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| Copyright Janet Cameron |
The
only life on our planet around 3.5 billion years ago was bacteria.
600 million years ago, animals appeared and began to evolve. Then, we
humans arrived a mere 200,000 years ago. In the overall timescale, we
have only just, this very minute, emerged into existence. The big
question, for Dr. Alice Roberts of Horizon,
is: "Have we continued to evolve?
Evolution,
we now know, is responsible for the great diversity of life forms on
our planet. Dr. Roberts travelled to Devon, where she learned about a
very special kind of earthworm that had evolved and flourished in
spite of the arsenic-poisoned earth around an abandoned copper mine.
This earthworm looks fairly ordinary, maybe a little paler at one end
than your common-garden type worm. But this little creature is far
from ordinary: it is a brand new species.
Worms
from our gardens, transported to the location of the old Devon copper
mine, would die of arsenic poisoning, and so the genetic differences
between the two worms are immense... "they are more different to
ordinary earthworms than we are to mice," a scientist told Dr.
Roberts, although Tim Dowling, who reviewed the programme for The
Guardian,
was understandably cynical, saying, "I believed him at the time,
but now I've written it down it looks silly."
Yet,
the fact remains, the worms have, in 170 years, evolved by adapting
to such high levels of arsenic poisoning that they are now a distinct
species.
From
African Beginnings to a Victorian Cemetery
60,000
years ago, humans began spreading out from Africa and over the
planet. We began to use clothes and fires for protection, and we
fashioned tools to make our lives safer and easier. Does this mean
that technology gradually began to prevent us evolving through
natural selection? Dr. Roberts went to Oxford to meet Revd. William
Buckland who showed her the oldest bones in the whole of the UK.
These were of a male pelvis, radio carbon dated from 33,000 years
ago, well before the peak of the last ice age. Dr. Roberts could see
nothing in the bones to indicate that they had changed in any
meaningful way.
"The
raw material of evolution is dead babies," said one geneticist,
as he accompanied Dr. Roberts through a Victorian cemetery and they
studied the tombstones. Only one in every two babies born in Darwin's
time reached the age of 21 - literally, the survival of the fittest,
so that only the healthy humans manage to reproduce. In other words,
reproductive success is what alters genes. Today, 99% of children
make it to 21. Evolution should, surely, be at a standstill.
Evolving
in Fundamental Ways
On
the other hand, in the past we were all dark-skinned, but not now.
Those of us who moved to cooler climates and did not need to develop
pigmentation to protect us from extremes of weather gradually evolved
a lighter skin. This, as Dr. Roberts pointed out, is a superficial
difference. She wanted to know if we had evolved in more fundamental
ways than those apparent on the surface.
Are
we protected from natural selection by medical progress, technology
and a wide and varied diet? It might seem so, but evolution can still
be seen at work in the following ways:
-
The sickle cell gene protects against malaria.
-
Europeans have evolved to digest lactose. (Apart from those who have allergies.)
-
Adaptations to blood circulation have enabled people to live at high altitudes, according to research conducted by Prof. Cynthia Beall.
Testing
Evolution in Areas of Extremity
Cynthia Beall, who is a Professor of Anatomy and Global Health, was studying
Nepalese Sherpas in the Himalayan mountains. She explained how the
mountain air was dangerously low in oxygen and that this was normally
physiologically stressful for human beings. There have been cases of
people dying when exposed to this oxygen-deficient air. Her research
revealed that the Sherpas had developed a unique system of blood
circulation with wide blood vessels and many intricate twists and
turns, a system that was sophisticated enough to cause them to be
unaffected by the poor air quality.
One
of the scariest stories exposed by Dr. Roberts was that of the
chicken virus that caused appallingly large and fatal tumours. At one
time, this same virus was merely a minor irritant and then a chicken
vaccination had been developed - but this changed the selective
landscape. The virus evolved a resistance to the drug, a change
exacerbated by modern factory farming methods, and so the virus
became stronger. The virus can now kill a chicken in just ten days.
Of course, bacteria was on our planet long long before we arrived and
no doubt, it will still be going strong when our species has
disappeared.
Meantime,
there's still genetic engineering. In the US, on the West Coast,
people can choose the gender of their babies and although no one is
permitted to select their child's hair or eye colour, it is certainly
possible to do so.
As
Tim Dowling says, this was a see-saw programme, with one scientist's
work supporting the view that evolution had come to a halt, and yet
another confirming that it continued despite our technological
progress.
The conclusion is that in the end, when our world changes,
we have to change and adapt or we cease to exist. The greatest threat
to our survival is probably that of disease.
"Are
We Still Evolving?" Dr. Alice Roberts, Horizon,
BBC2, 1 March, 2011.
"Last
Night's TV," Tim Dowling, The
Guardian,
2 March, 2011.
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