4,000 years ago, woolly mammoths went extinct. DNA evidence has led scientists to the conclusion that genetic defects caused the downfall of the last mammoth population.
Rebekah Rogers and Montgomery Slatkin, researchers from UC Berkeley, analyzed mammoth DNA to discover why the prehistoric animals went extinct. One set of DNA belonged to a mammoth that lived 4,300 years ago on Wrangel Island. Another set of DNA belonged to a mammoth that lived 45,000 in the Siberian mainland. Through the comparison of these two sets of DNA, researchers were able to pinpoint what may have caused the mammoths to go extinct.
Woolly mammoths were once found in Siberia, North America, and Beringia during the Pleistocene and Holocene. The 45,000-year-old mammoth from the mainland lived in a time when mammoth populations flourished. DNA evidence suggested that the older mammoth lived in a population with about 13,000 individuals. These mainland mammoths died out about 10,000 years ago.
The 4,300-year-old mammoth, however, lived about 300 years before the last mammoth population died out. This mammoth's DNA suggested that it lived in a population of as small as 300. This population held out on Wrangel Island for 6,000 years after the mainland mammoths died out. However, conditions on the island were not conducive to their survival.
Many factors contributed to the demise of the last woolly mammoths. The biggest ones were genetic mutations and their isolation on the island. A comparison between the DNA of the two mammoths mentioned above showed significant differences. There were excessive deletions from the Wrangel Island mammoth's genetic code, which were likely a response to low population numbers.
The mutations in the Wrangel Island mammoths were extremely detrimental to the survival of their species. For one, the Wrangel mammoth lost many olfactory genes, making it unable to sense pheromones. This would have made it difficult for the mammoth to find a mate and contribute to the population size.
Another mutation caused the mammoth's hair to become silky and smooth. Coarse, frizzy hair in woolly mammoths functioned as insulation against the extreme cold. The change in hair quality adversely affected the mammoths' survival in cold climes.
The researchers concluded that inbreeding in dwindling populations can cause harmful mutations in genetic makeup, thus accelerating the species' demise. "When you have these small populations for an extended period of time they can go into genomic meltdown, just like what we saw in the mammoth," Dr Rogers claims. This information is crucial in today's conservation efforts for living endangered species. A smaller population is less able to get rid of harmful mutations. Once a “genomic meltdown” occurs, it is irreversible.
However, the upside is that these harmful mutations can take generations, so conservation efforts have time to prevent a genomic meltdown. Due to advancements in DNA testing, scientists can test the health of a species's genetic health. Scientists can then assess a species's chances of survival based on its genetic diversity. It's best, however, for conservation efforts to stop population numbers from falling to dangerous numbers.
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