The Ratchet Effect: What is it and what does it mean in the context of the evolution of primates and humans?

In the first two weeks of our class discussions we have begun to review and contemplate what it is that separates us cognitively from primates and other mammals and how this difference may have occurred in our evolution. Tomassello's account in The Cultural Origins of Human Cognition approaches this topic by offering a hypothesis of cultural or social transmission which is species-unique in humans (Tomasello, 1999, p. 4) to account for the swift time scale of human evolution. According to Tomassello, there are very distinct abilities we have as humans that are not evident in the world of primates or other mammals. Specifically, one of the major abilities we hold as humans is our capacity for cultural learning. Through historical examples, Tomasello contends that we have continued to improve cognitively as a species because of our ongoing ability to build on our knowledge and performances through transmission of what we know between ourselves and additionally improvements of what we know through collaborations with other humans. An example of this historical evolution discussed by Tomasello is that of the hammer in its beginnings as a simple stone tool through to mechanical hammers of today. In effect, Tomasselo suggests that it is these two abilities, transmission and collaboration, that enable humans to move forward and progress. Tomasello, Kruger, and Ratner (1993) discuss human ability to make improvements or modifications to a process or object individually or in groups again and again over time as cumulative cultural evolution or the ratchet effect. Conversely, Tomasselo argues that primates do not possess this cognitive capacity for cultural transmission so that learned skills and abilities are not transmitted culturally between primates and are lost over time thus limiting evolutionary progression within the species; non-human primates do not have the ability to produce the ratchet effect.

If this hypothesis of the ability for cumulative cultural evolution as species-unique to humans is true then I wonder what is it that prevents non-human primates from this same ability if it is not, at least in part, biology. Tomasello briefly outlines another hypothesis discussed by Boyd and Richerson (1996) where they posit that non-human primates do practice cumulative cultural evolution but the difference may be quantitative. They argue that the ratchet effect does occur in non-human primates but not consistently enough or in the same breadth of contexts to advance the species cognitively through cultural learning. This does offer another alternative but it still leads me to ask the question about biology. I suggest that perhaps there is a combination of these two reasons, biology and culture, which in concert could explain why non-human primates cannot produce the ratchet effect consistently and in the same breadth of contexts as humans.

I have never considered any explanation of the differences between primates and humans other than that of sheer biology. I have seen the videos and news stories touting the amazing abilities of enculturated apes and agreed that they were quite remarkable. My understanding of what happened to allow these primates to improve beyond what I would perceive as normal primate intelligence was that they held some additional capacity to learn which was advanced by careful staging of scientific experimentation. While that still may be true, it is a new opportunity to contemplate the role of culture versus biology in human evolution and in explanation of the differences between humans and non-human primates. Understanding that historically humans at some point learned how to learn differently, namely through cultural transmission, is a key piece in the further exploration of the evolutionary puzzle.

References:

Tomassello, M. (1999). The cultural origins of human cognition, Cambridge, Ma.: Harvard University Press.

Tomasselo, M., Kruger, A.C. & Ratner, H.H. (1993). Cultural Learning, Behavioural and Brain Sciences. 16, 495-552.

Boyd, R. and Richerson, P. (1996). Why culture is common but cultural evolution is rare. Proceedings

of the British Academy. 88, 77-93.