In this middle part of the course we examine patterns of vertebrate evolution. We do not know, in most cases, the underlying developmental genetic changes that mediate the evolutionary change i.e., how a complex process of development itself evolves. In the next part of the course we look an example, limbs, where we can currently best connect between evo and devo. Many verts look different from one another. Evolution in this view means changes in gene frequencies in populations.
Most adaptations are complex, making understanding the process of adaptation difficult.
Suppose that such complex evolutionary changes that make up these kinetic skulls arise incrementally, and not in one fell swoop. Each small increment of change can often be seen as being adaptive and hence under selection. It is curious, perplexing to Darwin as well, that the vertebrate evolutionary tree that we see in the fossil record seems well-pruned, rather than being a massively branchy and twiggy bush. In fact 'transitional forms' that are difficult to assign to major taxa are very rare. In contrast, most evolutionary biologists believe that evolutionary change occurs in small increments, but that extinctions continuously prune the tree.