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2 O
How did the
eye evolve?
How old is the Earth?
What use is a half-evolved eye? That’s
Today, thanks to radiometric dating, we
a big question for creationists or anyone
know that the world is roughly 4.55 billion
else unconvinced by the gradual process
years old. But during Darwin’s day, Earth
of evolution. The eye is certainly a puzzle.
was said to be only 400 million years old
It’s soft, so fossils are hard to come by. It
or less. “Lord Kelvin had worked it out on
seems to have just one function, unlike
the basis of a cooling ball,” says University
many organs. And those, coupled with
of Plymouth geologist Iain Stewart. “How
its sheer complexity, makes you wonder
long would it take a molten ball the size of
how it could possibly have come about.
Earth to cool to the temperature it is now?”
Darwin didn’t have the answer. But
Kelvin’s sums were devastating for Darwin
what he did do was set the eye as
because he knew that evolution needed
an ultimate test for his own theory.
much longer to work. “Kelvin had said that
If anyone could show how the
unless there is some other heat source, then
eye evolved, he said, then natural
this is the age of the Earth,” Stewart says.
selection happens.
Luckily for Darwin, that missing heat source,
Biologists have since explained the
radioactivity, would soon allow geologists to
story by tracking down organisms living
date the main geological periods.
in the world today that show the range of
eye complexity, from simple light-sensitive
depressions to something with lots of
separate and sometimes imperfect parts,
like our own. Genetics, meanwhile, has given
us the genes that trigger the whole process
off. And once it starts, the eye can develop
very quickly. “Improvements are fast,” Simon
Ings, author of The Eye: A Natural History
says. “It’s easy to acquire the shape needed
to focus an image. For a fi sh’s eye to evolve,
The eye: it left Darwin that process might be as short as 40,000
Lord Kelvin’s sums caused Darwin problems
looking puzzled generations [40,000 years at the very most].”
What is the
origin of life?
Where did humans come from?
In 1863, Darwin wrote to the botanist
Joseph Hooker, explaining his uncertainty
When Darwin fi rst published his theory “Although the pressures for specifi c
concerning the precise origin of life. In
of evolution, most people believed that selection are not fully understood, there
1871, however, he wrote again imagining
God had created Man in his own image. are examples of the various steps that
a “warm little pond” with various salts and
So Darwin was acutely aware of the were taken.”
energy sources in which proteins could
implications that natural selection would Radiocarbon dating technology and
develop. “The role of DNA and RNA was
have. Not that there was much of a genetics have also been crucial in piecing
not yet known,” says Professor Robert
fossil record at the time to show that our together human evolution, allowing
Shapiro at the department of chemistry at
ancestors resembled apes if you looked scientists to study exactly when, why and
New York University, “But it does sound
back far enough. Neanderthal skeletons how certain adaptations came to the fore.
as if he was speculating about a prebiotic
had been discovered before On the Origin But there is still more to learn, Leakey
soup. We have learned a tremendous
of the Species was published in 1859, says. “There are several things that are
amount about biochemistry since Darwin's
but it wasn’t until ‘Java Man’, a specimen still critically important, such as the
time, but still don’t have proof as to which
later believed to be a Homo erectus, was circumstances that led to a bipedal ape
mechanism led to the origin of life.”
discovered in 1891 that hard evidence for getting established,” he says. “Prior to
the human story began to emerge. that, all primates were quadrupedal. We
“There’s now a very good fossil record don’t yet have a very clear fossil record of
What Darwin Didn’t Know is
Java Man,
going back fi ve or six million years,” says what this might be attributed to in terms of
on BBC Four in February.
discovered in 1891
palaeoanthropologist Dr Richard Leakey. environmental change and pressure.”
Check Radio Times for details.
1798 1809 1858
Thomas Malthus (right) writes an Jean-Baptiste Lamarck popularises the Charles Darwin and Alfred Russell
essay on the principle of population. inheritance of acquired characteristics: Wallace present their theory of
Population growth leads to a struggle organisms adapt to the environment during evolution by natural selection.
for survival as individuals compete their lifetime and pass any new features to Darwin publishes On the Origin of
for limited resources. their offspring. Species in 1859. February 2009 43
Focus 199 darwin2_9RB.indd 43 22/12/08 16:36:09
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