Subject: A nice example of non-utilitarian "mimicry"
In my paper I mention a remarkable instance of “mimicry” that is
not real mimicry, that of a
hummingbird and a hummingbird moth. The bird and the insect species traveled
separate evolutionary pathways; nevertheless, each has been shaped by the same
niche. Thus their appearances have
"converged." They both drew nectar from flowers, and consequently over time,
both species’ body, posture, and style of maneuvering have been shaped by the
same environmental pressures.
I have a friend, Hank Hogan, whose
photographs of hummingbird moths I have borrowed for my papers. (See
http://www.santafe.edu/sfi/publications/wpabstract/200110057) Yesterday, he sent
me pictures of a hummingbird and a hummingbird moth, which, on the same day,
came into his garden to feed on the same flower. (See
http://flzhgn.home.mindspring.com/clrwing.htm ) This hummingbird moth, I should
point out, has clear wings, a bit unusual for a moth. (Kurt can probably tell us
how unusual.) The hummingbird, as you all know, beats its wings so fast that
they are not quite visible. Thus, the clearwing hummingbird moth, which probably
does not beat its wings as fast, seems to be attempting to mimic the appearance
of the hummingbird with the clearwing innovation. This is a truly remarkable
non-utilitarian resemblance, a coincidence, one that Nabokov would have
appreciated. To my knowledge,
no one has ever made the argument that the resemblance between the hummingbird
and the hummingbird moth confers a reproductive advantage. The hummingbird moth
is not a mimic of the hummingbird. Neither the moth nor the bird required the
other as a model (for predators to recognize) on which to base its appearance.
The resemblance between hummingbird and hummingbird moth is one that was created
by natural selection, but which does not serve a purpose. (In my paper, I
contrast this form of "mimicry" to camouflage, to the monarch-viceroy relation
and to the deadleaf, which are all very different kinds of supposed mimicry.)
The resemblance of the hummingbird and hummingbird moth is incidental, i.e., it
does not exist because of the function it serves.
I should point out, though,
that Mr. Hogan’s wife, (whose name, unfortunately, I don't know) who happens to
be an entomologist, who also worked at Harvard where Nabokov did, cautions that
we don’t know for certain if the bird beats its wings faster than the moth, and
we’re looking into that now.
A
bit more on the nature of the resemblance between the hummingbird and
hummingbird moth, for those that may be interested:
The resemblance is
due both to similar histories of functioning and pressures from physical laws,
such as D’Arcy Thompson (often cited as the grandfather of modern-day
theoretical biology) described in his explanation of the similarities between
all winged animals. In On Growth and Form, written in 1917, Thompson
points out that the same external constraints are the common cause of the
structural dimensions of any winged species. "In order to balance its
weight ... momentum must ... be proportional to the cube of the bird's linear
dimensions; therefore the bird's necessary speed, such as enables it to maintain
level flight, must be proportional to the square root of its linear dimensions,
and the whole work done must be proportional to the power 3½ of the said linear
dimensions."