Biology Reference
In-Depth Information
The fifth line of evidence is the fact that organisms can be classified in an
hierarchical fashion in a nested pattern of groups within groups, as predicted by
evolutionary theory. The sixth line of evidence is the one favoured by Darwin, and
comes from biogeography, the study of the distribution of organisms across the
world. The observation that the most closely related species are found close together
geographically, regardless of their habitat or their specific adaptations, is explicable
in terms of evolutionary theory. Finally, the existence of vestigial organs and func-
tionless genes is consistent with their origin from earlier organs and genes that were
functional, but hard to understand if species were separately created,
Similarities at the Molecular Level
The Unity of Biochemistry
Figure 4.2 shows some similarities at the molecular level. There is a sense in which
the huge diversity of living organisms that is apparent to the naked eye, and which
delights us all, is an illusion , because this diversity becomes much smaller when
we compare organisms at the molecular level. This fact is summarised by the
phrase “The Unity of Biochemistry”. So the basic metabolic pathways, the energy
transduction mechanisms, the signalling systems, and the operations of replication,
transcription and translation are very similar in all organisms, no matter how differ-
ent these organisms look to the eye. A few examples from many that can be given
Fig. 4.2
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