Flashcards in Chapter 19 - Primate Evolution Deck (40):
What is the Binomial system?
-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.
What are the few sources of evidence that can be used in trying to develop an understanding of how human characteristics evolved?
1. Comparative anatomy of the primates
2. Comparative biochemistry
3. Behaviour of Living Primates
4. Fossils of Primates
A hierarchy is a series of groups that move from broad general categories to narrow specific ones.
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.
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.
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.
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.
How did the classification of Primates come about?
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.
Living in trees
e.g. some monkeys do.
Give a summary of the characteristics of members of the order Primates.
1. Body - Not specialised for a particular environment.
2. Limbs - Generally unspecialised.
- Pentadactyl - five fingers or toes
- Nails instead of claws
- Grasping fingers and toes with friction ridges for gripping
- First digit opposable
- 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.
- Large and complex
- Cerebrum size increases as primates become more highly evolved.
- Not restricted to a breeding season
- Rhythmical sexual cycle
- Usually only one offspring at a time
- Long period of parental care for offspring.
What are Digits ?
A finger, thumb or toe.
=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.
What are the most highly developed digits?
-The thumb and the big toe.
-Not only are they independent, but they are also opposable in the majority of primates.
Means that the first digit can be moved in such a way that it can touch each of the other digits.
What does the degree of opposability depend on?
-Varies from species to species and depends on the relative length of the first digit compared with the other four.
Why is our big toe not opposable at all?
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.
Why do primates have nails instead of claws on their fingers and toes?
-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"
Explain the further development of the claws.
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.
What is a precision grip?
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.
Define Dental Formula.
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.
What is the dental formula for Primitive mammals?
-That is, 3 incisors, 1 canine, 4 premolars and 3 molars on each side of each jaw - a total of 44 teeth.
Why have Natural selection resulted in a decrease in the number of teeth in primates when compared with early mammals?
This is probably related to the gradual reduction in the size of the face and jaw that has occurred in primates.
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.
Dentition in general terms.
-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.
How do primates gradually evolve with an arboreal life?
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.
the action or capacity of smelling; the sense of smell.
What has forward-facing eyes allow?
Stereoscopic Vision (3D).
What are the benefits and disadvantage of a Stereoscopic vision?
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.
Most primates have both rods and cones in the retina of their eyes. Explain its functions.
Rods - important for vision in dim light.
Cones - Concerned with fine visual discrimination and with colour vision (nocturnal primates, such as tarsier).
Why has the nerves connecting these rods and cones to the brain improved?
-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.
With the increasing importance of vision to primates...
The region of the brain concerned with the interpretation of visual information increased in size while that concerned with olfaction decreased.
What is the function of the Cerebral Cortex?
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.
Why do primates have large brains for their body size ?
-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.
How has the increase in size of the cerebral cortex affected on the way primates live?
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.
Why is Tool making such significance to the human evolution?
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.
Explain why Primates are placental mammals ?
Because the offspring developing inside the mother's body, taking nourishment from her bloodstream via a special structure called the placenta.
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.
Why do apes and humans have more efficient placentas compared to other primates?
This is because our placenta allows a closer contact between the blood supplies of the mother and the developing offspring.
Define Gestation .
It is the time between conception and birth and it is remarkably long in primates compared with other mammals of similar size.