Vultures, Human Evolution, Global Warming, and Windmills

Yes, these things are all connected.

Last weekend, Desiree Schell and I taped a segment of “Everything You Know Is (Sort of) Wrong” (apologies) for Skeptically Speaking, a radio talk show and podcast that Desiree hosts. The topic was the concept of humans as predators, or hunters, or really, eaters of meat, and I was discussing the many ways in which people misconceived this notion. One of the misconceptions that came up is the idea that human ancestors went through an evolutionary stage called “scavenging” during which time we were not capable hunters, but we were good enough to scavenge, so we did that for a while until we improved our lot and became the top predator.

This pointy-headed idea came from three places, and all three were in part reactions to the prevailing “Man the Hunter” (or “Killer Ape”) popularizations of human evolution (we also discussed those fallacies for the show). The first was Lewis Binford, who noted, correctly, that if you look at actual animal bones from actual archaeological sites, you could not objectively see clear evidence that would distinguish hunting from scavenging, and if you compared these “food remains” to hyena food remains, they looked roughly the same. Furthermore, Binford claimed, if we maintained ideas of recently studied modern human hunter-gatherers in our brains, as the model for ancient hominids who used tools (sometimes associated with bones) we would tend to see those foragers, more or less, in the archaeological record of our past, whether they were really there or not. He correctly criticized my advisor at the time, Glynn Isaac, for having done that.

As an aside, I well remember the time that Binford came to our quaint little department at Harvard to meet with Isaac and his research team (us) to sort out this difference in understanding of human evolution. A member of the faculty, Stephen Williams, loathed Binford because in an earlier incarnation, Binford had said bad (yet, actually, very true) things about Williams’ idols in a famous publication. Also, there was a Mayanist, Eric, who in an ill fated attempt to suck up to Glynn Isaac had prepared a scathing argument to show how Binford was an idiot and had completely messed up his interpretation of the famous South African site, Klasies River Mouth (where he claimed scavenging was in evidence).

Here’s how that went down. I met Binford at the airport, charged with bringing him safely to the University. But, the airport was under construction so I got lost on the way back to the parking lot and it took us about 45 extra minutes to find the car. We did eventually find it, and I drove Binford to the Anthropology Department were we were planning to have pizza. On the way, he told me a story of one of the senior (retired) archaeologists in the department sneaking into another archaeologist’s office to read a manuscript he had been hoarding. He sneaked into the office by crawling along the ledge outside the fifth floor windows and prying his way into the guy’s window. I told him, in exchange, my own story of someone in the department going out on the same ledge, but for an entirely different reason. Eventually we got to the Department. Williams sat there and steamed at Binford and sniped at every little thing he said. Eric showed up with his argument in tow, and still holding my copy of Binford’s Klasies River Mouth monograph, that he had borrowed from me. Eric started in on Binford, as Williams continued scowling and acting like a middle schooler, when suddenly Glynn Isaac stood up and drew everyone’s attention. Placing one hand over his pate, as he was wont to do, and pointing at the others as he spoke with the finger of his other hand, Isaac stated in his semi-elvian voice, colored with the British Colonial Accent he grew into as the son of a South African Brit exiled to Kenya, the following: “Eric, shut up. Your argument is invalid. Binford is absolutely correct about his concerns and you would know that I agree with him if you’d only read my latest paper. Steve, you are acting very immaturely and treating our guest very poorly. Both of you must leave now. Good day.”

And they got up and left, and I never did get that monograph back from Eric. Soon after, Williams retired and moved out of state, and Eric was arrested by the Texas Rangers for a combination of credit card fraud (something about a fake field school for high schoolers in Orange Walk Town) and child abandonment.

So that was the first argument for a scavenging phase. The second was advanced by Richard Klein, whom I’ve always tried to be nice to because he was my second wife’s baby sitter when she was little (African Anthropology is a very very small world) but who had this totally wrong. He interpreted the bones, also at Klasies but other sites in South Africa as well, to indicate that human ancestors hunted only Eland until they became fully modern very recently, then they started hunting the much more dangerous and harder to hunt Buffalo. Any buffalo bones from prior to that transition were obviously scavenged. Even though this referred to a period after the supposed “scavenging” phase, it lent support to the idea of a stepwise evolution of the ability to hunt.

I myself have spent a considerable amount of time living among the Elands and the Buffalo, as well as working with people who hunt both, either through mostly traditional means or with firearms, and I’m pretty sure Klein has that wrong. Eland are pretty darn hard to hunt. Buffalo, even the big giant extinct ones that previously roamed Africa, are in some ways easier, though with drawbacks. Perhaps we can discuss that some other time.

