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Israeli Archaeologists Resolve an Evolutionary Conundrum

There is a mystery in human evolution. As we progressed from knuckle-walking to striding, from swinging from branches to throwing rocks and then spears, surely our tools developed in parallel. Right? Put backwards, many assume that inferences can be made about our evolutionary state going by our industry. Right?

Well, there’s a snag. What does it mean that stone choppers, among the earliest tools, persisted for around two million years, and stone “Acheulean” hand axes for over a million years? The upscale Levallois-style tools were also used for hundreds of thousands of years. Did our evolution stagnate in that time?

It did not. Evolution is the nature of all things, but in thrall to neophilia (“love of the new”), and we tend to view human evolution through the prism of physical and mental change. Leaving the trees for the savanna necessitated physical and mental changes. Among other things, we grew: we’re about a third bigger than our australopithecine predecessors. Now, Dr. Meir Finkel and Prof. Ran Barkai of Tel Aviv University offer a paradigm-changing interpretation, published in Science Direct (Anthropology) of the stasis in these basic tools in the context of our continuing development.

As long as the animal environment remained stable, so did the tools we used to obtain these animals (to eat). If anything, this stability provided “safe ground” for technological and behavioral innovations, Barkai and Finkel write.

“The paradigm says these are problems in innovation, that the hominids didn’t innovate [during that time], for whatever reasons. For instance, that Homo erectus didn’t have sufficiently developed cognition, or that there were difficulties in innovation relating to social aspects. We say the opposite!” Finkel explains to Haaretz. “There wasn’t a problem with innovation: it was conservatism by choice. Innovation has a price.”

The myxozoan and the mosaic

Thinking on evolution in general has been changing. For example, we tended to simplistically perceive evolution as a roughly linear procession from primitive to complex. But evolution is broader than that. Take the delight that is myxozoans: microscopic parasitic jellyfish that evolved backwards, from sublime to slime. They evolved from proper multicellular animals to single-celled ones, or a few cells; and one went so far backwards as to even lose its genes for breathing. 

Yet these tiny parasites are remarkably successful, infesting what seems to be all species of fish and seafood, in all the oceans except possibly the Antarctic. They even made it onto land, alone among the cnidarians. Myxozoans thrive in the duck and the frog – and a strictly land animal: the shrew.

Also, the rationale of evolution may be fairly clear but scientists are still arguing over the process – fits and starts? Huge leaps? Other? All the above? Either way, paleontology has helped to enrich the debate with the concept of “mosaic evolution” (aka modular evolution), which posits that some body parts will change without simultaneous changes in other parts.

Mosaic evolution is key to the theory Barkai and Finkel propound: that technological persistency – like the hand ax remaining unchanged over a million years – was because their hominin users enjoyed stability of their prey, namely mega-fauna (big animals). As in, specific technologies were associated with specific animal types. It wasn’t broke so they didn’t fix it.

In the interim, while the hand ax persisted, we made great strides. Vast strides. The stability of mega-fauna and of the toolkit used to hunt them over a vast stretch of time gave early humans “space” to innovate, Finkel and Barkai explain.

We could depend on our trusty hand ax and chopper to predate on elephants and other mega-fauna, and meanwhile could monkey around with developing other technologies and tools – which came in handy when the mega-fauna disappeared. At which point, in turn, we didn’t need the trusty hand ax any more.

As humans shifted to smaller animals, new toolkits had to be adopted in order to better catch and process them. Once another change occurred in animal availability, a corresponding transformation took shape in the technological repertoire, and so on and so forth.

This approach could explain technological changes such as the replacement of hand axes by Levallois, to be replaced later by systematic blade production, Barkai and Finkel explain.

And absolutely, during those million-plus years of hand ax persistency, the very type of human being changed, starting with Homo erectus and ending with Homo heidelbergensis and Neanderthals in Europe. During those million-plus years, archaic humans learned how to use, and ultimately to sort of tame, fire. In that time they developed all sorts of hunting technologies, including maybe – it’s hard to say when – spear technology.

“All that was within the period of the hand ax,” Finkel says. “There were vast advances, yet the hand ax remained stable. We realized it’s an anchor: a stable basis on top of which we can innovate. Conservatism by choice gives you energy security, caloric security, enabling innovation and invention in other areas.” 

Thus, the technological persistency itself can be seen as an adaptive strategy, Barkai and Finkel argue.

Enter the megalodon

In separate work, Miki Ben-Dor and Barkai have argued that hominins took a turn to carnivory with Homo erectus over two million years ago. Our bodies did evolve to handle a high-protein diet, but only so far. Eat too much lean meat and protein poisoning will ensue. So the other chief source of calories was fat, which we came to crave. Large animals have abundant avoirdupois, while small ones don’t (as a rule).

Thus, we evolved to eat mega-fauna and ate them until they were no more. Only then did we have to adapt our tools to obtaining smaller, fleeter animals.

Drawing a parallel between technological and morphological persistency, Finkel and Barkai note that in animals, body design tends to persist as long as their food supply is stable. Morphological stasis over eons indicates that the animal has the wherewithal to survive in the changes of its environment – but that doesn’t mean its evolution ground to a halt.

