The common tenrec — a hedgehog-like creature from Madagascar — produces the largest litters among mammals. The average litter of this small animal includes approximately 18 young, but litters up to 32 have been recorded. Tiger snakes also produce very large litters; the largest ever recorded contained 126 baby snakes.

For most mammals, the average number of offspring produced is equal to half of the number of nipples the females possess. For example, humans have two breasts and usually produce only one offspring at a time. This is thought to be an adaptation that limits fighting between siblings as they struggle to feed themselves.