DNA Spells Evolution

If Darwin came back today, what would he be
most excited by in modern science? I think it would be the whole world of genetics. That’s
the answer to all the big questions he had – how does variation emerge? And how could
that be transmitted? Let’s return to our brown bears stranded
in the Arctic to consider the impact of genetics on our understanding of evolution. Each bear
is made up of cells. And if we take a brown bear cell, and tunnel into its nucleus, we
find DNA – the molecule with the genetic instructions for building, in this case, a
brown bear, written in a four-letter code. Now, the thing about DNA—it’s not perfect.
When it’s copied, mistakes get made. Mutations, in other words, that sometimes affect an organism’s
traits and that sometimes can be passed from parent to offspring. So the variation at the
heart of evolution—it’s genetic variation. Slight differences in DNA that—for example—could
make some bears a bit lighter in color, a bit more insulated against the cold, and a
bit more capable of digesting fattier foods like seals. Evolution is essentially any change in the
genetic composition of a population. Mutations are random, so they’re not always
helpful. But the bears with mutations that gave them some advantage for Arctic living
survived and reproduced more often than bears without them. They passed the genes responsible
for those adaptations onto their cubs. Over generations, more bears inherited and elaborated
on these and other changes in the DNA. The eventual result – a polar bear. And when
we tunnel into its cells, we find polar bear DNA. Think of DNA as the raw material that—across
billions of years—evolution has molded and built into countless forms of life. We are
all related, tied to one another by the most spectacular of double helical threads.


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