The problem is that in a biology lab, there's a lot more behind the materials and the tools than there is behind source code, and stuff isn't as neatly parameterized. Just from high school biology I can name three different ways to create a vaccine for a virus, and checking my knowledge on Wikipedia reveals a bunch more. Yet there are still many viruses we can't vaccinate against. Stuff in biology is incredibly complex and specific. Adapting a successful technique to a very slightly different situation can be straightforward, or it can be a major research project. You could easily pick, as your first "original" project, something that would require a scientific breakthrough to accomplish, and it would take you years to advance to the point of even realizing it. If that sounds rewarding to you, you're probably already professionally involved in an intellectual field deeply enough that you want your hobbies to have entirely different rewards and challenges.

Feynman's memoirs are some of the most intellectually macho posturing I've ever read, and even he stuck mostly to physics when he was doing physics. He favored hobbies like safecracking, drumming, and drawing, all of which could be summed up as showing off and getting laid. People looking for a professional-level intellectual challenge from their hobbies are in the wrong line of work.