Chapter 12 - Trends in hominid evolution Flashcards
sources of evidence used to show how human characteristics evolved
- Comparative anatomy
- Comparative biochemistry (DNA and proteins)
- Behaviour of living primates
- Fossils of primates
What are the classification levels of humans within the primate order
Order - Primates Superfamily - Hominoidea Family - Hominidae Subfamily - Homininae Tribe - Hominini Genus - Homo Species - Sapiens
Body characteristics of primates
Not specialised for a particular environment
limb characteristics of primates
Generally unspecialised
hand/feet characteristics of primates
- unspecialised in structure, allows for great diversity in use
- Pentadactyl
- Nails instead of claws
- Grasping fingers and toes with friction ridges for gripping
- First digit opposable
eye characteristics of primates
- Forward facing for 3D (stereoscopic) vision
- Most are able to distinguish colour
smell characteristics of primates
very poor
teeth characteristics of primates
four incisors in both the upper and lower jaw
Brain characteristics of primates
- Large and complex
- Cerebrum size increases as primates become more highly evolved
Reproduction characteristics of primates
- 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 the primates classified as great apes
Humans, Chimpanzees, Orangutans and Gorillas
Arboreal
living in trees
opposable
the ability to use the thumb to tough the tips of each other digit
Hominidae
family including humans and the great apes (chimpanzees, gorillas, orangutans and bonobos)
Hominid
A member of the family hominidae
Hominin
A member of the tribe Hominini (humans past and present)
what are the characteristics of species in the hominidae family
- A larger, more complex brain than other primates. Enables an increased cognitive ability
- Five cusps in the molar teeth of the lower jaw
- Arms that can freely rotate at the shoulder
- Wide shallow chest cavity
- No external tail
- An appendix
- Diurnal
what do the variations that reflect changes in the DNA nucleotide sequence during evolution of hominids relate to
- Relative size of the cerebral cortex
- Mobility of the digits
- Locomotion (adaptations to bipedalism and qaudrupedalism
- Prognathism and dentition
what is the most significant feature of primate evolution
The increase in size and complexity of the cerebrum
Cerebrum
The largest part of the brain, made up of left and right hemispheres
Cerebral cortex
The outer layer of the cerebrum, made up of grey matter. Region of brain concerned with higher functions (vision, memory, reasoning and manipulative ability)
what caused the brains of primates to increase in size
The pressure of natural selection in an arboreal environment would have favoured a more accurate visual and tactile perception along with better coordination between such sensory stimuli and any muscular response
Endocast
An impression of the inside of the brain case, either artificial or natural, made of rock or some other solid material
Cranium capacity
The volume of that part of the skull that is occupied by the brain
what is the average brain size of humans compared to other apes
1350cm^3 in adulthood compared to other apes which average between 400 and 500 cm^3
which part of the brain has the greatest enlargement in surface area compared to apes
The frontal lobe. In humans making up 47% of the cortical surface, whereas in apes it only comprises 33%
what are the benefits to an increase in size of the cerebral cortex
- Enabled primates to move about and locate food
- Develop social skills
- Tool making (most highly developed in humans)
- Greater variety of behavioural responses to meet a wide array of environmental problems
cranium
The part of the skull that contains the brain
Pentadactyl
Describes a limb with five fingers or toes
prehensile
refers to the digits of a hand or foot that can grasp an object
opposability
The ability to use the thumb to touch the tips of each of the other digits on the hand
what is the evolutionary trend of the digits
Towards increasing ability to move the digits independently of one another
precision grip
The grasping of an object between thumb tip and fingertip (eg holding pencil when writing)
power grip
Force applied by the fingers and thumb towards the palm to transmit force to an object
quadrapedalism
Walking on four legs
bipedalism
walking on two legs
foramen magnum
the opening beneath the cranium through which the spinal cord passes. During evolution has slowly moved forward to become more central, allowing skull to balance on top of the vertebral column so large neck muscles are not required
curvature of spinal column
The smooth ‘C’ shaped curve seen in spines of apes has evolved to an ‘S’ shaped curve in humans. This improves body balance in the upright position and enables the head to balance on top of the neck
lumbar
Describes the lower region of the spinal column, lumbar vertebrae support the lower back, achieving a double curvature
Prognathism
having a protruding jaw. Reduction of prognathism in evolution is important in allowing the skull to balance on the top of the spine because the weight in front of the foramen magnum is approximately equal to the weight behind it.
compare pelvis in humans and apes
The pelvis in humans is broader and shorter from top to bottom than in apes and bowl shaped
importance of bowl shaped pelvis in humans
Supports abdominal organs when standing erect, proving greater stability for bipedal locomotion and supports developing foetus during pregnancy in females
acetabulum
the socket of the pelvis in which the head of the thigh bone (femur) fits
carrying angle
Because the pelvis is broad, the hip sockets are wide apart, but the femurs tend to converge towards the knees. This arrangement of the femurs forms an angle to the vertical, called the carrying angle
adaptions of the knee for bipedalism
The wight of the body is transmitted down the outside of the femur to the knee. The knee joint is a two part hinge joint, with one hinge on either side of the ligaments in the middle of the joint. Because the weight is transmitted to the outer hinge, it is larger and stronger
Longitudinal arch
The arch of the bones of the foot, running from front to back
Transverse arch
The arch of the bones of the foot, running from side to side (humans have longitudinal and transverse arch, gorillas only have longitudinal)
leg adaptations for bipedalism
Longer than arms, contributing to a low centre of gravity. carrying angle allows weight of body to be kept close to the central axis
Muscle tone
Partial contraction of muscles to support the spine, hip, knee and ankle
What are the evolutionary changes that allow bipedalism in humans
- Central foramen magnum
- ‘S’ shaped spine
- Non protruding jaw
- Broad pelvis
- Carrying angle of the femur
- Knee that is larger on the outside
- Long legs
- Longitudinal and transverse arches on the feet
- Muscle tone
why have the hominins lost the opposability of the big toe
the human foot has evolved into a weight bearing appendage rather than a grasping one
Striding gait
A way of walking in which the hip and knee are fully extended
advantages of bipedalism
- More energy efficient
- Leaves hands free to use tools and carry items
- The upright stance achieves greater height and thus ability to see further
- Upright stance means less of the body exposed to sunlight
- Upright stance increases exposure to breezes, increasing cooling mechanisms
dental formula
A formula that gives the number of each type of tooth in one quarter of the jaw
Diastema
A gap in a row of teeth, usually refers to a gap next the the canine teeth in primates, with canine teeth that are much longer than the other teeth
Dental arcade
The shape of the pattern made by the teeth as they are set in the jaw. ‘U’ pattern in apes, parabolic in humans
Brow ridge
A ridge of bone above the eye sockets of the skull, as the size of the frontal lobe has increases, the brain occupies a larger volume, extending the cranium forward and reducing the brow ridges
