AQA GCSE- Biology 1.7

Core Science biology 1.7

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B1.8 Evolution
Darwin's theory of evolution by natural selection states that all species of living things have evolved from simple
life forms that first developed more than three billion years ago
The theory of evolution by natural selection was only gradually accepted because:
The theory challenged the idea that God made all the animals and plants that live on Earth; it was common in
religious belief systems that all we see around us was created by 'God', the divine creator. Many scientists
couldn't merger their religious views with Darwin's scientific approach to the origin of the diversity of species.
There was insufficient evidence at the time the theory was published to convince many scientists.
Darwin couldn't explain how beneficial and non-beneficial characteristics could occur and how beneficial
characteristics were passed on.
All he could argue was that organisms with good survival characteristics would survive and thrive and those
without would die out.
He did actually recognise the effects of selective breeding for characteristics e.g. in breeding stronger faster
racing pigeons, but had no idea why the pigeon fancier's methods worked
There was also a lack of fundamental research on organisms, e.g. plant/animal species, had changed over time,
so there were very few scientists actually pursuing similar research.
One very rare exception was the naturalist Alfred Russel Wallace (1823-1913), who developed a similar natural
selection theory by studying plants and animals in the forests of South America. He is accepted by the
scientific community as the co-discoverer of the theory of evolution by natural selection.
The mechanism of inheritance and variation was not known until 50 years after the theory was published;
although Darwin recognised, and argued, that species evolved he had no knowledge of genes, DNA and
molecular genetics and so had no idea of how mutations occur
Other theories, including that of Lamarck (1744-1829), are based mainly on the idea that changes that occur in an
organism during its lifetime can be inherited:
Lamarckism theorises, also known as the 'heritability of acquired characteristics', that an organism (plant/animal) can
pass on characteristics that the organism has acquired in its lifetime and can pass on these acquired characteristics to
its offspring. Lamarck envisaged that if some characteristic of an animal was particularly essential for its survival, then
that characteristic could become enhanced through successive generations.
There is a small, but growing body of evidence to show, that environmental conditions may have an effect on
the genes-DNA of subsequent generations i.e. the characteristics of 'gene expression' may be altered slightly.
The mechanism is not fully understood yet, but, it does show how science can reject a theory and then, quite
correctly, bring it back into recognition in a selected way.
This is quite contrary to Darwin's theory of evolution, which is based on the idea that variation occurs all the time and
the plant/animal species whose characteristics are best suited for it to survive will survive
By studying the similarities and differences between organisms, it allows us to classify living organisms into animals,
plants and microorganisms, and this helps us to understand evolutionary and ecological relationships and the possible
evolutionary relationships between them.
Species with similar genes will tend to show similar characteristics and species with similar genes will have a
common genetic ancestor.
Species with similar genes will tend to look the same and live in a similar way, and this probably means their
common ancestor was fairly recent.
Evolutionary trees show how modern species have common ancestors and how such ancestors have
developed through many stages and evolved into the animals and plants we see today.
For examples, from fossilised bones you can trace the developments of the skeletons of animals over periods
of millions of years and each successive species displays some skeletal differences.
Evolution occurs via natural selection:

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Individual organisms within a particular species may show a wide range of variation because of differences in
their genes e.g. differences in height and weight (size).
Individuals with characteristics most suited to the environment are more likely to survive to breed
successfully, e.g. a successful competitive predator, a successful well camouflaged prey,
The genes that have enabled these individuals to survive more successfully in greater numbers, are then
passed on to the next generation.…read more


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