Biology Reference
In-Depth Information
to their environment, for whatever reason, have a greater chance of leaving more
children that those who are less well adapted. We say such people are “fitter” in the
evolutionary sense because there are more copies of their genes in the next genera-
tion. Fitness in the Darwinian sense is defined quantitatively as the mean number of
offspring left by an individual relative to the number of offspring left by an average
member of the population.
Unfortunately, the phrase “survival of the fittest” was used in the twentieth cen-
tury for political purposes to justify the mistreatment and murder of those deemed
“unfit”, a practice that would have appalled Darwin. A cousin of Darwin called
Francis Galton proposed in 1883 the idea of eugenics - that human breeding should
be controlled to allow the reduction of unfavourable inherited traits and the increase
of favourable ones. Eugenics was one of those ideas that sounds fine in principle
but proved disastrous in practice because it was used to justify violence. Regimes
such as that in Nazi Germany argued that because people are clearly not genetically
equal, they should not be treated equally under the law - that it was permissible
to kill people with characteristics they did not like because this is how evolution
worked. Compulsory sterilization of thousands of people with genetic defects was
practised in the United States, Germany and Scandanavia during the first part of
twentieth century. This practice is now regarded as a crime against humanity by the
International Criminal Court.
Using evolutionary theory to justify political actions is an example of a type of
unjustified reasoning known as the “is-ought problem”. The Scottish philosopher
David Hume (1711-1776) was a leading Enlightenment figure who pointed out that
there is no justification to decide how the world
ought
to be from how the world
is
. That the appearance of humans is the end result of a process of natural selec-
tion that involves massive suffering and violence does not justify humans treating
fellow creatures in a similar fashion. On the contrary, the art of civilization consists
of humanity striving to rise above its biological past. However, the basic idea of
eugenics has not gone away. Developments in genetic technology in the twenty-first
century are raising the question as to what extent we should take evolution into our
own hands by altering human genomes directly.
Figure 3.7 illustrates the basic principle of natural selection by describing the
result of mutations producing changes in the coat colour of lions.
Lions are carnivores and their survival depends upon their ability to catch and eat
other animals. Hunting is not easy because the prey animals will survive and evolve
only if they are successful in avoiding the lions. Thus there is an evolutionary arms
race between hunter and hunted. Coat colour is important to lions because it pro-
vides the camouflage that enable them to get closer to the prey before the latter detect
their presence. Changes in coat colour that lower the efficiency of camouflage will
reduce the ability of the lions to survive long enough to reproduce, but any mutation
that increases the efficiency of camouflage will have the opposite effect. In time,
the mutant variant lions are so successful that they replace the descendants of their
ancestor with the original coat colour - both the original ancestors and the interme-
diate variants on the way to the successful variants that occur today become extinct.
This replacement by more successful descendants explains the lack of intermediate
