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My Mind and Matter column for the Wall Street Journal on 1
January 2012 is here:
Here's a New Year's thought. With some nine million species on
the planet, and with each species lasting a million years on
average, about nine species will go extinct naturally this coming
year (with more, almost certainly, going extinct unnaturally). But
about nine new species also will be born in 2012.
Biologists have long dreamed of catching a new species in the
act of forming. The problem, of course, is the time scale-and the
fact that most species are little-known beetles and bugs. New
species form constantly, but they take huge stretches of time to do
so. The actual moment when a "daughter" species can (or will) no
longer cross-breed with the population from which it sprang (the
definition of speciation) is almost impossible to pinpoint, let
alone to witness.
The best that evolutionary biologists can do is usually to point
to groups of species that have plainly diversified recently,
usually on a group of islands. The finches of the Galapagos, known
as Darwin's finches, are the best known example, a single ancestral
species from South America having given rise to 15 specialized
forms in just the last two million years. More impressively, the
cichlid fishes of Lake Victoria have generated 500 forms in about
14,000 years (lakes are islands of water).
Now scientists have described a group of continental, rather than
island, bird species that seem to be in the process of forming new
species. The southern capuchinos are nine species of small
seed-eating birds in South America (a missing "p" and a substituted
"h" separating their name from that of frothy Italian coffee).
Though the brown females are similar to each other, the males wear
strikingly different colors and sing quite distinct songs.
Yet, beneath the genetic surface, the nine species of southern
capuchino do not look like different species at all. Their genetic
"bar codes," based on DNA sequences unrelated to appearance or
song, completely overlap-meaning that the species cannot be
identified from genetic fingerprinting. It is as if they are one
big species with lots of differently colored males.
Still, the species do lead fairly separate lives. Though capable
of hybridizing, they plainly do not do so much. The explanation for
this paradox, put forward by Leonardo Campagna of the Argentine
Museum of Natural Sciences, is that they are incipient species,
separated by the mating preferences of females but not yet by
Mr. Campagna and his colleagues argue that at some time in the
past few hundred thousand years, during a part of the ice age when
much of South America was covered with grasslands, an ancestral
species of capuchino expanded rapidly across the continent. When
warmer and wetter conditions returned, the birds became isolated in
several islands of grass in a sea of forest. Each "island"
developed its own idiosyncratic plumage and song. Now the species
encounter each other again, but this time as distinct forms.
The starlings and sparrows that Europeans brought to North
America may one day evolve sufficient differences from those left
behind in Europe that they will constitute separate species. Given
enough time, town pigeons in New York may one day be averse to
cohabiting with town pigeons in San Francisco.
Initially, at least, this "man-made" biodiversity will be far
too small and slow to compensate for man-made extinctions, but it's
worth noting the possibility.