Advanced Biology. Kent, Michael. 2000. Oxford University Press, Oxford.
This popular textbook contains a concise double page spread for every topic which is relevant to the study of the AS and A2 Biology. Regrettably, when it comes to the subject of evolution, Kent does not seem to be very informed about the alternatives to Darwinism, and clearly ignores the extent of the controversy.
Without any qualifying statement about evidence, this textbook states:
When the evidence is eventually discussed (pages 436 to 463) the section begins by dismissing one alternative out of hand:
Living things are able to change into new forms of life. This evolution usually takes place gradually over successive generations in response to changes in the environment. (page 13)
Although a few biologists believe in creationism...most accept that the scientific evidence for evolution...is overwhelming. (page 436)Creationism is described as follows:
Creationism is the belief that God created all species in six days as described in Genesis, the first book of the Judaeo-Christian Bible. According to creationism, all species present on Earth today have remained unchanged since they were created by God. Darwin's theory of evolution contradicts this belief. (page 436).
This statement is an inaccurate charicature of the creationist position. Modern creationists accept limited change over time within "kinds" of organism. These "kinds" are generally a broader category than species, so creationists accept that some speciation occurs. By describing creationism as it does, the textbook makes it appear very easy to refute, because any change, however small would contradict it. Creationists accept that changes in, for example, finch beak shape, or moth colouration, can occur.
This book continues with some classic icons of evolution...
Evidence for Evolution
Palaeontology: the study of fossils
Fossils of extinct organisms which lie in between two present-day types provide strong evidence in support of evolution. Figure 1 (Archaeopteryx) shows a fossil found in rocks some 150 million years old. Although strong support for evolution, fossil evidence is far from perfect. Dating is often only approximate and there are no fossils of the majority of early or soft-bodied organisms. Fossils of most organisms are so rare that it is not possible to trace their evolutionary pathway. Even making an evolutionary pathway for the modern horse, which seems to have many fossilised ancestors, has produced hot debate. There is much evidence, but it comes from different geographical regions, and is open to various interpretations. (page 438)
We welcome the acknowledgement of the imperfection of the fossil record, and the debate over horse evolution. However, the text would be much improved if alternative explanations of the fossil record were also discussed. Even a very weak case can appear strong if it is the only option available.
Comparative biochemistry and cell biology
The most persuasive evidence that all organisms have evolved from a common ancestor comes from studies comparing the cell biology and biochemistry of different organisms, which reveal that:
- the genetic code contained within nucleic acids is almost universal...
- physiological processes vital to all organisms, such as respiration, follow very similar metabolic pathways
- ATP is the universal energy currency
...for example, ribosomes inside mitochondria and chloroplasts are similar to those in bacteria, suggesting that these organelles may have evolved from bacteria.
Mammalian blood proteins can be tested to see how similar they are to human blood proteins: blood serum from the mammal in question is added to rabbit serum containing anti-human antibodies. A precipitate forms due to an antibody-antigen reaction...The degree of precipitation is compared with that caused by human serum (taken as 100%): chimpanzee serum causes 97% precipitation, gorilla serum 97%, and gibbon serum 79%.
Comparing haemoglobin in the four species gives similar results: the amino acid sequence in chimpanzee haemoglobin is identical to that in humans (though the amino acids in other polypeptides differ); gorilla haemoglobin differs from human haemoglobin by 3 amino acids; and gibbon haemoglobin differs by 6 amino acids. In contrast, the haemoglobin of lamprey (a jawless fish-like parasite) differs from human haemoglobin by 125 amino acids. (page 439)
This 'most persuasive' for evolution is open to alternative interpretations. For a thorough critique see:
Comparative Genetics and Biochemistry.
Comparative embryology
Observations have shown that species that are known to be closely related show a similar embryonic development. Therefore, species that show a similar embryonic development are assumed to be closely related, even if the adult stages are very different. For example, echinoderms...are believed to be related to chordates...because of similarities in their early embryonic development. (page 439)
For an appraisal of this evidence, see: Embryology
Comparative anatomy
The fact that different mammalian species have pentadactyl limbs is a strong indication that they have evolved from a common ancestor. This type of evolution is called divergent evolution, and it clearly results in adaptive radiation. (page 441)
For an appraisal of this evidence, see: Homology in Vertebrate Limbs
Industrial melanism
Although industrial melanism of the peppered moth demonstrates evolution in action, the different forms (morphs) have remained members of the same species because they can interbreed. If the moths in polluted and unpolluted areas were prevented from interbreeding for long enough, they would probably become sufficiently different to evolve into two distinct species. (page 445)
For a critique of this evidence see: The Peppered Moth
Hominid evolution
When approaching the subject of Hominid evolution, this text is honest about some of the limitations of the evidence:
The study of the evolution of modern humans from hominid ancestors is very speculative. Much of our present understanding is based on very little evidence. Only a few thousand hominid fossils have been discovered and most of these are incomplete. Sometimes anatomically similar bones collected over a wide area are assumed to be from the same individual, but they may actually be from different individuals. The following account of hominid evolution does not pretend to be complete or undisputed. It is merely an attempt to bring together some of the information on hominids that has gained general acceptance. (pages 458-459)
It should be noted that "a few thousand" is a large over-estimate of the number of fossils found that appear to be intermediate hominids.
Following on from this, a number of Hominid fossil candidates are proposed, including: Australopithecus afarensis, Homo habilis, Homo erectus, Homo sapiens (Neanderthals). Again, in the absence of the presentation of an alternative theory, students have little choice but to believe this one, despite the caveats about the evidence.
Teaching the controversy?
This textbook fails to cover the controversy over Darwinism with any rigor, despite the fact that even 140+ years after the publication of the Origin, good evidence for macroevolution remains elusive.
When Darwin's book was first published, it received a very hostile reception from influential church leaders who felt that it was promoting atheistic ideas. Today, many Christians feel that a Darwinian theory of evolution does not exclude God: they believe that evolution is God's way of creating things. Nevertheless, there are still some people who believe in creationism and argue that evolution has never taken place. (page 436).Again, this depends upon the definition of 'evolution'. Everyone would agree that the allele frequency of many genomes has changed over time. However, this evidence does not necessitate or strongly imply Darwinian universal common ancestry.
Many people found it difficult to accept Darwin's ideas, especially the idea that modern humans and apes are probably descended from a common ancestor. However, his theory is supported by so much evidence that the majority of biologists accept it.
(page 437).
Earlier caveats about the weakness of evidence for hominid evolution cast doubt on the assertion that the theory "is supported by so much evidence". It is extraordinary that a textbook can present a range of evidence which it admits to be largely weak, then make such a bold claim.
The strength of the case for evolution in this textbook largely resides in its failure to present any moden alternative theories.
Last updated 23 March 2007