An example of simile and metaphor in public science discourse:
"The Nile river itself has been argued to be one of these corridors for this dispersal of modern humans out of Africa, and in looking at people living along these seasonal rivers, what we think is going on here, is the dynamics of these seasonal rivers sets up a kind of a siphon that actually moves people out along the river channels. So during the dry season, the resources at any given water hole will be exhausted in short order.
That means the people are either going to have to forage to another water hole, or actually move to that water hole, so just the dynamic of a seasonal river itself tends to siphon populations across the channel and we call these kind of euphemistically blue highways, for these corridors."
John W. Kappelman Jr
Prof. John Kappelman (Anthropology, University of Texas) was talking on an episode ('Out of Africa') of Science in Action.
The first instance here is a simile – what is set up is a kind of a siphon. However then the term is used without the qualification, i.e. as metaphor (a seasonal river itself tends to siphon populations across the channel). It could be argued that this is still simile as the qualification (kind of, but not literally, a siphon) was already established.
Read about examples of science similes
