30 Hunters
Accelerate the
Pace of Evolution
Humans are powerful agents of evolutionary change: Wild animals and plants
that are hunted or harvested evolve three
times as quickly as they would naturally,
according to a study from the University
of California at Santa Cruz. In our quest
to bag the biggest and the best, we introduce selective pressures that favor less
desirable creatures, such as those with
smaller bodies or less majestic horns.
Hunting also gives a competitive advantage to animals that have babies when
they are younger, before they become
tempting targets for humans.
A team led by biologist Chris Darimont combed through data on dozens
of species—predominantly ;sh but also
bighorn sheep, caribou, marine invertebrates, and two plants. (“Hunters
also want the biggest ginseng,” Darimont says.) Animals that are routinely
subject to pursuit are, on average, 20
percent smaller and reproduce at a
25 percent younger age than what would
be expected without human in;uence,
the researchers determined. Predation
is not the only way that people affect
populations. Creatures that are exposed
to environmental in;uences like pollution
also experience accelerated evolution,
although the effect is less dramatic.
The resulting changes have ripple
effects, Darimont notes. Smaller and
earlier breeders often produce fewer
offspring, for instance. “Size really
matters,” he says. “If a harvested animal keeps shrinking, it may no longer
be prey to its predator. The whole food
web can be altered.” AMY BARTH
31 Sun’s Changes Have Surprise
Effects on Earth’s Weather
Scientists have long suspected that the sun affects climate on Earth, but that
connection has proved hard to pin down. Researchers recently demonstrated that
the 11-year cycle of solar activity in;uences weather in the tropical Paci;c Ocean.
Even then the exact cause remained obscure, since the sun’s brightness varies by
just one-tenth of a percent. Two studies from 2009 are ;lling in the gaps.
In August an international team led by Gerald Meehl, a climatologist with the
National Center for Atmospheric Research, announced that the sun’s outsize
in;uence results from its combined effects on our atmosphere and oceans. When
the sun is at its most intense, ozone in the stratosphere absorbs more ultraviolet
energy, making areas near the equator warmer than usual. The added heat changes
wind patterns, bringing more rain to the western tropics. At the same time, the
extra sunlight causes more evaporation off the ocean, which adds to downpours
in the western tropics. Simulations that modeled just one of these effects failed to
match the real world. Meehl saw that the two mechanisms “feed off each other,
producing a stronger response than either can alone.” His results should help
climatologists predict monsoons in Asia and overall climate in North America and
might someday allow them to estimate seasonal rainfall years in advance.
Meanwhile, Henrik Svensmark of the Technical University of Denmark and his
colleagues are exploring a broader climate impact of solar activity. He believes
that cosmic rays—energetic subatomic particles from outer space—help seed
cloud-forming water droplets in the lower atmosphere. During peak solar activity, eruptions from the sun spew out huge clouds of plasma that shield Earth from
those cosmic rays. After examining cloud cover and cosmic ray ;uxes, Svensmark
concluded that declines in cosmic rays lead to fewer clouds, implying that an
active sun could lead to warmer surface temperatures. Following the strongest
solar eruptions, he found that the sky lost 7 percent of its cloud water. Many scientists doubt the signi;cance of these cosmic ray effects, but Svensmark sees the
question as ripe for investigation. “The sun is doing natural experiments on Earth’s
atmosphere, giving us the opportunity to test these ideas,” he says. JANET FANG
32 Fake DNA
Fools Crime Lab
DNA evidence has become a standard forensic tool because it can
pinpoint one individual out of millions. But the Israeli company
Nucleix has shown that it is
distressingly simple to make a
phony DNA ;ngerprint.
In Nucleix’s experiment,
researchers took a small
bit of DNA (which can be
collected from an object like
a cigarette butt) from a test
subject, replicated it millions
of times over, and used it to
build an arti;cial DNA sequence.
They then added the built-up DNA
to blood that had been processed to
remove the original, DNA-containing white
blood cells. When analyzed by a leading foren-
sics lab, the mixture was indistinguishable from
real blood and natural genetic material. Going a
step further, the researchers fabricated arti;cial
DNA using only sequence data and added it to a
saliva sample. This fake also passed inspection.
Although the experiment was done entirely
with commercial technology, DNA expert Larry
Kobilinsky of John Jay College of Criminal
Justice in New York doubts that most criminals
would have the skills to pull it off. Just in case,
though, Nucleix has developed a test that can
screen for fake DNA. BOONSRI DICKINSON
