The use of tools plays an important role in the ranks of human-specific behaviors; it stands beside our mastery of language, our upright posture, and even our propensity to make art.
But over the past century or so, many human-specific behaviors have been systematically shown to be present elsewhere in the animal kingdom. Research by scientists like Robert Seyfarth and Peter Marler show how some primates and song birds are able to make symbolic connections between vocalizations and abstract meanings, which is the foundation of language. Pavlov lead the way for research showing that animals as genetically different as crickets and pigeons can learn and problem-solve, skills humans often consider the basis of our “superior intelligence.” Orangutans and chimps can stand upright. Elephants can paint. We know chimps occasionally use tools, and new research in Science¸ which will be discussed below, shows that New Caledonian crows likely owe their healthy disposition and success as a species to their ability to hunt protein-rich larvae using twigs.
I do not mean to gloss over the impressiveness of these behaviors in humans – we certainly use language in a far more complex way than vervet monkeys, the famous Thai painting elephants were intensely trained by humans, and crickets can’t do algebra. However, while it is easy to point out the behavioral differences between us and the rest of the animal kingdom, the evolutionary causes of many human-specific behaviors are probably more similar to other organisms than we like to imagine.
I’ll only discuss one such evolutionary parallel here because, as with any discussion of evolutionary history, the data is scarce and the variables are numerous and intricate.
New research just published in Science concerning tool use in New Caledonian (NC) crows tells an interesting story – it seems that these clever birds are not only expert twig-yielders, but their use of twigs is central to their diet. They use twigs to custom fashion hook-like devices that help them fish out wood-boring beetle larvae. Some impressive calculations by Christian Rutz and his team reveal that the protein and fat-rich larvae account for a substantial portion of their diet. These crows have found a more intelligent way to fulfill their dietary needs quickly and efficiently than the spread-out, time-consuming foraging patterns normally seen in crows and their relatives (e.g. scouring the ground for less nutritious nuts and seed).
Furthermore, previous research has shown that NC crows are born with the propensity to use sticks, meaning that it is a heritable trait:
“Hand-raised juvenile New Caledonian crows spontaneously manufacture and use tools, without any contact with adults of their species or any prior demonstration by humans (Kenward et al, 2005).”
Lastly, young birds have to learn how to use the hunting tools. At an early age they have trouble wielding the twigs efficiently, and can only effectively hunt with twigs after months of practice.
Here are some parallels with the evolution of human tool use.
- First, while humans likely evolved the ability to alter objects in the environment (make tools) for specific adaptive applications about 2 million years ago and NC crows only acquired the trait in the past few hundred years, the behavior almost certainly evolved in hominins for dietary reasons (I use the word hominins because the first stone tool industry, the Oldowan industry, is usually attributed to Homo habilis, one of our early, pre-Homo erectus ancestors). Cut marks on bones found near tool sites point towards the role of early stone tools in butchery.
- Butchery implies meat-eating, and meat-eating is believed to be a watershed moment in human brain evolution because of both the direct benefits of protein-rich meat, and the social changes it brought through food sharing and collective hunting. Like the NC crows, use of tools allowed humans to steer their foraging strategies away from the chimp-like methods of scouring for nuts and fruits towards a hunting-based strategy.
- Once tools caught on in humans, they became ubiquitous. Stone tool assemblages have been found near fossils of every species since Homo habilis and ultimately led to the myriad tools of modern humans. Furthermore, tool use is thought to be somewhat heritable in humans (babies love their inanimate objects) and has even been attributed to distinct, human-specific brain areas in the frontal cortex.
While human and crow behavior is vastly different, evolutionary pressures can be very similar, and the adaptive products of those pressures sometimes line up. NC crows use tools to efficiently enrich their diet, as Homo habilis did in the East African rift valley 2 million years ago. This seemingly minor statement actually reflects an important, oft-overlooked concept in evolution. Vastly unrelated species often turn to similar behaviors when faced with similar environmental pressures: bats fly as birds do, some whales sing like cicadas, songbirds can communicate to each other like monkeys, and, like Homo habilis, New Caledonian crows invented tools to eat meat. And, like human ancestors, they also must learn (and teach) the behavior, allowing it to continue down the lineage.
Without denying our uniqueness and superlative abilities, humans must admit that our behaviors come from the environment; the same environment all animals share. And isn’t that comfortably humbling?