Because the National Science Foundation and other government entities give grant awards in the summer - mainly in July - I’ve been busy writing about new projects. And since science studies typically take several years, there haven’t been a whole lot of results to share in the past couple of months. So today’s post is exciting - well, at least it is to me - because it’s reporting on findings that were published last week in the Proceedings of the National Academy of Science.
The gist of the paper goes a little something like this. Archaeologists the world over are constantly digging up fossils and sticking an approximate date on the animal’s demise. Based on skeletal structure, they can analyze the history of the evolutionary tree and learn things like how many species have become extinct, how many new ones have been created, which species are related, when the evolution took place and about how long it took.
The only issue with this method is that it requires the skeletons be found first. Since not every fossil in the world has been found, there are gaps in the information for some groups of animals during different time periods.
So Luke Harmon - professor of biological sciences - and colleagues from UCLA took a different approach. They used genetic information to solve the puzzle. They created a giant “family tree” consisting of all the jawed-vertebrates ranging from fish to birds to people and used a computer program to answer the same questions posed by archaeologists.
What they found is pretty cool.
The number of new species being formed is just about equal to the number becoming extinct. But it doesn’t happen at a constant rate. Different orders and families of animals experience bursts of evolution and then remain stagnant for a time.
Given their age and number of different species, frogs in general are no more diverse than they should be, even though it seems like there’s a billion different kinds. Neoaves - modern birds - are much more diverse then they should be, as are percomorphs - fish related to perch.
On the other end of the spectrum, some families are much less diverse than they should be. Tuatara and crocodilians are exceptionally strange. Both are more than 200 million years old but have just 2 and 23 species, respectively. Even in the past, they had less diversity than they should have.
This implies that there must be mechanisms that elevate speciation and some that depress it. Scientists aren’t sure what causes a group of animals to neither evolve nor die out for such a long period of time, but there must be something to it in order for these “living fossils” to exist.
For more information, check out the PNAS article online or the recent press release.
