Biology Reference
In-Depth Information
world. This is wise of them, because their cause would be greatly weakened if they
did not accept evolution in the face of all the evidence in support of it.
Evolution by Natural Selection
The basic idea that Darwin, and others before him, presented is very simple.
Because organisms compete with one another for resources, individuals that are bet-
ter adapted to their particular circumstances will leave more offspring, and therefore
it follows that those better adaptations that are inherited will increase in frequency
from one generation to the next. The argument is spelt out in Fig. 3.6 in the form of
the four postulates made by Darwin in his topic On the Origin of Species .Themost
important feature of these postulates is that they are testable - they contain no hid-
den assumptions or require anything to be accepted uncritically. Most of Darwin's
topic is concerned with presenting a large range of direct observations taken from
nature that support these postulates. Since his time, many more direct observations
from both nature and experiments have reinforced this support.
Fig. 3.6
In Fig. 3.6, you will also find definitions of the terms “evolution” and “natu-
ral selection”. These are modern definitions - the term “genetic” was invented after
Darwin's time. Darwin knew nothing about genes or the mechanism of heredity. His
library does not contain any papers by the father of genetics, Gregor Mendel, who
discovered the particulate nature of inheritance in 1865, just after the first edition of
Darwin's topic appeared, but who published his work in a little-known journal. Five
further editions of Darwin's book appeared, the last in 1872, but none of them refer
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