Are human beings still evolving in response to any recognizable factors?


(Jay Johnson) #81

True. Just speculating, but cooperative hunting may have preceded cooperative living. In that case, one could say that the cognitive demands of hunting provided the “jump start” of the trend toward larger brains, and social complexity took over from there. But, in reality, most of these things co-evolved, so it’s often impossible to say which one came first.

Nevertheless, the connection between brain size and social living has been fairly well accepted since this 2002 paper: Social intelligence, innovation, and enhanced brain size in primates


(Phil) #82

Sounds right. I suspect our ancestors moved from a forested environment to a more open grassland or scrub brush type setting, where walking was more important than climbing, and perhaps strategy and moblility was more important than waiting for something to walk by.


(Jay Johnson) #83

Another crucial step along that road was H. erectus control of fire about 1 million years ago. Since cooked meats are more easily digested, this advance made far more calories available for the brain. The human brain is just 5% of body mass but consumes 20% of calories. It’s not a coincidence that large-brained mammals are prone to extinction and that we are the only surviving members of the genus Homo.


(Jay Johnson) #84

I’m more inclined to think that our ancestors scavenged for meat before they began to hunt for it, but that’s just my laziness talking. Much easier to steal a catch from others than to catch it yourself.


#85

I don’t know if I fully accept this conclusion. In this case, the selective pressure has moved from our immune system to our brain. What is being selected for is our ability to use our brains to overcome infections. We can see this same trend in other arenas, such as our ability to adapt to extreme weather in the arctic by using our brains instead of evolving physical adaptations to the cold. We could also say that selection pressure is being put on social interactions between humans that allows us to work together to make things like penicillin and structures that protect us from the elements.


(Lynn Munter) #86

That’s a fair guess, assuming by ‘cooperative living’ you mean more than the rest of the apes do anyway.

I think this shift resulted in the Australopithecines, and it was early Homo that really began to develop endurance running and hunting large animals. Our bipedality occurred in stages.

I totally agree that scavenging preceded hunting, scavenging really only requires walking efficiently over long distances, but as soon as you start following dying animals and then maybe chasing injured or ill ones, you see a very natural progression where evolutionary pressure would have been strongly applied.

Here’s a thought: what if the reason there’s no more australopithecines or other ‘cousins’ is because our ancestors ate them all?

(I wish I could rule this one out.)

I should add a modification to this thought, and that is that the heavy-set Neanderthals probably had more of an ambush-style hunting strategy. We know they certainly had a lot of injuries consistent with being in close quarters with big game. But they also definitely had weapons, like spears.

It would make sense that persistence hunting wouldn’t be as effective a strategy in colder climates, both because we’d have to wear more protective clothing and because other animals would be less prone to overheating. (Difficult but not impossible.) In fact, I could speculate that it was the development of projectile weapon-based hunting that allowed Homo erectus to thrive in colder climates at all.


#87

Another possible adaptation related to cooking is the fact that cooked food is easier to chew. This allowed our jaws and jaw muscles to shrink. Since the cranium didn’t have to support the same chewing force it could thin and expand. There is also an interesting mutation in a myosin gene that seems to correlate with physical changes in the hominid lineage:

Powerful masticatory muscles are found in most primates, including chimpanzees and gorillas, and were part of a prominent adaptation of Australopithecus and Paranthropus, extinct genera of the family Hominidae1,2. In contrast, masticatory muscles are considerably smaller in both modern and fossil members of Homo. The evolving hominid masticatory apparatus—traceable to a Late Miocene, chimpanzee-like morphology3—shifted towards a pattern of gracilization nearly simultaneously with accelerated encephalization in early Homo4. Here, we show that the gene encoding the predominant myosin heavy chain (MYH) expressed in these muscles was inactivated by a frameshifting mutation after the lineages leading to humans and chimpanzees diverged. Loss of this protein isoform is associated with marked size reductions in individual muscle fibres and entire masticatory muscles. Using the coding sequence for the myosin rod domains as a molecular clock, we estimate that this mutation appeared approximately 2.4 million years ago, predating the appearance of modern human body size5 and emigration of Homo from Africa6. This represents the first proteomic distinction between humans and chimpanzees that can be correlated with a traceable anatomic imprint in the fossil record.
Stedman et al. (2004)

I don’t know if more work has been done on this finding, but I have always found it interesting.


