views are sermonized as a love of life, of any and every human life. Issues relevant to the wishes of a mother, a threat to her health caused by the pregnancy, or the detection of severe foetal abnormalities, are insignificant compared with the value of carrying every baby to term. This is certainly the position of the Vatican and extends to other branches of Christian orthodoxy, as well as Islam, Hinduism and other faiths.
While some feel genuine horror at the thought of vacuuming a foetus from its mother, others have fewer qualms about early abortions when it is difficult to distinguish the foetus from the uterine tissue that is sucked with it. When the foetus develops limb buds and the brain becomes recognizable, the arguments intensify. Some legal challenges to abortion in the United States have invoked the time when the foetus has a detectable heartbeat; others consider when the foetus can survive in an incubator.
Foetal pain has figured prominently in discussions about abortion and illustrates the complexity of the issues involved. Anatomical studies of early stages of foetal development reveal a bright network of nerve fibres spreading like a miniature river delta from the primordial brain tissues and spinal cord to the extremities of the developing limbs. These are present in six- and seven-week-old embryos in which the different regions of the brain are prefigured as a string of pinhead-sized swellings. Some of these nervous connections deliver sensory
information to the brain; others conduct impulses that control movement. Much later, six to seven months into pregnancy, a central part of the brain called the thalamus is hooked up to the cerebral cortex. The thalamus works as a relay station, passing information arriving from sensory nerves distributed over the body to the outer cortex that processes these messages. After birth, these pathways allow us to feel hot and cold, to react to being pushed, to flinch when the skin is cut and so on. Things are more complicated before birth, because it is unclear whether the foetus is ever awake in the womb. Bathed in warm fluid, we are soothed with chemical sedatives that seem to place us in a dream-like state of unconscious awareness. The healthy foetus moves its limbs, responds to loud noises, and kicks and hiccups in the womb, but this does not mean that it is reactive in the conscious way that a newborn baby interacts with its parents.
An adult insect like a fruit fly has a richer capacity for decoding information from its sensory organs and exploring the opportunities and challenges of its environment than a human embryo with an elementary brain structure. Comparisons between insect and human sophistication become less compelling as the pregnancy advances and the most complex brain in nature arises in the unborn baby. Even if the foetus is asleep, it has an astonishingly powerful computer and is receiving information from the womb. What also seems important to me, however, is the unthinking ways in which we mistreat the vivisected and more numerous farmed species of sensitive animals. Beside our unique record of animal abuse, declarations about the unquestionable sanctity of the human foetus loom among the clearest evocations of our stupefying self-regard.