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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Platypus spur you? Grab a scorpion

The most painful egg-laying mammal: the platypus

The duckbill platypus is an impossible-looking, risible creature that we don’t typically associate with horrific pain. In fact, besides its odd looks, its greatest claim to fame is that it’s a mammal that lays eggs. But that’s just because you’re not paying close enough attention. On the hind legs of the male platypus are two spurs that inject a venom so painful, the recipient human writhes for weeks after the encounter. In spite of the fact that platypuses (platypi?) and humans don’t hang out together much, platypus venom contains a specific peptide–a short protein strand–that can directly bind to receptors on our nerve cells that then send signals of screeching pain to our brains. Ouch.

Hurting? Reach for a scorpion

If you’ve ever experienced platypus-level pain and taken pain killers for it, you know that they have…well…side effects. It’s because they affect more than the pain pathways of the body. The search for pharmaceuticals that target only the pain pathway–and, unlike platypus venom, inhibit it–forms a large part of the “rational design” approach to drug development. In other words, you rationally try to design things that target only the pathway of interest. In this case, researchers reached for the scorpion.

Their decision has precedent. In ancient Chinese medical practice, scorpion venom has been used as a pain reliever, or analgesic. But as developed as the culture was, the ancient Chinese didn’t have modern protein analysis techniques to identify the very proteins that bind only to the pain receptors and inhibit their activity. Now, a team from Israel is doing exactly that: teasing apart the various proteins in scorpion venom and testing their ability to bind pain receptors in human nerve cells.

The next step? Mimicry

With proteins in-hand, the next step will be to create a synthetic mimic that influences only the receptors of interest. It’s a brave new world out there, one where we wrestle proteins from scorpion venom and then make copycat molecules to ease our pain.

For your consideration

Why do you think the platypus makes proteins in its venom that human pain receptors can recognize if humans generally haven’t targeted platypuses (platypi?) as prey over its evolution?

In the human body, a receptor may be able to bind each of two closely related molecules–as a hormone receptor does with closely related hormones–but one of the molecules activates the receptor, while the other molecule inhibits it. Taking this as a starting point, why do you think some proteins in scorpion venom–which often causes intense pain–have the potential effect of alleviating pain?

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