(Jay Johnson) #88

Haha. Maybe. But I suspect there was easier game to catch than those guys. Going back to the “warfare” theme, I’m just as inclined to think we would have simply killed them off, whether to protect our own resources or to take theirs. On the other hand, scientists are fairly sure that H. sapiens was not responsible for the extinction of Neanderthal, so I doubt that we were the ultimate cause of other hominin extinctions, either. Just an educated guess.


#89

Finding one clever (and charismatic!) omnivore doesn’t mean that omnivory is correlated with intelligence.


#90

What is the evidence that our ancestors engaged in persistence hunting before weapon-making? Would they not need weapons for other prey, and tools or butchering?


#91

Walking became more important than climbing, but our ancestors were actually walking while they were still in the trees. Ardipithicus was a versatile lady.


#92

If that were the case, we would expect to see signs of butchering on the fossilized bones.

btw, The American Museum of Natural History has a diorama of a little Homo erectus at a bar watering hole, while a giant hyena is about to pounce on him. Why did the paleoartist choose this interpretation? Because many skulls of Homo have been found with tooth marks of just the right size. Ouch!

There is some evidence that Neanderthals practiced cannibalism.


#93

The Inuit today practice ambush hunting of seals. They put a feather next to the seal’s breathing hole in the ice, and wait for the feather to be ruffled by the seal’s breathing.


(Lynn Munter) #94

Perhaps it would be better to say that the general observation that carnivores tend to have greater brainpower than herbivores should exclude omnivores entirely, as they are far to unpredictable to allow themselves to be boxed in like that. :wink:

We evolved body types that are specialized in a number of respects for running as opposed to walking around the beginning of Homo erectus, which is also when we got much taller and larger-brained, most likely due to a shift to eating much more meat, which means hunting. We know that stone technology then was hand-axes and not a lot else, certainly no finely-knapped arrowheads. It’s certainly a reasonable supposition that sharpened sticks could have been used, especially considering chimps use them for hunting today. But hand-axes and sharpened sticks do not add up to anything I’d want to chuck myself at a big hoofed mammal with.

Not saying ambush hunting isn’t practiced successfully today, or in the recent past, by many cultures. Just that they tend to rely on projectile weapons, or at least metal/stone-tipped spears.

I believe this is the subject of an ongoing investigation…


#95

What species of human ancestors are you talking about here? How does one butcher a hoofed animal with a sharpened stick? And they would probably want to bring it back to camp and cook it. That is quite different than a chimp spearing a small bush baby with a sharpened stick. Chimps have powerful teeth for sharpening their wooden spears and eating the bush babies they catch.


(Phil) #96

In pre-horse days, native american hunters would cover themselves with buffalo hides and sneak up on a herd of bison with spears, supposedly. They would also run them off into ravines and such more commonly. Not an easy life, I’m sure a fair number wound up under hoof.


(Lynn Munter) #97

The hand axes would be the tools for butchering, I’m sure. They start appearing in the record ~2.6 mya, solidly in the late australopithecine era where I’m sure they came in very useful for scavenging activities. So the time period I’m talking about is late australopithecines to early Homo erectus, more or less. Homo habilus, etc.

Cookfire evidence is only 1 mya, well after hunting became established, although I suppose we could just be missing any earlier evidence of it.


#98

So you think Homo erectus was able to do long-distance persistence hunting, spearing hoofed game with sharpened sticks?


(Lynn Munter) #99

Yes.


#100

The problem is that the hunters in your video are anatomically modern humans.