Did humans and their fire kill off Australia’s megafauna?

Genyornis. Courtesy of Michael Ströck & Wikimedia Commons.

Timeline, 2005: For those of us who do not live in Australia (and live instead in, say, boring old Texas), the animals that live on that continent can seem like some of the most exotic species in the world. The kangaroo, wombat, and Tasmanian devil, and most of all, the platypus, are high on the list of the unusual and bizarre in the animal kingdom.

But modern-day Australia has nothing on the Australia of 50,000 years ago when humans first arrived from Java. They encountered huge kangaroos, marsupial lions, 25-foot lizards, and tortoises the size of a subcompact car. Yet, within 5000 years, many of these animals had disappeared permanently. And since the dawn of the study of paleontology, researchers have wondered why.

Of course, it’s our fault

Of course, humans feature as the culprits in most scenarios. Just as the first people in the Americas are usually blamed at least in part for the disappearance of the American megafauna, like mammoths or giant sloths, the first people in Australia have also been suspected of hunting these animals to extinction or exposing them to diseases that decimated the populations.

As it turns out, humans may be to blame, but not through direct destruction or disease transmission. Instead, it may be the mastery of fire, the turning point in our cultural history, that ended in the extinction of many species larger than 100 pounds on the Australian continent.

Fire!

Australia’s first people probably set huge fires to signal to one another, flush animals for hunting, clear paths through what was once a mosaic of trees, shrubs, and grasses, or to encourage the growth of specific plants. The byproduct of all of this burning was catastrophic to the larger species on the continent.

The fires, according to one study, wiped out the drought-adapted plants that covered the continent’s interior, leaving behind a desert of scrub brush. The change in plant cover may have resulted in a decrease in water vapor exchange between the earth and the atmosphere with the ultimate effect of ending the yearly monsoon rains that would quench the region. Without the rains, only the hardiest, desert-ready plants survived.

You are what you eat…or ate

How could researchers possibly have elucidated these events of 45,000 years ago? By looking at fossilized bird eggs and wombat teeth. Using isotopic techniques, they assessed the types of carbon present in the bird eggs and teeth that dated back from 150,000 to 45,000 years ago. These animals genuinely were what they ate in some ways, with some isotopic markers of their diet accumulating in these tissues. Because plants metabolize different forms of carbon in different ways, the researchers could link the type of carbon isotopes they found in the egg and teeth fossils to the diet of these animals.

They found that the diet of a now-extinct species of bird, the Genyornis, consisted of the nutritious grasses of the pre-human Australian landscape. Emu eggs from before 50,000 years ago pointed to a similar diet, but eggs from 45,000 years ago indicated a shift in emu diet from nutritious grasses to the desert trees and shrubs of the current Australian interior. The vegetarian wombats also appear to have made a similar change in their diets around the same time.

Or, maybe not

And the species that are still here today, like the emu and the wombat, are the species that were general enough in their dietary needs to make the shift. The Genyornis went the way of the mammoth, possibly because its needs were too specialized for it to shift easily to a different diet. Its teeth showed no change in diet over the time period.

The researchers analyzed 1500 fossilized eggshell specimens from Genyornis and emu to solve this mystery and to pinpoint human burning practices as the culprits in the disappearance of these megafauna in a few thousand brief years. Today’s aboriginal Australians still use burning in following traditional practices, but by this time, the ecosystems have had thousands of years to adapt to burns. Thus, we don’t expect to see further dramatic disappearances of Australian fauna as a result of these practices. Indeed, some later researchers have taken issue with the idea that fire drove these changes in the first place, with some blaming hunting again, and as with many things paleontological, the precise facts of the situation remain…lost in the smoky haze of deep history.

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Did division of labor defeat the Neanderthals?

According to some anthropologists, the classic depiction of Paleolithic man as a few strapping cavemen ganging up on a mammoth with their spears might need to be replaced with dioramas of women gathering seeds or a man scraping an animal carcass from the ground to take home for dinner. In addition, this division of labor between men and women may have given Homo sapiens the upper hand when it came to their competition with Neanderthals in the Upper Paleolithic, about 45,000 to 10,000 years ago.

You may be familiar with some of the usual reasons proposed for the extinction of the Neanderthals and the supremacy of H. sapiens in the competition for resources: The wily H. sapiens swarmed the Neanderthals, defeating them in war with superior weaponry or a greater ability to resist disease or defy climate change. Some experts have proposed that a combination of these climatological and cultural factors may have contributed to the Neanderthal’s loss. But until now, no one had focused on differences in division of labor as giving H. sapiens the advantage.

The crushing hand of the Neanderthal woman

Evidence shows that Neanderthal men and women may have shared similar robust builds. In addition to bone finds that suggest as much, a researcher who focuses on hand mechanics has found that the Neanderthal female hand could exert as much force as that of a male. In addition, Neanderthal home sites rarely include artifacts such as tools for grinding seeds or trapping small animals, or even evidence of clothing production, such as needles. Thus, it seems that the Neanderthals may have, as a group—men, women, and children—spent their time focusing on one thing: big game.

