Humans and other primates: primate order, the group of mammals that includes lemurs, lorises, tarsiers, moneys, apes, and humans, evolution through adaptation, adaptation. Organisms undergo this process to achieve a beneficial adjustment to an available environment, plus the results of that process: natural selection. The evolutionary mechanism by which individuals with characteristics best suited to a particular environment survive and reproduce with greater frequency than those without these characteristics. 1: primate dentition: diet available to arboreal primates requires unspecialized teeth, over time, fewer and smaller teeth doing more work. 2: sense organs: decreased dependency on smell, increased dependency on sight. Corresponding increase in brain size in the visual area: more acute sense of touch. Adaptation through behaviour: arboreal life involved changes in behaviour as well as changes in anatomical features. Learned social behaviour plays an important role: social behaviour is rarely observable on the fossil record. Human ancestors: chimpanzees and gorillas, closest living relatives to humans.