We have done two topics in this: sexual selection and brain size. I'll just give you some beginning noises that you can pick out of and will hopefully get you going..
- Size of males generally larger. (Clutton-Brock & Harvey, 1977) - variation in body-size dimorphism is due to intra-sexual competition.
- Humans are the only great ape with enlarged breasts outside of lactation - sexual selection ornamentation rather than serving any function.
- Here's a list of primate brain sizes: H. s. sapiens [1300cm3], H. s. idaltu [1450cm3], H. heidelbergensis [1200cm3], H. neanderthalensis [1400cm3], H. ergaster [800cm3], Ausralopithecus [500cm3], Common chimpanzee [400cm3]
As you can see, there has been a gradual increase then a slight dip to sapiens, showing that we must have reached our limit for maximum brain size. The intelligence has increased as brain size goes up. You can compare brain size to other animals to, and compare specific parts of the brain (neocortex does a lot of high order functioning).
- Comparison of precocial (small litters of developed and social)and altricial (large litters of poorly developed non-social) species. Humans are secondarily altricial when primates are generally precocial.
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General principle of Comparativism is that by comparing extinct or extant species, we can learn about the evolutionary history of traits, and about unique features of a species