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"Instant" Evolution Seen in Darwin's Finches,
Study Says
Mason Inman
for National Geographic News
July 14, 2006
Evolution may sometimes happen so fast that it's hard to catch in action, a new study of
Galápagos finches suggests.
Researchers from New Jersey's Princeton University have observed a species of finch in
Ecuador's Galápagos Islands that evolved to have a smaller beak within a mere two decades.
Surprisingly, most of the shift happened within just one generation, the scientists say.
In 1982 the large ground finch arrived on the tiny Galápagos island of Daphne, just east of the
island of San Salvador (map of the Galápagos).
Since then the medium ground finch, a long-time Daphne resident, has evolved to have a
smaller beak—apparently as a result of direct competition with the larger bird for food.
Evolutionary theory had previously suggested that competition between two similar species can
drive the animals to evolve in different directions.
But until now the effect had never been observed in action in the wild.
In the new study Princeton's Peter and Rosemary Grant closely tracked the two related species
for decades.
Their results appear in this week's issue of the journal Science.
Changing Beaks, Changing Diet
For both finch species, the researchers note, feeding is a trade-off between effort and payoff.
The birds generally prefer to eat larger seeds, which are harder for their nutcracker-like beaks to
break open but hold a bigger reward inside.
The bigger the bird's beak, the easier it is to crack open the seeds' coatings.
The already smaller-beaked medium ground finch couldn't keep up with the newly arrived large
ground finch, which is about twice as big and dominates feeding grounds.
Apparently in response, the medium ground finch evolved to have an even smaller beak,
making the species more adept at eating small seeds that didn't interest the larger finch.
"This is a phenomenon known as character displacement," Peter Grant said.
"It is a very important one in studies of evolution, because it shows that species interact for food
and undergo evolutionary change which minimizes further competition."
The researchers say they have seen other types of evolution in action in Galápagos finches
before.
But this was the strongest shift they've seen in their 33 years of study, the scientists say.
Nutcrackers, Woodpeckers, Vampires, Oh My!
The Galápagos Islands' 14 species of finches all evolved from one ancestral species, which
arrived from the South American mainland about two to three million years ago.
That original species branched out into many others, with each one specialized for different
roles.
The woodpecker finch, for example, has evolved to the point where it can drill holes in trees,
while the vampire finch drinks other birds' blood (watch video of vampire finches).
Ironically, naturalist Charles Darwin missed signs of evolution among these finches during his
1831 visit to the Galápagos.
Only later, with the help of other collectors and scientists, was he able to see how evolution was
responsible for the variety of finches. (Read "Was Darwin Wrong?" inNational
Geographic magazine [November 2004].)
Since then, the 1982 arrival of the large ground finch on Daphne is the first known instance of a
new finch arriving in the Galápagos.
"The event we observed is the only one that we know about, the only establishment of a new
breeding population anywhere in the archipelago," Peter Grant says.
"Once this happened before our eyes, we realized we had a very unusual and potentially very
important event to follow."
The two bird species immediately began competing for larger seeds.
The situation reached a tipping point when a severe drought hit the island in 2003 and 2004.
Both finches suffered, since there were far fewer seeds overall. The dominant large ground
finch ate most of the available large seeds.
"With the near removal of the supply of large seeds, the large-beaked birds [among] the medium
ground finches did not have enough food to survive," Peter Grant said.
"They died at a faster rate than the small-beaked members of the population."
The effects of competition are apparent when this event is compared to a drought in 1977,
before the large ground finch arrived on the island, the researchers argue.
During the earlier drought the medium ground finches' average beak size actually increased.
Textbook Classic
Jonathan Losos is an evolutionary ecologist at Harvard University in Boston, Massachusetts,
who was not involved with the Grants' work.
"This study will be an instant textbook classic," he said.
"The most intriguing aspect of the study is its nuanced understanding of how and when
character displacement occurs," Losos added.
"It supports suggestions by the Grants and others that [natural] selection will be most intense
during crunch times."
David Pfennig at the University of North Carolina at Chapel Hill agrees that the study has
important implications.
For Pfennig, the study's greatest surprise was "the apparent speed with which the character
displacement occurs—within a single year!"
Usually we think of evolution as being a slow grind, he says.
But, Pfennig added, the study suggests that evolution due to competition between closely
related species "paradoxically may often occur so rapidly that we may actually miss the process
taking place."
Darwin Lives! Modern Humans Are Still Evolving
By Eben Harrell Friday, Oct. 23, 2009
From: http://www.time.com/time/health/article/0,8599,1931757,00.html#ixzz24woBzTuW
Modern Homo sapiens is still evolving. Despite the long-held view that natural selection has
ceased to affect humans because almost everybody now lives long enough to have children, a
new study of a contemporary Massachusetts population offers evidence of evolution still in
action.
