How many parasites live inside us? What is the relationship between internal parasites and allergies? And could one parasite even have affected our brain chemistry over the course of millennia? Science journalist Carl Zimmer ("Parasite Rex") stopped by Big Think this week to discuss these and a host of other hot topics in science.

The conversation also touched on neuroscience (what is the "speed of thought"?), viruses in the human genome, and Zimmer's popular blog, The Loom. Zimmer's interview will be posted later this month.