Once upon a time, our world was home to many giants. Actually, it wasn't so long ago. Once the dinosaurs had had their day, our planet was home to a whole new range of giant animals, from sloths that towered over humans, to wooly mammoths, to huge wombats and kangaroos, to the magnificent giga-goose.
Between around 50,000 and 10,000 years ago, nearly 200 of the world's largest animal species disappeared forever, leaving nothing but their humongous bones (and burrows). It's unclear what ultimately claimed these magnificent creatures.
During the time frame in which the megafauna disappeared, the world warmed and an ice age ended, suggesting one potential mechanism: climate change. Meanwhile, our own species was expanding into new lands, chasing the wealth of resources that came with the retreating ice. And so the debate over the roles of these two potential contributing factors has raged. Now a new study on the decline of giant herbivorous mammals – megaherbivores – points a finger at humanity.
Fossils show that, 50,000 years ago, there were at least 57 species of megaherbivore. Today, just 11 remain. They include notable behemoths such as hippos and giraffes, as well as several species of rhino and elephant, many of which continue to dwindle.
Such a dramatic decline, researchers say, is inconsistent with climate change as the sole cause. "The large and very selective loss of megafauna over the last 50,000 years is unique over the past 66 million years. Previous periods of climate change did not lead to large, selective extinctions, which argues against a major role for climate in the megafauna extinctions," says macroecologist Jens-Christian Svenning of Aarhus University in Denmark. "Another significant pattern that argues against a role for climate is that the recent megafauna extinctions hit just as hard in climatically stable areas as in unstable areas."
The new study consists of a comprehensive review of the available evidence since the extinction of the dinosaurs 66 million years ago. These include locations and timings of extinctions, habitat and food preferences, estimated population sizes, evidence of human hunting, human population movements, and climate and vegetation data going back millions of years.Loss of megafauna changed patterns of vegetation, which for example lead to denser forests in the Americas. (Svenning et al., Extinction, 2024)
We know that humans coexisted with megafauna, and we have evidence of some species being hunted to extinction. We know our ancestors were capable of hunting large animals effectively. "Early modern humans were effective hunters of even the largest animal species and clearly had the ability to reduce the populations of large animals," Svenning says. "These large animals were and are particularly vulnerable to overexploitation because they have long gestation periods, produce very few offspring at a time, and take many years to reach sexual maturity."
The new research shows that these human hunters were effective enough to significantly contribute to many extinctions. The megaherbivores, the team found, died out across a variety of climate scenarios, in which they had been able to effectively thrive even during times of change. Most of them would have adapted well to a warming environment, the researchers found.
It's all their fault for tasting good grilled.
Ever since the first Neanderthal bones were discovered in 1856, people have wondered about these ancient hominins. How are they different from us? How much are they like us? Did our ancestors get along with them? Fight them? Love them? The recent discovery of a group called Denisovans, a Neanderthal-like group who populated Asia and South Asia, added its own set of questions.
Now, an international team of geneticists and AI experts are adding whole new chapters to our shared hominin history. Under the leadership of Joshua Akey, a professor in Princeton's Lewis-Sigler Institute for Integrative Genomics, the researchers have found a history of genetic intermingling and exchange that suggests a much more intimate connection between these early human groups than previously believed.
"This is the first time that geneticists have identified multiple waves of modern human-Neanderthal admixture," said Liming Li, a professor in the Department of Medical Genetics and Developmental Biology at Southeast University in Nanjing, China, who performed this work as an associate research scholar in Akey's lab.
"We now know that for the vast majority of human history, we've had a history of contact between modern humans and Neanderthals," said Akey. The hominins who are our most direct ancestors split from the Neanderthal family tree about 600,000 years ago, then evolved our modern physical characteristics about 250,000 years ago.
"From then until the Neanderthals disappeared—that is, for about 200,000 years—modern humans have been interacting with Neanderthal populations," he said.
The results of their work appear in the current issue of the journal Science.
Li and Akey's key insight was to look for modern-human DNA in the genomes of the Neanderthals, instead of the other way around. "The vast majority of genetic work over the last decade has really focused on how mating with Neanderthals impacted modern human phenotypes and our evolutionary history—but these questions are relevant and interesting in the reverse case, too," said Akey.
They realized that the offspring of those first waves of Neanderthal-modern matings must have stayed with the Neanderthals, therefore leaving no record in living humans. "Because we can now incorporate the Neanderthal component into our genetic studies, we are seeing these earlier dispersals in ways that we weren't able to before," Akey said.
The final piece of the puzzle was discovering that the Neanderthal population was even smaller than previously believed.
Genetic modeling has traditionally used variation—diversity—as a proxy for population size. The more diverse the genes, the larger the population. But using IBDmix, Akey's team showed that a significant amount of that apparent diversity came from DNA sequences that had been lifted from modern humans, with their much larger population.
As a result, the effective population of Neanderthals was revised down from about 3,400 breeding individuals down to about 2,400.
Put together, the new findings paint a picture of how the Neanderthals vanished from the record, some 30,000 years ago.
"I don't like to say 'extinction,' because I think Neanderthals were largely absorbed," said Akey. His idea is that Neanderthal populations slowly shrank until the last survivors were folded into modern human communities.
I don't subscribe to the naïve belief that early man was more pacific and moral than modern man. If you look around the world two things are almost universal when two different cultures meet, warfare, and interbreeding. Cannibalism is not out of the question either.
The Wombat makes up time with Rule 5 Sunday: Hangar Queen Double-Scoop Sunday!
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