Hunting a large animal that has defense ranging from tooth to antler to hoof to claw is a dangerous business, more so when your only weapon is a pointed stone attached to the end of a stick. Neanderthals got a big payoff when their spears worked, however, in the form of calorie- and protein-rich meat for the group. Evidence suggests that the whole group participated in this dangerous task—the bones of females as well as males bear the signs of many fractures, possibly the result of this dangerous lifestyle. Women and children may have been responsible for driving game or forging escape routes should the angered and frightened animal have turned on the group.

The pitfalls of group big-game hunting

This focus on a single kind of food source can have predictable consequences. In times of scarcity, the Neanderthals lacked other options. If they had no training or skills to obtain other food sources, then scarce big game translated into scarce Neanderthals. Homo sapiens, on the other hand, may have developed a division of labor between men and women before emerging from Africa 150,000 years after the Neanderthals, equipped with women who knew how to make protective clothing, trap small animals, and collect and prepare seeds and vegetation, and men with advanced weaponry who could efficiently hunt game. In addition, these people may have relied on scavenging as well as hunting to boost their food supply.

Division of labor gave H. sapiens the upper (non-crushing) hand?

The division of labor, which in some societies was reversed or not allocated in the same way between men and women, allowed Homo sapiens to adjust when food was scarce and boom when food was plentiful, or so some researchers now argue. These archaic humans could use their clothes-making skills to handle climate change and their efficient allocation of time resources to bring in food simultaneously from different sources, even when times were tough. Their booming population may have given them the numbers they needed to outcompete the Neanderthals.

…Or maybe not

Some researchers disagree with this hypothesis, suggesting that evidence of a division of labor dates back one or two million years, and there have been some predictable references in the news media to men’s and women’s roles today. One of the authors of the “division of labor” study explicitly cautions that what was beneficial 40,000 years ago isn’t necessarily a guide to what is beneficial today. Traits that provide a competitive edge are after all entirely reliant on context: What’s good in one environment may not necessarily be that helpful in a different set of circumstances.

Of lice and men

The loneliest Homo

When watching movies about hobbits, dwarves, and elves, I often think that our fascination with other human-like forms comes from our loneliness as a species—we are the sole living representatives of our genus. So we invent other species that might fit into our genus, creating companions for Homo sapiens.

Or…not quite that lonely

New research suggests that in our history we passed enough evenings with other members of our genus to exchange a few parasites—specifically lice—with them. Lice are very host-specific, and requires direct contact to transfer from organism to organism. Host-parasite specificity provides a tool to use the parasite to explore the evolutionary history of the host. This approach is especially handy in situations like the one we face with human evolution: little DNA data from our ancestors, but lots of information about the parasites that colonize us.

Before lice research, we used tapeworms, malaria protozoa, and human papilloma viruses to explore the contours of our family tree. All such studies agree with the fossil and genetic data we have demonstrating our origins in Africa. But the lice tell an even more thorough story with a surprise twist.

A research team that included a high-school student examined the genetics and morphology of the lice that colonize our heads and bodies. What they found was that this louse species—Pediculus humanus—has two lineages, one that colonizes both our heads and our bodies, and another that colonizes only our heads. The head-only louse is found only in the New World (the Americas), while the head-body louse occurs worldwide. The two lineages appeared to have diverged from one another 1.18 million years ago.

As the lice go, so go the Homo

It just so happens that Homo sapiens diverged from Homo erectus about…1.2 million years ago. Head-louse was an H. erectus parasite, and head-body louse was an H. sapiens parasite. When the Homo lineages went their separate ways, the lice co-evolved right along with them and formed two lineages.

They spent about a million years separated, but then something strange happened in the louse lines. They met up again on the same host, turning up on H. sapiens about 25,000 to 30,000 years ago. Head-only eventually made its way to the New World on the heads of H. sapiens.

Reunited…and it feels so…itchy

But how did this meeting of the lice occur? The only way it can: by direct contact between the two hosts. In other words, we found we were not alone. Whether or not we obtained the head-only lice via fighting, mating, or sharing clothing with H. erectus can’t be told. But for awhile there, we had company. Then pretty soon afterward, we didn’t, as H. erectus became extinct.

The lice seem to confirm one of two competing theories about our origins. One idea holds that H. sapiens emerged from Africa, spread around the world, and outcompeted other Homo species. The other theory is that H. sapiens ancestors emerged from Africa, spread around the world, and evolved into Homo sapiens while keeping genes flowing freely among populations. The lice appear to support the “out of Africa” or “replacement” school of thought. The head-body lice underwent the kind of genetic bottleneck that H. sapiens did at the same time in history, possibly because a relatively small group of humans emerged from Africa to find success through the rest of the planet, and took their lice with them.

Look to the pubes?

The research is not complete—there is still the question of how the transfer happened. Turns out, there’s another parasite that might clear up whether or not mating was the method: pubic lice. But we also seem to have a pattern of association with our generic brethren, including H. erectus and H. neanderthalensis: we meet them, and they become extinct. It’s no wonder that we’re alone now.

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