Answer:
1A. Follow your dreams
1B. The reason I believe the theme is follow your dreams is because that's what Darrell did. You can tell Darrell takes a liking to science. In paragraph 2 it states that he once made a hypothesis and it later became true. He happened to find mice and he tamed them as stated in paragraph 8. I believe his dream had something to do with animals. In the last paragraph it was said Darrell studied biology later on he became a zoologist. Zoologist take care of animals and I believe that's what he always wanted to do. That concludes why I think the theme is follow your dreams.
2A. Hard working and intelligent
2B. I think Darrell is intelligent because he studies a lot. In the first paragraph it states he likes to learn. Most likely someone who likes to learn is very smart. He also tamed mice that must take a lot of brain power and patience. That's where I get into hardworking. To tam mice you must work hard to get it right. Not only that but in paragraph 8 it states the mice were tamed in a short amount of time. He also went to college. Although I've never been to collage it must take a lot of work to get in. That's why I think the characteristics hard working and intelligent fits Darrell best.