DNA analysis reveals house cat's origins|Ed Malonefirstname.lastname@example.org|01/10/06 at 12:33:07|obadiah|xx|0|18.104.22.168|DNA analysis reveals house cat's origins
URGE TO ROAM LED FELINE FOREBEARS TO POPULATE GLOBE
By Lisa M. Krieger
Curiosity didn't kill the cat but helped it thrive, diversify and reign over new habitats all over the world in a brief 11 million-year time span, according to a major new analysis of feline genetics.
By studying DNA from blood samples of 37 cats, representing every species, scientists with the National Cancer Institute reconstructed feline migration from its ancestral home in Asia to distant new lands in North America and elsewhere. Their results were published in Thursday's online issue of the journal Science.
``Through this work, we were able to retrace 10 historic continental migrations,'' said Warren E. Johnson, who helped lead an international team of scientists.
The first ancestral cat-like creature appeared about 35 million years ago. By 11 million years ago, its various descendants, including multiple species of the saber-toothed tiger, had all disappeared -- except for the common progenitor of today's modern cats.
By that time, it is likely that this ancestral cat needed more elbow room. Maybe there wasn't enough food. Or perhaps disease was rampant.
When the climate changed and sea levels dropped, new routes of travel suddenly opened.
So the cat went off to find larger territories -- or perhaps just more mice. Some wandered across the Bering Strait into North America. Others ventured across the Panama Strait into South America.
``The curious ancestors of modern cats were looking for places to go,'' said Stephen J. O'Brien, a co-researcher on the team. ``If there were land bridges, the youngest animals -- the teenagers -- saw an opportunity to migrate.''
All the new habitats demanded different adaptations. For instance, the black panther can be found in the dark and dense forested areas of India, while the mountain lions of North America's dry grasslands are tawny.
Then, rising sea levels closed off these travel routes, isolating populations and setting the stage for distinctive traits.
So in a geologic blink of the eye, more than three dozen new cat species evolved -- ranging from the mighty lion to the domestic tabby that now sits in sunny windowsills all over the world.
Cats are now recognized as one of the world's most successful carnivore families, inhabiting all continents except Antarctica, according to the study.
Cat fossils are few and far between, so feline genealogy has always been a bit of a mystery.
The scientists could track feline emigrations because of a train of mutations that accumulate in certain regions of DNA over time. Cats that went off in one direction have a distinct set of errors from those that traveled in a different direction.
On the basis of these mutations, scientists constructed a family tree of eight different cat lineages. By estimating the mutation rate, they can figure out the time that has elapsed for each lineage.
They compared genetic changes with geologic changes -- and found that they matched. The emergence of new cat species could be linked to specific geological events, such as the rise and fall of sea level.
Some species spread from Asia into America, like the jaguar. Others, including the lion and leopard, went to Africa.
And who were Fluffy's forebears? The new study reasons that about 6 million years ago, the domestic cat lineage diverged from Eurasian cats. Its most recent relative is a wild cat that inhabits Africa and Europe. In fact, these two species can still interbreed.
Wild cats first became house cats in Egypt about 6,000 years ago -- perhaps explaining why cats are more wary of humans than dogs, which have 9,000 more years of domestication under their collars. The cat may have followed the mouse into humans' earliest granaries, researchers hypothesize.
Domestication may have been attempted multiple times, in multiple places, said O'Brien.
``We selected the cats that didn't eat us,'' he said.