A previous study of mammoth remains, in Hot Springs, S.D., had found that among 14 dead specimens, 13 were young adult males and only one was female. But Ms. Pečnerová’s study investigated sex ratios using genetics.
The 98 specimens that the team had analyzed came from across the northern part of Siberia and had been collected over the course of four decades. The oldest were more than 60,000 years old, and the youngest, a specimen known as “Lonely Boy,” was about 4,000 years old. The genetic data did not provide insight into how old the mammoths were when they died, only their sex.
To obtain the DNA, the team first had to limit contamination. For that, they worked in a clean laboratory and wore lab suits similar to what Ebola doctors wear. They shaved off a few millimeters from the surface of their samples and then drilled into them to extract genetic data. They found that 66 were males and 29 were females.
The biggest limitation in the study is that their explanation for the skew is speculative and based mostly on the behavior of present-day elephants. The thought is that mammoths, like today’s elephants, lived in matriarchal societies where adult females protected the young. But around the ages of 14 or 15 when puberty set in, males left their herd and either became loners or joined bachelor groups, which were often led by inexperienced males. That was when they were more likely to do something risky, and find themselves stuck in frozen muck.
The natural traps buried their bodies quickly, protecting them from scavengers. The researchers said that their findings say nothing about the sex ratio of mammoths when they were alive, which they think may have been 50-50, only that males were more likely to die in ways that kept their remains preserved for thousands of years.
Beth Shapiro, an evolutionary molecular biologist at the University of California, Santa Cruz, who was not involved in the study, said she was surprised by the results and that the team’s hypothesis was sensible given what we know about elephant behavior. She added that it would be interesting to see if there is a sex ratio difference for other prehistoric mammals preserved in the permafrost, like bison and horses.
Daniel Fisher, a paleontologist at the University of Michigan, said the hypothesis was well-founded, but that tusks should not have been used in the study because males often broke their tusks while fighting each other, but that did not mean they died.
The authors said that even discounting their tusk fragments and only using teeth, bone and hair samples, they still had more dead males.
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