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Still Counting the Species

Carl Linnaeus, a.k.a. “the father of taxonomy,” meant well. A giraffe probably looked like a giraffe. Easy to identify, right? Well, it was the 18th Century and you can’t blame him. He gave us the modern system of naming organisms and he gave the giraffe the name Giraffa camelopardalis.

 

In fact, there may be four different species of giraffe. Different and distinct. 

 

This work of identifying all the species on Earth is ongoing and, according to a fascinating article in the New York Times by Carl Zimmer, “remains one of the great unfinished jobs in science.”

 

In fact, there may be millions (or even billions) of species left to be discovered.

 

What? How is that possible when we’ve sent a spaceship around the back side of the moon?

 

One issue is that biologists use 16 different approaches to categorize species.

 

This isn’t a matter of academics getting their act together. This is a matter of urgency, the article states, because “scientists urgently need to take stock of the world’s biological diversity” given the ongoing extinction crisis (detailed in another thoughtful article written by Carl Zimmer). Marine life, in particular, is now starting to really feel the effects of seabed mining, overfishing, and coral reef bleaching from global warming.



Back to Carl Linnaeus. He thought species were divinely created. “As one sits here in summertime and listens to the cuckoo and all the other bird songs, the crackling and buzzing of insects, as one gazes at the shining colors of flowers, doth one become dumbstruck before the Kingdom of the Creator,” he said.

 

And then along came Charles Darwin and his keen recognition that species evolved. But when does a new species establish itself as “new” and not merely a subspecies of an old one?

 

In the 1940s, Ernst Mayr, a German ornithologist, submitted the proposition that breeding was he key indicator. In his 1942 book Systematics and the Origin of Species, he wrote that a species is a group that can breed only among themselves, excluding all others.

 

As the New York Times article pointed out, Christophe Dufresnes, a herpetologist at Nanjing Forestry University in China, used DNA analysis on frogs to determine that “groups with a recent ancestor—that is, those that were more closely related—readily produced hybrids. He estimates that it takes six million years of diverging evolution for two groups of frogs to become unable to interbreed.”

 

Six million years!


Meanwhile, other researchers have used DNA sequencing and looked for differences in genetic codes. Those four giraffe species, for instances, have different DNA. One specific species of shrimp may, in fact, be 32 different species. The split in those shrimp lineages happened, scientists believe, 25 million years ago.

 

That DNA analysis has also shown that polar bears and brown bears split about half a million years ago, but they interbred and exchanged DNA for thousands of years before becoming more distinct as species. Much later, about 25,000 to 10,000 years ago, they started interbreeding again and, today, about 10 percent of the DNA in brown bears comes from their polar pals. (Climate may have driven polar bears south to intermingle with brown bears.)

 

Are they separate species? Yes.

 

Among birders, the debate over barn owls can turn heated and botanists are scrambling hard to identify species before they disappear (again, thanks to climate impacts). 

 

The bottom line? The world today isn’t the same world of a millennium ago. Or 10,000 years ago, for sure. And it’s changing right under our collective noses, even as the push continues to identify all the living organisms. 

 

Care to follow along? Sign up for information at the “Red List,” sponsored by the International Union of Conservation of Nature.

 

Our world is not a static place.

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