The basic ideaThe idea that the enlarged human cranium might be an adaptation for housing our mutualist symbiont visitors is an astonishing and counter-intuitive one. However, culture and co-evolution with culture has resulted in most of the main ways in which we differ from chimpanzees. It really makes a lot of sense for our large brain to be an adaptation to human culture.
Other ideasTo see how plausible the idea is, one has to consider its merits relative to other theories that purport to explain the same observations:
- Probably the leading theory is the Machiavellian intelligence hypothesis - also known as The Social Brain Hypothesis. This states that humans became as smart as they did as a result of an arms race involving social skills - lying, cheating, manipulation - and the detection of these things in others.
- There is also the idea that sexual selection was involved. That some aspect of being smart was sexy - and that selection by members of the opposite sex (probably mostly females) resulted in large brains being favoured. This makes the brain the human equivalent of a peacock tail. This idea - along with the Machiavellian intelligence hypothesis - is discussed at length in a fine book: The Runaway Brain.
- Another idea is that neoteny was responsible. Young infants have disproportionately large heads compared to adult forms. Human evolution features neoteny. So, our large heads could be a side effect of neoteny.
- Another idea is that our large craniums resulted from the tendency toward bipedality in our species. Bipedality, in turn, forced a narrowing of the pelvic region making it more difficult for females to give birth. Selection would have then favoured females who gave birth to premature, less developed, and, therefore, smaller infants. Being born premature allows human babies to come into the world while their brains are still developing. Human brains continue to grow at rapid, fetal rates after birth - allowing a greater eventual size to be attained. This hypothesis is covered in Lynch and Granger (2008).
- Another idea is that omega-3 fats represented a nutritional constraint that got lifted by dietary changes. That hypothesis is laid out in the book The Driving Force.
- Early hypotheses suggested that environmental challenges and tool use drove the evolution of big brains. Such ideas have now mostly been superseded by more social hypotheses.
The place of the meme hypothesisThe idea that our big brains are meme nests is broadly compatible with the idea that runaway sexual selection is responsible. It suggests a sexually-selected arms race where what was sexy was a good sense of humour, being able to sing love songs, the ability to dance the latest dance - and other products of cultural evolution.
The Machiavellian intelligence hypothesis no doubt has some truth to it as well. It doesn't really explain why our brains blew up, while chimpanzee brains did not. What humans have that chimpanzees mostly don't is language and culture.
CostThe cost of a large brain in enormous. Brains must be providing a huge benefit to allow them to pay for themselves in the way that they did among our ancestors. Since the effects of culture are enormous, the meme theory shows promising signs of being able to account for the magnitude of the observed benefits.
TimingThe oldest archaeological sites containing tools are dated to 2.6-2.55 million years ago - around the beginning of the stone age - which is an excellent match for when the human brain first really started to inflate. Timing considerations provide significant support to the meme theory.
DomatiaSince memes are typically beneficial cultural symbionts, cranial meme nests are a lot like ant domatia. My pages on domatia videos and domatia corridors have more information about this.
TestingOf course, to qualify as being genuine science, hypotheses need to be testable, and one obvious weakness of these ideas is they they relate to events millions of years ago - and so are not trivial to test. I won't go into the experimental possibilities here - except to say that there are some. Both skulls and some aspects of culture fossilize. We will probably have access to enough evidence on the issue to get to the bottom of it in due course.
AcademiaThe idea of big brains as meme nests has been taken up by academia recently - with the cultural intelligence hypothesis and the cultural brain hypothesis and the Vygotskian intelligence hypothesis. Blackmore and the other memetic pioneers don't get mentioned.
Check it outFor the moment, I just want to point at this hypothesis, and make some noise to help draw people's attention to it. It is one of the more radical proposals of meme theory, one that has a good chance of being correct, and one that has so far received very little attention.
Some of Sue's other proposals - for example, the origins of human ultrasociality - have been showing good signs of panning out in recent years. The "big brain" hypothesis she pioneered is also deserving of attention.
References - culture hypothesis
- Blackmore, Susan (1997) The power of the meme meme;
- Blackmore, Susan (1999) The Meme Machine;
- Tyler, T. (2011) The big brain as a meme nest;
- Van Schaik, Carel P., Isler, K., Burkart, Judith M. (2012) Explaining brain size variation: from social to cultural brain.
- Van Schaik, Carel P. and Burkart, Judith M. (2011) Social learning and evolution: the cultural intelligence hypothesis;
- Henrich, Joeseph (2012) HOW CULTURE DROVE HUMAN EVOLUTION - A Conversation with Joseph Henrich
- Dawkins, Richard (1998) Unweaving the Rainbow: Science, Delusion and the Appetite for Wonder
- Dawkins, Richard (2005) The Ancestor's tale
- Herrmann, Esther; Call, Josep; Hernández-Lloreda, María Victoria; Hare, Brian and Tomasello, Michael (2007) Cognition: The Cultural Intelligence Hypothesis
- Moll, Henrike and Tomasello, Michael (2006) Cooperation and human cognition: the Vygotskian intelligence hypothesis
- Bjorklund, D. F. (1997) The role of immaturity in human development;
- Rendell, Luke, Fogarty, Laurel, Laland, Kevin N. (2011) Runaway cultural niche construction. Philosophical Transactions of the Royal Society of London - Series B: Biological Sciences.
References - other hypotheses
- Dunbar, Robin (1998) The Social Brain Hypothesis;
- Crawford, Michael and Marsh, David (1989) The Driving Force: Food, Evolution and the Future;
- Binns, Corey (2006) Something Fishy: How Humans Got So Smart;
- Lynch, Gary and Granger, Richard (2008) Big Brain: The Origins and Future of Human Intelligence ;
- Whiten, Andrew and Byrne, Richard W. (1997) Machiavellian Intelligence: Social Expertise and the Evolution of Intellect in Monkeys, Apes, and Humans - Book 1
- Whiten, Andrew and Byrne, Richard W. (1997) Machiavellian Intelligence: Extensions and Evaluations - Book 2
- Whiten, Andrew and Byrne, Richard W. (1988) Machiavellian intelligence: social expertise and the evolution of intellect