13. Hominid Evolution Flashcards
Human classification
Class: mammalia Order: primates Superfamily: hominoids Family: hominids Tribe: hominin Genus: home Species: sapiens
Distinguishing features of mammals
- Three bones in the middle ear
- Teeth made up of canines, incisors, premolars and molars
- Lower jaw made of a single bone
- Milk producing mammary glands
- Fur or hair over the body surface
- Diaphragm separating chest cavity from abdomen
Features of primates
- Opposable thumbs for grasping hands
- Five digits on hands and feet with nails not claws (exposes fingertips and allows increased sensitivity)
- Eyes protects by bony brow ridge (increased perception by sight)
- Large eyes at the front of the head pointing forward (3D stereoscopic vision)
- COlour vision (increased perception of the environment)
- Large brains
- Variation in tooth size and diet (omnivorous diet)
- Well developed collarbone (brachiation, movement by swinging)
- Well developed social groups bc of communication and behaviour
- Long gestation period and long parental care (large brain development and extended learning)
Hominiodea
Humans belong to the superfamily hominoidea and we share this taxon with lesser apes or gibbons and great apes such as orang-utan, chimps and gorillas
Hominoid
Great apes, lesser apes and humans
Hominid
FAMILY
Great apes and humans
Hominin
Humans and their extinct close relatives (home genus, australopithecus and paranthropus)
Anatomical features and habits common to hominins are
- Bipedal
- Large cerebral cortex
- Reduced canines
- Nose and chin prominent, reduced brow ridges
- Highly sensitive skin
- Body hair short or very reduced to assist cooling
- Complex social behaviour
Features to compare between hominids
forehead angle brow ridge teeth size canines chin jaw cranium size crest spine, position of foramen magnum
Teeth size, ape vs human
ape: variable and large canines, diastemic gap present
human: similar and small canines, diastemic gap absent
Brain case size, apes vs humans
Ape: 300-800
Modern man: 1300-1450
Difference in posture between ape and human
- Ape is quadripedal and stooped with hind limbs bent and knuckles supporting front limbs. Neck and shoulder blades are horizontal. The vertebral column enters the skull almost horizontally
- Human has upright stance, moves bipedal and neck and shoulder blades vertical. the vertebral column enters the skull vertically from beneath
Compare skull of ape and human
Ape: the cranium is small, capacity of 300 to 800ml. the face is sloped, pronounced brow ridge
Human: the cranium is large, a capacity of 1350-1450 ml. Greater intelligence. The face is vertical, reduced brow ridge and presence of a chin
Shape of spine comparison between ape and human
APE: c shaped spine with forward centre of gravity
HUMAN: S shaped spine with centre of gravity over the hips to assist bipedal locomotion
Position of foramen magnum
APE: towards the back of the skull which infers the organism walks stooped on all fours (knuckle walking)
HUMAN: In the centre of the skull so that the skull is balanced on the spine. Indicative of bipedal walking
Teeth and jaw
APE: The jaw is bigger and box shaped. Teeth varied in shape with large canines (in males) and diastema. Diet contained fibrous food
HUMAN: the jaw is reduced and parabolic in shape and the teeth are smaller and similar in shape. Change in diet. Food needed to be chewed less
Feet
APE: the big toe is opposable to some degree
HUMAN: the big toe points straight ahead which assists in transmission of weight in forward direction when walking. The foot has arches which help absorb shock
Hand
APE: There are five digits with an opposable thumb. Each hand is capable of grasping and curling around objects
HUMAN: Humans also have five digits capable of grasping and curling around objects, however the human hand is capable of power grip and precision grip
Arm and shoulder
APE: arm longer in apes compared to humans. Shorter collar bone and shoulder blade positioned on the side of chest. Arms used for walking and swinging in trees
HUMANS: Arm is shorter in humans compared to apes. Shorter arms suited to bipedal walking. Longer collar bone and shoulder blade is positioned on the back of the chest. Upper arm bone can be twisted. Better thrower than apes
Pelvis
APES: pelvis is long and narrow. It has a hip joint with the thigh bone angled at right angles to the knee
HUMAN: Pelvis is short and broad. It allows for large muscles attachment for bipedal walking. It has a thigh bone attached angled towards the knee. The pelvis has become more bowl shaped to support the organs of the torso
Leg
APE: The femurs and the tibias joins in a straight line. Therefore apes are unable to walk upright but use both their feet and knuckles to walk, knuckle walking
HUMANS: The femur meet the tibias at an angle, bicondylar angle, which allows for bipedal walking. This carrying angle assists in positioning the body over the centre of gravity
When did the human line diverge
5 to 7 MYA
When did primates diverge
65-60 mya
When did hominids and chimpanzees diverge
6 mya
What are the prehuman hominin fossils
hominins that evolved in the millions of years immediately following the divergence of the human line from the african ape line before the emergence of the first homo species
Tung child
- 2 mar old fossil
- Skulls has both ape and human features
- Foramen magnum positioned closer to the front of the skull, bipedal walking
- Australopithecus africanus
Lucy from afar
- 3 mya fossil
- skeletal structure suggests lucy walked upright due to the slant of the femur relative to the tibia
- Australopithecus afarencis
Why did bipedalism evolve?
- Scientists speculate that australopithecus afarencis (lucy) was able to spend time in tree where they would swing from branch to branch and their skeletal structures also allowed them to stand and walk erect when they descended to the ground
- Upright walking may have evolved due to climate change which changed their habitat. Being able to walk on the group in a shrinking forest and forage for food found on the ground may have had a selective advantage to other phenotypes
Bipedalism advantages
- Carrying offspring while following large games herds
- Seeing over grass may have helped spot predators or locate carcasses at a distance
- Holding tools and weapons consequence of bipedalism, not a cause
- Thermoregulation (smaller surface area presented to the sun at midday, greater air flow across the body when it is lifted higher off the ground assists cooling)
- efficient locomotion (provides energy efficient methods that favours low speed, long distance)
- carrying food away from a kill site or growing site to position of safety
When did bipedalism evolve?
The structural changes that allow for erect walking evolved more than 3.5 million years ago, long before genus homo appearing in fossil records.
-Features skeletal changes present in hominids that had a small brain and before stone tools appeared in the fossil record
How did the human skull change over time
- size of cranium increased
- increase in size of the height and vertical slope of forehead
- increase in width
- small brow ridge
- large brain capacity
homo habilis
FIRST TOOL MAKER 2.4 MYA
- larger brain size and smaller teeth than australopithecus
- tools used to cut thick skin off an animal, scrape meat off bone and extract marrow
- could be first meat eaters which provided necessary nutrients to support increase in brain size
- worked together and used stones to drive scavengers away from a kill
Homo rudolfensis
2 myr
h. habilis and h. rudolfensis existed in africa at the same times, fossils not found out of Africa.
Larger brain than h habilis and smaller brow ridge
Homo erectus
First emigrant from 1.8 mya
- Earliest fossil found in africa, other fossils found outside of africa and about 300,00 mya. This suggests species migrated out of africa to other continents
- h. erectus had larger brain than h. habilis and was smarter: able to manipulate fire for, tools, systematic hunting, sounds for communication but no sophisticated speech
homo floresiensis
100,000 to 60,000 years ago
- Fossils found in flores island indonesia, evolved from homo erectus
- 1m tall and had brain capacity 380 ml
- Artefacts found with fossil suggests use of tools and fire
homo heidelbergensis
Intermediate species between homo erectus and homo sapiens 400,000 yr
- Found in Heidelberg germany, also found in other parts of europe africa and asia, suggesting african origin (oldest fossils)
- Similar to h. erectus because it had prominent brow ridge, big teeth, sloping forehead and large face
- Similar to h. sapiens as it had a large brain
- Ancestor of homo neanderthals
homo neanderthalensis
-Different species from homo sapiens but close relative 400,000 yr
-First fossils found in neander valley france, europe and middle east
-Large brain, used tools lived in caves, made shelter and buried the dead
0homo neanderthals not an ancestor of modern humans, existed in the fossil record at the same time
-Dna evidence suggests interbreeding between h. sapiens and neanderthals
-Interbreeding occurred early as 100,00 years ago. suggests modern human migrated out of africa before out of africa migration 65,000.
Why did neanderthals disappear from the fossil record?
30,000 years ago due to competition from between equipped modern humans or climatic instability
denisovans
400,000 years ago
- Fossils found in denisova cave in south western siberia
- Coexisted with humans and neanderthals
- first time recognised by comparative dna analysis
- modern humans, neanderthals and denisovans are descendants of homo heidelbergensis
homo sapiens
- First humans called cro-magnons
- 200,00 years
- cro-magnons have large brain, high steep forehead, short narrow skulls, small brow ridge and eye socket, pointed chin, no gas between third molar and jawbone
Biological evolution
changes that have resulted from natural selection acting over generations on inherited phenotypes and producing differential survival and reproduction under a particular set of environmental conditions
cultural evolution
Change that occurs in human populations as a result of transmission of learned or imitated behaviours
Culture
Accumulated knowledge passed on to the next generation by verbal, written or symbolic communication
