Megafauna are animal species that can grow to weigh more than 100 pounds (44 kg). Our hominin ancestors emerged in Mother Africa maybe four million years ago. They walked upright on two legs, and eventually learned how to kindle fire, and hunt large game. These ancestors have been suspected of influencing the extinctions of some African megafauna that occurred between about 2.5 and 1.4 million years ago.
Much later, after Homo sapiens emerged, many more species of megafauna disappeared. These extinctions happened on the five continents outside of Africa, mostly between 50,000 and 12,000 years ago. The term “megafauna extinction” usually refers to this era, when humans were colonizing the planet, and feasting on large herbivores. Questions about the cause of these extinctions have inspired many theories, more than a little screechy controversy, and a few bloody noses.
End of the Megafauna is the latest book on this subject. It was written by Ross MacPhee, a scientist at the American Museum of Natural History in New York. It helpfully updates the discussion with the findings of recent research. It is also extremely careful not to present a firm conclusion about the cause of the extinctions, for the simple reason that absolute certainty is impossible — almost all of the puzzle pieces will never be found. Every theory contains an uneven mix of strengths and weaknesses. The two theories that are taken most seriously are climate change and human impacts.
Today, few believe that climate change could have been the sole cause. The one exception is the extinctions in Sahul, the landmass of Australia, New Guinea, and Tasmania, when they were joined together by low sea levels. In Sahul, evidence of early human activities is quite scarce. Elsewhere, climate change theories are now getting less and less support.
Charts of global climate trends during the Pleistocene are a lively zigzag of sharp spikes and dives. The lineages of most megafauna species extend back millions of years, and most of them managed to survive through numerous big swings. But, the actual timing of megafauna extinction spasms rarely corresponds with climate transitions. Climate certainly impacted regional ecosystems — woolly mammoths were not delighted when tundra was displaced by annoying forests. Nor were herds on the Sahara, when lush grasslands withered into scorching desert.
The arguments for human hunting are far more compelling. As the human diaspora migrated out of Africa, and colonized one continent after another, extinctions repeatedly followed their arrival. Hey! This is important! Extinction spasms did not precede human colonization, and there is no controversy about this. While megafauna extinctions shadowed the arrival of humans in the U.S. and Canada, the nearby Caribbean islands were unaffected — until humans first set foot on them several thousand years later. Islands around the world were the last regions to get zapped.
A primary voice in the hunting discussion was Paul Martin, who first published his overkill hypothesis in 1966. Working at sites in North America, and using the latest specimen dating technology, he concluded that most of the extinctions there took place during a thousand year period, following the first arrival of humans from Siberia. At least 50 species of large animals vanished — horses, camels, mammoths, and so on.
During this same thousand year period, humans also colonized all of South America, where the megafauna got hammered even harder. In Martin’s vision, as the colonists spread across the New World, they routinely ran into animals that had never before seen a human, and therefore had no fear of them. The naïve critters were easy to kill, and delicious to devour. Before they could figure out that humans were deadly dangerous, they were roasting over the fire. Hunting bands lived well, ate well, grew in number, and expanded into new regions.
It takes a lot of imagination to explain how so many species, over so vast an area, disappeared so quickly, when everything was roadless wilderness, and primitive humans were few in number. Martin envisioned the thousand year process in the Americas as something like a blitzkrieg (lightning war) of overkill. Hunters spread out from Alaska to the bottom of South America, rushing forward like a bloody tsunami wave, killing all they could, and leaving little behind — fanatical annihilation. Do you find that a bit hard to believe? I do.
With regard to the possibility of overhunting, MacPhee expresses doubts about some aspects of Martin’s hypothesis. Martin wasn’t the first to propose overhunting, he joined many others, but his views were the most extreme. In the book, the less extreme views get little mention.
Obviously, from an evolutionary timeframe, the New World spasm of extinctions was lightning fast. But, from a human timeframe, a thousand years can seem like quite a while. I expect that at least a few of my readers are younger than 200. A much earlier extinction spasm in Africa took place over hundreds of thousands of years, when our ancestors were fewer in number, had smaller bodies and brains, and still had much to learn about the art of hunting.
Killing megafauna just slightly in excess of their fertility rate could wipe them out over the passage of centuries. It wasn’t so much about the intensity of the hunting as the fragility of the hunted. Over a thousand years, and many generations of hunters, the process of extinction may have been essentially imperceptible. Scarcity increased at a gradual pace.
Elizabeth Kolbert noted that modern elephants do not reach sexual maturity until their late teens, each pregnancy takes 22 months, and there are never twins. Because they reproduce so slowly, mammoths could have been driven to extinction by nothing more than modest levels of hunting. Peter Ward estimated that if hunters had regularly killed just two percent of the mammoths each year, the extinction process would have taken 400 years — too slow for multiple generations of hunters to notice.
MacPhee noted that he often jabbers with other scientists about the extinctions. He has found that the majority believe that humans played a major role, but not all agree that our role was exclusive. Out of curiosity, I read several reviews of his book that were written by other readers, and was surprised to see that some of them, with great relief, believed that the book’s message was that humans had been found innocent. It seems that in the desire to appear completely impartial, clear factual statements about the elephant in the room seem to have gotten diluted enough to be confusing.
If we believe that the ancestors of environmentally conscious Native Americans (or anyone else’s wild ancestors) were responsible for causing extinctions, it’s tempting to presume that the human species must be inherently flawed. Therefore, there is no urgent need to care about anything. To avoid this, educators, and other concerned adults, seem to have a tendency to deliberately downplay or deny the darkness of reality, because if kids (or anyone else) comprehend the truth, intense despair will reduce them to walking dead zombies. But, if we sweep reality under the bed, their hope will survive, and they can fully devote their lives to a heroic adventure in mindless, planet-thrashing Sustainable Growth™. As they say, we live in interesting times.
Overall, MacPhee wrote a fine book. I had just two issues. (1) The discussion of human hunting was limited to Martin. Other non-blitzkrieg, imperceptible overkill viewpoints were not included. (2) If some readers concluded that humans were innocent, then maybe some important facts were not stated with sufficient emphasis. Megafauna extinction is a prickly subject.
I very much appreciated the numerous illustrations by Peter Schouten. His megafauna portraits add a powerful dimension to the reader experience. Schouten’s illustrations portray megafauna living in their ecosystems. They seem to conjure some deep ancestral memories of the reality we evolved in — a world of abundant life, fresh air and pure water, home sweet home. Today, those same ecosystems would look like highways, factories, shopping districts, cornfields, suburbs — populated by busy mobs of the megafauna known as Homo sapiens. So much has been lost.
Google images also presents many excellent pictures in response to searches for “megafauna extinction.”
MacPhee, Ross, End of the Megafauna, W. W. Norton Company, New York, 2019.