Evolution essentials

2010-11-24 00:00

ACCORDING to reports, teaching of evolution will be dropped from Grade 7. Apparently this is because it is a concept that is too difficult for primary school children and their teachers. The reasoning is that they should first fully understand geological time and genetics. To me this is rather like having to take a detailed comparative anatomy course before identifying a dog and cat. Evolution can be taught at a basic level. This is done elsewhere in the world.

There is, of course, the suspicion that the decision may not be due entirely to the perceived intellectual inabilities of South African children and teachers, rather it may reflect the blinkered faith of certain sects that reject evolution. “Ah, but evolution is just a theory,” they cry. That is correct, but so is gravity yet everyone would agree that gravity exists. In science a “theory” is the explanation of a fact that is known from observations, measurements and analyses.

There are three lines of evidence for evolution: observations in the modern world, observations from fossils and DNA analysis. Each line is independent of the others yet each line provides results that can only logically be explained in terms of evolution. When all three are combined, they produce a beautifully interlinked overarching framework that supports evolution as the reason for the wonderful history of life on Earth.

The first person formally to interpret the observations in the modern world in terms of evolution was Charles Darwin. At that time, it had been known for centuries that selective breeding could produce better domestic animals. What Darwin brought to the party was an explanation of how selective breeding could take place in a natural environment. Critical to this was his appreciation of the length of geological time.

He had been mulling over this during the Beagle’s travels around South America and it all came together when he examined the finches of the Galapagos. He realised that when these volcanic islands formed, they were colonised by a single South American finch species. Natural variations of the beaks in this species resulted in different feeding habits. Birds with slightly shorter, thicker beaks would have found seeds to eat and therefore would tend to live in a different part of the ecosystem from birds with longer, thinner beaks. Over time, these two groups would cease to interbreed, so their offspring would inherit and, over successive generations, gradually enhance their type of beak. Eventually two different species emerged that could not interbreed.

Darwin had deduced that a progressive evolution had taken place from the end-members of this process. Since then the progressive or transitional situations have been recognised. For instance, staying with birds, in Europe the indigenous Lesser Black-Backed Gull does not interbreed with a North American immigrant, the Herring Gull. They are clearly separate species. However, eastwards across Europe through northern Scandinavia and Siberia to Alaska and Canada, there is a continuous gradation of sub-species that can interbreed, leading from the Lesser Blacked Gull through to the Herring Gull. It is only the end-members that are different species.

This gull gradation is geographical: to see gradation through time it is necessary to look at fossils. The oldest rocks on Earth contain the most primitive single-celled life, while progressively younger rocks contain an unequivocal record of progressively more advanced life. There are well-documented examples of transitions, for instance, from fish to amphibians, feathered dinosaurs to birds, and land mammals to whales. The rocks enclosing these fossils contain evidence of the physical and chemical environments in which life lived. When combined with the fossils, the only logical interpretation of the evidence is an evolutionary response to changes in environments.

The third line of evidence comes from DNA. This is an immensely long “miracle” molecule that can replicate itself and its very presence is the definition of life. The unravelling DNA has revealed codes that passed from parent to offspring, and allowed the genetic links between different species to be deduced, down to the most primitive single-celled life. Independently of the other lines of evidence, the conclusion from DNA evidence is that an evolutionary process has been taking place throughout time.

Life’s response to changing environments through time by evolving is one of the greatest scientific discoveries. Not teaching this to our children deprives them of formally learning about this and appreciating their place on Earth. Such knowledge is critical to understanding and making informed decisions about our planet’s future. If we wish them to grow up to be responsible citizens, isn’t this fundamental knowledge that they should have?

Surely it is possible to teach the basics to Grade 7 school children? If teachers cannot do this, I would be interested to know how they explain to the children how God made the Earth and the infinitely large universe in one day.

• Professor Mike Watkeys is based in the School of Geological Sciences, Westville Campus, UKZN.

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