SPECIATION — the appearance of a new species — is the topic of a new column by the splendidly-evolved Olivia Judson. She is an evolutionary biologist and a research fellow in biology at Imperial College London.
The article is titled All Hail the Apple Maggot!, and it’s part of Dr. Judson’s series in the New York Times. Here are some excerpts, with bold added by us:
Next Monday — Nov. 24 — is the 149th anniversary of the day that Charles Darwin’s masterpiece, “On the Origin of Species,” was first published. In honor of that, I thought I’d look at a remark that a friend recently made: “We spend so much time wailing about extinction, but we never celebrate new species.”
We never thought of that. Let’s read on:
Good point. But there are several reasons for the asymmetry. The most obvious is that extinction is easier to see. In the 18th century, the passenger pigeon was one of the most numerous birds on earth. … But by 1880, the numbers had plummeted; by 1915, the passenger pigeon had gone.
The appearance of a new species is not so dramatic. The first members of a new species will typically be indistinguishable — to us — from the species they have evolved from. And while extinction has a clear final moment — the last member of a species dies — the formation of a new species does not usually happen in a single recognizable instant. Which is why we haven’t yet raised our glasses to celebrate, say, Rhagoletis pomonella, the apple maggot fly.
With that delightful introduction to the topic, Olivia then lucidly describes a speciation event which is currently under way:
This species is in the process of splitting into two. Until the mid-1800s, R. pomonella was a hawthorn fly: adults met at hawthorn fruits to mate and lay eggs. But then apples were introduced to North America. Some haw flies found these fruits attractive places to gather, and began to mate and lay their eggs on apples instead.
Amazing, isn’t it? From such a seemingly trivial matter, speciation begins. The next time you encounter a creationist uttering the usual nonsense about never seeing a duck give birth to a dog, you can offer him a copy of Olivia’s column. Even if he can’t read, he can look at her picture.
Here’s a bit more:
So why don’t we consider the apple specialists a new species? Because they aren’t quite all the way there.
The most common way to define a species is a group of individuals that breed with each other successfully. … For individuals to be considered as belonging to separate species thus means that they are “reproductively isolated”: they can’t, won’t, or don’t breed with each other.
I say, “can’t, won’t, or don’t” because reproductive isolation can come about through any of these routes.
We can’t copy much more from the Times, but Olivia describes “can’t, won’t, or don’t” rather well, and then says:
Haw and apple flies are in the “don’t” category: flies from the different fruits don’t mate because they don’t meet. … But because offspring from such matings have a survival disadvantage, it seems likely that there will come a time when the separation will be complete, and we will be able to raise a cheer of welcome for the newly speciated apple maggot. Yippee!
Olivia’s columns are all good, but this is one of her best. Click over to the Times and read it all.
Copyright © 2008. The Sensuous Curmudgeon. All rights reserved.