Subject: Evolution of Wings and Flight Mon Jun 23, 2008 12:16 am
Flight Origins: How and Why?
The most difficult question about the origin of flight is "Why?". "Why" questions are the most difficult ones to ask when they concern evolution; evolution does not ask "why?" Evolution has no sense of future; the here and now is the only place where evolution occurs.
Evolution is limited by developmental and genetic constraints. If an adaptation is useful to a lineage, chances are that it will be preserved. If an adaptation is co-opted from a previous use to a new use, it is called an exaptation. The only scientific way to approach why flight evolved in a group is to first figure out how it evolved; what the temporal sequence of exaptations and adaptations was.
A comparative study of the functional morphology of the wings of the earliest known flying members of the lineage with the "pre-wing" structures of likely ancestors and close relatives provides the best evidence for how wings evolved. Why wings (and hence flight) evolved from this point is a matter of contention among scientists; various hypotheses proposed include:
How and Why Did Wings Evolve?
Scientists generally agree that wings must have been exaptations; they were used by the ancestor for one function, and became useful for flight among the descendants
1. Wings evolved from arms used to capture small prey. (This seems rational, so we can ask whether the ancestral forms were actually doing this.)
Many birds still use this strategy to capture insects ;
Old World flycatcher
The Old World flycatcher family Muscicapidae is a large family of small passerine birds restricted to the Old World. These are mainly small arboreal insectivores, many of which, as the name implies, take their prey on the wing.
2.Wings evolved because bipedal animals were leaping into the air; large wings assisted leaping. (This is possible; any amount of wing could assist leaping. Remember that we first need phylogenetic evidence for a bipedal running or leaping origin.)
3.Wings were used as sexual display structures; bigger wings were preferred by potential mates. (This is a non-falsifiable evolutionary hypothesis — we cannot test it.)
4.Wings evolved from gliding ancestors who began to flap their gliding structures in order to produce thrust. (This is reasonable and possible, but only with phylogenetic evidence for an arboreal gliding origin.) Few Examples :
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