Having sex to become pregnant: Why it is necessary?

15 Aug

The gorgeous plumes of a peacock are a classic example of a trait that emerged solely for sex appeal.

“Some are fancy on the outside.  Some are fancy on the inside.  Everybody’s fancy.  Everybody’s fine.  Your body’s fancy, and so is mine.”  –Fred Rogers (♫ listen here)

“Some mollusks (not many) can have children merely by sitting around and thinking about it.”   — E.B. White, Is Sex Really Necessary?

As it turns out, snail sex (a snail is a type of mollusk) is really far out:  Some can self-fertilize, some stab their mates during foreplay with harpoon-like “love darts,” and most snails have two sex organs, so they can do it both ways at the same time.  As E. B. White observed, “mollusks are infinitely varied in their loves, their hates and their predilections.” 

Photo by Flickr user Nellee100

And aren’t people, too.  But to make a human baby we need one way or another to bring together a sperm, from a man, with an egg, from a woman.

In people, male bodies are different from female bodies. This differentiation is what science people call sexual dimorphism, and both genders, according to Mister Rogers, are fancy.

But why are we so fancy?  This question baffles biologists.  And isn’t being fancy complicated? This question inspires every form of art.

Still, we know that sex can be fun, and, on a species level, advantageous.

Let’s look into this. Picture a set of genes as a bag of candy.

The asexual model says:  “I am a bag of Hershey’s kisses.  Everybody loves me, so I’ll just duplicate myself.  Maybe there’s a little mutation, a tweak in the chocolate recipe, but I’m basically making a clone. This will keep things the same over time.”

The sexual model says, “Hubba, hubba.  I am a delicious mixed bag of candy and it looks like you are too.  Let’s get together and make a new combo, some of me, some of you.”  Variation begets still more variation.  The recipe becomes complicated, and more exciting.

Both models have merit.  With less variation, there’s less risk of getting a dud in the candy sack.  The asexual method is easy and sure.  There’s no dating.  No cologne.  No spinnbarkeit and whatnot.

It’s a lot harder to create a viable human genome. A set of genes that “succeeds” is functional enough to turn a fetus into an embryo into a child into an adolescent into an adult.  That’s an amazing recipe!  Getting organs to work alone is like getting a Boeing 747 off the ground.  Why not stick with a good thing? And after all this work, why the added burden of finding a mate? Couldn’t we just sprout duplicates?

The trouble is that sameness has huge drawbacks.

Could we have a world in which everyone were Martha Stewart, for example?  Bless her heart, but that’s Not A Good Thing.

Nevermind how a society of Martha Stewart clones would function; the evolution of our species would slow almost to a halt.  If the mogul of domesticity could reproduce just by thinking about it, she would be more like bacteria, which with their lean and simple chromosome machines can make billions of cells out of one overnight.  Bacteria are very effective at making a sock stanky!  But they are less able to make important evolutionary jumps.  We don’t see them sprouting arms and legs.   It took us a while to do that, too, but it’s sexual reproduction that made it happen, speeding up the creation of our species and others.

The RECOMBINATION that happens with sexual reproduction allows a species to change over time. Variation is the engine of evolution.

Meiosis, or the jumbling and divvying up of genes inside of cells that will become eggs and sperm, creates genetic differences among kids. (Ask anybody from a large family, there’s always one that you’re sure probably is not related to the rest.)

The more variation you have, the more chance you have to select the best target for your snaily love darts.  Or at least, says the peacock, the sexiest.

And by the way, getting to share the work of parenthood with a partner down the line can be sweet loving mercy, not only for your species, but for your soul.

Look back: Week 0, Menstruation
Look ahead: Week 2, Fertilization

Related posts:
The Big. Ass. Egg.


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