Humans Not Off the Hook for Megafauna Extinction
The debate flares up again as to whether humans wiped out the giant beasts of the last Ice Age. Continue reading →
Did we do it or was it just a coincidence? That's what two groups of researchers are arguing with regards to the demise of mammoths, sabertooth cats, giant ground sloths, horses and other "megafauna" that roamed the Americas when humans wandered over from Asia.
A team of Australian scientists led by Chris Johnson of the University of Tasmania is arguing that there are serious flaws in recent work by two Brazilian researchers that exonerates humans. The pair that did that work, Matheus S. Lima-Ribeiro and José Alexandre F. Diniz-Filho of the Universidade Federal de Goiás, have answered that nope, their work isn't perfect, but still gets humans off the hook.
"They find that in many places megafauna were apparently extinct before humans arrived; in many others, megafauna coexisted with humans for thousands of years before going extinct," writes Johnson and company in the Oct. 2 issue of the journal Quaternary International. "They conclude that human impact made at most a minor and geographically restricted contribution to megafaunal extinction."
Johnson argues that the Brazilians' conclusions are off because they messed up the dating of fossils and extinctions. They re-analyzed the same data and reached the opposite conclusion: the demise of the big animals followed the arrival of humans by about one or two thousand years. That figure meshes with what models predict in terms of how long it would have taken humans to kill and consume so many animals.
But the Brazilians aren't budging, much.
"...We are...aware that our approach is not necessarily the best, final way, either to deal with such uncertainties or to solve the puzzle of" the megafuana extinctions, the Brazilians responded, in the same issue of the journal. They go on to defend their conclusions and produce yet another analysis of the data that supports their original conclusion: that the timing is wrong for humans to have wiped out all those beasts.
Who is right? Heck knows. It's a bit of a ping-pong game for those of us watching from the sidelines. But it's just one of those examples of how science works and is played out in the pages of journals. Someday we might have more clarity on it, but for now, we just have to enjoy the game.
Image: Dire wolves battle a saber tooth cat over a carcass in ice age California. (Robert Bruce Horsfall (1913), Wikimedia Commons)
New technologies could make it possible to bring extinct species back to life, concludes a paper published on April 4 in the journal Science. These advances include back-breeding (assembling or reassembling an extinct species' genes), cloning and genetic engineering.
A leading candidate for de-extinction is the woolly mammoth. Russian scientist Semyon Grigoriev, of the Sakha Republic's mammoth museum, plans to replace the nuclei of an elephant egg with nuclei extracted from woolly mammoth bone marrow. The elephant would theoretically become a surrogate mother to a baby mammoth.
Tasmanian tigers died out in 1936, in part because they had little genetic diversity which translates to "bad news for a species," said Katherine Belov, professor of comparative genomics at the University of Sydney. "Species are less able to adapt to change." Even if Tasmanian tigers -- or other animals -- are resurrected, it will take some time to build up diversity again.
Experts believe billions of these birds populated the Americas when Europeans arrived. Loss of habitat and commercial exploitation of the birds for their meat are thought to have killed them all off.
Efforts are now underway to revive the species by extracting DNA fragments from preserved specimens, and later, using band-tailed pigeons as surrogate parents.
The Pyrenean ibex, a horned mammal once common in Europe, was one of the first subspecies targeted for de-extinction. Scientists began the attempts in late 1990s, when the last female Pyrenean ibex was still alive. Even if researchers could successfully clone that individual, there would be no males for her to breed with. Instead, genetic engineering might be required.
Since saber-toothed cat bodies are sometimes found frozen, it might be possible to extract preserved DNA and clone the animal. About 5 years ago, scientists did just that with a mouse that was dead and frozen for 16 years. Woolly mammoth remains are also sometimes found in a well-preserved, frozen state.
The dodo, a flightless bird, proved to be a tasty meal for humans and other predators. In 2007, scientists found a remarkably well-preserved dodo in a cave. Dodo DNA could be used to resurrect this avian species.
Ground sloths, relatively slow, lumbering animals, were easy targets for prehistoric big-game hunters. Scientists have found remains that still bear soft tissue. As with woolly mammoths, there's a chance extracted DNA could be used to back-breed or clone the large sloths.
The Irish elk has been extinct for 11,000 years. Like the woolly mammoth, it inhabited colder regions. As a result, bodies are sometimes found frozen and in relatively good condition, making them candidates for DNA extraction.
Earlier this year, Harvard geneticist George Church -- with tongue in cheek -- said that he was seeing an "adventurous female human" to be a surrogate mother to a cloned Neanderthal. While Church was really just theorizing about what it would take to bring a Neanderthal back to life, the possibility could be a reality, should any scientist undertake such a controversial project.
Paleontologist Jack Horner is leading a project to create a dinosaur out of a chicken -- a "dinochicken." He told Discovery News that birds "are dinosaurs, so technically we're making a dinosaur out of a dinosaur." He and his colleagues have been genetically engineering chickens to reactivate ancestral traits, such as long tails, which are more associated with non-avian dinosaurs.