The third argument comes from the Berkeley group. This is a bunch of crazy archaeologists led by Rob Blumenschine, many of whom were friends and colleagues of mine even though they were all crazy. Hyena crazy. You see, Blumenschine and his crew had access not only to ancient and recent bones on the African landscape (like we all did), but also to a pack of Hyenas living at Berkeley. This allowed them to carry out experiments such as giving some bones to the hyenas to see what they would look like after being munched on for a while. They could also give bones to a lion (lions are easy to come by), and they could simulate an early human ancestor butchering an animal with stone tools (we Africanists normally do this at parties). This allowed the Blumenschine crew to carry out experiments that involved every possible series of events, using animals of different sizes. So, you would end up with a paper titled “Medium-size antelopes butchered by homninids, communiated by hyenas, then swallowed by a lion” and “Large bovid killed by lion, scavenged by hyenas, rescavenged by a lion, then scavenged by a homninid” and “Mixture of medium and small ungulates hunted by hominids who couldn’t stay long because they were being chased by a lion, who ate part of one of the ungulates but then the rest were chewed up by a hyena and then picked over by vultures” and so on and so forth. There were dozens and dozens of these papers given at conferences until finally someone made a rule against them.

I don’t think for a second that Blumenschine and his crew really believed that a scavenging phase was necessary in human evolution, but they were sure getting a lot of papers out on the basis of the fact that everyone else had been convinced by Binford that there must have been.

Here’s the thing: I personally never believed it, not even for one second. I did do some research on this topic, working with others. We fed bones to lions and tigers, we’ve picked up after wild hyenas, we’ve even spent days looking for something to eat, traversing the African landscape armed only with a spear (followed closely by a guy armed only with an AK47, though with only one bullet) and I can attest to the fact that on the bone-richest landscape known in Africa, there is about enough out there to get 200 grams of nice quality food per day, if you are about 7 or 8 people looking everywhere and doing nothing else. You’d starve.

In the end, I concluded that while Binford was right about avoiding misconceptions, it is in fact much much easier to imagine early human ancestors taking down Bambi, than chasing off a pride of giant saber-toothed lions who have themselves recently killed Bambi.

Turkey Vulture. Photo by Mikebaird.

But really, it is vultures that are the nail in the coffin when it comes to a scavenging phase; not as a form of proof, but as a wake up call to get real about scavenging. There are all kinds of vultures, but we can make some generalizations that apply to most of them: Vultures can’t kill or manipulate things with their talons, because that would require strong muscles that have nothing to do with flying, and they don’t really have any strong muscles that have to do with anything but soaring flight. Vultures can’t easily take off from the ground or a tree unless there is a breeze, and they can’t flap their wings for very long. They can really only glide. Vultures have given up the ability to do many of the things other birds do with their feet, wings, beaks, and other body parts because those parts are all shaped by natural selection to be good at only two things: Soaring around with minimum expenditure of energy looking for dead things, and then eating the dead things. Many birds have no sense of smell, many vultures do (helps to find dead things). And so on.

Vultures are an organism that is “in” a scavenging “phase,” as it were, and the only way they can make this whole scavenging thing work at all is to be so fully and totally committed to it that they can’t do anything else worth a damn. Hominids did not go through any such phase.

Which brings us to global warming and the windmills. The connection between global warming and windmills is obvious; windmills can make electricity in a way that uses, on a day to day basis, no fossil carbon, and thus help prevent or slow down global warming. So, we want to build lots of them. The problem with this is that birds are sometimes injured by windmills. One response to this is to make the windmills easier to see, and this apparently works for many birds, but not for vultures.

Vultures, in North America (and this may or may not apply to all vultures) are so damn adapted to scavenging that they can’t see in front of themselves in flight. The visual fields of their eyes have moved around to intensify visual acuity in areas that allow them to scan the ground very very accurately while at the same time keeping track of vultures flying to their flanks, who are in turn also scanning the ground. So a number of vultures flying around together are like a radio-telescope array, but instead of looking for ET or interstellar dust, they are looking for Bambi, expired, down in the brush, and exchanging that information to a certain degree with each other.

So, while the vulture is flying along, it could move its head to makes sure that there is nothing in front of it, but it does not, because in nature there are not things up that high other than large wide-at-the-base things (hills, mountains, cliffs) which the vulture probably senses non-visually anyway.

Windmills, like giant popsicles of death propped unnaturally far up in the sky, are totally unexpected by vultures, and are not routinely noticed by them. Thus, for vultures, windmills = death.

Here is the abstract from an article in Ibis about the vulture vision:

The visual fields of vultures contain a small binocular region and large blind areas above, below and behind the head. Head positions typically adopted by foraging vultures suggest that these visual fields provide comprehensive visual coverage of the ground below, prohibit the eyes from imaging the sun and provide extensive visual coverage laterally. However, vultures will often be blind in the direction of travel. We conclude that by erecting structures such as wind turbines, which extend into open airspace, humans have provided a perceptual challenge that the vision of foraging vultures cannot overcome.

Also, Ed Yong has written this up for Nature: Vultures blind to the dangers of wind farms: Collisions with turbines a result of visual adaptation for foraging. While you can’t have the Ibis paper unless you are special, Ed Yong’s piece is available to all. Thank you Nature.