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Trends in the Primate Order

Human Biology (Year 12) - Hominid Evolution

Ben Whitten

What trends do we need to know about?

When looking at the trends in the order Primates, we need to consider the following:

  • Digits

  • Dentition

  • Vision and olfaction

  • Brain

  • Reproduction (gestation and parental care)

We look at how these features change from more primitive primates to more advanced primates, e.g., lemur to human.

What are the trends in digits?

Mobility: Increasing mobility and ability to move digits independently of one another

Opposability: First digit is opposible; an increasing length results in increased effectiveness of opposability - advanced primates have full precision grip

Claws/nails: Primitive primates retain claws on some digits, higher pimates have nails on all digits

What are the trends in dentition?

Number of teeth: There is a reduction in the number of teeth from 36 to 32

Size of the canines: Monkeys and apes have large canines with diastema, humans have small canines with no diastema

Molars: 4 cusp molars in monkeys to 5 cusp molars in apes and humans

What are the trends in vision and olfaction?

Olfaction: There is a decreased reliance in olfaction (smell) as a form of communication (reduced size of snout)Vision: There is an increased reliance on vision as a method of communication; eyes become more forward facing (stereoscopic vision), and an increased proportion of the cerebral cortex is devoted to vision

What are the trends in the brain?

Size: Increasing size of the brain relative to the body

Convolutions: Gradual increase in the number of folds on the surface of the cerebrum (cerebral cortex becomes more convoluted)

Cerebral cortex: The cerebral cortex makes up an increasingly large proportion of the brain

What are the trends in reproduction?

Gestation: Increasing length of time between fertilisation and birth

Parental care: Increasing length of time that the offspring are dpeendent on the parent or parents

Sexual maturity: Increasing later development of sexual maturity

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