Vivak Vikteraman and his team of scientists at Dartmouth college, studied the ankle dorsiflexion of the hunter-gatherer Twa people, their neighboring "land dwelling" agriculturalists the Bakiga, and chimpanzees to confirm that more extreme ankle dorsiflexion, similar to chimpanzees, has evolved in the Twa.
Essentially the Twa people, due to the heavy incorporation of climbing in to their culture, have adapted the same efficient vertical climbing style of the chimpanzee! The higher the ankle dorsiflexion that a Twa person had, the more suited they were for this climbing style. These higher levels of ankle dorsiflexion are associated with longer fibers in the gastrocnemius muscle in the calf. Not surprisingly, the Twa people, when compared with the non-climbing Bakiga, exhibited these significantly longer muscle fibers. Since death is an ever looming danger for Twa climbers, those more suited to navigating the tree tops to retrieve honey and fruits were more likely to survive and pass on their long calf fibers for more efficient climbing.
These new discoveries bring in to question the mobility of our ancestors. Traditionally, there has been a distinct separation between our bipedal and tree climbing ancestors but this study has researchers thinking. If the Twa people are able to expertly navigate both trees and land, it may be that our human ancestors were not completely separated from apes by their bipedal movement, as previously thought. It may be that human locomotion was not always limited and maybe the famous australopithecine Lucy herself was able to both walk and climb trees.
References:
Carolyn, Johnson. "Modern Hunter-Gatherers' Remarkable Tree-Climbing Skills Shed Light on Human Prehistory." Boston News. 2013. http://www.boston.com/news/science/blogs/science-in-mind/2013/01/03/modern-hunter-gatherers-remarkable-tree-climbing-skill-sheds-light-human-prehistory/oMeZs1MSn4Hrad3YDmHyJI/blog.html
Twa. (2012). Encyclopedia Britannica. http://www.britannica.com/EBchecked/topic/610821/Twa
Venkataramana, Vivek. Krafta, Thomas. Dominya, Nathaniel. "Tree Climbing and Human Evolution." PNAS. 2012.
Thank you for this post! I have never before heard of the Twa people and their amazing adaptability. Also, I once read that classically trained ballerinas are able to artificially increase their foot arch up to 50° through extensive training. I now think this claim may have been overstated, seeing as the Twa can get it up to 47° on average.
ReplyDeleteWow, that's really interesting about the ballerinas. I think it could perhaps be true since the Twa people aren't actively training each day to increase their foot arch. Talk about commitment to a profession.
Deleteunfortunately this post in very unclear as to what happens when training a muscle. Just as you do not pass on a missing leg to your children if you are missing a leg, you do not pass on much longer muscles then are seen when you are born. The real inherited trait may be increased ability to stretch or resilience because muscle length is almost entirely determined by use. If one of the new-borns was to have their Achilles tendon severed, the muscle would instantly atrophy unless reattached, it would not grow to a pre determined length.
ReplyDeleteSorry to tare into you like this but muscle length itself is not being passed on, instead it is the muscles ability to elongate to the desired length.
Perhaps it wasn't clear that the allele frequency change is evident in the "longer fibers in the gastrocnemius muscle in the calf." These longer fibers are an inherited specially developed trait which allows them to have greater ankle dorsiflexion. Perhaps a normal individual, through simply stretching this muscle diligently can achieve higher dorsiflexion similar to the Twa. The Twa people, however, are born with these longer gastrocnemius muscles that cause their high ankle dorsiflexion to be an inherited physical ability, not one they train to increase.
DeleteDoes the ability of muscles to elongate vary greatly enough from person to person to make this an evolutionarily inherited trait? For instance, do the Bakiga people really have a genetic component that decreases their ability to elongate muscle to the same extent as the Twa people? I must agree with Alex by saying that this does not seem to be a very strong evolutionary case. If the Bakiga children to were to begin climbing as small children and force the same stretching of the muscle, I would predict that their flexion would become similar to that of the Twa children.
ReplyDeleteHey Emily, thanks for reading! I agree, it's definitely possible for Bakiga children to exhibit flexion similar to the Twa given intense training. Take a look at my reply to Alex as I outlined the evolutionary component of the study.
DeleteIn athletics we hear a lot about what is called a "muscle memory", in which the body muscle "remembers" certain techniques and movements that are not given at birth. If climbing tree is part of these people's lives, could muscle memories be passed down to each generation?
ReplyDeleteI'm not quite sure I understand the connection between the Twa people and the likelihood of the ancestors of all humans having tree-climbing abilities. It seems that the Twa people are simply a special case of how natural selection has favored people with longer muscles. I agree with Emily that it may be possible to show this evolution by putting evolutionary pressure on Bakiga children. It seems a bit over-generalized to conclude from this that our ancestors must have also had this specialization
ReplyDeletewow! this is a very interesting example- it seems a bit like LaMarckian evolution but it really does have a genetic basis. There are likely many more examples of this type of adaptive characteristics in isolated populations.
ReplyDeleteThis was an interesting post. The fact that tree climbing is dangerous puts strong selective pressure on better climbers. It was also interesting to see that the selective pressures favored a very specific climbing style. It was cool to read about the Twa especially comparing them to neighboring people. I also found this interesting because I know that other populations which often climb trees have a very different technique then the Twa. For example, those who are proficient climbing coconut trees often have there feet flat on either side of the tree instead of upright on it.
ReplyDelete-Jeff Brown
I actually really like this post and think it is a good example of evolution. While the actually muscle specifics may be trained only during ones life, there are also inherited characteristics of muscle that allow for more stretch and thus better tree climbing ability. This reminds me of some South American and African people who have trained for centuries to be able to run barefoot for great distances. Their feet are stronger and more flexible, not just due to acquired traits through a lifetime of running, but from selective inherited characteristics.
ReplyDeleteWow! i really like your post Rande. it is straightforward, easy-to-understand, and extremely interesting. To your point about bipedalism as the distinct ancestral trait that defined us from other great apes, one other explanation could be that the high Ankle dorsiflexion value of the Twa people might actually be evidence of convergence evolution from needing to climb trees. It would be interesting to conduct some form of genetic research to investigate which is actually the case!
ReplyDeleteGreat post, but it leaves me wondering, but it leaves me wondering what they are trying to reach! I suppose it could be any food item, fruit, berries, birds' eggs, bugs...
ReplyDelete