Continuing the discussion from Are human beings still evolving in response to any recognizable factors?:
This was getting moderately off-topic, but it’s something that interests me deeply. (My apologies for getting long-winded; I’m trying hard to only cover the main points!) Keeping in mind all evidence will be more circumstantial than not, intriguingly, this article, which purports to be evidence against ancient persistence hunting, may actually be anything but. In my opinion, the data set does not support the authors’ conclusions nearly as well as they want it to.
First, for anyone who wasn’t following the other thread and hasn’t heard the idea before, endurance running is something humans are surprisingly good at, compared to the rest of the animal kingdom. It’s not just our stubbornness and insanity that keeps tens of thousands of us finishing marathons year after year: many quadrupeds will physically overheat before we will. There’s a reason the Iditarod is run in the cold.
Many quadrupeds have to breath in unison with their stride at top speeds (galloping). This is efficient (they don’t have to spend extra energy expanding and contracting the lungs) but has an important limit: the animals can’t pant to cool themselves until they drop to a trot or walk. And panting is most animals’ primary method of dumping heat; animals that sweat a lot, like us and horses, are rare.
A fit human can chase a bigger, faster animal to heat exhaustion over several hours or days, and this is recorded in various hunter-gatherer cultures: rarely, but in far-flung locations. This is persistence hunting, and a growing number of scientists think it is not mere coincidence that we can physically do this: that we evolved specifically for it, in a time before arrowheads or other evidence of sophisticated weaponry. And yet somehow we were getting a lot more meat in our diets, enough to grow our brains bigger and our bodies taller.
Pickering and Bunn, 2010 (linked above) set out to test and disprove this by surveying the ages of the bovid bones associated with ancient human sites. They hypothesize that if they were run down, they should look like the age profiles of what we might see from modern cursorial predators, i.e. mostly young and old so they are easier to catch. They explain that ambush predators have effectively random age profiles, i.e. whatever animal walks into it first.
The results are interesting: instead of either option, large bovids are dominated by prime animals, biased away from young ones. Small bovids are mostly old, but the sample size of these is smaller. There are several species in the large bovid category, but waterbuck are represented the most, and some remains may be of late-stage fetuses because they have no tooth wear.
This raises an intriguing possibility in relation to the small prime adult waterbuck individuals (MNI= 7 adults, of which three are smaller, early prime females and four are larger, late prime males) from FLK Zinj: the targeted prey of hominin ambush hunting was likely pregnant or recently pregnant
female and somewhat older, perhaps non-territorial male waterbucks.
Even though E(ndurance )R(unning)-P(ersistence )H(unting) was argued to be most productive for hominins when used against large, size group 3 prey, we reiterate that the old-male-dominated pattern in A. recki mortality at FLK Zinj does not contradict the prediction of the ER-PH hypothesis for small bovids. We question, however, the relative merits and adaptive value of targeting small, old gazelles in their preferred bush–woodland habitat by jogging with eyes fixed to the ground in a most challenging tracking exercise…
Because (some of) the data does not match the authors’ expectations for persistence hunting, they conclude that hominins were likely ambush hunters who waited in trees with wooden spears for prime large bovids to come along and leapt upon them as a group.
Wait, what? You may well ask. (I did.) Why would you only jump out of a tree onto a pregnant female or an older male? Wouldn’t those be the most dangerous? Why, if hominins spent half a million years or more doing this as our primary hunting strategy, would we have lost so much of our hair and fast-twitch muscle fibers and tree-climbing adaptations? And why are there so few younger animals in the data set? Ambush predators take whatever animal wanders into the ambush first.
Is there any other explanation? I think the huge factor being overlooked is that in the persistence hunting model, animals are not being run to muscle fatigue, they are being run to heat exhaustion. The data on modern carnivore prey distribution is broken down by species, and it is interesting to note that the sprinting cheetah has the highest proportion of younger animals. What if hominin hunting is as far removed from the wild dog/hyena distributions as those are from the cheetah’s?
A focus on heavily pregnant females and mature males (with heavy horns) all of a sudden makes sense if we consider the energy needed to drive the animal to overheating. Why run a smaller juvenile down when you could have more meat for the same or more time and energy? And the real kicker occurs when you go onto Wikipedia to wonder why waterbuck might have been the favorite target of these ancient hunters:
The waterbuck cannot tolerate dehydration in hot weather, and thus inhabits areas close to sources of water. Predominantly a grazer, the waterbuck is mostly found on grassland.
Sounds like the ideal persistence hunting opportunity to me. Anyone want to tell me if I’m barking up the wrong tree?