The Very First Animal Appeared Amid an Explosion of DNA
&quot;Humans and sharks, for example, make hemoglobin using nearly identical genes. That means hemoglobin genes were already present in their common ancestor.&quot;<p>Um. If this gene was the result of a mutation, isn&#x27;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?<p>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&#x27;t the fact that genes mutate - sometimes triggered by viruses - imply the process was not at all linear?