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"Change alone is unchanging," the ancient Greek philosopher Heraclitus
once wrote. But even such a wise man didn't know the half of it. As NATURE's
THE BODY CHANGERS shows, researchers have discovered that all kinds of
animals -- from sea slugs and caterpillars to songbirds and people --
undergo constant and often remarkable physical changes during their lives.
And scientists continue to discover that we can change our bodies in ways
once thought impossible.
A butterfly will emerge
from this body changer. |
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Each of us knows from personal experience that the passage of time
is marked by constant variation and modification. From a single cell
unable to live on its own, we multiply into creatures composed of trillions
of cells able to move about freely. Our bodies grow taller, heavier,
and hairier as we mature, then shrink and wrinkle as we age. Our hair
may change color and our voices modulate from a howling cry to a quivery
whisper.
But even these dramatic physical alterations are overshadowed by the
extraordinary transformations experienced by other creatures profiled
in THE BODY CHANGERS. Fleet-flying dragonflies, for instance, start
life as swimming nymphs that paddle about beneath the surface of a pond
or river. High-leaping frogs take their first trips as awkward, wriggling
tadpoles. And the elegant, fragile butterfly
emerges from a capsule spun by a chunky, crawling, earth-bound caterpillar.
Still other animals are able to execute even more amazing tricks. Salamanders
can regrow legs snipped off by hungry turtles, while lizards routinely
rebuild tails that break away, by design, in the mouths of predators.
Male deer grow magnificent antlers that are used for just one season
and then discarded, like a wedding dress banished to the back of the
closet. And some songbirds remold their brains every spring, adding
and subtracting neurons as needed. When more brainpower is needed to
sing and remember their courtship songs, their brains swell. But when
breeding season is over, they conserve energy by scaling back.
Such modern-day adaptations are the product of millions of years of
evolution -- another process dependent on change. Many researchers,
for instance, believe today's birds began as dinosaurs, while people
evolved from tree-dwelling apes. Over the eons, seemingly insignificant
changes began to add up, separating new species from the old. The genetic
flaw that produced feathers on some mutant dinosaur, for instance, may
have helped keep it warmer and enhanced its survival. Later, the feathers
might have helped its offspring become better hunters and eventually
fliers. It was just a short flap, in geologic time, to modern birds,
which bear just a fleeting resemblance to their forebearers.
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