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Thursday, December 17, 2009

A Question about Species

Dear Liana,

I have a question about your post on Founder's Effect. You wrote about speciation but didn't say how long it takes for a species to evolve into a new one. How many generations does it take for a species to change into a new one?

Gene in ME

Dear Gene,

If I knew that I'd be writing nonfiction, not science fiction!

It's an excellent question, but I don't have a hard and fast answer for you. I'm not sure if anyone does.

Speciation does not happen quickly. And defining a species is more than appearance.

The standard test for species is whether or not a male/female pair can breed and produce fertile offspring.

It sounds simple, but this has caused more biology department scuffles (and zoo surprise! babies) than one would imagine.

Think of big cats: lions, tiger, leopards... Technically, we consider them separate species. In the wild they do not regularly mate or produce offspring. Captive born offspring are widely thought to be sterile, thus fitting the rules of speciation.

But, there's a whole list of hybrids between the three big cats. And evidence that lion/tiger crosses can produce fertile offspring (usually the females are fertile and males are sterile).

And then you have a species like the Milk Snake, the picture which you see all over the blog post today. See all the pretty snakes? They're all the same species. Different phenotype (physical attributes), different sizes, different home ranges, but genetically similar enough to be the same species.

On the one end of the range milk snakes are only a few inches long. On another end, the milk snakes eat medium sized rats. If ever the twain should meet (not likely except in cases of captive breeding) could they reproduce and make viable offspring? Yes.


In practice what is more likely to happen is the big snake will eat the little snake for dinner.

Milk snakes are a species well on the way to speciation, the species has divided into subspecies, but they aren't done evolving yet. They are functionally speciated, but not genetically speciated.

So, what does this mean for a writer?

This means that you need to plan your half-breeds with care. If you can have a half-elf/half-orc bartender that has a wife and three kids it means that orcs and elves are the same species. And easy enough feat in most fantasy novels.

In sci-fi aliens are generally assumed to be a different species. If you produce a half-human/ half-alien hybrid you suggest to the reader that they might not be an alien species at all. And then you have to explain how the two are related.

Functional speciation (back to the milk snakes) is a bit easier. Anything preventing the crossing of genes (distance, politics, religion, death threats) will lead to genetic isolation and functional speciation.

If you want to make two races in your book so disimilar that there is no chance the main characters will think of romantic entanglements you can use distance (long distance relationships do not produce children), or social mores to divide the characters.

Clear as mud?

If you have more questions just click the EMAIL link above.


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