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  • Writer's pictureJolene Pappas

Evolutionary Arms Race

Updated: Feb 19

The evolutionary arms race simulation is loosely based on the Brodie & Brodie studies of newts (Taricha granulosa) and garter snakes (Thamnophis sirtalis). The newts produce enough toxin to kill large animals...much more than what would be necessary to kill most of their potential predators. One predator, a species of garter snake, has resistance to the toxin. It is thought that the two species are evolving in response to each other with selection favoring newts with high toxicity and snakes with high resistance.

The newt and snake example also illustrates the concept of evolutionary trade-offs. This is when an adaptation is in some way also linked to a negative outcome. In this case, snakes with high resistance can eat the newts, but are slower. Newts that are highly toxic are less likely to be eaten, but have lower reproductive rates. This simulation only focuses only on a trade-off in the predator, although there is opportunity to discuss the impact of evolutionary trade-offs on the prey as well.

Here are a couple resources that discuss this classic example of an evolutionary arms race:

In Part I of this virtual lab, a predator makes four runs through a shoot; once without toxin exposure and then three runs after injection with increasing "units" of the toxin.

A predator is tested in an evolution simulation
Part I of the Evolutionary Arms Race simulation

Students examine the effect that the toxin has on predator speed. The more resistant an individual is, the less their speed is reduced when exposed to the toxin. For the provided worksheet students graph the relationship between the starting speed (control) of the predator and the difference when the predator is exposed to the toxin.

Student data graph for Arms Race simulation
Sample of student work for the Arms Race simulation

In Part II, students can control the degree to which the toxic prey makes up the predator's diet. The results show the difference in control speed (0 units of toxin) and toxin speed at the start of the study (generation 0) and after 10 generations. Students analyze how the percentage of toxic prey in the predator's diet affects the level of resistance in the population over time. Part I tests individual predators, while the data presented in Part II represent population averages.

Testing predator resistance to a toxin over time
Part II of the Evolutionary Arms Race simulation

After completing the lab, students should be prepared to discuss the concept of an evolutionary arms race and the trade-offs that can place limitations on adaptations.

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