Coach Glassman:

Gymnasts have no peer in trunk and hip flexion, upper-body strength in multiple joint angles, agility, accuracy, balance, coordination. Their domain is body control.

Weightlifters are masters of power, speed, and hip and leg strength. Powerful hip extension is the most critical element of human performance and none have the capacity of the weightlifters.

Sprinters have enormous physical potential due to their metabolic competency across anaerobic and aerobic pathways and because of the speed, power, and total conditioning that sprinting demands.

Blending workouts from each domain gives us a total greater than the sum of the parts – a gorgeous hybrid.

CrossFit Journal Article: 

http://library.crossfit.com/free/pdf/05_03_Interview_Glassman.pdf