17. primate evolution Flashcards
what is a primate?
an animal of any order that is distinguished by having hands, feet similar to hands, forward facing eyes, and typically being tree dwellers
what are characteristics of hands/feet in primates?
- pentadactyl
- nails instead of claws
- grasping fingers and toes, friction ridges for gripping
- opposable first digit
what are characteristics of eyes in primates?
- forward facing for stereoscopic vision
- most able to distinguish colour
characteristic of smell in primates
very poor sense of smell
characteristics of teeth in primates
four incisors in both upper and lower jaw
characteristics of the brain in primates?
large and complex
cerebral size increases as primates become more highly evolved
characteristics of reproduction in primates?
not restricted to breeding season
rhythmical sexual cycle
usually only one offspring at a time
long period of parental care for offspring
what are limbs like in primates?
tend to be unspecialised
they are pentadactyl (five digits on each limb)
digits are highly mobile
What is the evolutionary trend towards digits?
they increase in ability to move the digits independently of each other- most highly developed digits are the thumb and big toe
do all primate have opposable first digits?
yes
the degreee of opposability varies between species and depends on relative length of first digit
humans only primate that doesnt have opposable big toe but have great opposability with thumb due to lng length
Do primates have nails or claws?
nails instead to improve grasping action, nails evolved from claws (some primates still have singular claws)
why do the end of digits have sense receptors?
so they can grip and manipulate objects
tactile pads under the surface evolved with nails and developed small ridges to increase grip between the ends of the digits and an object - friction ridges vary between individuals and species
how does dentition change between primates?
the number of teeth and their structure
changes to deciduous and permenant sets of teeth that each perform different functions
has the number of teeth increased or decreased through evolution
decreased compared to early mammals, related to the gradual reduction in size of the face and jaw
What teeth size has been reduced in evolution of primates?
the canines and the diastema
how have the molars changed?
little change
movement from 4 to 5 cusps in humans, presumably to have evolved due to fruit diet of the apes
How has vision changed through evolution?
- increasing emphasis on vision accompanied by a decreasing reliance on olfaction accompanied by change in the overall shape of the skull
What do forward facing eyes allow for?
fully stereoscopic vision, with fields of vision that overlap so distance can be judged accurately, narrows field of view (compensated by development of highly mobile head and neck)
What are the general tendency for facial portions through evolution?
region around nose and snout become smaller and flatter
What do the rods and cones allow primates to see?
- see in dim light
- colour and visual discrimination for colour vision
Have nerves connecting sight to brain improved or deteriorated in primates?
improved so vision is more acute in each eye, coordination improves, enhanced 3D vision
How has the eye socket changed in primates?
developed to provide protection, bone closing in on the sides of the socket as the eyes face forward
How has the cerebral cortex changed in primates?
cerebrum has progressively increased in size, as the outer cortex is associated with high thought functions necessary to cope with changes in the environment, general trend of an expansion and reorganisation of the brain with resultant consequences in behaviour
Effects of the larger cerebral cortex size?
- large brains for body size the result of tree-dwelling environment and high natural selection pressures which favoured more accurate visual and tactile perception along with better coordination between sensory stimuli and muscle response
- reliance on vision creates a large amount of complex sensory information, resulting i expansion of cerebral cortex
- convultions enable greater SA of the brain
- Enables development of movement, social skills, tool making, greater variety of behavioural responses to meet environemtntal problems
How is primates gestation and parental care different to other animals?
most not restricted to a reproductive season and show a rhytmical sexual cycle, most only have single offspring, associated with long period of growth and maturation
How has the placenta evolved?
becomes more efficient as it takes nourishment from the mothers bloodstream
what is difference in the gestation of primates and other animals?
it is remarkably long in primates compared with other mammals of a similar size and offspring are born immature- requires more care and protection
how many nipples do most primates have?
usually a single pair
what does the late arrival of sexual maturity allow?
due to the limiting number of offspring a female can have during her lifetime, it makes each offspring particularly important- significant time is invested in their care and survival
Why does the extended period of parental care and learning help primates?
enables them to learn techniques and ideas to be passed from one generation to the next
- increases chance of survival
How do humans differ from apes?
in appearance, structure, behavioural functions
relatively hairless
structure of limbs allows for bipedal locomotion
