I see my special interests like trees. Some grow big, and strong, and some only make it to saplings, grown out of a seed of another tree. My interest in psychology, for instance is a mighty oak who has grown for about 20 years. It has spawned many other saplings in it's time, but none have outlasted the tenacity of the psychology interest.
Autism is another that is related, but not on the same tree. It's been around for almost 8 years now, and is strong, and been by far my most compelling interest, as it has a lot to do with my everyday life. Some of the branches on that tree include this blog, and my Inner Aspie FB page. They're definitely a part of my interest, but they're not the totality of it.