In the final blog in our GCSE Science series on evolution, we look at more recent, genetic, evidence for evolution.
As mentioned in ‘Explaining Evolution 2 – Early observation’ some fossil, geological, anatomical and behavioural evidence was available to Darwin and his colleagues in formulating the theory of evolution, but not the science of genetics that has developed greatly in recent years.
All cells of an organism contain a DNA strand (a blueprint for its development) in its nucleus. Each DNA strand has a number of chromosomes and each chromosome contains a large number of genes. These are large molecular structures that give an organism its characteristics e.g. size, colour, structure, etc. The DNA strand splits into two identical parts when a cell subdivides to make a copy of itself. However the strand is so complex that, occasionally, the copy is not identical and a mutation takes place that gives an organism a slightly different characteristic e.g. larger ears.
The genes of an organism can now be isolated. Genetic research has supported the concept of evolution and has added detail in the way that genes can randomly change. Genetics has also confirmed and refined the branches in the ‘tree of life’ framework (see Explaining evolution 8 – Evidence for Evolution).
We can now see evolution in action in simple organisms. The study of influenza virus DNA shows that it can mutate on a continuing basis, resulting in a strain which humans initially have no immunity to. The influenza virus then thrives and spreads.
Is evolution well understood? This was brought home to me recently when someone said that humans will evolve bigger and more flexible thumbs because we are using our thumbs more for keys on mobile phones and computer game handsets. According to evolution, theory humans will only develop bigger and more flexible thumbs if a random mutation of a bigger and more flexible thumb gives an individual a survival and breeding advantage compared to other individuals. This may happen in a natural environment, but is very unlikely in our ‘caring’ society (See Explaining evolution 7 – ‘Survival of the fittest’).
The most important aspect of evolution is that it is a theory (or should we say ‘fact’?) that is supported by extensive scientific evidence from different disciplines. However, like all theories, we must keep an open mind and continually test the available evidence using standard scientific techniques and, if new evidence is presented that changes or contradicts a theory, then the theory should be re-examined and, if necessary, changed.
This series of blogs has been aimed at helping AQA GCSE Combined Science students to understand Darwin’s theory of evolution. This is a complex area, bringing together different scientific disciplines as well as appreciating that the planet Earth has been in existence for an extremely long time and has a complex environment which is changing, always slowly, but sometimes very quickly.
The blogs have hopefully simplified the concept of and evidence for evolution, sufficient for the Combined Science syllabus. Interested students are encouraged to research further.
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