Chapter 19 - Primate Evolution

Question 1

What is the Binomial system?

Answer 1

• The binomial system uses the generic (genus) and specific (species) names for the scientific name of a species.
• Using this system, humans are referred to as Homo sapiens, chimpanzees as Pan troglodytes, and gorillas as Gorilla gorilla.

Question 2

What are the few sources of evidence that can be used in trying to develop an understanding of how human characteristics evolved?

Answer 2

1. Comparative anatomy of the primates
2. Comparative biochemistry
3. Behaviour of Living Primates
4. Fossils of Primates

Question 3

Define Hierarchy.

Answer 3

A hierarchy is a series of groups that move from broad general categories to narrow specific ones.

Question 4

1. Kingdom
2. Phylum
3. Subhylum
4. Class

Answer 4

1. Animalia - the Animals
2. Chordata - Chordates include sea squirts, acorn worms, fish, frogs, lizards, snakes, birds, platypuses, kangaroos, bats, rabbits, dogs, elephants, horses, tarsiers, lemurs, monkeys, apes and humans.
3. Vertebrata - Vertebrates include fish, frogs, lizards, snakes, birds, platypuses, kangaroos, bats, humans, etc.
4. Mammalia - Mammals include platypuses, humans, rabbits, etc.

Question 5

1. Order
2. Suborder
3. Infraorder
4. Parvorder

Answer 5

1. Primates - Primates include tarsiers, lemurs, lorises, monkeys, apes and humans.
2. Haplorrhini - Haplorrhini include tarsiers, monkeys, apes and humans.
3. Simiiformes - Simiiformes include monkeys, apes and humans.
4. Catarrhini - Catarrhines include Old World monkeys, apes and humans.

Question 6

1. Superfamily
2. Family
3. Subfamily

Answer 6

1. Hominoidea - Hominoids include apes and humans.
2. Hominidae - Hominids include all modern and extinct orang-utans, gorillas, chimpanzees and humans.
3. Homininae - Hominines include all modern and extinct chimpanzees and humans.

Question 7

1. Tribe*
2. Genus
3. Species

Answer 7

1. Hominini - Homininis include extinct ancestors of humans and modern humans.
2. Homo -Some extinct ancestors of humans and modern humans.
3. Sapiens - Modern humans.

Question 8

How did the classification of Primates come about?

Answer 8

1. Earlier classifications divided the primates into 2 groups - prosimians (primitive primates) and the anthropoids (monkeys, apes and humans).
2. In those classifications, the tarsiers were included with the prosimians.
3. Many scientists now consider the tarsiers to be more closely related to monkeys, apes and humans.
4. They divide the order Primates into the suborders Strepsirrhini and Haplorrhini.
5. Strepsirrhini contain the non-tarsier prosimians, while the Haplorrhini include the tarsiers, monkeys, apes and humans.

Question 9

Define arboreal.

Answer 9

Living in trees

e.g. some monkeys do.

Question 10

Give a summary of the characteristics of members of the order Primates.

Answer 10

1. Body - Not specialised for a particular environment.
2. Limbs - Generally unspecialised.
3. Hands/feet
   - Pentadactyl - five fingers or toes
   - Nails instead of claws
   - Grasping fingers and toes with friction ridges for gripping
   - First digit opposable
4. Eyes
   - Forward facing for 3D vision (stereoscopic)
   - Most are able to distinguish colour.
5. Sense of Smell - Very poor
6. Teeth - 4 incisors in both the upper and lower jaw.
7. Brain
   - Large and complex
   - Cerebrum size increases as primates become more highly evolved.
8. Reproduction
   - Not restricted to a breeding season
   - Rhythmical sexual cycle
   - Usually only one offspring at a time
   - Long period of parental care for offspring.

Question 11

What are Digits ?

Answer 11

A finger, thumb or toe.

Question 12

Define Pentadactyl.

Answer 12

=Which means they have 5 digits on each limb.

• The digits are highly mobile, a feature that can be related to the arboreal way of life of primate ancestors.
• Grasping, or prehensile, digits were essential for climbing by wrapping the digits around the branches of trees.
• The evolutionary trend is toward increasing ability to move the digits independently of one another.

Question 13

What are the most highly developed digits?

Answer 13

• The thumb and the big toe.

- Not only are they independent, but they are also opposable in the majority of primates.

Question 14

Define Opposability.

Answer 14

Means that the first digit can be moved in such a way that it can touch each of the other digits.

Question 15

What does the degree of opposability depend on?

Answer 15

-Varies from species to species and depends on the relative length of the first digit compared with the other four.

Question 16

Why is our big toe not opposable at all?

Answer 16

Opposability was lost when the human foot became a weight-bearing rather than a grasping appendage.

-However, humans do posses the longest thumb of all primates and this has contributed considerably to our ability to manipulate objects with our hands.

Question 17

Why do primates have nails instead of claws on their fingers and toes?

Answer 17

• Claws limit grasping, as they prevent the opposable surfaces from coming together.
• Nails evolved from claws that became flattened.
• Some of the evolutionarily less advanced primates still possess claws.
  e. g. aye-ayes have claws on all their digits except the big toe and lemurs have a claw on their second toe. “toilet-claw”

Question 18

Explain the further development of the claws.

