Humans blamed for moa demise

DNA says we are guilty. Early human settlers probably did wipe out the moas of New Zealand. Moa DNA suggests that their population  was stable before we turned up. New Zealand was home to nine species of flightless moa until humans arrived around AD 1300. Within a century, they were all gone. The archaeological record shows humans hunted moas, perhaps to extinction. But it is hard to separate human impacts from other effects such as climate change. Morten Allentoft of the University of Copenhagen, Denmark, and colleagues studied DNA from 281 fossils of four moa species. Moa genetic diversity was nearly constant for 3000 years before their extinction, a sign of a stable population (PNAS, DOI: 10.1073/ pnas.1314972111). “We can only blame ourselves,” says Allentoft. Earlier studies used DNA to claim the moa population was 3 million  at 4000 BC and just 159,000 when humans arrived. That looks like a fall in population before humans. But those estimates aren’t reliable, as DNA isn’t a good record of population size, says Allentoft. It is only good for showing trends. The new study “appears to take care of the ‘long fuse’ decline in  moa species”, says Ross MacPhee  of the American Museum of Natural History in New York.