Recipe for life

Midwifery school starts with the basics of life. Reproduction on the level of cell division. Meiosis and mitosis, and how that can create a whole beautiful diversity of babies.  Most strong and healthy, but some less strong.

Mitosis is what happens in most of the body; one cell making another just like it. A skin cell making another skin cell. Meiosis, on the other hand, is the special type of cell division that makes gametes: either sperm or eggs. Each gamete cell is half a recipe for a human, ready to meet up with another half. And each gamete is different from the next because the the DNA is scrambled up first then combined with the other scrambled up gamete.

There’s an astounding difference in the production of gametes between men and women. We females start making our eggs when we are fetuses ourselves. In other words, we start early, working on our future progeny before we are even fully formed. But we also take our time and put the finishing touches on each carefully honed egg as we’re getting ready to release it. Just one egg every month or so.

In contrast, men wait until puberty to get started, but boy once they get going they have several hundred million sperm maturing every day. Yes, several hundred million. Every day. In this mass production model, not all sperm are created equal. Some may have two heads or two tails. But most are viable and the viable ones tend to win. And I say win because for sperm, classic fertilization is a competitive event, where they race each other to the egg. And of course it only takes one to do the trick.

All this scrambling and recombining means a wonderful diversity of human beings. And it also means things don’t always turn out like you thought. So we’ve learned about the complicated and imperfect screening and testing designed to give families information about whether their baby is at risk for being among the few less strong. These tests screen for lots of differences, including trisomy 21, or down syndrome, which happens when an extra copy is made of the 21^st chromosome.

These anomolies are created by the same mechanism that makes the beautiful diversity of the planet. And people have different feelings about them. I am certain that the people who I’ve known with extra chromosomes are part of the beauty of our planet. That doesn’t mean it’s easy.

Barbara Kingsolver describes this biological mechanism of diversity beautifully in her novel Prodigal Summer. It’s a conversation between two characters. Nannie is a stepmother of teenage Deanna. Rachel, who is also mentioned, is Nannie’s daughter, Deanna’s step-sister, and has down syndrome and many associated health problems. The conversation starts with Deanna asking Nannie “What made Rachel that way?”

Here is the excerpt. I hope you like it a much as I do:

Photo by Vincent Crown

“Here’s how I think about it,” Nannie said. “You know there’s two different ways to make life: crossing and cloning. You know about that from grafting trees, right?” 

Deanna nodded tentatively. “You can make a cutting of scionwood from a tree you like and grow a new one.”

“That’s right,” Nannie said. “ You call that a scion, or a clone. It’s just the same as the parent it came from. And the other way is if two animals mate, or if two plants cross their pollen with each other; that’s a cross. What comes of that will be a little different from either one of the parents, and a little different from all the other crosses made by those same parents. It’s like rolling the dice together: you can get a lot more numbers than just the six you started with. And that’s called sex.”

Deanna nodded again, even more tentatively. But she understood. She followed the path through the tall grass that Nannie was tramping down in front of her.

“Sexual reproduction is a little bit riskier. When the genes of one parent combine with the genes of the other, there’s more chances something can go wrong. Sometimes a whole piece can drop out by mistake, or get doubled up. That’s what happened with Rachel.” Nannie stopped walking and turned around to face Deanna. “But just think what this world would be if we didn’t have the crossing type of reproduction.”

Deanna found she couldn’t picture the difference, and said so.

“Well,” Nannie said, pondering this, “probably for just millions of years there were little blobs of things in the sea, all just alike, splitting in two and making more of themselves. Same, same, same. Nothing much cooking. And then, some way, they got to where they’d cross their genes with one another and turn out a little variety, from mutations an such. Then starts the hullabaloo.”

“Then there’d start to be different kinds of things?” Deanna guessed.

“More and more, that’s right. Some of the kids turned out a little nicer than the parents, and some, not so hot. But the better ones could make even a little better. Things could change. They could branch out.”

“And that was good, right?”

Nannie put her hands on her knees and looked Deanna earnestly in the eye. “That was the world, honey. That’s what we live in. That is God Almighty. There’s nothing so important as variety. That’s how life can still go on when the world changes. But variety means strong and not so strong, and that’s just how it is. You throw the dice. There’s Deannas and there’s Rachels, and that’s what comes of sex, that’s the miracle of it. It’s the greatest invention life ever made.” 

Prodigal Summer, pp 389-390. HarperCollins: New York, 2000.