A common theme of this blog is to share cases of "linear evolutionary thinking". These are instances, usually graphics, that illustrate the common conception of evolution as a line of progress, from worst to best. Evolution actually occurs by branching processes. We could pull out a line of evolution from the tree, but that line by necessity has an arbitrary endpoint, often humans or a human-like feature. And living species or their traits cannot necessarily be equated with ancestral forms.
Ostracod eye evolution has been depicted as a straight line from simple to compound eye, illustrated here. Textbooks use such diagrams (see also this), and these diagrams can impact the way people think about evolution.
Here is another variation on the human march of progress, which shows Barack Obama as the more advanced political candidate, compared to John McCain.
Thanks to my brother for sending this to me.