periods. This is due to both genetics and selective breeding practices.

Multiple other biological and environmental factors influence litter size within and between species:

* Maternal body size: Larger individuals within a species typically produce larger litters
* Maternal age: Litter sizes often increase with age up to a point, then decline
* Nutrition: Better-fed mothers produce larger litters with higher survival rates
* Number of mammae: Average litter size often approximates half the number of teats

Advantages of being born into a litter

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