Monday, November 10, 2008

Probing Darwin's Black Box

The 'God of the Gaps' strategy is to assert that anything we do not yet understand is attributable to a god or gods. Two thousand years ago there were a lot of gaps in our understanding, and plenty of room for inventing ad hoc explanations for things. There were a lot of gaps where gods might reside.

Even recently, the god of the gaps argument is sometimes used. One example is the idea of 'Darwin's black box', the false assertion that the exquisite details of molecular biology cannot be understood in an evolutionary context.

There are two facets of 'god of the gaps' that are particularly bankrupt, one scientific and one theological. Scientifically, god of the gaps is equivalent to suicide, an admission that one simply cannot imagine how to go on any farther. God of the gaps is giving up on science, with no reason to do so. Theologically, god of the gaps means that the realm of god gets smaller each time a gap in our knowledge is filled.

Here, I give two recent examples from my life where the molecular details of evolution have been explicated in greater detail. In neither case are the gaps fully filled - this can never be the case - split a gap in half and we have two smaller gaps. But the gaps are getting sooo small - is it really worth trying to stuff gods in those tiny little gaps?

First, I saw a seminar by Joe Thornton on his work on the evolution of steriod receptors. Joe uses statistical inference to reconstruct the sequence of ancestral proteins. Then he brings them to life in the lab and conducts experiments on the proteins. He is able to reconstruct the order of specific mutations that occurred and that change the function of the proteins he studies.

I found particularly interesting that one particular receptor could identify 3 different steroids at the origin of the protein. Later on, specializations occurred through particular mutations that Joe and his group could identify. When thinking about the evolution of novelty, we often assume that multiple functions are added over evolutionary time. However, Joe's results show how functional complexity can be the original state, and that structural complexity can follow by parsing an ancestral function across subsequently duplicated genes.

To view Joe's presentation, go here.

The second recent example is that a paper from my lab was recently published that reviews our progress on understanding the evolution of the molecular basis of vision (phototransduction). This paper is available for free from the Springer web site.

Todd Oakley and M. Sabrina Pankey (2008) Opening the "Black Box": The genetic and biochemical basis of eye evolution. Evolution Education and Outreach. [Link]


T Ryan Gregory said...

Excellent presentation. I actually used that example in my paper from the eye issue.

Gregory, TR. 2008. The evolution of complex organs. Evolution: Education and Outreach, in press. [Link]

The original publications:

Bridgham, JT, SM Carroll, and JW Thornton. 2006. Evolution of hormone-receptor complexity by molecular exploitation. Science 312: 97-101. [Link]

Adami, C. 2006. Reducible complexity. Science 312: 61-63. [Link]

ajna said...

Tiny tiny tiny gods. Or else one big one shaped like a comb.

Todd Oakley said...

Ryan - Thanks for the refs, I was too lazy to look them up and stick them in the post. Thornton's lab and colleagues also published the ancestral protein's crystal structure in Science. Cool stuff.

Ajna- RATS! I never imagined the comb-shaped god hypothesis. I might become a believer yet! The god of 2-thousand years ago was like a horse-mane comb with really thick teeth. Today we have one of those flea-combs like the one I was using on my cat an hour ago - wiry little teeth. Good for extracting fleas.

Bjørn Østman said...

I can just hear Laplace: "I had no need of the comb-god hypothesis either."