I know for myself it was a few different things. When I was growing up we always used to watch the nature/animal planet/science channel tv shows. Those gave me a fascination of plants and animals.
And another was my sister had a science set that she outgrew, so it was then MY science set! I loved it. I remember looking at a dead bee that had stung my cousin under the microscope and was in awe.
And when I was in high school biology I was just in love with learning everything in that class. Especially when I learned about DNA! I was in love after that very minute. Oh and I actually enjoyed the dissection part of the class too. Learning the different parts, and where they were and what they did! So much fun!
I love hearing these stories!