Hiya
I do GSD and life sciences too and am in second year. I love the ideas behind GSD and what we learn, but I have to warn you that collaboration between departments isn't good at all, so you will probably have the odds stacked against you. I regret choosing this course simply because its new, so they don't really know what they're doing and look to us (the students) to tell them where they went wrong so they can improve it year on year. In terms of learning, its not very well-rounded, but again this should improve over time.
The uni itself is amazing socially and GSD is great, but admin isn't good at all. For example, in my first year we were made to do a second year module (and go on a field trip with second years and write a lab report after never having done one before), and were told "don't worry, we'll just bump up your grades a bit" which kind of makes it impossible to get a first. The same thing happened this year where we were forced to do a third year biology module.
As far as I know, issues like this are the worst in biology but there are similar issues in all other partner degrees. For example, I have a friend doing psychology and GSD. In first year, she didn't get good marks on any of her psychology essays, and it turns out this was because she wasn't allowed to attend any of the essay writing preparation sessions as she isn't a full psychology student (psychology have a different essay writing style to GSD). The same thing happened to me (and continues to happen) - for example, I had biology modules last year that were meant to be accompanied with tutorials, but I couldn't attend any of the tutorials as I wasnt a full biology student so could only attend lectures and not have things explained to me. In fact, in some lectures the lecturer would say things like "I'll explain this more in the tutorial on Friday", and again I couldn't go.
Like I said, this could have improved somewhat, but until the degree has been established with a set structure, we're all essentially guinea pigs. I would advise you to take a full economics course or politics course, as you still have the option to take GSD modules so you won't miss out on anything. I hope this helps!