The last of the mammoth population may have experienced high rates of birth defects due to the dwindling numbers and inbreeding, along with prenatal stress.
Fossils of mammoths found near the North Sea and dating to the late Pleistocene, about 12,000 years ago, frequently sported extra ribs along their neck vertebrae. Though harmless on their own, these cervical ribs are often signs of development gone awry. A 2006 study of extra cervical ribs in humans published in the journal Evolution found that about 78 percent of fetuses with cervical ribs die before birth; 86 percent of fetuses that develop with these extra ribs won’t make it to their first birthday.
“The high incidence and large size of the cervical ribs indicates a strong vulnerability, given the association of cervical ribs with diseases and congenital abnormalities in mammals,” the researchers wrote. “The vulnerable condition may well have contributed to the eventual extinction of the woolly mammoths.”
But they were already well in decline. This is the inevitable result of decline, the final blow. It’s a hazard that must also be considered when humans intervene to save threatened animals. The genetic variablity is of great importance.
The paper is available here.