> Isn't it true that biologists have no direct proof of any specific trait
> of any animals being developed by natural selection ? Is Darwinism
> falsifiable as formulated ?
>
Depends on what you mean by proof. The classic 'proof' - the differently coloured moths that got selected because of the effects of the industrial revolution - has been shown to have been an experimental error. The problem was that the original scientist had put the moths in clearly visible spots, where their colouring - light or dark - blended in / did not blend in with the surroundings. That is not their natural habitat, apparently.
I'm not certain what other work has been done in 'natural selection observable in the time we have been looking for it' - for complex organisms, which evolve comparatively slowly, it isn't surprising that not much has been spotted.
On smaller scales, however, natural selection is clearly demonstrable. In one example, Manfred Eigen took a group of RNA viruses, and put them in a certain solution which is hostile to a particular component of their make-up. After forced evolution (exposure, selecting a sample, more exposure, selecting another sample, etc) the population was composed of a mutation of the virus which responded to the hostility by a modification of its RNA. (Eigen, M in Gene 135 (1993) pp. 37-47).
Also, of course, antibiotic resistance in bacteria is clearly a demonstration of natural selection at work (and this trait is used by geneticists for various purposes - leading to interesting interactions of the 'biological' and the 'social').
None of this means that the existence of a trait means that that trait is a 'response' to natural selection.
Peter -- Peter van Heusden : pvanheus at hgmp.mrc.ac.uk : PGP key available Criticism has torn up the imaginary flowers from the chain not so that man shall wear the unadorned, bleak chain but so that he will shake off the chain and pluck the living flower. - Karl Marx
NOTE: I do not speak for the HGMP or the MRC.