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Wednesday, 30 August 2017

Darwin's error

This is a small excerpt from a new book, probably to be called Background to Science. Drawing on a lifetime of writing essays, articles and talks about matters of science, I am repurposing a lot of old prose, 405,000 words at the last count.  It should be released on Kindle, later this year. I am rewriting most of it, and all so filling in some of the gaps.

It is that work which has led to the lack of posts here. Sorry!

While I always say Darwin’s work has never been shown to be false, there were a few minor errors in some of his examples, mistakes which don’t affect his overall correctness. There was also one major error in his thinking, which also made no difference in the long run, but it has to do with one of my favourite animals, the ant lion, so it gets a quick run here.

In Australia, ant lions are the carnivorous larval stage of lacewings. They make little pit traps in sandy soil and catch ants and other insects (I have seen one catch a small weevil). Their prey fall into the pits the ant lions make, and they are sucked dry.
Ant lions are small. I move them with a small paint brush.

Because there is some rather marvellous physics involved in the way they make their pits, I have often used these animals in teaching and in books, so I know quite a bit about keeping and feeding them.

In the early days of 1836, a young man called Charles Darwin slipped into Sydney on HMS Beagle. Nobody really noticed him, as he rode out to Lithgow, stayed for a while, saw a few animals, returned to Sydney, slipped aboard his ship, and departed.

Temporary guest ant lions.
He left, though, with the key idea that started him thinking about evolution, because he had seen ant lion pits of two sizes, and started musing on variation. Two species, two sizes of pit, he thought, and that was, legend tells us, the start of the whole evolution-by-natural-selection saga.

Jump forward now to the 21st century, when a film maker was planning a doco on the Darwin story. The producer came across the ant lion story, and thought it would be neat to recreate this, but where does one find an ant lion wrangler at short notice?

Because I had written a book on the Darwin story (Mr Darwin’s Incredible Shrinking World, still available as a e-book), a researcher contacted me to see if I had any idea of where a wrangler might be found, able to take ant lions to a suitable site, and get them making their pits.

I said modestly that I was probably just about the best bet they could find, and then explained a few of the realities. The researcher said that all they wanted was the two sizes of pit, and I said that was easy: the photograph at the head of this section shows that much.

But, I said, it was my firm opinion that the two sizes of pit were made by the same species, and would be the result of two lots of eggs being laid in the sand: the older and larger ant lions make larger pits, and the younger and smaller ant lions made the lesser pits.

In short, Darwin had been inspired to think about variation after a false inference. It made no difference to the validity of his later thinking, but it would be difficult to get this across in a short documentary. I offered to help with the wording.

The result was that the producer had a melt-down, followed by a hissy fit, and the whole sequence ended up on the cutting-room floor, even before it was shot.

In this way, I missed out on the chance to feature “ant lion wrangler” on my CV, but at least we side-stepped the risk of giving cherry-picking idiots the chance to shout “Look! Darwin got it wrong, so logically, evolution is wrong!”, all the while ignoring the many other valid examples of variation within a species that might have got him started.

The secret behind evolution is genetic variability that can be passed on to offspring. Fair-haired people mostly have fair-haired children, dark-haired people mostly have dark-haired children, but they are all humans, all part of the same species.

That was the part that Darwin got right, and that was the part that mattered.

Now here's a tip if you are keeping them: ants added as food have an annoying habit of escaping. The outer tub here has water in it, so the ants can't escape.

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