Answer 18

1. The ends of the digits have sense receptors so that the digits and tactile pads on the under surface evolved together.
2. These pads developed small ridges to increase the grip between the ends of the digits and an object.
   - These are called friction ridges, or fingerprints, and the pattern varies between individuals and from species to species.

Question 19

What is a precision grip?

Answer 19

Such as that used for holding a pencil when writing, or a needle when sewing, is one of the hallmarks of being human, amount of contact between the index finger and thumb.

• This provides humans with the ability to effectively handle small or delicate objects.
• The precision grip requires the presence of a truly opposable thumb and is also seen in Old World monkeys, particularly the ground-living baboons, mandrills and macaques.
• These monkeys are 2nd only to humans in their manipulative abilities.

Question 20

Define Dental Formula.

Answer 20

It is the number of each type of tooth that a species has.

-The formula gives the number of each type of tooth in one quarter of the jaw.

Question 21

What is the dental formula for Primitive mammals?

Answer 21

3: 1:4:3

- That is, 3 incisors, 1 canine, 4 premolars and 3 molars on each side of each jaw - a total of 44 teeth.

Question 22

Why have Natural selection resulted in a decrease in the number of teeth in primates when compared with early mammals?

Answer 22

This is probably related to the gradual reduction in the size of the face and jaw that has occurred in primates.

Question 23

Define Diastema.

Answer 23

A gap in a row of teeth; usually refers to a gap next to the canine teeth that occurs in primates with canine teeth that are much longer than the other teeth.

Question 24

Dentition in general terms.

Answer 24

• In general terms, the molar teeth of primates show little change from those of early mammals.
• This may be related to the somewhat generalised diets that most primates have.

Question 25

How do primates gradually evolve with an arboreal life?

Answer 25

An increasing emphasis on vision accompanied by a decreasing reliance on the sense of smell, or olfaction.

• This shift in sensory orientation was accompanied by an overall change in the shape of the skull compared with other mammals.
• There has been a general tendency for the facial portions of the skull, particularly the region around the nose and snout, to become smaller and flatter, while the region that houses the brain has become larger.
• Observable behaviours in living primates supports this shift.

Question 26

Define Olfaction.

Answer 26

the action or capacity of smelling; the sense of smell.

Question 27

What has forward-facing eyes allow?

Answer 27

Stereoscopic Vision (3D).

Question 28

What are the benefits and disadvantage of a Stereoscopic vision?

Answer 28

1. This enables the fields of vision of each eye to overlap, so that distances can be judged accurately.
2. Primates have compensated for this by evolving a highly mobile head and neck.

Question 29

Most primates have both rods and cones in the retina of their eyes. Explain its functions.

Answer 29

Rods - important for vision in dim light.

Cones - Concerned with fine visual discrimination and with colour vision (nocturnal primates, such as tarsier).

Question 30

Why has the nerves connecting these rods and cones to the brain improved?

Answer 30

• So that the vision is more acute in each eye and the coordination between the two eyes is far better than in other mammals.
• These modifications has also enhanced stereoscopic vision.

Question 31

With the increasing importance of vision to primates…

Answer 31

The region of the brain concerned with the interpretation of visual information increased in size while that concerned with olfaction decreased.

Question 32

What is the function of the Cerebral Cortex?

Answer 32

It is the region in the brain that is concerned with so-called higher functions - vision, memory, reasoning and manipulative ability - functions necessary to cope successfully with changes in the environment.

Question 33

Why do primates have large brains for their body size ?

Answer 33

• Again this seems to be a consequence of their tree-dwelling environment.
• The pressure of natural selection in an arboreal environment would have favoured more accurate visual and tactile perception along with better coordination between such sensory stimuli and any muscular response.
• Unlike smell or hearing, the reliance on vision to move about, and to locate and manipulate food,generates a large amount of complex sensory information that has to be processed and stored.
• Progressive expansion of the cerebral cortex has resulted in it becoming so large that it covers the rest of the brain.

Question 34

How has the increase in size of the cerebral cortex affected on the way primates live?

Answer 34

1. It has enabled them to move about and locate food, and to develop special skills
2. One of the most significant of these is tool making.
3. In addition, an increase in the size of the cerebral cortex would have allowed a greater variety of behavioural responses to meet a wide array of environmental problems.

Question 35

Why is Tool making such significance to the human evolution?

Answer 35

Tool making, as opposed to tool use, involves a predetermined image of what the completed tool should look like - something only possible with a highly developed brain.

Question 36

Explain why Primates are placental mammals ?

Answer 36

Because the offspring developing inside the mother’s body, taking nourishment from her bloodstream via a special structure called the placenta.

Question 37

Define placenta.

Answer 37

The placenta is attached to the wall of the uterus, or womb, the structure in which an embryo develops until it is ready to be born.

Question 38

Why do apes and humans have more efficient placentas compared to other primates?

Answer 38

This is because our placenta allows a closer contact between the blood supplies of the mother and the developing offspring.

Question 39

Define Gestation .

Answer 39

It is the time between conception and birth and it is remarkably long in primates compared with other mammals of similar size.

Question 40

Explain Gestation and Parental care evolution trend thingy mabob in humans.

Answer 40

• Along with this trend in the lengthening of the period of growth and development, there is an associated delay in maturation.
• The fact that apes and humans have such a long period of maturation means that their period of learning is also greatly extended.
• This is an important facet of a primate’s life as it enables ideas and techniques to be passed on from one generation to the next.