This is a simple demonstration of the Hardy-Weinberg equilibrium and how natural selection affects the allele frequency of a population. To help Mrs Karnika and other teachers who face the same difficulties, I would like to introduce the Counting Buttons activity. Many of them wonder about the relevance of the Hardy-Weinberg principle to understanding evolution. They may feel threatened by mathematics and the quantitative aspects of population genetics, and may be unable to apply the principle to make sense of evolutionary phenomena. The Hardy-Weinberg principle is one of the most difficult topics in evolution for many teachers and students ( Mertens, 1992). * It was later discovered that an American, William Castle, had suggested a similar idea in 1903.ĭean Madden, National Centre for Biotechnology Education, UK Today the science of population genetics, of which it is part, provides the most important theoretical basis for evolutionary biology and can be used to test almost all evolutionary ideas. In 1943 the principle became known as the Hardy-Weinberg principle (or the Hardy-Weinberg equilibrium or law) when it emerged that the same idea had been proposed independently in 1908 by a German physician, Wilhelm Weinberg.* ‘Hardy’s principle’ contributed towards the reconciliation of Darwin’s natural selection with Mendelian genetics that developed gradually over the 1920s and 1930s to form our modern ideas about evolution. Variation would be preserved over the generations. The ‘very simple point’ that Hardy went on to prove was that in a relatively large population where there is no migration, in which mating occurs at random and in the absence of selection or mutation, the frequency of genes will remain the same. Punnett has called my attention, suggest that it may still be worth making….” “I am reluctant to intrude in a discussion concerning matters of which I have no expert knowledge, and I should have expected the very simple point which I wish to make to have been familiar to biologists. In 1908 he wrote to the editor of the journal Science: Hardy, a pure mathematician, generally treated applied mathematics with contempt. Harold Hardy (with whom he played cricket) to help. Unable to solve this latter problem, the British biologist Reginald Punnett asked G. If the units of inheritance were discrete, how could the small, continuous variations observed by biologists be produced? And why, if Mendel was correct, didn’t the frequency of dominant characteristics increase in the population? Rather than bolstering Darwin’s theory, however, these discoveries were taken by many to be incompatible with natural selection. Mendel also observed that although a characteristic may seem to vanish in a particular generation, it is merely hidden by a ‘dominant’ characteristic – thus it can reappear, unchanged, in a subsequent generation. It suggested that characteristics are discrete and do not blend. The first steps were taken at the start of the 20th century, when Gregor Mendel’s work on inheritance in plants was rediscovered. A chance encounter between a biologist and a mathematician on a cricket pitch some 50 years later played a crucial role in solving the problem. Over several generations this would, however, lead to a reduction in variation, giving natural selection little on which to operate. Like most biologists of his time, Darwin supposed that the characteristics of parents were ‘blended’ in the offspring. When, almost 150 years ago, Charles Darwin made public his theory of evolution by natural selection, the idea had one serious weakness.
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