Most of the world’s large animals are no longer present, and scientists continue to debate why these extinctions occurred. Dan Mann, a professor at the University of Alaska Fairbanks, recently presented his hypothesis during a campus lecture. According to Mann, the main factor may be that the Earth’s climate has become too stable in recent times compared to the fluctuations experienced during the last ice age.
Mann, who studies ancient environments in Alaska alongside UAF’s Pam Groves, has uncovered thousands of bones from extinct horses and remains of other large animals such as lions, giant short-faced bears, mammoths, and mastodons. Their fieldwork includes discoveries like a 40,000-year-old steppe bison found along an Arctic riverbank.
Groves co-authored a 2019 paper with Mann exploring possible causes for the extinction of many large animal species at the end of the last ice age—about 11,700 years ago. Theories often cite human hunting as a major reason for these extinctions due to people’s need for food and their development of effective tools. However, Mann said that multiple factors likely contributed.
“There’s no silver bullet that killed them all,” he said.
Research by Mann, Groves and others suggests that dramatic climate shifts favored large animals weighing over 100 pounds. In contrast, today’s more stable conditions have benefited smaller species.
“The small, meek and cute inherited the Earth. Climate stability favored them,” Mann said.
Over the past 100,000 years, about 64 percent of large animal species have gone extinct worldwide. The pattern is similar across most continents except Africa, where less than 20 percent of large animals have disappeared. “Africa never lost its (extreme climate swings, including from dry to wet seasons),” Mann noted.
During the peak of the last ice age around 20,000 years ago much of Canada was covered by thick ice sheets extending into mid-America; Alaska remained largely ice-free during this period. Ancient climate records show that temperature changes were frequent and severe throughout this era.
“The ice age is a time of crazy, rapid change,” said Mann. “To keep up, you really have to be on the move, whether you’re a plant or an animal.”
According to Mann’s research findings presented at UAF lectures and papers co-authored with Groves since at least 2019—large animals had advantages during times when environmental conditions shifted quickly because they could travel long distances for food and withstand periods without resources better than smaller creatures.
Mann also referenced late Pleistocene expert Dale Guthrie’s idea that longer northern summers during the ice age supported more diverse plant life in Alaska. As climates warmed into present-day conditions with shorter growing seasons and increased peat formation—nutritional resources declined for large herbivores like mammoths and horses.
While some argue humans drove these megafauna to extinction through hunting or other activities even in areas with low human populations such as Alaska wild horses vanished before significant human presence according to fossil evidence presented by Mann.
He acknowledged humanity’s broader impact on global ecosystems: “Humans are preventing the current ice age,” he said. “We should be growing ice sheets again.” He added that warming caused by humans may have eliminated species adapted for colder periods who might otherwise have survived until another glacial cycle began.
This column is provided by Ned Rozell from UAF’s Geophysical Institute in collaboration with university researchers; a version appeared previously in 2019.
