Biology Reference
In-Depth Information
imply direction, but the effect is purely random, unlike natural selection, which is
highly non-random.
Suppose two men are in the forest, collecting wood. One man has a set of genes
conferring high evolutionary fitness i.e. he is capable in principle of fathering six
children, but has fathered only one so far. The other man is less fit, because his
genes do not result in him being able to pass so many copies of his genes to the
next generation and he has no children. Suddenly a storm blows up and a tree falls
on the first man, killing him. The second man goes on to father two children, so
the genetic composition of the next generation is different from what it would have
been if the first man had survived to father five more children. A purely random
event has changed the genetic composition of the population produced by these
two men.
Biologists continue to argue about the relative effects of natural selection and
genetic drift in evolution, but what is agreed is that genetic drift will be more impor-
tant in small populations than in large populations. A human example of genetic drift
involves a small group of people that crossed the Bering Strait between America
and Russia about 10,000 years ago, at the end of the last Ice Age. This group gave
rise to the Native Americans that live in the USA and South America today. The
observation that these Native Americans almost totally lack the gene for the pro-
tein determining blood group B suggests that this founding group was very small
in number because about 16% of the entire world's population of humans possesses
this blood group. This type of genetic drift is called the founder effect for obvious
reasons, and is commonly seen in island species that are descended from a group of
organisms too small in number to contain a representative sample of all the genes
present in that species on the mainland.
Further Reading
1.
Introducing Darwin.
Jonathan Miller and Borin van Loon. Published by Icon Books 1982.
ISBN 1 84046 715 0. An account in cartoon form of the impact of Darwin's work on biology.
2.
www.darwin-online.org.uk
This website contains all the publications of Charles Darwin.
3.
www.darwinproject.ac.uk
This website contains all the correspondence of Charles Darwin.
4.
http://evolution.berkeley.edu
An Introduction to evolutionary theory from the University of
California at Berkeley.
5.
Evolution:
Nicholas H. Barton, Derek E.G. Briggs, Jonathan A. Eisen, David B. Goldstein
and Nipam H. Patel. Published by Cold Spring Harbor Laboratory Press, 2007. ISBN 978-0-
87969-684-9.
6.
Evolutionary Analysis:
Scott Freeman and Jon C. Herron. Published by Pearson Education,
Inc. 2007. 4th edition. ISBN 0-13-239789-7.
7.
Evolution:
Mark Ridley. Published by Blackwell Publishing, 2004, 3rd edition. ISBN 1-4051-
0345-0.
8.
Understanding Evolution: History, Theory, Evidence and Implications.
Geoff Price, 2006.
www.rationalrevolution.net/articles
/ - scroll down to 'Understanding Evolution: History,
Theory, Evidence, Implications'. This is a comprehensive account of the historical relations
between science and religion in the context of evolution.
