[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Arms into wings
<< I don't think that you can presume any characteristic of birds is basal
>because all the birds you've observed have the characteristic. >>
>Um. I do presume this. I guess if it were only one or two species, then what
>you say makes sense. But when it gets to be general, why not presume?
>Furthermore, if EVERY bird I observe does it, then I MUST assume it's basal,
>mustn't I. All the humans I know have two thumbs and eight fingers. I think I
>can assume our common ancestor had the same, can't I?
I am not sure this is quite so automatic. Your example refers to a
structure, which, to appear, requires a fairly complex series of genetic
steps. Parsimony would certainly suggest the character is basal. But I am
not sure you can translate this into suggesting that wing-brooding MUST be
basal to Neornithes (as opposed to assuming it is reasonably likely).
First of all, not every bird does it, and some clearly do not (though it is
fair to point out that most of those that do not have reduced or
highly-modified wings and probably represent a derived condition; this may
also be true for megapodes). Secondly, it is such a basically simple and
obvious thing to do with wings that it is, to me, not impossible to imagine
it evolving over and over again. To use your human analogy, the concept of
holding something over your head to keep dry in the rain is so basic that
the use of umbrellas or something like umbrellas has probably arisen many
times in human history.
And, to repeat an earlier point, why should we regard brooding as more
basal than other non-flight uses of feathers such as display (or
insulation, which really is a feather use found in every living bird)?
Ronald I. Orenstein Phone: (905) 820-7886
International Wildlife Coalition Fax/Modem: (905) 569-0116
1825 Shady Creek Court
Mississauga, Ontario, Canada L5L 3W2 mailto:email@example.com