Defaithed

Happy Darwin Day! It's birthday #199 for the great old man of evolutionary science.

The beauty of Darwin's theory of evolution by natural selection, as a billion better minds than mine have amply pointed out, is its remarkable simplicity. Simple enough even for me to grasp!

In honor of Darwin Day, here's what I'm going to do: summarize, in all its wonderful brevity, the theory of how natural selection works to create change in a population – how it powers evolution, in other words. To challenge myself, I'll do it from the brainpan: no glancing at any sources to refresh my memory or make sure I've got things right. (That's a risky undertaking for a semi-witted layman like me, so I greatly welcome corrections and suggestions for improvement.)

After which, I'll opine a wee bit on Creationist-vs-evolution debates. (I admit to being a total junkie for those. They offer better smackdowns than WWF cage matches.)

Diving right in, here's my understanding of the modern theory that Darwin put into motion:

How creatures change: the basic steps

1. Creatures have offspring, which inherit traits from their parents.

Nobody should hesitate to agree with that.

2. However, the traits aren't perfectly copied from one parent, or perfectly averaged over both. The offspring's traits show some random variation.

Again, nobody should have a problem with that. Just look at any family: the kids clearly get traits from the parents, but not in the same mix. And kids are always dealing surprises – height, smarts, looks, something – that you wouldn't have expected from either parent!

3. If you selectively breed individuals based on some traits – that is, you let individuals with certain traits breed, and stop individuals without those traits from breeding – the population will change as the generations go by.

So far so good? I hope that everyone – Creationists, rationalists, and all – are all on board with the above, including #3. Because any objector has a real problem on hand: he's just denied the origin of dog breeds, cattle breeds, crop strains, and countless other products of selective breeding by humans over millenia. The objector is in for a smackdown from any country farmer, who not only knows the above four items as facts, but bases his livelihood on them!

The implications so far

Great Danes and Chihuahuas make it clear: Take offspring that inherit traits from their parents, mix some random variation into those traits, and based on those traits select who breeds with whom – and voila, the population changes over time. We know that that's how we humans created our dog breeds, and we know that a Mighty Sky Father wasn't part of the Kennel Club process.

But wait! Isn't the selective breeding of #3, as wonderfully exemplified by human breeding of dogs, the very epitome of "Intelligent Design"?

Yes! When humans make use of phenomena #1 and #2 to carry out #3, that is indeed intelligent design by humans. Our modification of the first canines that we met up with, to create the Dachshunds and Retrievers we have today, is human intelligent design. Take a bow, humanity! (Though what you were thinking with those yappy little toy dogs, I can't imagine.)

The plot thickens

We know, of course, that human intelligent design – what we call breeding – explains only a small amount of the variety of life: only breeds and strains of certain domesticated animals and plants. Humans certainly can't take credit for creating the original canines, cows, and grains!

So where did the vast bulk of life's variety come from? One answer offered is "from a Supreme Creator" – Intelligent Design with capital letters. But Darwin's wonderfully simple inspiration offers a brilliant alternative explanation. Here it is, a simple #4 added to the above list of things we already know and agree upon:

4. Without human or other invention, nature alone provides a mechanism for selective breeding based on traits: breeding success. In nature's rough-and-tumble world, not everyone gets to breed (or even live long enough to have a shot at it). Creatures with traits that better aid breeding success – which typically means traits that aid survival to the breeding stage – tend to breed more, and leave more offspring that carry on their traits. Creatures with traits that are less beneficial to breeding success will tend to breed less, and leave fewer offspring that carry on their traits. This process – natural selection – causes the population to change over time.

It's a wildly simple insight (though it takes me more words than I'd like to spell it out. I welcome any shorter way to state it!)

Here some proponents of Creationism start to fall away, though the dissenters have a really tough row to hoe. The process described is overwhelmingly logical and sensible. We can even observe it in nature: we're fighting an ongoing war with bacteria whose weaker members succumb to our drugs but whose stronger members survive and leave strong offspring. Precisely as Darwin's theory predicts.

Where we part ways

Smarter Creationists will readily agree with the existence of the natural selection mechanism. Fortunately for their cause, there's one more step remaining in the process, and it's one that's far more amenable to debate. It's this:

5. Darwinian natural selection over billions of years is sufficient to explain the breadth and diversity of life forms we see today.

Ah, there's the crux. Sure, it makes sense that those more fit to survive and breed will outlive and outbreed the less fit, changing the population over time. But is the process powerful enough to create whole new species? Even if so, has enough time passed for it to do so? And even if it has, can we say with certainty that the process explains how all current life forms, including humans, arrived at their present state from a common primitive ancestor?

The debate usually starts from there. Point #5 is indeed the one that requires detailed, often difficult scholarship to support, as obviously we haven't directly observed the formation of species over billions of years. I have no doubt that science has done an excellent job of proving its case, and that the dissenting arguments have offered nothing substantial in the way of proof. But all that's a huge topic for elsewhere.

Finding the starting point for debate

So, how'd I do in my off-the-top-of-my-head layman's overview of the natural selection process?

I find it interesting to break down the theory's assumptions, starting from the most obvious and working up to those requiring the most supporting proof. It's very useful in determining where an objector stands.

Supporters of the theory are all in agreement on every assumption above (barring mistakes on my part!), from #1 to #5. Detractors, alas, are not in agreement on where they part ways from the assumptions. I think most do so at #5, though there's a fringe that denies #4, and maybe even loons who balk at #3. (Those would be the "Chihuahauas don't exist!" crowd.)

As non-science positions can fall anywhere along an infinite field of beliefs, any debate needs to first establish where the non-science debater stands. I've seen science-vs-Creationism debates that failed to do so, leaving the viewer uncertain as to exactly what points of the natural selection theory the Creationist objects to – and leaving the Creationist wiggle room to jump from one position to another when things get too hot. (Convenient flopping from one loosely-held conviction to another is the defining tactic of the non-science debator, it seems to me.)

In future debates, I'd like to see the pro-science debater (or the moderator) start the proceedings by walking through the theory's assumptions in order. That'll serve to instruct and remind the audience of what the theory of natural selection actually says, prevent later silly Creationist claims about the same, and force the Creationist to actually commit to one of many non-science positions on the evolution of life.

And from there... Let the rumble begin!

List recap

I'll repeat my list here – and I promise to improve it as I learn better.

1. Creatures have offspring, which inherit traits from their parents.

2. However, the traits aren't perfectly copied from one parent, or perfectly averaged over both. The offspring's traits show some random variation.

3. If you selectively breed individuals based on some traits – that is, you let individuals with certain traits breed, and stop individuals without those traits from breeding – the population will change as the generations go by.

4. Without human or other invention, nature alone provides a mechanism for selective breeding based on traits: breeding success. In nature's rough-and-tumble world, not everyone gets to breed (or even live long enough to have a shot at it). Creatures with traits that better aid breeding success – which typically means traits that aid survival to the breeding stage – tend to breed more, and leave more offspring that carry on their traits. Creatures with traits that are less beneficial to breeding success will tend to breed less, and leave fewer offspring that carry on their traits. This process – natural selection – causes the population to change over time.

5. Darwinian natural selection over billions of years is sufficient to explain the breadth and diversity of life forms we see today.

How right or wrong did I get it?

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