Biology Reference
In-Depth Information
Fig. 4.14
the best design possible. Because there is no way to determine the preferences of a
hypothetical creator, the supernatural explanation lacks the predictive power of the
natural explanation. This is an example of my earlier suggestion that the essential
difference between science and religion is that the latter lacks a methodology by
which its claims can to be tested.
Direct Observation
A strong line of evidence for evolution is that it can be observed for some species,
both in the field and experimentally (Fig. 4.15).
We distinguish two levels of evolution.
Microevolution
is defined as evolution
below the species level, and
macroevolution
as above the species level, but this dis-
tinction is only for convenience - both processes are part of a continuous spectrum
of change across differing time scales, and different techniques are used to study
them. For some organisms that reproduce rapidly, such as viruses, bacteria and some
birds and insects, changes in their genetic composition from generation to genera-
tion can be observed directly. This is the case for example with the HIV virus that
causes AIDS in humans - the evolution of this virus in an infected person treated
with antiviral compounds can be seen in just three weeks.
There are two reasons for the rapid evolution of the HIV virus. Firstly, the inva-
sion of a single white blood cell by a single virus particle results in the production
of about 10,000 new virus particles every 24 h by that cell. Secondly, the mutation
rate (the rate of change of the base sequence of the genetic material) is high enough
