‘On the planet Earth, man had always assumed that he was more intelligent than dolphins because he had achieved so much – the wheel, New York, wars and so on – whilst all the dolphins had ever done was muck about in the water having a good time. But conversely, the dolphins had always believed that they were far more intelligent than man – for precisely the same reasons.’ Douglas Adams, Hitchhikers guide to the Galaxy, 1979.
Regardless of whether or not we are more intelligent than dolphins, our ability to innovate and make tools is a factor that is often referred to when attempting to describe how we are ‘different’ from other species. This skill, which is closely associated with our large brains, has arguably allowed us to compensate for our lack of specialized morphological and physiological adaptations. After all, our sight is nothing compared to that of a hawk, our sense of smell is pitiful when compared to that of a dog and our hearing doesn’t come close to that of an owl. Instead, flexibility, insight, ingenuity and an ability to use the world around us to our own benefit are the key to our success. Goodall and Kummer (1985) gave a good analogy for this when attempting to explain the evolution of innovation in chimps. They described instincts and specialist adaptations as keys that, although easy to use, would only open a single lock. In contrast, the potential for innovation is more like a lock picking set. Although it requires the development of skills to use it, once competent in these skills, it can be used to open many locks.
Early human tools
Fossil remains of tools have been dated to as far back as 2.5 million years ago and there is now evidence that most hominids (our own ancestors and the species that were closely related to them) present after this time used tools to exploit their own particular ecological niches (Susman 1994). Fine motor control and precision grasping are thought to have played a key role in early hominid’s ability to craft such implements and studies into the hand structures of apes, humans and early hominids give an interesting insight into how tool use may have evolved.
Most apes and monkeys get from A to B using arboreal motion (swinging through trees). This type of locomotion places particular selection pressures on hand morphology, with the outcome tending to involve long, strong fingers and relatively weak, short thumbs. In many species this makes precision grasping (holding items between the thumb and forefinger) impossible, and in species where it can occur, very little force can be applied (often not enough to hold an item securely). A transition to bipedal movement (walking upright on two legs) could have freed up the hands, allowing increased manual dexterity to evolve. Alternatively, selection for increased manual dexterity in times of hardship could itself have resulted in the relocation of our early ancestors from the trees to the ground (Moya-Sola et al. 1999).
An ability to exhibit such fine motor skills is associated with increased neuronal control, with regions of the body associated with high sensitivity or precise movements being represented by disproportionally large parts of the brain. The picture below, known as a sensory homunculus, demonstrates this point by showing the relative sizes of the regions of the brain dedicated to specific regions of the body.
A sensory homunculus. Notice particularly the sizes of the regions dedicated to tongue and lips in comparison with those dedicated to the torso.
In a fairly recent study, Peeters et al. (2009) scanned the brains of humans and monkeys whilst they were being shown videos of tool use. They found that although most of the regions of the brain that were active in the two species were the same (including those involved with the grasping of the hands) the human subjects had an additional active region, which was found to be dedicated to tool use, function and recognition. The scientists suggested that this region had developed from the area associated with hand grasping.
However, the lack of this brain region in other species by no means makes tool use a uniquely human trait. Jane Goodall was one of the first people to show that other species were capable of using objects such as sticks and blades of grass to perform simple tasks. She observed chimps using twigs to tempt termites out of their mounds and sponges, fashioned from crumpled leaves, to access water that was difficult to drink. Since then, many instances of animal tool use have been discovered. Capuchin monkeys use stone hammers and anvils to crack open nuts, otters use stones to crack open tough clam shells and woodpecker finches use sharp twigs to remove grubs from beneath the bark of trees. Perhaps the most extensive example of non-human tool use is found in New Caledonian Crows.
