I too have a social science background and am now in a biological science field. Here is my advice:

1. Email the graduate coordinator or department head for graduate programs you are interested in, and ask them how best to prepare yourself to apply. 
2. Consider doing a post-bacc degree or filling the gaps in your transcript (eg. statistics, CS, life science classes) with continuing education courses. 
3. Get research experience, ideally in a biological science or CS lab at an academic institution.

Points 2 & 3 will give you letters of recommendation from people in the field and experience doing the work, making you a more competitive applicant. Some programs may allow you to make up the gaps in your transcript after being admitted, but if you do it on your own beforehand you will have more choice for programs, and a more concrete sense of what exactly you want to research in your graduate degree. These programs care less about what inspired your desire to follow this path and more about what experience you have and what, specifically, you want to research. Additionally, doing this work before applying will show that you are committed and that this isn't just a passing fancy, something anyone switching fields needs to demonstrate.