chapter 17 - primate evolution

Question 1

what is a primate and how are they classified

Answer 1

• a member of an order of mammals (humans, great apes)
• all share characteristics but there are differences between them
• classification is dynamic (constantly changing), new evidence from DNA sequencing have changed this classification

Question 2

what is the binomial system for humans

Answer 2

• kingdom (animals)
• phylum (chordata)
• class (mammalia)
• order (primates)
• family (hominidae)
• subfamily (homininae)
• tribe (hominini)
• genus (homo)
• species (sapiens)

Question 3

who are the great apes

Answer 3

• orangutangs, chimpanzees, gorillas

- closest living relative to humans, share characteristics (including 98% of DNA)

Question 4

describe some of the characteristics of primates

Answer 4

• body: not specialised for particular environment
• limbs: generally unspecialised
• hands / feet: pentadactyl, nails not claws, grasping fingers (friction edges), first digit is opposable
• eyes: forward facing (3D stereoscopic vision), ability to distinguish colour
• sense of smell: poor
• teeth: four incisors
• brain: large and complex, size increases as evolution occurs
• reproduction: not restricted to a breading system / season, long period of parental care

Question 5

what are the examples of evolutionary trends

Answer 5

• digits
• dentition / prognathism
• cerebral cortex

Question 6

describe the evolutionary trend of digits being pentadactyl

Answer 6

• pentadactyl: 5 fingers / toes, variation in size
• nails: not claws, protective shield, don’t require claws for grasping or killing
• fingerprints: small ridges, increased grip, pattern varies between individuals and species
• fingertips: sensory nerve fibres, enhance sense of touch
• great apes: highly mobile, arboreal way of life
• humans: hand is short and broad, short straight fingers, long thin thumb, allows for holding and manipulation of objects

Question 7

describe the evolutionary trend of digits and the precision grip

Answer 7

• humans: have the ability to grasp objects with precision (writing)
• unique contact between index finger and thumb
• presence of truely opposable thumb gives us fine motor skills

Question 8

describe the evolutionary trend of digits being prehensile

Answer 8

• prehensile: grasping, ability to be wrapped around an object
• apes: essential for climbing branches, evolutionary trend towards increasing mobility / ability to move digits independently of one another
• humans: highly mobile digits, enables manipulation of objects with great skill, not used for climbing

Question 9

describe the evolutionary trend of digits being opposable

Answer 9

• opposability: ability of the thumb to touch the tips of all digits on same hand / foot
• degree: varies between species, depends on relative length of fingers and the use of the hands (arboreal / manipulation)
• opposable toe: humans are the only exception of primates, lost opposability when they became weight bearing rather than a grasping appendage
• opposable thumb: humans posses longest thumb of all primates, allows precision grip and manipulation

Question 10

describe the evolutionary trend of dentition and dental formula

Answer 10

• dental formula: number of each type of tooth in 1/4 of jaw
• humans: 2:1:2:3 incisors, canine, premolar, molars x4, 32 teeth, less teeth due to gradual decrease in jaw and face size, uniform
• apes: same number, larger canine important in predator defence, slanting of premolar to allow canine to fit

Question 11

describe the evolutionary trend of dentition and diastema, dental arch and prognathism

Answer 11

• diastema: gap in row of teeth next to canine, apes have diastema teeth / jaw much larger, gap and tooth decreases as jaw has over time
• dental arch: very ‘u’ shaped in great apes, humans is less ‘u’ and shorter to accomodate for increased size of brain and skull
• prognathism (P): large, protruding snouts and jutting jaws, apes need this for olfaction (smell), accomodate for large canines
• humans (P): flat, reduced jaw, smaller teeth and chin, prominent nose, decreased in size to accomodate for change in position / balance of skull and foramen magnum

Question 12

describe the evolutionary trend of dentition and dental cusps

Answer 12

• dental cusps: represents the ‘valleys’ of molars
• humans / apes: have 5 cusps on lower molars (Y-5), useful in identifying ape and human teeth (fossils), thought to have changed due to predominantly fruit diet
• fossils: well preserved due to the hard enamel that helps resist decomposition

Question 13

describe the evolutionary trend of the cerebral cortex, natural selection and the cranium

Answer 13

• natural selection (apes): arboreal environment, favours accurate vision, tactile perception, increased coordination between sensory organs and muscle response
• cranium: skull, increased in size relative to the size of the body and the brain, more rounded in apes and humans

Question 14

describe the evolutionary trend of the cerebral cortex and convolutions

Answer 14

• convolutions: increase SA by 50%
• tool making: requires pre-determined image of what completed tool should look like, humans / chimps have this due to larger brains
• behavioural responses: greater variety to meet an array of environmental problems
• cleaning / grooming: increased relations with relatives, allies and adversaries
• fighting: threats, maintains hierarchy of dominance that pervades primates