1. Biological Evolution of Primates
Need help with Biology? Contact Mrs. Eleanor Adviento for some feedback or tutoring.
Embedded Files
Success Criteria
Success Criteria
Your learning has been successful if you can do the following:
I can explain the difference between primates, hominids and hominins, using specific species as examples.
I can identify and describe the physical traits that are common to all primates.
I can describe the specific physical characteristics associated with brachiators, knuckle walkers and bipeds.
I can explain that quadrupeds use all four limbs for locomotion and bipeds use their two rear limbs / feet for locomotion.
I can use information provided to explain the general trends in human evolution.
Vocabulary
Vocabulary
Learn these so you can communicate this concept well.
Larynx (voice box): Helps to create different sounds when we speak.
Hei Mahi (Do Now):
Do Now:
Use the diagram below to answer the question: Where did Humans come from?
Humans are Primates
Humans are Primates
Characteristics of Primates
Characteristics of Primates
General characteristics of order Primates
General characteristics of order Primates
Mammals in the order Primate have the following characteristics:
Structural:
Prehensile (grasping) hands and feet - allows them to grip/manipulate objects.
Sometimes a prehensile trail - used for balance.
Nails instead of claws, sensitive finger pads - helps with manipulating objects.
5 functional digits on each foot
Forward facing eyes/overlapping visual field. Allows them to easily see the world in 3D
Good hand-eye coordination
Bony ridges to protect eyes
Tendency toward having an erect upper body - associated with sitting, standing, leaping, and in some, walking.
Physiological:
Oestrus/reproductive cycle of female, 2 nipples
Gestation (pregnancy period) is longer than most other mammals.
Typically have one young per pregnancy
Behavioural:
Longer periods of infant dependency, and large parental investment. This nurturing increases survival rate and allows cultural development.
Highly sociable, greater dependency on highly flexible learned behaviour.
Modes of Primate Locomotion
Modes of Primate Locomotion
Arboreal (tree-dwelling)
Arboreal (tree-dwelling)
Quadrupedalism (on all fours)
Leaping
Brachiation (arm swinging from tree to tree).
Ground
Ground
Quadrupedalism (on all fours)
Knuckle-walking (arms hold the fingers in a partially curled posture that allows body weight to press down on the ground through the knuckles).
Bipedalism - habitual (walking on two legs consistently).
Hominids and Hominins
Hominids and Hominins
HOMININS: all the species belonging to the human lineage. This includes modern humans, extinct human species, and all our immediate ancestors (including members of the genera Homo, Australopithecus, Paranthropus, and Ardipithecus.
HOMINIDS: the group of all modern and extinct Great Apes (e.g. modern humans, chimpanzees, gorillas, and orangutans, plus all their immediate ancestors).
Bipedalism is the main trait that separates hominins from all other hominids.
Bipedalism is the main trait that separates hominins from all other hominids.
Hominins include living humans, our ancestors (pre-humans) and the bipedal apes with whom we share our evolutionary history.
About 6-7 mya, the ancestor of living humans and chimpanzees diverged into two geographically isolated populations. One of those groups eventually evolved into us, the other evolved into chimps. Thus, we and the living chimps share a common evolutionary ancestor who lived about 6-7 mya in Africa. This is demonstrated by the fact that we share about 99% of our DNA.
The most defining characteristics of hominins is our bipedal (two footed) locomotion and upright posture. It is a form of locomotion found 6-7 Mya. The earliest hominins also show changes in tooth form that mark a change in diet and social organisation.
You must be familiar with the following species involved in human phylogeny:
Last Common Ancestor
Last Common Ancestor
Human and African Apes shared a common ancestor - one that lived in the forest, moved in trees swinging from arms and walking on all fours.
At some point one of the ancestors took the critical step to becoming a modern human - Walking on two legs, making the change from quadrupedal locomotion to bipedal locomotion.
This change led to profound anatomical changes especially in the limbs, pelvis and skull and marked the separation from apes.
Overview of Trends in Hominin Evolution
Overview of Trends in Hominin Evolution
Humans are habitually bipedal. It is likely that the development of bipedalism around 4-5 mya is the main trait that separates hominins from all other hominids, and was the driving force of our biological and cultural evolution.
Humans are habitually bipedal. It is likely that the development of bipedalism around 4-5 mya is the main trait that separates hominins from all other hominids, and was the driving force of our biological and cultural evolution.