A team of scientists led by Yale University evolutionary biologist Stephen Stearns suggests that
if the natural selection of fitter traits is no longer driven by survival, perhaps it owes to
differences in women's fertility. "Variations in reproductive success still exist among humans,
and therefore some traits related to fertility continue to be shaped by natural selection," Stearns
says. That is, women who have more children are more likely to pass on certain traits to their
progeny.(See the top 10 scientific discoveries of 2008.)
Stearns' team examined the vital statistics of 2,238 postmenopausal women participating in the
Framingham Heart Study, which has tracked the medical histories of some 14,000 residents of
Framingham, Mass., since 1948. Investigators searched for correlations between women's
physical characteristics — including height, weight, blood pressure and cholesterol levels — and
the number of offspring they produced. According to their findings, it was stout, slightly plump
(but not obese) women who tended to have more children — "Women with very low body fat
don't ovulate," Stearns explains — as did women with lower blood pressure and cholesterol
levels. Using a sophisticated statistical analysis that controlled for any social or cultural factors
that could impact childbearing, researchers determined that these characteristics were passed
on genetically from mothers to daughters and granddaughters.
If these trends were to continue with no cultural changes in the town for the next 10 generations,
by 2409 the average Framingham woman would be 2 cm (0.8 in) shorter, 1 kg (2.2 lb.) heavier,
have a healthier heart, have her first child five months earlier and enter menopause 10 months
later than a woman today, the study found. "That rate of evolution is slow but pretty similar to
what we see in other plants and animals. Humans don't seem to be any exception," Stearns
says.(See TIME's photo-essay "Happy 200th Darwin Day.")
Douglas Ewbank, a demographer at the University of Pennsylvania who undertook the statistical
analysis for the study, which was published Oct. 21 in the Proceedings of the National Academy
of Sciences (PNAS), says that because cultural factors tend to have a much more prominent
impact than natural selection in the shaping of future generations, people tend to write off the
effect of evolution. "Those changes we predict for 2409 could be wiped out by something as
simple as a new school-lunch program. But whatever happens, it's likely that in 2409,
Framingham women will be 2 cm shorter and 1 kg heavier than they would have been without
natural selection. Evolution is a very slow process. We don't see it if we look at our
grandparents, but it's there."
Other recent genetic research has backed up that notion. One study, published in PNAS in 2007
and led by John Hawks, an anthropologist at the University of Wisconsin at Madison, found that
some 1,800 human gene variations had become widespread in recent generations because of
their modern-day evolutionary benefits. Among those genetic changes, discovered by
examining more than 3 million DNA variants in 269 individuals: mutations that allow people to
digest milk or resist malaria and others that govern brain development.(Watch TIME's video
"Darwin and Lincoln: Birthdays and Evolution.")
But not all evolutionary changes make inherent sense. Since the Industrial Revolution, modern
humans have grown taller and stronger, so it's easy to assume that evolution is making humans
fitter. But according to anthropologist Peter McAllister, author of Manthropology: the Science of
Inadequate Modern Man, the contemporary male has evolved, at least physically, into "the
sorriest cohort of masculine Homo sapiens to ever walk the planet." Thanks to genetic
differences, an average Neanderthal woman, McAllister notes, could have whupped Arnold
Schwarzenegger at his muscular peak in an arm-wrestling match. And prehistoric Australian
Aborigines, who typically built up great strength in their joints and muscles through childhood
and adolescence, could have easily beat Usain Bolt in a 100-m dash.
Steve Jones, an evolutionary biologist at University College London who has previously held
that human evolution was nearing its end, says the Framingham study is indeed an important
example of how natural selection still operates through inherited differences in reproductive
ability. But Jones argues that variation in female fertility — as measured in the Framingham
study — is a much less important factor in human evolution than differences in male fertility.
Sperm hold a much higher chance of carrying an error or mutation than an egg, especially
among older men. "While it used to be that men had many children in older age to many
different women, now men tend to have only a few children at a younger age with one wife. The
drop in the number of older fathers has had a major effect on the rate of mutation and has at
least reduced the amount of new diversity — the raw material of evolution. Darwin's machine
has not stopped, but it surely has slowed greatly," Jones says.(See TIME's special report on
the environment.)
Despite evidence that human evolution still functions, biologists concede that it's anyone's
guess where it will take us from here. Artificial selection in the form of genetic medicine could
push natural selection into obsolescence, but a lethal pandemic or other cataclysm could
suddenly make natural selection central to the future of the species. Whatever happens, Jones
says, it is worth remembering that Darwin's beautiful theory has suffered a long history of abuse.
The bastard science of eugenics, he says, will haunt humanity as long as people are tempted to
confuse evolution with improvement. "Uniquely in the living world, what makes humans what we
are is in our minds, in our society, and not in our evolution," he says.