Ants use the panoramic skyline as a visual cue during navigation

through genetic constraints that limit the diversity of classes produced or recruited through evolution is not yet clear. At the same time, rapid evolutionary diversification and variability is the hallmark of venom evolution. Marine cone snails (Conus) are predatory mollusks that fire a venomous harpoon that almost instantly immobilizes target prey (Figure 3). These darts carry an astonishingly diverse blend of neurotoxins that block ion channels or disrupt neuronal receptors. Molecular genetic analysis demonstrates that these compounds are under strong diversifying selection. The rate of protein evolution in conotoxin genes is three to five times higher than the highest rates observed for other proteins. There is evidence for gene duplication and diversification leading to the radiation of toxin forms. Similar rapid diversification is also observed for snake venom proteins. In both cases, it is assumed that strong selection to subdue prey is driving such fast evolution. Cone snails tend to feed on a relatively limited range of prey within populations, but the group as a whole feeds on many groups of invertebrate and vertebrate prey. Snails that feed on different prey types diverge in venom blends, but the biochemistry of conotoxins is much more diverse than snail diets (an individual snail may have 50–200 distinct toxic components). Geographic variation in venom composition also correlates with diet diversity in some vipers. Among species of elapids (cobras and their relatives), the three-fingered neurotoxins diversify rapidly as do diets of the venom producers. These examples all suggest that an arms race matching toxicity and resistance between predator and prey drives diversification of venoms. However, functional analyses that would more solidly confirm the existence of this process have yet to be conducted.