This textbook has
a chapter on evolution, which starts with a general introduction to the
theory, and ends with a detailed account of the hypothesised evolution
of humans from apes.
Evolution is introduced in theoretical
terms, with an outline of Darwin’s argument. The different types of
selection are illustrated with a hypothetical mammal which is selected
for different fur length according to its environmental conditions.
Polymorphism is illustrated using the real world examples of human blood groups, the colouring of the land snail
Cepaea nemoralis, and
The Peppered Moth Biston betularia. Antibiotic resistance in bacteria is used as an example of mutation and selection.
There
are sections on artificial selection and on isolating mechanisms which
can lead to speciation. Few real world examples are given for these
processes.
This textbook assumes that humans have evolved from
ape-like creatures. The question in the authors’ minds is not whether
evolution of humans has occurred, but which path it took, as this
extract shows:
9.6 Evidence for human evolution
It
is important to realize that we are faced with many difficulties when
trying to sort out fact from fiction in the evolution of mankind. (p.
182).
Three lines of evidence on human evolution are used:
1. The first set of evidence used for human evolution is homology.
We
can test relationships between species by looking for characteristics
that are similar in different species because they have been inherited
from a common ancestor. Such similarities are called homologies. (p.
182)
This is used, not to show that evolution has occurred, but by what pathway:
we can look for similarities…and try to decide which apes are our closest relatives. (p. 182)
2. The fossil record, but this section begins with a very significant admission:
All
fossil records are very incomplete and that of primates is no
exception: far more forms must have lived than are represented as
fossils. In addition the record is geographically imbalanced with few
examples from the Oligocene period (around 23-35 million years ago) in
Africa, even though there is good reason to suppose it was a major
centre of primate evolution.
In other words, there is no evidence for key steps in the evolution of primates.
3.
Lastly, comparative physiology and biochemistry – another argument for
homology, this time relying on similarities between primates in protein
and DNA sequences. The text does admit that such studies sometimes give
conflicting results, but favours the view that humans are most closely
related to chimpanzees.
The textbook then surveys a range of fossil “man-apes”: australopithecines,
Homo habilis,
Homo erectus, Neanderthal man, and Cro-Magnons. These are all contested as genuine examples of hominid intermediates.
Teaching the controversy?
This
book does not teach any scientific controversy over evolution. The only
controversies taught are those within the evolutionist camp. The
authors’ appear to see this as justified because most scientists are
evolutionist:
Evolution is the process by which new
species are formed from pre-existing ones over a period of time. It is
not the only explanation of the origins of the many species which exist
on earth, but it is the one generally accepted by the scientific world
at the present time” (p. 168).
Most people
now agree that the first man-apes were the australopithecines which
lived between 5 million and 1.2 million years ago and that Homo arose in Africa 2.4 million years ago” (p. 188)
This
textbook makes no mention of the significant number of credentialled
scientists who do not believe in molecules-to-man evolution. The
strongest reason given by this textbook for belief in evolution as a
theory of origins is that it is
generally accepted by the scientific world.
This is questionable, and the absence of good evidence presented in the
book may leave the reader wondering why scientists believe in
evolution. Is the textbook missing out the best evidence, or is there
really a paucity of hard evidence for evolution?
All