Evolution

About this course

In 1858, lying in his hut with a fever on the island of Ternate, Wallace worked out how species could change: the individuals best suited to their surroundings survive and breed and pass their useful features on. He wrote it up and sent it to Darwin, who had been working on the same theory for about 20 years without publishing. The course starts with these two people and then asks what the idea needs in order to work.

The seven units are Darwin and Wallace, variation and inheritance, natural selection, fossils and rock layers, common ancestors and phylogenetic trees, how new species form, and human evolution. Natural selection can only work on differences that are inherited. A child who grows tall because of good food will not have taller children for that reason, and a muscle built in the gym does not pass on either. In the 1950s Bernard Kettlewell marked hundreds of light and dark moths and released them in woods. In polluted woods a larger share of the dark moths came back, and in clean woods a larger share of the light ones. The lab uses made-up beetles on bark of different shades, with sliders for selection pressure and mutation rate and a bar chart for each generation.

The later units widen the view. Rock layers are read from the bottom up, with a dike that cuts through A, B and C but stops under E. Island chains are ideal for adaptive radiation, as with the Hawaiian honeycreepers, which come from one founding species. Walking on two legs evolved more than 4 million years ago, while Australopithecus afarensis lived in eastern Africa between about 3.85 and 2.95 million years ago. The sources are OpenStax Biology, the Natural History Museum in London and the Smithsonian's Human Origins Program.