Fossils show male woolly mammoths were more likely to fall into natural traps.
Fossils of woolly mammoths have been discovered to contain a disproportionate number of male specimens. This skew in the sex ratio is thought to be due to the mammoth social structure, with adult males leaving the herd to find their own way, only to blunder into a natural trap.
Like elephants, mammoths lived in matriarchal herd structures with the oldest, largest female leading a group of related females and juveniles. Male mammoths would have left the herd at around 13 to 15 years of age to find unrelated females to mate with. It seems wandering alone often led them into trouble.
“Without the experience of a matriarch, the young and solitary males are more prone to end up in natural traps, for example sinkholes, mud pools, or falling through thin ice over a frozen lake. They might take more risks, be more adventurous,” explains Patrícia Pečnerová, one of the scientists who performed the study at the Swedish Museum of Natural History.
The team identified the sex of each of their 98 samples using DNA extracted from tiny bone fragments. They propose that a similarly skewed ratio could be seen in fossil samples from other Ice Age mammals that lived in herd structures, such as horses, bison and woolly rhinos.
The findings, published in Current Biology, are a reminder to scientists that fossil specimens might not always represent a random sample of a species. For example, assumptions made about the size or appearance of a species could be off the mark if the fossil record only contained male specimens.
This discovery is just a small part of the team’s wider research into the genomes of the last population of woolly mammoths. These mammoths were living on Wrangel Island in the Arctic until around 4000 years ago, some 6000 years after the mainland populations died out. This means the Wrangel Island mammoths were still roaming until about 1000 years after the Pyramids of Giza were built, but the reason for their final demise is still unclear.
“We are trying to look at the changes that happened on Wrangel Island once it became an island because originally it was part of the Siberian mainland. When the sea levels rose at the end of the last Ice Age, mammoths got trapped there. We want to see how much this isolation affected them: what was the population size and what was happening in the few millennia before they went extinct.”
Pečnerová hopes this study will determine the cause of that extinction.
“We can’t really say if it was climate change, if it was humans, but what we are trying to study is whether it could have been genetic reasons and the fact that the population was too small or the island was too small to sustain a long term viable population.”
Whatever eventually caused the mammoths to die out may remain a mystery, but the team’s findings do offer some useful advice for survival: always listen to your mother.