Saturday, August 10, 2013

Dept. of Further Amplification: Grazing

Awhile back (June 7, 2013) in a post entitled “Man the Grazer,” I discussed findings about hominin dietary change 3.5 mya. I critiqued an article which said:

“The most significant findings indicate that human ancestors expanded their menu 3.5 million years ago, adding tropical grasses and sedges characteristic of a savannah-like environment to the typical ape-like diet of leaves and fruits from trees and shrubs of a forest environment.”

It should be pointed out that the author of the article, not the author of the study, said that. The study’s author, Thure Edward Cerling of the University of Utah, said:

“‘We don't know exactly what they ate. We don't know if they were pure herbivores or carnivores, if they were eating fish [which leave a tooth signal that looks like grass-eating], if they were eating insects, or if they were eating mixes of all of these.’”

The article’s author went on to clarify:

“He says this because the isotope method used in the new studies cannot distinguish what parts of grasses and sedges human ancestors ate – leaves, stems, seeds and/or underground elements of the plants such as roots or rhizomes. The method also cannot determine when human ancestors began getting much of their grass indirectly by eating grass-eating insects or meat from grazing animals.”

My critique centered on the probability of hominins eating grasses directly versus indirectly. I was concerned about the statement that we had added grasses and sedges to our diet.

Well, maybe Cerling didn’t say that; maybe it was the writer’s interpretation. I couldn’t find the research that was being discussed; but I did find other Cerling work, although it only discussed diets of large herbivores, not primates.

Better yet, though, I wrote him an email with my concerns and he wrote a quick reply. He wrote: “In our paper(s) we decided to present the data and make no interpretations as to the relative contributions of different food sources,” which is quite different from what the media presented. Although not finding his original paper makes it impossible to fairly compare, nonetheless, I’ll give him the benefit of the doubt.

If for no other reason than his replies made me think even more that he is on the right track. He wrote: “…Early hominins (6 to 4 Ma) had a C3-based diet (and were likely in the forest, even if a narrow forest), by 3.5 Ma they clearly were obtaining non-forest resources.” “Obtaining non-forest resources” is light-years away from “adding tropical grasses and sedges characteristic of a savannah-like environment to the typical ape-like diet of leaves and fruits”; much less, “we… make no interpretations as to the relative contributions of different food sources.”

Cerling expanded that concept even more significantly: “The earliest hominins, whose diet was purely C3-based, could have lived only in the forest (including a riparian forest).” Except for the interpretation of what foods we were eating back then, the data fit perfectly with my pet theories, thank you very much; and they are contrary to conventional wisdom. While it’s not even mentioned, much less stressed in the article or, as far as I can tell, the research, Cerling’s data completely negate the standard line that we left the trees and stood up because the forest was disappearing underneath us. Cerling fairly conclusively demonstrates that, while we stood up 6.5 mya, we didn’t leave the forest cover until 3,5 mya; which fits perfectly with the contention that it was food source opportunity which drew us out of the trees and not their disappearance. It turns out, we didn’t even leave the forest for three million years.

Cerling’s evidence does not determine what humans ate way back when, it only determines where the food came from. The important information here is the food source, not the food type; where the food comes from, not what the food is.

The truth is, it’s hard to change one’s eco-niche. The mere disappearance of an eco-niche is not enough to cause a change in a species’ niche. Usually, the dependent species will shrink with the disappearing niche or simply disappear. As the forest shrank, so did our niche; and, it turns out, we didn’t adapt out of our niche but rather shrank with it and didn’t emerge for another three million years. And three million years is enough time for our species to get thoroughly accustomed to hunting to where we could start venturing out onto the savannah where the bigger herds lived. Makes perfect sense. That scenario is simple and direct: hunters following the game. The competing theory of our continually changing our diet, accepting and then abandoning food sources as we moved through different environments, is complex to the point of unlikelihood. If we stood up to go hunting, we would have done it right where we were, and it would have taken us time to invade new territories, but at least we’d have a way to eat once we got there. If we were constantly having to find new ways to eat, it would have taken us a lot longer, I would imagine. And why would we invade a new eco-niche if there wasn’t already there a food resource we were accustomed to using? In fact, how could we? Could we have metabolized the food available on the savannah well enough to support our needs? Wouldn’t we have had to spend all day searching for food just like the other grass-eaters? Wouldn’t we have been at great danger far out on the velde eating grasses, if we couldn’t escape by running and had no weapons with which to defend ourselves? On the other hand, if we were out in the open hunting, we would have been a match for anything. Lions even. Which scenario is more likely?

It was one thing for us to let meat-eating take such a prominent place in our diet, but we were already meat-eaters before we split from the chimps; all we did was shift our emphasis; we didn’t adopt whole new food sources; but it would be an completely different matter for us to have adopted entirely new food sources—in this case grasses and sedges—only to abandon them later on. That’s asking an awful lot; and apparently that theory is promulgated by people who have a bias towards thinking humans started out as vegetarians. It is a religious argument, not a scientific one. Many people want humans to be natural vegetarians so they interpret data accordingly. Unfortunately, they make big mistakes. Like interpreting the appearance of non-forest foods in our diet to mean that we took up eating grass. That’s a stretch. It’s much more likely that we were simply continuing our hunting ways and following the game into the open.

The bottom line is that data bolster the argument that we left the trees to go hunting. It says that, when we climbed down from the trees, we didn’t leave the forest, that we kept eating food grown in the forest. It says that we didn’t starting eating food grown in the open until 3.5 mya. I can live with that.

Yet even diet isn’t the entire picture. The question of where one lives is not cut and dried. “Living” usually comprises two locations: where one feeds and where one sleeps. For predators bringing food back to the nest, where one raises one’s young is the same as where one sleeps. Predator young are raised away from the hunting grounds in a protected location. When hominins began harvesting the open grasslands, they could well have kept their camps/lairs in the forest. Most likely, they were close to water; there would be no particular need to leave the water’s edge just because one had taken up hunting the savannahs.

I’m not alone; hence, Cerling’s suggestion that humans may have evolved in a “riparian forest,” which accords with the contention that, when we left the trees we 1) began to live in semi-permanent camps as do all predators; and 2) those camps were likely down by the river.

That’s what I like about the theory: it’s clean, simple, direct, and the data all fit. Hoo-boy, what more could one ask?

No comments:

Post a Comment