Biological evolution refers to the changes in the genetic makeup of populations of organisms over successive generations.
Cultural evolution refers to the changes in human societies and cultures over time.
Unlike biological evolution, which is driven by genetic changes, cultural evolution is driven by the transmission of knowledge, behaviours, and technologies from one generation to the next through learning and social interactions.
Zoom in on parts of the diagram below, which shows the trends in hominin evolution over time. Only the five species representative of the general trends are shown here.
Australopithecus afarensis - The early australopithecines were ancestral to Homo habilis.
Homo habilis - Ancestral to modern humans.
Homo erectus - Some populations of Homo erectus migrated out of Africa, eventually giving rise to populations of Homo in the Middle East and Europe.
Homo neanderthalensis - Eventually evolved in Western Europe
Homo sapiens - Evolved in Africa
The hominin fossil record shows clear evolutionary trends towards bipedalism, increased brain size, increased height, and increased technical ability.
Biological Evolution - Trends seen in skull fossils:
Biological Evolution - Trends seen in skull fossils:
Increased cranial capacity.
Diminished brow ridge
Decreased zygomatic arch
Decreased prognathism
Increased frontal lobe
Decreased sagittal crest
Foramen magnum centred
Reduction in teeth / molar size
Biological Evolution - Trends in brain volume, height and dentition.
Biological Evolution - Trends in brain volume, height and dentition.
Biological Evolution - Trends in other skeletal features: pelvis, foot, foramen magnum, spine and valgus angle.
Biological Evolution - Trends in other skeletal features: pelvis, foot, foramen magnum, spine and valgus angle.
Cultural Evolution - Trends seen in stone tool technologies
Cultural Evolution - Trends seen in stone tool technologies
Need help with Biology? Contact Mrs. Eleanor Adviento for some feedback or tutoring.
Success Criteria
Success Criteria
Your learning has been successful if you can do the following:
I can describe the change from forest to savannah.
I can explain how this change in environment meant that arboreal lifestyle was no longer efficient, and selected for bipedalism.
I can discuss how this change in environment has influenced the evolution of skeletal features allowing for successful bipedalism.
I can discuss the adaptive advantage of bipedal movement.
I can describe some disadvantages linked to the evolution of bipedalism.
Vocabulary
Vocabulary
Learn these so you can communicate this concept well.
Larynx (voice box): Helps to create different sounds when we speak.
Hei Mahi (Do Now):
Do Now in your books:
Which species are Hominids and which are Hominins?
Australopithecus africanus, Gorilla, Homo ergaster, Chimpanzee, Homo sapiens
Selection for Bipedalism
Selection for Bipedalism
One of the possible theory for the transition to bipedalism has centered on drastic environmental changes that swept Africa more than five million years ago. Africa (and the Earth) had become significantly cooler and drier.
As it did, grasslands in sub-Sahara Africa expanded and rain forests contracted. This means that the landscape turned from near-continuous forest into an open grassland with smaller clumps of trees with no continuous forest.
Due to these environmental changes, different selection pressures acted on the common ancesters of hominids and chimpanzees.
According to the hypothesis, at least one type of these primates responded to the environmental crisis by venturing more and more into the open grasslands, looking for food, but retreating to nearby trees to escape predators and sleep at night.
Advantages of Bipedalism
Advantages of Bipedalism
Around 5-6 million years ago some primates began standing up and walking on two legs. Their success presumably improved their chances of surviving and passing on genes favoring this unusual stance and gait, leading eventually to bipedal hominids.
More efficient locomotion - bipedalism provided an energy efficient method that favours low speed and long distance
Seeing over the tall grass may have helped to spot predators or locate carcasses and distant food (but easier to be spotted be predators) carrying food away from kill site to a safe place or back to other members
Thermoregulation – keeping cool smaller surface area exposed to the sun (60% less) greater air flow across the body when it is higher off the ground air cooler above the ground (further from the hot ground)
Freeing the hands - Bipedalism frees up the hands for other functions such as using tools, carrying offspring, and carrying food.
Disadvantages of Bipedalism
Disadvantages of Bipedalism
Narrowed birth canal – painful birth. Birth canal size reduced because of bipedalism and the fact that babies have bigger heads can cause childbirth problems.
Large pelvic inlet negatively affects locomotion - