Evolution Flashcards
12 Characteristics of a primate
Characteristics:
- grasping fingers and toes
- first digit opposable
- pentadactly
- nails instead of claws
- poor sense of smell
- four incisors both upper and lower jaw
- brain large and complex
- cerebrum size increases as primates evolve
- not restricted to breeding season
- rhythmic sexual cycle
- one offspring at a time
- long period of parental for offspring
Order of primate evolutonary changes
- Noticeable trend from lemurs → monkey → ape → humans
6 Changes in size of cerebal cortex in primates
- One of most significant features of primate evolution.
- Part of brain responsible for complex function (vision, memory, reasoning, manipulative ability) –> progressively increased in size.
- Natural selection explains increasing size of brain relative to size of body
- Apes & humans – strong pattern of convolutions.
- Brain becomes larger and more convoluted.
- Allows development of skills and response to environmental problems.
Describe 9 trend in mobility of digits in primate
- Increasing mobility and ability to move digits independently of one another - highly mobile
- First digit opposable and increasing length results in increased effectiveness of opposability
-opposability of big toe lost in humans when foot became weight-bearing rather than grasping - maintain longest thumb increasing ability to manipulate objects with hands.
- claws flattening to nails allowing grip in trees
- sense receptors under nails and friction ridges on ends of digits for grip/manipulating objects.
- higher primates have nails on all digits
- Highly mobile digits allow skilful manipulation of objects – e.g. precision grip.
- Amount of contact between index and thumb unique in humans enables most effectively handling of small objects
What is an adaptation?
any characteristic that helps an organism survive and reproduce in its natural environment.
What is the foramen magnum and what is the position
- Hole in skull where spinal cord joins brain.
- Located centrally in base of cranium
in humans - towards back of skull in quadrupeds.
- Gradually moved forward to balance on top of vertebral column (bears weight)
- Apes require large neck muscles to hold head in position.
4 Adaptations toCurvature of spinal column
- Double curvature in humans (S-shape)
- Wedge-shaped vertebrae (from forward to back) in lumbar region form S shaped curve.
- improves body balance in upright position & enables head to balance on neck.
- S shapes curve brings vertebrae directly under centre of gravity of the skull.
3 Adaptations to Jaw
- Apes have protruding jaw which has been gradually reduced (by natural selection) to flatter facial profile of humans
- Jaw bone is small and non-protruding
- Allow skull to balance on top of spine with minimal muscular effort.
6 Adaptations toPelvis
- Vertebral column articulates with pelvis
- Shorter and broader in humans
- Bowl shape supports abdominal organs when standing/foetus in pregnancy (wider in females)
- Broad hip bones provide attachment for large buttock muscles – moving legs and keep upper body erect.
- Attachment of femurs(its large head) is wide apart, contributing to carrying angle
6 Adaptations to the Carrying Angle
- Shape/orientation of pelvis result in hip joint being directly under trunk/head
- allows weight of body to be transferred to legs.
- legs Longer than arms, contributing to a low centre of gravity.
- Head of femur fits into hip socket (acetabulum) and converges towards knee forming angle (carrying angle).
- Ensures weight distribution close to central axis which enables striding gait instead of swaying side-to-side.
- Weight falls through outside of femur (opposite for apes)
3 Adaptations to the knee
- two-part hinge joint (one on either side) surrounded by ligaments – outer hinger larger and stronger due to greater weight distribution.
- Centre of gravity falls in line slightly in front of knee resulting in force trying to bend knee backwards – opposed by ligaments.
- This resistance produces joint that requires no energy to support standing body.
3 adaptations to the foot
- distinctive adaptation for bipedalism due to lost prehensility (big toe aligned with others).
- Weight distribution: tibia → talus (ankle bone) → tarsals → metatarsals & phalanges (via arch)
- Metatarsal shaped to form two arches - longitudinal (front to back) and transverse (side to side) enabling perfect bipedal, striding gait (walking in way hip and knee fully extend).
4 Adaptations for Centre of Gravity
- Point where all weight of body concentrated.
- Approx ½ total height is leg length which lowers centre of gravity (and increase length of stride)
- Apes 1/3 height is leg length and therefore, centre of gravity at chest.
- Lower centre of gravity contributes to stability when moving bipedally.
2 Characteristics of Striding gait
- When foot hits ground, weight transmitted from heel along outside of foot, cross ball of foot (via transverse arch) and to big toe.
- At final moment of striding, whole weight of body propelled by big toe.
Hominids?
Family: Hominidae
- Humans, Chimpanzees, Gorillas and Orang-utans (Great Apes)
What are hominines?
Subfamily: Homininae
- Humans, Chimpanzees and Gorillas.
What are the two classifications of humans?
Hominids and hominins
What are hominins?
The group consisting of modern humans, extinct human species and all our immediate ancestors (including members of the genera Homo, Australopithecus, Paranthropus and Ardipithecus).
Tribe: Hominini
- Humans and their extinct ancestors
What are hominids?
The group consisting of all modern and extinct Great Apes (that is, modern humans, chimpanzees, gorillas and orang-utans plus all their immediate ancestors).
In 7 ways how do Hominids differ from other primates?
- Large, more complex brains
- 5-cusps molars on lower jaw
- Freely rotating arms
- Wide, shallow chest cavity
- No external tail
- An appendix
- Diurnal – active during the day.
in 4 ways How do Hominins differ from apes in appearance, structure and behaviour?
- relatively hairless
- Fully bipedal (walk on two legs)
- Erect posture & striding gait
- Great brain development & speech.
Who are the human ancestors?
- Apes and humans have common ancestor – ape-like creature – from which first hominins evolved, the australopithecines. (Genus: Australopithecus)
- Genus Homo developed from one or more of the australopithecine species.
What is the avergae brain difference ffor humans and apes?
Average human brain = 1350cm3, Apes = 400-500cm3
Size difference associated with cerebrum.
Cerebral cortex in humans compared to apes
- Cerebral cortex (outer portion) shows greatest development
- Convolutions give 50% greater surface area
- Frontal lobe in human brain contributes 47% of cortical surface area (apes 33%) – where higher functions occur (thinking, reasoning, planning, processing, etc.)
How is the evolutionary trend of brain in hominins determined?
- early hominins brains similar to apes
- Studied by cranial capacity (volume inside cranium) and endocasts (impressions of brain surface inside skull).
- Fossil endocasts show gradual increase in number of convolutions and size of frontal lobe.
- As brain size increased, face became flatter & noticeable forehead developed – likely due to expanding frontal lobe.
4 Evolutionary trend of early hominins through to modern humans: dentition
- Human dentition very distinctive from other primates.
- Canines don’t project beyond other teeth or interlock, looking more like incisors and taking up less room.
- Dental arcade (shape of tooth row) evolved to different shape – more parabolic than U-shaped.
- smaller molars and decrease in strength, gradual loss of wisdom teeth.
5 Characteristics of the mandible and teeth more ape like (primitive)
- More prognathic jaw
- Heavier/thicker mandible
- No chin
- Larger teeth (especially molars) - Diastema present
- Canine teeth more prominent
2 Characteristics of the torso more ape like (primitive)
- Narrower hips (pelvis)
- Back (lumbar) vertebrae less wedge-shaped
2 Characteristics of the torso more human like (modern)
- Broader hips
- Lumbar vertebrae more wedge-shaped
2 Characteristics of the upper limbs more ape like (primitive)
Shorter thumb
Fingers more curved
2 Characteristics of the upper limbs more human like (modern)
Longer thumb
Fingers straighter
2 characteristics of the lower limbs more ape like (primitive)
Femurs more parallel
Arms longer than legs
2 characteristics of the lower limbs more human like (modern)
Femurs sloping inwards towards the knee
Arms shorter than legs
5 Effect of environment on hominin evolution
- After split from chimpanzees, hominins thought to live in woodland/forest environments.
- Believed that bipedalism originated in arboreal ape-like hominin – arm and hand features suited to living in trees (much like orangutans often move bipedally across branches using arms for balance).
- 5-6 million year ago – environment changed.
- Temperature decreased, forest are decreased leaving increasing open grassland/space
- Natural selection favoured more erect stance to move bipedally across landscape.
4 Fossil evidence of Australopithecus genus
In Laetoli - 23m trail of Australopithecine afarensis footprints in volcanic ash made 3.56 million years ago – Footprints indicate bipedal locomotion.
HADAR- 40% complete female skeleton – ‘Lucy’.
- lived 3-3.6 million years ago.
-. Now classified as Australopithecus afarensis.
Taung – Raymond Dart, 1920s
- First Australopithecine fossil found - whole face, jaws and teeth
- Named Australopithecine africanus – ‘southern ape of Africa’
Sterkfontein & Kromdraai – Robert Broom, 1930s
- Second Australopithecine fossil found in Sterkfontein
Kromdraai fossil found later appeared different – named Paranthropus robustus – ‘beside human’
3 Leg features of Australopithecus
- Femur and pelvis more similar to human than ape – combined with fossil footprint evidence, safe to assume true bipedalism.
- Non-opposable big toe.
- Femur angled so foot was under centre of gravity, allowing bipedal locomotion with striding gait.
2 Hand features of Australopithecus
- shorter, less mobile thumb than humans, more heavily built fingers/hands
– suggest adapted for power over precision or arboreal lifestyle.
3 teeth/jaw features of Australopithecus
- Short non-projecting canines (look like incisors) – making row of cutting teeth.
- No gap between them and premolars.
- Parabolic shape of teeth.
2 Face features of Australopithecus
low forehead and more projecting lower jaw than modern hominins.
3 Brain/skull features of Australopithecus
- 480cm3.
- Endocasts show brain surface more like humans than apes.
- Foramen magnum more forward than apes and skull rounded at back.
When were australopithecus afarensis alive?
Between 3.9 and 2.8 mya
Where did australopithecus afarensis live?
East africa
What was the height of males and females of australopithecus afarensis?
- Female: 105-110cm
- Male: 150cm
What was the brain size of australopithecus afarensis?
430cm3