Sunday, 4 September 2011

Tim Tyler: Memes and the upright gait hypothesis


Hi! I'm Tim Tyler - and this is a video about memes and the upright gait hypothesis - and it is concerned with the idea that culture may have had an important role to play around the time of our split from chimpanzees.

Modern humans have an upright stance and gait, whereas the other great apes do not. Fossil evidence suggests that walking upright was one of the first traits to evolve among our ancestors that distinguished our lineage from that of chimpanzees. In my book on memetics - which is out now - I consider the hypothesis that an upright stance and gait started out as a culturally-transmitted trait that eventually became partially assimilated into the human genome.

Since chimpanzees are now known to have a diverse range of cultural traditions, it seems quite plausible that early humans also had had a form of culture. An upright gait and stance probably started off as a culturally-transmitted phenomenon which was passed down from parent to child. Over time the human foot, leg bones, knee, pelvis, spine and organs gradually adjusted to accomodate this new habit - via a process of genetic assimilation.

The evidence that an upright gait started off as a cultural trait mostly consists of the observation that an upright gait is largely still a culturally-transmitted trait - even today. Some of the supporting evidence for that from comes from feral children. Feral children lack culture, and so represent minature natural experiments showing what humans would be like without very much in the way of cultural transmission. I go into that evidence a little in the book, giving the example of the case of Oxana Malaya - who lived mostly in a kennel and was raised by dogs. When found, she barked, growled, panted, ran around on all fours, and sniffed at her food before she ate it. From such cases, we can see that both walking and talking behaviours both require cultural transmission to be successfully elicited.

There are some rivals to the idea that humans chose to walk upright - but they are not very convincing. For most of human evolution, our ancestors were probably standing up because they chose to.

An upright gait is partly culturally transmitted in modern humans. However, among our early ancestors cultural inheritance was probably even more important - since organic inheritance would have been less of a factor.

The memetic upright gait hypothesis is interesting for several reasons. Walking is dated back to close to the split between the human and chimpanzee lineages. That makes walking one of the oldest culturally-transmitted traits we know of - and we can see the scale of its effect on the human genome. Also, if memetic evolution is implicated in the split from our nearest living relatives, then we should consider the possibility of links between memes and speciation.

In the modern world, memes have brought down many of the reproductive barriers between humans but it is possible that - among our tribal ancestors - they had the opposite effect - acting to produce tribal markers for xenophombia to act on - thereby raising reproductive barriers between people from different tribes.

There are cases where parasitism causes speciation in the organic world - some bacteria can create reproductive isolation in their hosts - and thus cause speciation. It has been speculated that the cultural influences may have caused speciation in other species. The high diversity of songbird species could well be the result of memetic evolution generating reproductive barriers between them by influencing mating signals. Vertebrates evolve slowly, but memes can evolve much more quickly - allowing briefer periods of separation to result in reproducive isolation - which could lead to greater speciation rates. Paleoanthropology indicates frequent branching of hominid species historically, which is broadly- consistent with regular symbiosis-induced speciation.

If memes really are responsible for the split between humans and our nearest living relatives, that makes it even more important that we study them in more depth.


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