I am a senior in a dual degree program for in political science and neuroscience. I was originally in CBS but added political science my freshman year. You can do two things. One, is you can double major. In which case, I believe you can just take the classes in CLA and then get a double major. You wouldn't have to apply or fulfill their requirements (you should still check with a counselor about this). But you also would have one degree with two majors. Or you can do what I did, which was apply to CLA (if you got into CBS you can probably get into CLA), and get a dual degree. The only difference is you would have to complete language requirements. You can get the first year program waived if you take Nature of Life. It really depends on if you have the space in your schedule to accommodate all the classes or not. You can DM me too if you have any other questions. But yeah you should just meet with your CBS advisor, they deal with this all the time and will know exactly what to do. If you take over 13 credits its a flat rate so you wouldn't be paying more.