Chapter 17: Primate Evolution

Question 1

• Living things are grouped first into kingdoms. Two of the kingdoms are the plants and the animals. Work your way down the hierarchy of animals.
• How can the characteristic of “body” be used to separate primates?
• How can the characteristic of “Limbs” be used to separate primates?
• How can characteristic of “hands/feet” be used to separate primates?
• How can the characteristic of “eyes” be used to separate primates?
• How can “sense of smell” be used to separate primates?
• How can the characteristic of “teeth” be used to separate primates?
• How can the characteristic of “brain” be used to separate primates?
• How can “reproduction” be used to separate primates?
• Why do limbs of primates tend to be unspecialised in structure?
• Why are grasping or prehensile digits essential for primates?
• Differentiate between the terms ‘Prehensile’ and ‘Opposability ‘.
• Why was opposability of human’s big toe lost?

Answer 1

• Animal kingdom->phyla (singular phylum)->classes->orders.
• Not specialised for a particular environment.
• Unspecialised.
• Pentadactyl, nails, grasping phalanges, friction ridges, 1st digit opposable.
• Forward facing for 3D vision and most can distinguish colour.
• Very poor.
• 4 incisors in upper and lower jaw.
• Large, complex, cerebrum size increases as primates evolve.
• Not restricted to a breeding season, rhythmical sexual cycle, usually only 1 offspring at a time and long period of parental care.
• Allows for great diversity in their use.
• For climbing by wrapping the digits around the branches of trees.
• Prehensile: grasping by wrapping around an object. Opposability: 1st digit can move so that it touches all other digits one at a time.
• Became a weight-bearing instead of grasping.

Question 2

• Why did primates lose their claws and obtained nails?
• What are friction ridges?
• Define precision grip
• When searching for human and primate ancestors, why do anthropologists frequently find teeth?
• Describe the shift that occurred in primates from strong reliance on smell to almost complete dependence on vision.
• An evolutionary trend in primates is increased forward facing eyes. What does this allow for?
• Explain the evolution of the structure of eye sockets in primates. Why has this changed?

Answer 2

• Primates climb trees and require grip. Claws limit this as they prevent opposable surfaces from coming together.
• Tactile pads with small ridges under the surface of digits to increase grip between the end of digits and an object.
• The grasping of an object between thumb tip and finger tip.
• The hard enamel covering helps resist decomposition.
• Increased vision is due to arboreal lifestyle and the need to judge distances accurately. Olfactory therefore became less important.
• Total field of view decreases with increasing degree of overlap and stereoscopic vision, allowing distances to be judged more accurately. .
• Bone has gradually closed in the side and rear of the socket because of increased importance of vision and so protection for the eyes.

Question 3

• Describe the evolutionary trend in primates concerning the digits..
• Explain the evolutionary trend of dentition in order primates
• Explain the evolutionary trend of visual area of brain with vision in order primates.
• List the advantages of having a large number of convolutions in the cerebrum of the brain.

Answer 3

• Increase mobility and opposability of the thumb. Other digits became longer and more mobile.
• 36 teeth in lemurs and lorises (2:1:3:3), New world monkeys have same dental formula, but show an evolutionary trend for a smaller 3rd molar and often absent in these monkeys, 32 teeth in old world monkeys, apes and humans (2:1:2:3). Monkeys and apes- large projecting canines with diastema. 4 cusped molars in monkeys; 5 cusps in apes and humans.
• Increasing proportion of the cerebrum devoted to vision.
• Greater surface area in the cerebral cortex, and therefore a greater number of neurones. This is allows for higher order brain functioning and results in higher-order skills in primates eg tool making and complex behavioural responses.

Question 4

• Explain the evolutionary trend of gestation in order primates.
• Explain the evolutionary trend of dependence with the development in order primates.
• Explain the evolutionary trend of sexual maturity with the development in order primates.
• To which family do humans belong? Who shares this family with us?
• List the 15 characteristics that tend to be shared by all primates.
• Animals that have an acute sense of smell tend to have larger snouts than those that do not rely as heavily on smell. Humans have a reduced snout and our sense of smell is not as good as that of many other primates. What other sense organ has compensated for this reduction? How do you think this may have evolved?
• Explain why tarsiers only possess rods, whereas most primates have both rods and cones in the retina of the eye.

Answer 4

• Increasing length of time between fertilisation and birth
• Increasing length of time offspring are dependent on parents.
• Increasingly later development of sexual maturity.
• Hominidae with great apes eg chimpanzees and gorillas
  1. Large complex brain 2.Forward-facing eyes 3.stereoscopic and colour vision 4.Poor sense of smell 5.four incisors in both upper and lower jaw 6.Non-specialised body 7.Unspecialised limbs 8.Pentadactyl 9.Nails instead of claws 10.Grasping digits with friction ridges 11.Opposable first digit 12.No restricted breeding season 13.Rhythmical sexual cycle 14.Usually one offspring at a time 15.Long period of parental care after birth.
• In humans the eyes are well developed. is may have developed as primates became arboreal and needed to move through trees. Good eyesight was needed to judge distance for vertical clinging and leaping, and for brachiation. An acute sense of smell became less important for survival.
• The rods are important for vision in dim light, while cones are concerned with fine visual discrimination and colour vision. Because Tarsiers are nocturnal, less light is available and the possession of cones in the retina would be of no use.

Question 5

• Explain why the skull of an ape has a proportionately larger cranium than that of lemurs and monkeys.
• Why would it be necessary for the placenta of apes and humans to be more efficient than that of other primates?
• List 3 advantages and disadvantages for the trend of increased gestation period.
• Explain how life in trees would contribute to the evolution of vision.
  -Explain how life in trees would contribute to the evolution of prehensile digits.
  -Explain how life in trees would contribute to the evolution of intelligence.

Answer 5

-Due to increased brain size, resulting in the evolution of better vision, memory, reasoning and manipulative abilities.
-The placenta of apes and humans needs to be more efficient as the gestation time is longer and the foetus is larger.
-AD: Allows development to occur with parental protection, longer period of learning and increased rate of offspring survival.
DIS: Increased risk of death from predators while parents are looking after offspring, decreased number of offspring, parents may be exposed to risk when feeding/protecting offspring.
-Living in trees requires greater vision so eyes became more forward-facing to improve stereoscopic vision through the process of natural selection.
-Prehensile digits may have developed as tree-dwelling primates would need to grasp branches when moving between trees and climbing. The digits would also be needed for grasping fruit and seeds from trees and for holding their young while in trees.
-Arboreal lifestyle requires primates to solve problems such as finding food and shelter. Communication would have been more difficult and contributed to the need for more problem-solving ability.