Science and the Bible
Biology Appendix 1
Notes on the Theory of Evolution
Charles Darwin's theory of evolution by natural selection is based on the concept of
survival of the fittest. This principle states that only the best adapted organisms in
any given generation will survive to reproduce and pass on their genes to the next
generation (the rest will die of malnourishment, disease or predation).
Every once in a while a new genetic mutation will occur which gives one particular
organism a significantly better chance of reproducing than other members of his or
her species. All other things being equal these strong genes will become more and
more common in the population as those animals who possess them have a better
chance of reproducing than those who don't. Similarly, if the environment changes
drastically some organisms will be better suited to the new environment than others
and these organisms will be more likely to reproduce and pass on their positive
genetic adaptations to their offspring.
For example, during the Industrial Revolution the huge amounts of pollution in many
parts of the UK meant that lots of the trees became covered in black soot. This
meant that the light coloured 'Pepper moths' that lived on the previously light
coloured, lichen covered trees became easy targets for predators. As a result, their
numbers decreased dramatically and the previously rare black variety of the
'Peppered moth' became very common because it was perfectly camouflaged
against the black trees. As environmental standards improved the soot gradually
disappeared and the light covered lichen that covered most trees re - grew. At this
point the tables were turned once more. Suddenly it was the black moths who could
be seen by predators against the light lichen background and the light moths who
were camouflaged. As predicted by the theory of evolution, the numbers of black
moths went into freefall and the light moth population exploded. In the 21st Century
the proportion of light to dark moths is fairly similar to the Pre-Industrial age
because trees today are roughly the same colour as they were prior to the Industrial
Revolution.
New species are created over time because small groups of individuals that become
reproductively isolated from other members of their own species (for any reason be
it rising sea levels, deforestation etc) will gradually accumulate changes which suit
their new environment until eventually a member of the isolated group will no
longer be able to mate with an organism of the original species. At this point a new
species will be born.
As the changes associated with speciation events can take a very long time to build
up the effects can be seen most clearly in areas which have been geographically
isolated for a prolonged period of time. Long isolated islands are perhaps the best
known example, and of them Madagascar is a particularly excellent case study. Most
of the animals and plants there are similar to animals and plants found in mainland
Africa or India because they share common ancestors with them (surprisingly
Madagascar actually split from Africa a long time before it departed from India - 165
million years ago compared to 88 million years ago).
For instance, lemurs share a common ancestor (in Africa) with nearly all other
primates about 63 million years ago but because the common ancestor that found its
way to Madagascar (presumably by unintentionally rafting there on driftwood) found
a different environment to the primates in Africa the Madagascan creature went on
to become modern day lemurs. As small groups of these early lemurs became
isolated within Madagascar lots of similar but distinct species of lemurs developed
over time there but not a single naturally occurring lemur can be found anywhere
else on earth. In fact, precisely because of the effects of being isolated for so long
fully 80% of the plants and animals species found on Madagascar are unique to the
island. Although Madagascar only contains one thousandth of all the land on earth it
accounts for no less than 4% of the species found on the planet. It is no exaggeration
to say that it is a perfect illustration of evolution in action.
The evolutionary process, as outlined above, has been playing out since the dawn of
life nearly 4 billion years ago. After billions of years this gives the impression in
today's world that animals and plants that inhabit planet earth have been 'designed'
to live where they currently live because they are so well adapted to the conditions
they find themselves in. This is no coincidence. Well adapted organisms are precisely
what evolutionary theory predicts because at each and every generation all poorly
adapted organisms die out leaving only the strongest organisms to pass on their well
adapted genes onto the new generation. However, the appearance of design does
not mean there must have been a designer - it is the natural consequence of a
process which only allows those organisms that are well adapted to survive.
Further resource:
Dawkins, R., New edition 2005, The Ancestor's Tale: A Pilgrimage to the Dawn of
Evolution, Phoenix.