Posted: Oct 09, 2018 12:50 pm
Fenrir wrote:
How big would this "small cluster" have to be, exactly, in your esteemed opinion?
Keep in mind that C. elegans has either 959 or 1031 somatic cells (depending on the sex) and the "small cluster" of neurons required to elicit robust phytotaxis appears to be precisely 4.
So, how many would you posit as required in a putative ancestor and why?
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2652401/#!po=11.5385
It would certainly help if you have more photosensitive cells than less. But the nematode's phototaxis depends on a robust signal transduction, amplification and interpretation mechanism that is required for it to respond to the presence of light. This allows it to use just four nerve cells, as you say. Anyway, this fact detracts from Rumraket's unsupported assertion that we would have started out with a cluster rather than, as is much more likely, a single light-sensitive cell.