The cubs of spotted hyenas often begin fighting within moments of birth, and often one hye...

The cubs of spotted hyenas often begin fighting within moments of birth, and often one hyena cub dies. The mother hyena does not interfere. How could such a behavior have evolved? For instance:

a. From the winning sibling’s point of view, what must  B (benefit of siblicide) be, relative to C (cost of siblicide), to favor the evolution of siblicide?

b. From the parent’s point of view, what must B be, relative to C, for the parent to watch calmly rather than interfere?

c. In general, when would you expect parents to evolve “tolerance of siblicide” (watching calmly while siblings kill each other without interfering).

For more about the unusual social system of spotted hyenas and for studies of wild hyenas, see:

Frank, L G., S. E. Glickman, and P. Licht. 1991. Fatal sibling aggression, precocial development, and androgens in neonatal spotted

hyenas. Science 252: 702–704.

Frank, L. G. 1997. Evolution of genital masculinization: Why do female hyaenas have such a large “penis”? Trends in Ecology and Evolution 12: 58–62.

Golla, W., H. Hofer, and M. L. East. 1999. Within-litter sibling aggression in spotted hyaenas: Effect of maternal nursing, sex and age. Animal Behaviour 58: 715–726.