Boundaries, separations, differences, borders, distinctions -- these words point to the places where new things, unexpected things, can happen. Maybe they make room for something or maybe they don't fit on either side, so must invent a new space.
This new thing might be organic -- as it has to be in the biological world-- or cultural -- as it is in the social world. That is, molecules interacting, ecosystem shifting, lightning striking, flooding, may change the nature of cells and how they grow. Our expanding ability to figure out what is going on is fascinating and scary, which is why Quammen's book, "The Tangled Tree", is so compelling. (I hope that most people realize that the title refers to Darwin's "tangled bank," a quote from Darwin that has been used as a title by Zimmer.) Brilliantly, Quammen includes centuries of various proposed genetic trees, only to sweep them all aside. The various sketches also illustrate how much the culture influences the artist.
For years I've been reading about how humans develop from two cells into a walking, talking, thinking individual. It's clearly a two-step process: 9 months inside a "mother" and then three YEARS in a family, which ought to be thought of as a social womb. The boundary we call "birth" is when the infant is pushed out or cut out of the mother. This is arduous, dangerous, done with assistance or not, and momentous. Nevertheless it is less drastic than the "birth" transition of some insects, like a caterpillar giving "birth" to a butterfly in a "womb" chrysalis it created itself, stuck to a twig. This change is so transforming that some scientists suggest that the individual has just changed itself from one animal species to another -- from a crawling thing to a flying thing.
For humans the cultural implications are huge, because it is proposed that our bodily "being" is actually just access to all the other humans and their living circumstances, which will shape that person in many subtle ways, right down to molecular processes. (My grandmother, deprived of iodine by living in northern Manitoba, developed a goiter. It was cured by moving to Portland where there is iodine from the nearby ocean. The impact, including our emotions affected by the thyroid, have come down to my generation.) Capacity for empathy to other people is a huge survival characteristic. I've been mouth-hanging-open amazed by the polyvagal theory of emotion/expression, which explains the crossover from brain molecules to the expression on your face.
Another question that was never clearly framed but always there, was about how it happened that mammals were invented out of egg-laying reptiles. What Quammen explains carefully but few reviewers have touched, is a sequence of mutations among certain viral/genetic codes that invented the placenta to bridge the space between a conceptus and the wall of the womb, generating the umbilical cord as a literal life-line between two beings. How is it that the mother's body doesn't simply think this new being is an intruder and reject it? (Sometimes it does.)
I've been watching the "The Yorkshire Vet," a BBC movie about the work of those who run James Herriot's veterinary practice. Much of it is reaching up a cow's butt to tease free and remove a placenta that failed to detach from the cow's uterus wall. Easy enough to cut or tear the umbilical cord away from the calf. "Plop" goes the placenta into the straw, a kind of flesh pudding.
Quammen identifies the tiny entities, microbes with the ability to bind several cells into one new entity -- and do other tricks. Mice that have had these "genes" knocked out, die in the womb in days. In other circumstances, the same placenta-makers kick up cancer. Several different strands of mammal incarnation have "discovered" placenta-making at different times from slightly different versions of the originators. Quammen tells a lot more about the variations, like mammals who lay eggs or marsupials.
The point is that bodies accept microbial plans from other kinds of animals or from microbe doin's. They call this "horizonal heredity," never suspected until we knew it existed. Now we 're a little stunned by it.
It seems clear that gestating a baby inside a mother is an advantage because the growing cells can be quickly transported inside her to avoid danger or get food. An arrangement that requires eggs that must be kept warm means that someone with body heat has to sit there on the eggs, a "sitting duck" so to speak. A recent Twitter bit was about eagles brooding on rough stick nests high in trees who sat there keeping those eggs warm (and succeeding) despite horrendous storms. Turtles, which are cold-blooded reptiles, depend on warm beach sand to be incubators. The babies run for the sea when they hatch, not needing any three years of development.
I wonder if anyone has written a short story that entwines the story of an indigenous-to-North-American woman, heavily pregnant, determined to escape the invasion of Columbus (all men), with the story of a mother turtle and the fate of her egg-babies with gulls descending upon them as they scuttle. It would make the point.
The break between eggs gestating in a woman and formed individuals birthed to the world, is that anyone can be a caregiver: a father, a grandparent, an older child, or even another species. There are many stories about human babies raised by animals.
A local Blackfeet story is about a real woman I knew in her old age. Her name was Mary Ground because Ground (He Who Dismounts to Fight from the Ground) was her husband's name. She was also called "Grass Woman". When she was born, the father saw that she had blue eyes but Blackfeet have dark eyes. He thought this meant his wife was unfaithful but it could have been a mutation or a recessive gene or the action of some microbe intruder. Thinking to let fate solve the problem, the baby was put out in the tall grass alone through the night. She was a tough baby and survived in the womb woven by the tall grass around her. It doesn't get anymore indigenous than that.
We are all in this together.