There is a huge scope to specialise incl. within social anthropology (which I am intending to specialise in myself.) Specialisation begins in the 2nd year when one of the 3 or 4 subjects (if opted for political theory as well) is taken up alone. Then in the third yr specialisation is complete and you take an area of your chosen subject such as gender and identity to look at in detail.
I was also concerned about the science based part of the course. It involves some fairly scary genetics but with a little work even a "gave it up after GSCE science phobe" type like myself found it interesting and very useful for other areas of the course. There are also sections in bio anth on primates and evolution so even if you're terrible at genetics, all is not lost.
This is a very wide course - be ready for philosophy, economics, politics, ethnology, genetics, paleontology and much more! My advice if concerned about bio anth is to read Matt Ridley any from "Genome" "The red queen" and "Nature via Nurture" (a really good one to have read before interview.)
Feel free to pm me with any further questions.
Harriet