A characteristic of social evolution in humans is that we build on past learning and accumulate skills. Animals also show impressive capacity to learn but do they build on what they learn and pass on to the higher skill?

SA Jelbert, RJ Hosking, AH Taylor and RD Gray from the Universities of Cambridge, Auckland, the Australian National University, Canberra and the Max Planck Institute for the Science of Human History, Germany, write in the Nature group journal, Scientific Reports, that the New Caledonian crow is able to recall a mental template and fashion a copy, which may be the mechanism for a form of cumulative social learning.

Quite apart from the trainability of many animal species, which are conditioned responses and involve no aspects of cognition, many species have been found to learn skills from others of the same species. One example is of macaque monkeys that learn from others to wash potatoes in the sea before they eat them.

Another was when piercing the caps of milk bottles to get the cream, spread, by imitation, through flocks of the blue tit in the UK. There is, however, little evidence that such practices in animals have evolved and accumulated improvements over time, the paper says.

In human populations, in contrast, there is obvious preservation and evolution of skills. There is archeological evidence of additive, or cumulative improvement of technology since 1.6 million years ago, the paper says. This capacity of humans is generally believed to come from the many adaptations that humans have made, including teaching, language and imitation.

Social learning, however, is not just the copying of actions but consists of learning that is influenced by watching and interacting, not only with others but also with the final products or results of what others do. There are those who consider that emulative learning or learning from end products, rather than imitation of the process, can only lead to approximate copies of the products and not cultural change or cumulative growth.

Copying end products, however, could also be an effective avenue to cultural evolution in some cases. The paper cites studies where it has been shown that children and adults are able to replicate and progress to improve on the design of things even when they are presented only with end products, and not the manufacturing process, which they could have imitated.

Different animal species display remarkable intelligence and problem-solving ability. The crow is legendary, even Aesop speaks of the one that dropped pebbles into a jar to raise the water level. In Japan they report that crows see cars split walnuts open when the run over them. Hence, crows strew walnuts, which they cannot open themselves, on the freeway for cars to run over.

The authors of the paper in Scientific Reports note that the New Caledonian crow is known to fashion hooked stick tools and barbed tools using leaves of plants. The tools, which appear to be adaptive improvements over a basic design, have persisted over many generations, at least since 2000. “Thus, New Caledonian crows may possess a material culture that has incorporated incremental changes over time,” the paper says.

The evidence, however, does not suggest that the tool-making skill is culturally transmitted in crows. That is because crows display none of the social learning mechanisms that it would call for. They do not display imitative behaviour and in trials of retrieving food from a puzzle box, the presence of other, trained birds, that were proficient, did not seem to improve their performance. Imitation and teaching-learning are thus unlikely means of transmission of the tool-making skill. An alternative that has been suggested, the paper says, is end-product emulation, termed mental template matching.

In this process, younger crows see and possibly use tools fashioned by parents or others. The birds then form a mental picture — a mould or template — of the shape and properties of the tool they have seen, and they reproduce that. The paper suggests that the process is similar to the way young birds learn birdsong in some species. The fledgling bird begins by hearing the song of others of its species and acquires a song template. The bird then trims its own vocalisation to match the memorised song structure.

In the same way, the young crow has a mental picture of the tool and is able create another on its own. More importantly, the paper says, any improvements that the crow makes would stay in the templates that she would pass on to the next generation.

To test this suggestion, the team designed an experiment where New Caledonian crows would need to remember shapes and generate them when needed. A group of eight New Caledonian crows were trained to drop pieces of card into a slot machine to obtain rewards of food. It was done by placing eight large and eight small pieces of card and allowing the crows to drop them into the machine till all the cards that resulted in reward were used. This training continued till the crows consistently dropped in only the cards that produced rewards.

Once the birds had learnt the size of card that led to rewards, they were presented with a large sheet of card, too large to insert into the machine. No templates were visible and the birds were allowed to rip the sheet of card with feet and beak to insert into the machine.

This time, there was no template available and the insertions were rewarded at random, regardless of the size of the card. The result of the test was remarkable, the birds, despite there being no reward for doing so, consistently ripped the card into the size that they had learnt would result in the reward.

The conclusion, the authors note, is that New Caledonian crows have the capacity to manufacture articles from a mental template. This, then, could be the mechanism for cumulative cultural transmission of tool-making skills, despite there being no record of communication, teaching-learning or imitation behaviour.

The idea that emulation of a finished product, in place of imitation of a process, may not be effective for cumulative evolution, the authors, say, may be because known examples in the human context, like Stone Age tools, are “cognitively opaque”. This is to say that the final form does not suggest how it may have been arrived at. This, however, is not generally true, as the tools that New Caledonian crows make with leaves have tears along the ribs, which can be inferred.

The capacity to reproduce simple articles through emulation may be the one of the bare necessities for cumulative cultural evolution, the authors say. They suggest that before the appearance of complex tools in the hands of primitive humans, end product emulation may have been the means of cultural transmission and evolution.

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