Welcome to the Macat Multimedia Series.
A Macat Analysis of Charles Darwin’s On
The Origin of Species
How do we explain how animals have evolved
over time?
Charles Darwin, the British naturalist and
geologist, famously answered this question
in his book On The Origin of Species, which
proposed the mechanism of evolutionary change
within animal species.
He called this theory, ‘natural selection’.
Darwin’s key argument was that environmental
pressures define what species look like, how
they behave and why they survive.
Species usually evolve over thousands of years,
but occasionally, rapidly changing environments
give us cases of evolution, sped up to a human
timescale.
So, how about an example of evolution in action?
Introducing the peppered moth.
Habitat?
English birch forests.
The moth had a mottled white body and wings
as camouflage protection against predatory
birds.
Within a species, Darwin said, there is always
natural species variation.
In the case of the peppered moth, some moths
were a darker colour than others.
Although this variation existed, the darker
moths were rarer because they were more likely
to stand out and get spotted by hungry birds.
Their lighter counterparts survived in greater
numbers and were therefore more likely to
pass their ‘light winged’ trait on to
the next generation of moth.
Darwin called this ‘the struggle for existence’
– in other words, how different characteristics
(in this case, colour variation) provide advantages
or disadvantages.
Some will win and some will lose – that’s
the struggle for existence.
During the industrial revolution, soot from
factories burning coal darkened birch tree
trunks in areas of forest closest to industrialised
towns and cities.
Here, we see the struggle for existence change.
Now, the lighter coloured moths are more likely
to be spotted by birds and eaten and the darker
moths are the ones more likely to survive.
As a result, the darker moths are able to
breed more prolifically than the lighter ones.
This sort of environmental change drives species
to adapt to their environment and shift one
way or another.
Over time, it explains how populations have
evolved into new species from a common ancestor.
For instance, if birch forests around industrialised
towns remained covered in soot, we would,
over time, see the peppered moth develop two
distinct sub-species – a light moth adapted
to cleaner areas of forest and a dark moth,
adapted to industrialised areas.
The Origin of Species was published in 1859,
and Darwin’s theory of natural selection
revolutionised the way we study animals today.
A more detailed examination can be found in
the Macat Analysis.
