Brian Asbury looks at Darwin’s life and work and suggests classroom ideas for studying the man and his theories in a primary science context
One such expedition was a planned voyage by HMS Beagle to map the coastline of South America, and Darwin managed to get himself a recommendation to sail on the Beagle as naturalist. The Beagle set sail on 27 December 1831 on a voyage that would last five years and write Charles Darwin’s name into the history books.
Darwin spent two-thirds of the voyage on land, carefully recording geological features, fossils and living organisms, and collecting many specimens, many of them new to science at that time. He made extensive notes, which would later prove invaluable, and he also wrote a journal for his family, which was later published as The Voyage of the Beagle.
However, it was when the Beagle visited the Galápagos Islands, off the coast of Ecuador, that Charles became most intrigued about the origins of the living things he encountered. He discovered many species of finches (14 in all), mockingbirds and other types of birds, and he noticed that these birds differed from one another depending on which island they came from. He realised that although they had many similarities, they were actually different species. His observations of birds, tortoises and other animals which were similar but seemed to have differences caused by living apart from one another on these small isolated islands, seemed, as he described it, to ‘undermine the stability of species’. In other words, perhaps species were not fixed in one form as had previously been thought, but changed over time. Perhaps these different species had at one time been the same, before they were isolated from one another. Such considerations, Darwin later wrote, ‘seemed to me to throw some light on the origin of species’.
Developing a theory
By 1838, Darwin’s observations about how species seemed to change had developed into his theory of natural selection. He discussed his ideas with several naturalists, but they were controversial and he was wary of upsetting the Establishment. Another 20 years passed before the biologist Alfred Russel Wallace sent Darwin an essay which described the same idea. This finally prompted Darwin to suggest to Wallace that they should both immediately publish their theories and, in 1859, when he was 50 years old, Darwin’s book On the Origin of Species was finally published, telling the world about his theory of how living things evolved over time into new and different species, with everything ultimately descending from a common ancestor billions of years ago.
Although there was some heated opposition to Darwin’s ideas on evolution, especially from religious groups, his theory became accepted by the scientific community and the general public in his lifetime. Today, natural selection forms the basis of modern evolutionary theory and is one of the main foundations of modern biology.
What were Darwin’s theories?
In the science of biology, evolution is the process by which living things change from one generation to the next. Parents pass on their genes to their offspring, but these genes can change in two ways. The first of these ways, Darwin realised, is natural selection. This is what happens when some individual creatures have features which make it more likely for them to survive than those which do not have these features. For example, if an animal species feeds on vegetation that grows high in trees, and this becomes scarce, then they may have to feed from higher branches than they did before. As a consequence, those animals with longer necks will be better able to feed, survive and breed than those with shorter necks – so, the creatures with shorter necks will die, will not pass on their genes and the species as a whole will tend to have longer necks.
The second way that genes can change is by mutation. This can produce new or altered traits in individuals, which may be favourable or unfavourable, but which can be inherited by later generations.
Of course, Darwin knew nothing about genes or DNA, but his observations led him to theorise that these changes accumulate as time passes. If one group of a species has changed but is isolated from other members of the species which did not have to adapt, the differences may become so great two separate species are established. This is what Darwin believed had happened in the cases of the finches, tortoises and other creatures that he observed on the Galápagos Islands.
Suggestions for projects in class about Charles Darwin and his work:
1. The voyage of the Beagle
Use maps and the internet to make a chart showing Darwin’s journey on the Beagle. Mark the countries that he visited and what he discovered there, and learn more about what these countries are like today. Darwin’s book on the voyage can be downloaded from Project Gutenberg.
2. Investigating bird life
Darwin’s studies of birds were a major inspiration for his theories. Make a study of the various species of birds local to your school. Which species are similar to, or related to, one another? Which ones appear to be similar to other species but are actually quite different? Are all these birds seen everywhere in your area or only found in certain places or habitats, or at different times of the year?
3. Adaptation for survival
Study some animals in detail and discuss which of their features are adapted to survival in their native habitat. For example, polar bears have thick fur for protection against the cold and the fur is white, to make them harder to see against snow and ice. Ask the children to speculate about what these animals might be like if they had adapted to live in a different environment. What might a desert-dwelling polar bear be like?
There are a number of popular misconceptions about Charles Darwin and his work.
1. Darwin ‘invented’ evolution. In fact, the concept had been around for a long time before Darwin. The Greek philosopher Anaximander, in the 6th century BC, had ideas very similar to what we would call evolution, as did the Muslim biologist al-Jahiz in the 9th century AD, and others.
For at least a century before Charles Darwin, naturalists and philosophers had been discussing the idea of evolution, including his own grandfather Erasmus Darwin and the French biologist Jean-Baptiste Lamarck.
2. Darwin’s work informed opinions on the age of the Earth. Darwin was a skilled geologist, but the geological timescale had been established long before his time. As far back as the 11th century AD, Persian and Chinese geologists were beginning to realise that the Earth was constantly changing and that for the strata of rocks to have formed as they had, the planet had to be much, much older than previously believed. By the late 18th century, geologists had begun to divide the Earth’s timeline into specific periods in which various kinds of rocks formed, and they were already talking in terms of many millions of years. By the time Darwin published his work in 1859, the accepted geological timescale had been roughly worked out and looked very similar to what is accepted by scientists now. Darwin and his ideas about evolution had nothing to do with this.
3. Evolution is ‘only’ a theory. In science, the word ‘theory’ has a special meaning. In everyday use, we usually use the word ‘theory’ to refer to an unproven idea or a guess. In science, however, the word does not mean that at all; it is used to describe a model of how something works – and to be given the title ‘theory’ it has to be a model that is testable. It must tie together all the facts about something as well as provide an explanation that fits all known observations and can be used to make predictions. The Theory of Evolution has been tested and scrutinised for more than 150 years, and is supported by observations and tests made by countless numbers of scientists. It is not called a ‘law’ of science because laws and theories are not the same thing. A scientific law states that something will happen; a scientific theory describes why it happens. This is why gravity is also called a theory, even though no one would seriously suggest that gravity is not real.