A video of BBC’s Darwin season featuring ‘Charles Darwin and the Tree of Life’ – a cool animation which illustrates an idea that Darwin and his contemporaries used to explain the evolutionary links between living things. Charles Darwin was a British scientist who laid the foundations of the theory of evolution and transformed the way we think about the natural world.
Transcript of Video:
So, a hundred and fifty years after the publication of Darwin’s revolutionary book, modern genetics has confirmed its fundamental truth. All life is related. And it enables us to construct with confidence the complex tree that represents the history of life. It began in the sea, some three thousand million years ago. Complex chemical molecules began to clump together to form microscopic blobs: cells. These were the seeds from which the tree of life developed.
They were able to split, replicating themselves – as bacteria do. And as time passed they diversified into different groups. Some remained attached to one another so that they formed chains. We know them today as algae. Others formed hollow balls which collapsed upon themselves, creating a body with an internal cavity. They were the first multi-celled organisms. Sponges are their direct descendants.
As more variations appeared the tree of life grew and became more diverse. Some organisms became more mobile and developed a mouth that opened into a gut. Others had bodies stiffened by an internal rod. They, understandably, developed sense organs around their front end.
A related group had bodies that were divided into segments with little projections on either side that helped them to move around on the sea floor. Some of these segmented creatures developed hard protective skins which gave their bodies some rigidity. So now, the seas were filled with a great variety of animals.
And then around 450 million years ago some of these armoured creatures crawled up out of the water and ventured on to the land.
And here the tree of life branched in to a multitude of different species that exploited this new environment in all kinds of ways. One group of them developed elongated flaps on their backs, which over many generations eventually developed into wings. The insects had arrived. Life moved into the air and diversified into myriad forms.
Meanwhile, back in the seas, those creatures with a stiffening rod in their bodies had strengthened it by encasing it in bone. They increased in size. They grew fins equipped with muscles that enabled them to swim with speed and power. So fish now dominated the waters of the world.
One group of them developed the ability to gulp air from the water surface. Their fleshy fins became weight-supporting legs and 375 million years ago, a few of these backboned creatures followed the insects on to the land. They were still not independent of water. They were amphibians with wet skins and had to return to water to lay their eggs.
But some of their descendants evolved dry scaly skins and broke their link with water by laying eggs that had watertight shells. These creatures, the reptiles, were the ancestors of today’s tortoises, snakes, lizards and crocodiles. And of course, they included the group that, back then, came to dominate the land: the dinosaurs.
So the tree of life burgeoned into a multitude of different branches.
But 65 million years ago, a great disaster overtook the Earth. Whatever its cause, a great proportion of animal life was exterminated. All the dinosaurs disappeared – except for one branch, whose scales had become modified into feathers. They were the birds.
While they spread through the skies, a small and seemingly insignificant group of survivors began to increase in numbers on the ground beneath. These creatures differed from their competitors in that their bodies were warm and insulated with coats of fur. They were the first mammals. With much of the land left vacant after the great catastrophe they now had their chance. Their warm insulated bodies enabled them to be active at all times – at night as well as during the day – and in all places: from the Arctic to the tropics, in water as well as on land, on grassy plains and up in the trees.
Charles Robert Darwin was born on 12 February 1809 in Shrewsbury, Shropshire into a wealthy and well-connected family. His maternal grandfather was china manufacturer Josiah Wedgwood, while his paternal grandfather was Erasmus Darwin, one of the leading intellectuals of 18th century England.
Darwin himself initially planned to follow a medical career, and studied at Edinburgh University but later switched to divinity at Cambridge. In 1831, he joined a five year scientific expedition on the survey ship HMS Beagle.
At this time, most Europeans believed that the world was created by God in seven days as described in the bible. On the voyage, Darwin read Lyell’s ‘Principles of Geology’ which suggested that the fossils found in rocks were actually evidence of animals that had lived many thousands or millions of years ago. Lyell’s argument was reinforced in Darwin’s own mind by the rich variety of animal life and the geological features he saw during his voyage. The breakthrough in his ideas came in the Galapagos Islands, 500 miles west of South America. Darwin noticed that each island supported its own form of finch which were closely related but differed in important ways.
On his return to England in 1836, Darwin tried to solve the riddles of these observations and the puzzle of how species evolve. Influenced by the ideas of Malthus, he proposed a theory of evolution occurring by the process of natural selection. The animals (or plants) best suited to their environment are more likely to survive and reproduce, passing on the characteristics which helped them survive to their offspring. Gradually, the species changes over time.
Darwin worked on his theory for 20 years. After learning that another naturalist, Alfred Russel Wallace, had developed similar ideas, the two made a joint announcement of their discovery in 1858. In 1859 Darwin published ‘On the Origin of Species by Means of Natural Selection’.
The book was extremely controversial, because the logical extension of Darwin’s theory was that homo sapiens was simply another form of animal. It made it seem possible that even people might just have evolved – quite possibly from apes – and destroyed the prevailing orthodoxy on how the world was created. Darwin was vehemently attacked, particularly by the Church. However, his ideas soon gained currency and have become the new orthodoxy.
Darwin died on 19 April 1882 and was buried in Westminster Abbey.