"Humans and sharks, for example, make hemoglobin using nearly identical genes. That means hemoglobin genes were already present in their common ancestor."
Um. If this gene was the result of a mutation, isn't it possible, at least in theory, that mutation happened more than once? At two different times? At two different branches on the species tree?
Not really my area but there seems to be an assumption that species development (dare I say evolution) was linear, with humans being the ultimate achievement in that process. But doesn't the fact that genes mutate - sometimes triggered by viruses - imply the process was not at all linear?
Um. If this gene was the result of a mutation, isn't it possible, at least in theory, that mutation happened more than once? At two different times? At two different branches on the species tree?
Not really my area but there seems to be an assumption that species development (dare I say evolution) was linear, with humans being the ultimate achievement in that process. But doesn't the fact that genes mutate - sometimes triggered by viruses - imply the process was not at all linear?