New York Times contributor Olivia Judson examines a new species in the making:
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.
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.
Today, flies that like apples have become genetically distinct from those that like haw. There are a couple of reasons why. First, flies meet each other at fruits. Since most flies have a preference for one fruit over the other, haw-preferring flies tend to meet other haw-preferring flies, and ditto for apple flies.
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