"Can't Fight Biology" is the fourth episode of the seventh season of Grey's Anatomy and the 130th produced episode of the series. It is also the 187th produced episode of the Grey's Anatomy franchise. It was broadcast on October 14, 2010.
A visit to the obstetrician results in a disturbing revelation for Meredith and Derek and the news forces Meredith to face up to the possibility that she may have inheritted her mother's Alzheimer's gene while Lexie begins to question her sisterly relationship with Meredith when she notices how close she has become to April. Teddy confronts Jackson when tries using his physical attributes to get ahead in the operating room while Cristina's self-doubt carries outside of the hospital and into her house hunting with Owen. Mark and Callie's friendship causes problems for Arizona.
- "Biology determines much of the way we live. From the moment we're born we know how to breathe and eat. As we grow older new instincts kick in; we become territorial, we learn to compete, we seek shelter. Most important of all, we reproduce. Sometimes biology can turn on us though. Yeah, biology sucks sometimes."
- "Biology says that we are who we are from birth, that our DNA is set in stone. Unchangeable. Our DNA doesn't account for all of us though, we're human, life changes us. We develop new traits; become less territorial, we stop competing, we learn from our mistakes, we face our greatest fears. For better or worse, we find ways to become more than our biology. The risk, of course, is that we can change too much to the point that we don't recognize ourselves. Finding our way back can be difficult with no compass, no map. We just have to close our eyes, take a step, and hope to God we'll get there."
- "Won't Be Fooled" - Walking Sleep
- "You Got What I Need" - Joshua Radin
- "Shark In The Water" - VV Brown
- "Until The Last Falling Star" - Matthew Perryman Jones
- "Tumblin' Down" - Jenna Andrews
- "Further" - Correatown
This episodes' title references the song Can't Fight Biology, originally sung by Drop Dead, Gorgeous