Wednesday, August 6, 2008

Evolve: Guts

Many evolution buffs, like myself, have been watching the History Channel Series called Evolve, which are airing here in CA at 10pm on Tuesdays. These are well produced pieces that focus each week on a particular trait (eyes last week, guts this week). Both shows have been collections of ~5 narratives, mostly showing how the focal trait works in different animals. The narratives are tied together by asserting that evolution occurred (which I am quite certain it did). As such, these are not really about the historical science of evolution, but rather they are using evolution as an organizing principle to tie together experimental science on how particular traits work in different animal groups, with a preference for charismatic vertebrates. In the end, it all works quite well, and I would recommend the series.

In honor of Guts, I thought I would post a link to some of my favorite gut science. Work by Dirk Haller and (separately) Ruth Ley lies at the interface of ecology, evolution, and medicine. They wonder, how does the composition of bacteria in the gut of humans and mice affect the host - and how does that composition of bacteria get established?

You can think of the bacteria as a community, like a forest or grassland ecosystem, living inside each of us. Communities can have different levels of diversity - they can be comprised of many of just a few species. Those species could be closely or distantly related evolutionarily. And those communities could be established from environmental sources, or established by inheritance.

I saw Dirk and Ruth talk about some of this work at last years GAFOS conference, which is a conference of about 20 Americans and 20 Germans, under the age of 40, who were invited because someone took notice of his or her work. GAFOS is funded by the National Academy of Sciences and the von Humboldt Foundation. I described it in a bit more detail in a previous post, where I linked a symposium this year on the evolution of complex adaptations.

Some of the conclusions that Ruth and her colleagues have made are that certain groups of bacteria are associated with obesity of the host. There exists an experimentally generated line of sterile mice - mice that are born and live in sterile conditions, ie with no bacteria anywhere (amazing!). Some of these sterile and genetically identical mice were seeded with different bacteria, and some combinations were more likely to result in obesity of the mice, given the same amount of food.

Another interesting result is that gut bacteria tend to be passed from mother to offspring, as opposed to being obtained from the environment. This result is based on phylogenetic trees of gut bacteria from different populations. It is heritage, not locality that determines the bulk of gut bacteria.

Dirk's presentation was a really great example of pluralism, which I like to promote. He contrasted the germ theory of disease with the genetic/inherited theory of disease. He hints at a possible link between our currently germ-o-phobic society and the increase of genetic, especially auto-immune diseases like Crohn's disease and asthma. It may be that without the insult of germs, our bodies find it more difficult to distinguish self from non-self. By just having a germ theory of disease, we lose the full picture.

(These are my memories from over a year ago, so I may have some details wrong. Check out Ruth's and Dirk's presentations on this site, to see for yourselves!)

Next week Evolve, Jaws!

1 comment:

Jim said...

Hey - I really wish there were an official comment area for this episode ("Evolve - Guts"), but this is the best I've found so far.

I felt the need to point out the rather baseless (at least extremely poorly explained) hypothesis that cooked meat is more energetically accessible and than non-cooked entirely fails the scientific smell test. To suggest such a thing is equivalent to suggesting the energy consumed through oxidation (aka the fire) is less than the energy biologically available to the organism. This kind of claim requires more than a sum total of the CO2 output of a Python over an indeterminate amount of time.

I love science documentaries, but I hate psudo-scientific documentaries....

Happy reasoning,