The last woolly mammoths to walk the Earth were so wracked with genetic disease that they lost their sense of smell, shunned company, and had a strange shiny coat.
That's the verdict of scientists who have analysed ancient DNA of the extinct animals for mutations.
The studies suggest the last mammoths died out after their DNA became riddled with errors.
The knowledge could inform conservation efforts for living animals.
There are fewer than 100 Asiatic cheetahs left in the wild, while the remaining mountain gorilla population is estimated at about 300. The numbers are similar to those of the last woolly mammoths living on Wrangel Island in the Arctic Ocean around 4,000 years ago.
Dr Rebekah Rogers of the University of California, Berkeley, who led the research, said the mammoths' genomes "were falling apart right before they went extinct".
This, she said, was the first case of "genomic meltdown" in a single species.
"You had this last refuge of mammoths after everything has gone extinct on the mainland," she added.
"The mathematical theories that have been developed said that they should accumulate bad mutations because natural selection should become very inefficient."
The researchers analysed genetic mutations found in the ancient DNA of a mammoth from 4,000 years ago. They used the DNA of a mammoth that lived about 45,000 years ago, when populations were much larger, as a comparison.