1. what stage is the middle stage of speciation? a. the populations become adapted to different environments and eventually become so different that they cannot interbreed to produce fertile offspring. b. the populations are isolated and thus do not interbreed. c. the populations become totally separated from one another. d. the populations successfully interbreed. 2. which stage is the last stage of speciation? a. the populations become adapted to different environments and eventually become so different that they cannot interbreed to produce fertile offspring. b. the populations are isolated and thus do not interbreed. c. the populations become totally separated from one another. d. the populations successfully interbreed. 3. the formation of the canyon acted as a barrier that prevented any mating between the separated populations. this is an example of which stage of specialtion? a. the populations become adapted to different environments and eventually become so different that they cannot interbreed to produce fertile offspring. b. the populations are isolated and thus do not interbreed. c. the populations become totally separated from one another. d. the populations successfully interbreed.