Size, shape and populations
Variation in size and shape of teeth and jaws distinguishes between species (Chapter 1), but also occurs within species. Each species can usually be divided into several populations, or groups of males and females who tend to breed together rather than with members of other populations. They may be isolated by geography, or by behaviour that acts as a barrier. Some features or characters of tooth shape may be more common in some populations than in others, or the average of a measurable feature may differ. Within any population, there is also variation between individuals so, over a range, a feature may take on different forms or its measurable size may vary. Some individuals may have a form or size of this feature that fits within the range found in other populations, but the population as a whole can be distinguished by the frequency of different forms, or distribution of sizes. In most mammals, males and females differ in tooth and jaw size and shape – so-called sexual dimorphism – within each population. This dimorphism is largely in size, and males of most mammal species tend to have larger teeth than females. The level of dimorphism often varies between populations of the same species, and this needs to be taken into account when populations are compared. With archaeological material, it is difficult to distinguish males from females in some species, which often complicates interpretation.