Modelling the Evolution of the Complex Eye
I'm wading through a few books at the moment and came upon something I thought folks might be interested in - a description of a mathematical model of the evolution of the eye by Dan-Eric Nilsson and Susanne Pelger of Lund University in Sweden. The pair decided to model the evolution of the eye to see if a precursor of the eye found in flatworms could develop into a complex eye in a sensible amount of time.
They started wth a patch of light sensitive cells backed by a layer of pigment which forms the most basic retina through its light absorbent properties. Next, they allowed the tissues around the simple structure to deform randomly with potential single changes limited to one per cent of size or thickness in each step. Their model accepted only those beneficial mututions that would enhance the capability of an organism to survive and reproduce thanks to improved visual performance. The model was then set in motion.
First the basic eye folded inward to make a cup. Then the eye cup became capped with a transparent surface. Next, the interior of the cup gelled to form a lens with dimensions that produced the best possible image. The number of incremental steps taken for progression from a flatworm's cell patch to a complex eye was 1829. Using conservative numbers the researchers estimated the entire process of evolution from cell patch to complex eye took less than 400,000 years.
Estimates suggests the complex eye has evolved at least 1500 times in the history of life on earth - the true number is likely to be many more.
Credit goes to Nilsson and Pelger, and to Jerry Coyne. I am paraphrasing his Why Evolution is True here.
"Experiments are the only means of knowledge at our disposal. The rest is poetry, imagination." Max Planck