Bird guides once listed the myrtle warbler and Audubon's warbler as distinct species. Recently, these birds have been classified as eastern and western forms of a single species, the yellow-rumped warbler. Which of the following pieces of evidence, if true, would be cause for this reclassification? a. The two forms interbreed often in nature, and their offspring survive and reproduce well. b. The two forms live in similar habitats and have similar food requirements. c. The two forms have many genes in common. d. The two forms are very similar in appearance.

Video transcript

Hi everyone. Let's look at our next question. Sharks and dolphins are animals that have developed many similar characteristics. Which of the following is clear evidence that they come from two different ancestors. So let's walk through our choices here. Choice A. Says they have different predators. Well that doesn't really say anything about their ancestry. It just speaks to their current environment their current ecosystem. They could have had shared ancestor and just evolved to take different places in the food chain in their current ecosystem. So Choice A. Would not fall under clear evidence. Choice B. Says they have different bits of intelligence. Again we could have seen some divergent evolution where they shared a common ancestor but evolved differently to give them different advantages in their environment. So Choice B. Again it's not clear evidence. Choice C. They socialize differently. Again you could have a common ancestor and have evolved differently um to give them advantages in different aspects of their environment. So, Choice C. Not clear evidence. Choice D. Says they have a different genetic makeup. And indeed when we want to look at evidence for ancestry we want to look for shared D. N. A. Sequences between species that may have been conserved from an ancestral species. So we can look at those shared sequences and use that to find uh genetic relatives that may have undergone divergent evolution to develop differences such as intelligence or socialization. And so if we look at sharks and dolphins and we don't see these conserved ancestral DNA sequences to a great extent. We can see that they do not have descent from a similar ancestor. So the different genetic makeup choice D. Provides actual evidence Of two different ancestors. See you in the next video.