Is it on purpose that the name of Biology.SE and Biology.meta are written with a lower-case 'b'?
It's on purpose.
When the site got its design back in May 2015, Stephane (SE's senior product designer) posted a discussion about the proposed site design (Site design for Biology community). Since its first revision, he proposed the site logo with a lower-case "b"
Logo & Identity
For the logo, as [suggested by the community], I was looking for a unique symbol that represents DNA. It might not represent all of biology but it's the most popular symbol though I tried to get as far as possible from the original shape while keeping it recognizable.
Along with the logo, all the illustrations work as a whole to mimic molecules. They grow in a seamless non-geometric pattern to convey an organic feeling.
Since then, while there were some feedbacks on the site logo, no one touched the letter casing. Thus, it's what we have until now.