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Evidence for evolution
Evolution is the theory that the differences between modern living organisms are because of changes
that happened under the influence of natural selection over a very long period of time.
Darwin and Wallace
Evidence for evolution
In the mid-1800s, Charles
Darwin and Alfred Russel Wallace
independently came up with a
theory of evolution by natural
selection. Natural selection
is a mechanism to explain how
evolution could have occurred.
The two men collaborated and
co-published a paper in 1858.
Darwin published his book, ‘On
the Origin of Species’ in 1859.
There is an overwhelming amount of evidence for evolution, from
different sources.
•The fossil record – we can examine extinct species and compare
ancient organisms with modern ones. The age of the fossils can
be measured by dating the rocks that they are found in. The
fossil record gives us the fossils in chronological order.
Some species, such as the horse, have an entire fossil
record, showing all of the intermediate forms.
Evolution of
resistance
Evolution in some species has
implications for humans. This
can be seen in resistance to
chemicals. As we invent new
pesticides to kill pests on
crops, some of the pests can
develop pesticide resistance.
This means that there will be
less yield from the crop.
The same thing happens with
bacteria and antibiotics, as
certain bacteria develop
antibiotic resistance. Look back
at page 77 for a reminder.
Eohippus
Oligohippus
Merychippus
Pliohippus
Modern horse
•DNA – the DNA sequences of species can be compared to see
how closely related species are.
Species A - G C C A T A A C C T G A G G Species B - G C C A T A T A C T G A G G Species C - G C C A C A T A G T G A G G Species D - G C C A C A T A G T A A G G -
The arrows show
the bases that are
different across
species.
•Molecular evidence – the amino acid sequence of common
proteins, such as cytochrome c, can be compared to see how
closely related species are. Cytochrome c is an essential protein
involved in respiration and is common to almost all organisms.
Suggest what could happen in the future if no new antibiotics are found. (4 marks)
increased antibiotic resistance
infections fail to be treated, even with multiple antibiotics
increased death from bacterial infection
increased use of older techniques / salt bathing / maggots or modern
techniques such as bacteriophages / disinfectants / antiseptics
1 From the DNA sequences above, explain which two species are the most closely related.
2 Explain the problems with relying on the fossil record for evidence of evolution.
88
(2 marks)
(3 marks)