Human Bio Ch 12 Flashcards
What evidence can be used to show how characteristics have evolved?
- Comparative anatomy
- Comparative biochemistry, including DNA and proteins
- Behaviour of living primates
- Fossils of primates.
The great apes are the most recent common ancestor to humans.
What are the levels of classification?
- Subfamily - Homininae (all modern and extinct chimps, gorillas and humans)
- Tribe - Hominini (extinct ancestors of humans and modern humans)
- Genus - Homo (extinct ancestors of humans and modern humans)
- Species - Sapiens (Homo sapiens are modern humans)
What are the main characteristic of primates?
Primates - humans, apes(gorilla, chimps, bonobos and orangutans), monkeys, tarsiers, lorises and lemurs
- Body - not specialised for a particular environment
- Limbs - generally unspecialised
- Hands/feet - pentadactyl (5 fingers/toes), nails instead of claws, grasping fingers and toes with friction ridges for gripping, first digit opposable (thumb).
- Eyes - forward facing for three dimensional vision, most are able to distinguish colour.
- Sense of smell - very poor
- Teeth - 4 incisors in both the upper and lower jaw (4 cusps on top, 5 on bottom)
- Brain - large and complex, cerebrum size increases as primates become more highly evolved.
- Reproduction - not restricted to a breeding season, rhythmical sexual cycle, usually only one offspring at a time, long period of parental care for offpring.
What is the hominidae family?
Includes humans, orangutans, gorillas, chimpanzees, and bonobos. These are all members of the hominidae family and are called hominins.
What characteristic do the hominidae family share and what characteristics are different?
They share some characteristics that include:
- a larger more complex brain than other primates
- 5 cusps in the teeth of the lower jaw
- arms that can freely rotate at the shoulder
- a wide, shallow chest cavity
- no external tale
- an appendix
- being active during the day (diurnal)
However, there are some changes that have occurred due to changes in DNA nucleotide sequences during evolution. These include:
- relative size of the cerebral cortex
- mobility of the digits
- locomotion of the digits (adaptations to bipedalism and quadrupedalism)
- prognathism and dentition.
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Why was there increase in brain size across the primates?
There was an increase in the cerebral cortex so that animals could withstand the pressures of natural selection and would be able to have more accurate visual and tactile perception along with better coordination between such sensory stimuli and any muscular response.
The brain sizes are as follows:
- Lemur = 24 cm3
- Monkey = 108 cm3
- Chimpanzee = 393 cm3
- Human = 1350 cm3
As the brains evolve the convolutions are greatly increased which increases the surface area.
What is the mobility of digits for the primates?
Pentadactyl which mean they have 5 digits on each limb, which are highly mobile.
Grasping or prehensile digits were essential for climbing trees.
The evolutionary trend is towards increasing ability to move the digits independently of one another.
Not only are they independent but they are also opposable, which means that the first digit can be moved in such a way that it can touch the other digits.
The foot lost opposability due to the upright stance.
What is a precision grip and a power grip?
Precision - the grasping of an object between thumb tip and fingertip, like holding a pen when writing.
Power - Force applied by the fingers and thumb towards the palm to transmit force to an object.
What are the major adaptations that caused the change from quadrupedalism to bipedalism during natural selection? (x9)
- Foramen magnum - located centrally in the base of the cranium allowing the skull to balance on top of the vertebral column.
- Jaw bone - small and non-protruding (prognathism), enabling the skull to balance on top of the vertebral column, weight is evenly distributed between front and back.
- Vertebral column - lumbar vertebrae have an s-shaped spine rather than c-shaped that brings the vertebral column directly under the centre of the skull
- Pelvis - broad and shallow from top to bottom. Provides support for he abdominal organs, the attachment of femurs as far apart contributing to the carrying angle. Females are slightly wider for childbirth.
- Femurs - large head of the femur contributes to the carrying angle (the arrangement of the thigh bones to form an angle to the vertical), which makes sure that the weight distribution remains close to the central axis of the body when walking.
- Knee joint - outer hinge larger and stronger to take the weight of the body, knee is able to be straightened.
- Legs - longer than arms, contributing to a low centre of gravity. Carrying angle allows the weight of the body to be kept close to the central axis.
- Foot - large heel and aligned (non-opposable) big toe form a pedestal on which the body is supported. Foot have both longitudinal and transverse arches.
- Muscle tone - partial contraction of muscles to support the spine, hip, knee and ankle.
What is a striding gate?
Walking upright in such a way that the hip and knee are fully straightened is referred to as a striding gate.
Stridig gate: a way in walking in which the hip and knee are fully extended.
When the foot hits the ground the weight is transmitted from the heel along the outside of the foot as far as the ball, it crosses the ball of the foot (via transverse arch) and is finally borne by the big toe.
What are the advantages of bipedalsim?
- more energy efficient means of moving
- it leaves the hands free to use tools
- it leaves the hands free to carry items
- the upright stance achieves greater height
- the upright stance means that less of the body is exposed to sunlight
- the upright stance increased exposure to breezes, increasing cooling mechanisms.
How has the number and shape of teeth changed/evolved?
Primitive mammals had a dental formula of 3:1:4:3. This means there were 44 teeth:
- 3 incisors
- 1 canine
- 4 premolars
- 3 molars.
Natural selection has resulted in a decreased number of teeth in primates. this is due to the gradual reduction in the size of the face and jaw. Primates (old world monkeys, apes and humans) now have a dental formula of 2:1:2:3. This means they have 32 teeth:
- 2 incisors
- 1 canine
- 2 premolars
- 3 molars
However the shape and structure of the teeth in the old world monkeys and apes is different to humans. Old world monkeys and apes have large, sharply pointed and projecting canines, such large canines have required modifications of adjacent teeth so that the mouth can be closed. Most primates now with large canines have diastema, which is a gap between the upper second incisor and the upper canine to accommodate the large lower canine.
The molars of apes and humans have 5 cusps on the lower molars and 4 cusps on the upper molars.
Because humans have smaller incisors and canines the dental arcade is different to the ape. The ape has a U-shaped dental arcade whereas humans have a parabolic-shaped dental arcade.
What is prognathism and bow ridges?
Prognathism is the protrusion of the jaw, with evolution the tooth size gradually lead to a flatter face development of a chin and a prominent nose which reduced prognathism significantly. This was also due to bipedalism, as a flatter face shifts the weight to a more central position.
Non-human apes also have a distinct brow ridge which is a ridge bone above the eye sockets, with evolution became a flatter face which reduced the brow ridges significantly.
