On 27 December 1831, HMS Beagle set sail from Plymouth Sound, carrying an assortment of scientists. It visited Europe and Africa, South America and Australia, along with several islands in between. Most famously, on 15 September 1835, it stopped at the Galapagos Islands.
It was there that Shrewsbury native Charles Robert Darwin found the final pieces of the puzzle he had begun to assemble based on his observations of these different places. This would lead to his groundbreaking Theory of Evolution.
The mysteries of Darwin’s world
1835 might not sound all that long ago – the last person born in that century died just a few years ago – but it was a time when many now-familiar things about our world were still a mystery. Darwin didn’t know, for instance, about continental drift – the theory which describes how continents slowly move across millions of years, and explains why the east coast of South America looks like a jigsaw piece designed to fit neatly into the west coast of Africa. He could see that animals on different continents appeared to have common ancestors but he couldn’t work out how they had reached their different habitats.
Palaeontology was in its infancy in the 19th century. Darwin had some knowledge of the prehistoric world (and collected quite a few fossils himself), but he knew little about other species of humans. It was not until 1848 that a Neanderthal skull was found while remains of Homo Erectus began to be discovered around the end of the century.
Today, we can see evolution happening very quickly – when drug-resistant microbes proliferate as less resistant strains are killed by antibiotics, for example. But Darwin knew none of this.
Early ideas about heritability
Nonetheless, there was some awareness that a parent’s physical attributes could be inherited by a child. Farmers had been aware of it for centuries. Dog breeders knew it. Scholars who studied the royal families of Europe had observed that certain traits, such as the Hapsburg chin and haemophilia, were passed between generations. In 1801, Jean-Baptiste Lamarck postulated that offspring inherited characteristics based on how much a parent used them – suggesting that, for instance, if a giraffe was constantly straining upwards to reach leaves at the top of a tree, its children would have longer necks.
Darwin’s discovery
Darwin took the idea of heritability and tried to apply it to the animals and plants he encountered in the different habitats visited on his voyage. He knew that animals living in cold areas generally had thicker fur than their counterparts in warm areas and he realised that if a group of animals moved from a warm area to a cold one, those whose fur happened to be a little bit thicker would be more likely to survive and reproduce. If the survivors passed their traits along, each subsequent generation would have thicker fur.
From observations like this, Darwin formulated the underlying idea of his Theory of Evolution: the survival of the fittest. That idea would go on to be abused by political opportunists and others who thought that fitness meant being rich, clever and good at fighting. But, in fact, Darwin had established that fitness depends on the environment. A giant panda is much fitter than a human when it comes to surviving in a bamboo forest. But if the forest dies, the panda finds itself in trouble.
Human evolution
The most controversial part of Darwin’s theory was his assertion that humans are also a product of evolution. This contradicted widespread beliefs, religious and otherwise, that humans were separate from nature and had a special destiny. Many people were disgusted by the idea that humans could be related to monkeys. This prejudice made it hard for them to accept it, despite the obvious physical similarities. As a result, it took several decades before there was widespread acceptance.
Selection pressures
Some struggled with the idea of evolution because they didn’t understand the concept of selection pressure – the environmental factors, like cold or a sudden lack of bamboo, which drive change. They imagined evolution as throwing a group of dice and getting a random result in each generation. In fact, it’s more like throwing the dice, keeping all the sixes, and then throwing the rest again for each subsequent generation. Pretty soon, all the dice will be sixes!
Darwin himself also struggled. He had grasped his core idea, but there were other factors at work that he didn’t know about. Later, he would realise that sexual selection played a role. Peacock tails may be impractical but they result in more offspring being born because they are attractive to potential mates.
It would take later generations of scientists, however, to figure out that cooperation also influences evolution. Selection pressure works for traits which help the survival of close relatives even if they don’t help an individual directly. And it wouldn’t be until the discovery of genetic inheritance in 1943 that anybody understood the mechanism through which evolution works.
Darwin’s last challenge: the tale of the parasitic wasp
Darwin was a devout Christian, despite the hostility he faced from religious groups. But he began to struggle with his faith when he encountered one particular creature: the parasitic wasp. These wasps sting caterpillars with a toxin which paralyses them. They then lay their eggs inside the body of the still-living caterpillar, which provides insulation until the babies hatch, whereupon they eat it from the inside out.
“I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of caterpillars,” he wrote.
But he didn’t know that such wasps would save around 20 million people from starvation.
Cassava is a staple crop across Africa, having been originally imported from South America. In 2008, a mealybug infestation caused it to die off on a devastating scale. Nothing seemed able to stop the loss of the crop and save the people who depended on it until ingenious biologists went back to its homeland to see if it had a natural predator there. Which it did: a parasitic wasp. The wasps were introduced to Africa, the mealybug epidemic was brought under control and millions of lives were saved.
Later work on the Theory of Evolution focuses on how species develop within and as part of an ecosystem, explaining phenomena like this. Had Darwin known what the wasp would do, perhaps he might have concluded that God works in mysterious ways.
