Question

Which of the following is not an example of an evolutionary arms race?

A. Herbivores evolve tolerance to increasingly toxic secondary metabolites produced by plants

B. Lead morphology within a species of plant becomes more efficient at gathering light over time

C. Phytolith abundance within plant tissue increases over evolutionary time as the thickness of herbivore tooth enamel becomes thicker

D. Cactuses on the Galapagos Islands become taller and more tree like in the presence of giant tortoises

Answer 1

an evolutionary arms race is a struggle between competing sets of co-evolving genes, traits, or species, that develop adaptations and counter-adaptations against each other, resembling an arms race. These are often described as examples of positive feedbacks. The co-evolving gene sets may be in different species, as in an evolutionary arms race between a predator species and its prey or a parasite and its host.

In examples A, C and D there are counter adaptations shown. Like in A and C the struggle is between herbivores and plants and thus adaptations occur in both. In D  the struggle is between cactus and giant tortoises and to win the struggle adaptations occur in both. In B there is no struggle shown, so this is not the example of an evolutionary arms race.