Take sharks. Or horseshoe crabs, or the coelacanth – living fossils one and all. They seem unchanged over hundreds of millions of years, suggesting that they didn’t need to.

The great megalodon, the biggest of all sharks (as far as we know), seem to have dominated the seas from about 16 million to 2.6 million years ago – shame we missed them. Their remarkable size remained static in that time, dear reader: possibly up to 25 meters (82 feet) in length. It has been posited that megalodons went extinct because the oceans cooled and/or because their favorite meal – small- to medium-size baleen whales half their size – vanished and were supplanted by gigantic baleen whales, too big for even the great and terrible Meg to cope with. Yet the discovery of megalodon mouth marks on fossil seal remains suggests that while basking in the security conferred by their morphological persistency, they may have expanded to new prey types. Namely, pinnipeds. They do say the starving will eat anything.

Take the humble lungfish, which evolved over about 75 million years, then seems to have remained in morphological stasis for 250 million years. Lungfish were old before dinosaurs were even a gleam in the eye of the Creator. Yet to this day the lungfish feeding mechanism has remained largely primitive, which Finkel and Barkai argue enabled them to amble on through the eons while evolving advanced abilities to survive in variable conditions.

Turning to another fish, in February a team revealed that the coelacanth, which didn’t go extinct 66 million years ago after all, gained 62 new genes in the last 10 million years ago. How? From other fish, via transposons, aka jumping genes. It looks pretty much the same, though. Morphological stasis did not mean genetic stasis, evidently. It is possible that over the eons, the coelacanth exploited its morphological stability to expand its feeding options.

Haaretz is not suggesting that archaic humans exchanged genes with fish or did anything untoward with fish. But the apparently unchanged exterior of the shark and coelecanth can be misleading. Obviously they did change, statistics obliges it; and even if they look like their primordial predecessors, they can’t be the same.

The bottom line of the beasts is that morphological persistency, including body size and shape, is quite common in nature, Barkai and Finkel explain. This enables the animal to depend on a specific prey type, or habitat, while expanding its trophic horizons, and when the fecal matter hits the fan, they are prepared to adapt – find a new prey, nocturnal feeding instead of diurnal, etc.

This piscine stasis brings us to the analogy drawn by Finkel and Barkai: that the lithic stasis, the unchanged appearance of tools, doesn’t mean the humans didn’t change in other ways. Their theory of mosaic evolution suggests that the early humans were happily and confidently hunting with their old-time tools while developing new behaviors and making other advances, which enabled them to cope when the mega-fauna disappeared and rendered their long-standing toolkit obsolete.

For further support, they go to the archaeological record to find examples of faunal stability matched with technological persistency; fish, even the great megalodon, will only take us so far.

The tale of the hand ax and the herbivore

The Olorgesailie Basin prehistoric site in the Kenyan section of the Rift Valley boasts the gamut of the Acheulean from 1.2 million to 500,000 years ago, and the Middle Stone Age span from about 322,000 to 300,000 years ago.

A separate paper showed a massive shift in the animals populating the Olorgesailie basin from the Acheulean to the Middle Stone Age. The change in fauna – likely caused by the climate change associated with a period of heightened aridity starting 575,000 years ago – is associated with a shift in technology.

“Hand ax persistency during the Acheulean, in this case, is directly correlated with faunal stability, as mega-herbivores, and in particular elephants, are present throughout the pre-500,000 sequence alongside hand axes,” Finkel and Barkai write. But both the hand axes and giant herbivores disappeared there following the environmental and climatic conditions that prevailed in the region from 400,000 years onward.

In the Levant, meanwhile, elephants also disappeared about 400,000 years ago, forcing the local hominins to find some other source of meat and fat. They went for fallow deer, it seems, resulting in technological persistency of the tools needed to hunt, skin and butcher deer: blades and flakes. In fact, as Barkai and Finkel point out, the blades and flake technologies were developed while hand axes were still in broad use: “Hand axes might have served as an anchor, allowing early humans to test and practice new technological developments that would later play a crucial role in their adaptation to dependency on smaller game,” they explain.

They also bring examples of much more recent technological persistency as a function of game persistency from Sri Lanka and Brazil.

And thus, Meir Finkel and Ran Barkai propose a unifying theory of biological and human evolution, in which a biological or technological trait will persist as long as the main caloric source persists. If there’s an elephant, we need the appropriate tools to hunt the elephant. And when the elephant is gone, we need the tools appropriate to hunting a deer, and when they’re gone, to catching the rabbit and so on. Safe in this stable zone, we had the opportunity to innovate without risking our lives in the process, producing a mosaic evolution pattern.

For Finkel, who came to archaeology after a military career, it’s obvious. “In both early humanity and the army, one doesn’t innovate for no reason,” he explains. “You could starve or lose the war. You innovate cautiously. Conservatism is a very successful strategy – neophiliacs ignore the fact that conservatism works.”

Ruth Schuster