Sheet 10.1 Revision Evolution
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Sheet 10.1 Revision
Evolution
Evolution
The genetic make-up of a single organism does not change in its own lifetime, but species
can change over very long periods of time. This process is called evolution.
Darwin and Wallace
In 1859 Charles Darwin published a book called On the Origin of Species in which he
described how new species evolve. His book presented not only strong evidence for natural
selection, but also a hypothesis for how it occurs. This single book changed the way humans
thought about themselves, and their understanding of the natural world
Figure 3.8: Charles Darwin
Figure 3.9: Alfred Wallace
At almost the same time as Darwin, Alfred Wallace was publishing work that showed he,
too, had similar ideas and strong evidence for natural selection. Today the credit for the
discovery of natural selection is given to both men. Darwin and Wallace noticed that life was
very varied, with thousands of species often living in a single area, but they did not yet
understand how these changes had happened or how these variations were passed from parent
to offspring. It would be another 100 years before the discovery of DNA, chromosomes and
mutations would show how evolution works.
Science for the New Zealand Curriculum Years 9 and 10
© Donald Reid, Catherine J. Bradley, Des Duthie, Catherine Low, Matthew McLeod, Colin Price 2010
Published by Cambridge University Press www.nzscience.co.nz www.cambridge.edu.au
Sheet 10.1 Revision Evolution
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Evidence for evolution
1 Variation
All around us organisms are producing offspring that vary. Many of these variations suit the
particular lifestyle of that organism. Those organisms best suited to an environment are more
likely to survive and produce offspring.
2 Natural selection
Evolution can be seen and measured happening around us. For example, the dark variety of
the peppered moth became more common during the industrial revolution in Britian, when
pollution made the bark of trees darker. The light coloured variety of this moth replaced the
dark ones after the forests returned to their natural state.
A recent example of evolution taking place rapidly is the resistance bacteria evolve to
antibiotics. Viruses also demonstrate evolution. Larger animals can also evolve resistance to
disease quite quickly, such as rabbits becoming resistant to rabbit calicivirus (RCV).
3 Molecular biology
Molecular biology is the study of the chemicals inside cells. The most important chemical in
cells is DNA, which makes up the chromosomes. Sexual reproduction produces varied
offspring because each parent gives half its chromosomes to the offspring and also because
occasionally errors (mutations) occur when the DNA is copied. The structure and chemistry
of DNA provide a mechanism that can be used to explain how evolution happens.
Molecular biology also allows ancestors to be traced, as certain similarities are passed on
through the generations. It is also possible to estimate how long it has been since two species
diverged (evolved into two new species from a common ancestor), based on the number of
mutations in the DNA of the two present-day species. These changes are like ‘molecular
clocks’; the more changes, the more time has passed since the two species diverged.
common ancestor The ancient species that two new species evolved from
fossil Remains, usually of the harder parts, of a plant or animal that have been chemically
transformed into rock over millions of years
Science for the New Zealand Curriculum Years 9 and 10
© Donald Reid, Catherine J. Bradley, Des Duthie, Catherine Low, Matthew McLeod, Colin Price 2010
Published by Cambridge University Press www.nzscience.co.nz www.cambridge.edu.au
Sheet 10.1 Revision Evolution
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Figure 3.10: A peppered moth
4 Fossils
Today we find fossils of species that are no longer around. It is also possible to compare
fossils of a species from different time periods to see how the species has evolved. A good
example of this is the fossils showing how birds evolved from reptiles. The fossil record
(even though it is incomplete) provides evidence that Earth is very old.
5 Selective breeding
People have selectively bred for particular features in plants and animals for many years.
Today there is a great variety in crops, vegetables, pets and farm animals even within the
same species. For example, all the breeds and varieties of modern dogs are descended from
the wild wolf. Likewise, cauliflower, broccoli, brussels sprouts, cabbage, kale and kohlrabi
were all bred from one species of wild mustard. This evidence demonstrates that large
changes in species can result from selection of particular traits.
6 Anatomy
Closely related organisms tend to have similar anatomies, that is, they are built in a similar
way. As young develop they pass through stages that resemble their ancestors. For example, a
human embryo passes through a fish-like stage where it has gills. Shared features are
evidence of shared ancestors.
Science for the New Zealand Curriculum Years 9 and 10
© Donald Reid, Catherine J. Bradley, Des Duthie, Catherine Low, Matthew McLeod, Colin Price 2010
Published by Cambridge University Press www.nzscience.co.nz www.cambridge.edu.au
Sheet 10.1 Revision Evolution
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7 Geography
Different continents often have different species, but sometimes these species seem to be
related. This is understandable if the organisms are able to swim or fly between the
continents; however, if this is not possible, how did this come about? This question was
solved when, 100 years after Darwin and Wallace, it was shown that continents move by the
process of plate tectonics and that in the past they had been connected. Therefore, many of
the similar organisms we find on different continents have evolved from a common ancestor
they once shared.
Convergent evolution
An important part of the study of evolution is working out which species are related. Usually
this is based on appearances; however, this can be misleading because a similar adaptation
can occur in two different, unrelated species. Convergent evolution means that these
adaptations occurred separately and converged to look the same. This can be seen in
thousands of different species and many different features. For example, bats and birds
diverged from a common ancestor that did not have wings. However, natural selection has
resulted in both of these species evolving a wing structure with some similarities.
convergent evolution A process where two unrelated species develop similar adaptations
Figures 3.11 and 3.12: Bat and bird wings are the result of convergent evolution
Science for the New Zealand Curriculum Years 9 and 10
© Donald Reid, Catherine J. Bradley, Des Duthie, Catherine Low, Matthew McLeod, Colin Price 2010
Published by Cambridge University Press www.nzscience.co.nz www.cambridge.edu.au