[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Evolutionary Theory (convergence is not inevitable)



John Bois wrote:

>Evolution _is_ more directed than this (or "quasi-directed" as Dawkins
>puts it).  This is true at least on the macro scale.  A seeing "end
>product" on any "tape rewind" will develop a lens, a set of
>photo-receptive sensors, and so on.  A swimming "end-product" will have a
>body shape resistant to drag (thus we see a great deal of convergence to
>the fish shape--this shape is not a stochastic end-product)...

Lenses aren't found in all eyes: Nautilus uses pinholes, scallops use 
mirrors.  (Obviously photoreceptors are a must.)  Compound eyes give much 
less acuity than simple eyes for a medium-sized animal, but most arthropods 
are stuck with them.

Turtles aren't fish-shaped, neither were plesiosaurs, or most of the wide 
variety of swimming invertebrates.  I agree that the fish shape is most 
efficient for larger, faster swimmers (high Reynolds numbers), but due to 
both constraints and local fitness maxima, most haven't attained it.   

                                                        All the best,

                                                                        Bill