Primate Morphological Traits

1. Primate Morphological Traits Allometry of Brain and Body Size

2. Us and Them • No single trait differentiates primates from other animals

3. 2 Features that Stand Out • Larger brains, with variation within • Greater dexterity and mobility than other animals, with variation within

4. Brains • Neocortexis larger • Cognitive abilities • Reasoning • Consciousness • 50-80% of total brain volume Neocortex in blue, from: http://www.nibb.ac.jp/brish/Gallery/cortexE.html

5. Why develop a bigger brain? • Typically, morphological traits are a function of ecological adaptation, tied to the: • Need for food • Need to mate to reproduce • Need to diminish predation and other threats

6. “Social Brain Hypothesis”Robin Dunbar, 1988 • Larger brains correlate with more social primates • Larger brains = larger social groups Colored areas: frontal cortices http://www.nature.com/neuro/journal/v5/n3/fig_tab/nn0302-190_F1.html

7. Competition or Cooperation • Allies in social groups ensure access to resources and protection… but… • Neocortex size is also correlated with tactical deception

8. Competition or Cooperation • Tactical deception: acts or behaviors that deliberately mislead others; a form of Machiavellian intelligence • Machiavellian or Social Intelligence Hypothesis(read particularly the last few paragraphs) • Machiavelli defined Rhesus macaques; from: http://scienceblogs.com/zooillogix/Langurs%20Fighting.jpg

9. Competition or Cooperation • Others argue in favor of expedience • Primates have the ability to adjust competitive and cooperative behaviors as needed • Larger neocortex: cooperation stimulates reward centers located in this part of the brain Bonobos; from: http://www.primates.com/bonobos/wild-bonobos.jpg

10. Memory • A larger neocortex has ecological advantages • Memory: remembering where food is located, how to extract food

11. Allometry • 2 traits can be related in 2 ways: • Isometrically: 2 variables increase or decrease in direct proportion to one another • Allometrically: 2 variables increase or decrease at different rates • e.g., hominid brain size relative to body size beginning around 2-3 mya

12. Body Allometry: Diet • Basal Metabolic Rate: BMR • Rate at which energy is used to maintain bodily functions at rest

13. Allometry: Body and Brain • BMR (and brain size): allometrically related to body weight • Greater weight = lower metabolism = eating more lower energy foods (e.g., gorillas are folivores, top photo) • Lesser weight = higher metabolism = eating more high energy foods (e.g., chimps favor fruit (bottom photo), nuts)

14. Allometry: Body and Brain • Gorillas: larger bodied, smaller brain • Chimpanzees: smaller bodied, larger brain • Brains: require high amounts of energy to run • 2% of body weight • 20% of energy to run

15. Why bigger or smaller brains? • Metabolic rates might constrain brain size Or • Skills needed to find high energy foods might result in selection for bigger brains

16. Jarman/Bell Principle • Originally explained antelope behavior, but applies to primates… • Relationship between body size, metabolic rate, and food quality

17. Life Histories • Larger brains relate to extended life histories • Social consequences? • Long infant dependency allows for more time to develop socially Far right: collared lemurs Near right: macaques

18. Life Histories • Presocial: animals well-developed at birth • Altricial: animals under-developed at birth; long dependency (see Table 2.1 page 43)

19. Jarman/Bell Principle and Sexual Dimorphism • Body size and physical differences between the sexes • Within the same species, when compared to females, larger males: • Require more time to develop • Have a greater dietary intake • Spend different amounts of time eating • May eat different types of foods

20. The End Next topic: More primate morphological traits