Capuchin monkey using a stone anvil and hammer to crack nuts
In the wild these crows make a variety of tools, such as hooks, from several different materials including twigs and leaves. The design of these implements is fairly consistent within populations but is subtly different between populations. This suggests cumulative technological evolution i.e. the passing of tool use knowledge between generations, allowing each subsequent generation to build on the knowledge of the previous one, rather than having to start again. Experiments in the wild, where the crows were presented with familiar problems that had been modified slightly, showed that they use a two step heuristic mechanism. For example, when food was presented in a hole deeper than ones previously encountered , the crows initially tried to use their normal hook tools to retrieve it. When this failed they subsequently fetched a longer stick and used that instead i.e. they made an educated guess about what was required to succeed, using previous knowledge and then modified it for the task in hand (Hunt et al. 2006). In the lab this has been taken further and one individual in particular (a female named Betty) has demonstrated extraordinary innovative skills. In one instance, a plastic tube with a bucket of food at the bottom was placed in the enclosure with a wire hook tool and a straight piece of wire. The aim of the experiment was to test whether the crows chose the correct tool for the task but, when Betty’s mate ran off with the hook, she quickly used to straight wire (an unfamiliar material) to fashion her own hook and retrieve the food (Weir et al. 2002).
Betty the New Caledonian crow
What is perhaps more interesting is that whilst New Caledonian crows are natural tool users, suggesting that selection has favored this skill, other members of the crow family (corvids), such as rooks, have also demonstrated the same ability, even though they don’t use tools in the wild. This would suggest that tool use in these birds is a bi-product of their already high intelligence (members of the corvid family are renowned for their cognitive capacities and have very large brains for birds of their size), rather than the other way around i.e. a need for tool use resulting in a large brain (Seed et al. 2006).
Human fossil evidence shows that it took a long time for simple tools to progress to more complex ones and scientists suggest that it was a lack of brain power, rather than a lack of dexterity, that limited early human technology. Referring back to Peeter’s brain scan experiments, this could have been linked to the time it took for the tool associated brain region to evolve. Piecing together the evidence, the evolution of human technological abilities could have followed the following trajectory. Selection for increased manual dexterity in times of food shortage resulted in bipedal locomotion, which freed up the hands, allowing precision grasping to occur. This manual dexterity made it possible to make simple tools but our brains were still lacking that important tool specific region and so for a while increased complexity was out of reach. As our brains got bigger (whether due to selection for increased tool complexity, or for other reasons), the region associated with combining tool manufacture, function and causal reasoning also grew, allowing our technology to become more intricate i.e. assembling tools from different components etc.
This causal reasoning, or an ability to understand the relationship between the action of the tool and the task being attempted (as well as basic physics), is arguably what sets our own abilities apart from those of apes and monkeys. It allows us accurately design tools for a specific job without having to use trial and error and is often referred to as insight, a concept that I shall discuss further in subsequent posts.
For further demonstration of animal tool use, I recommend David Attenborough’s excellent series; ‘Life of Mammals
References
Kummer, H., & Goodall, J. (1985). Conditions of Innovative Behaviour in Primates Philosophical Transactions of the Royal Society B: Biological Sciences, 308 (1135), 203-214 DOI: 10.1098/rstb.1985.0020
Susman, R. L. (1994). Fossil Evidence for Early Hominid Tool Use. Science, 265(5178), 1570-1573. doi:10.1126/science.8079169
Moya-Sola, S. (1999). Evidence of hominid-like precision grip capability in the hand of the Miocene ape Oreopithecus Proceedings of the National Academy of Sciences, 96 (1), 313-317 DOI: 10.1073/pnas.96.1.313
Peeters, R., Simone, L., Nelissen, K., Fabbri-Destro, M., Vanduffel, W., Rizzolatti, G., & Orban, G. (2009). The Representation of Tool Use in Humans and Monkeys: Common and Uniquely Human Features Journal of Neuroscience, 29 (37), 11523-11539 DOI: 10.1523/JNEUROSCI.2040-09.2009
Hunt, G., Rutledge, R., & Gray, R. (2006). The right tool for the job: what strategies do wild New Caledonian crows use? Animal Cognition, 9 (4), 307-316 DOI: 10.1007/s10071-006-0047-2
Weir, A. (2002). Shaping of Hooks in New Caledonian Crows Science, 297 (5583), 981-981 DOI: 10.1126/science.1073433
Seed AM, Tebbich S, Emery NJ, & Clayton NS (2006). Investigating physical cognition in rooks, Corvus frugilegus. Current biology : CB, 16 (7), 697-701 PMID: 16581516
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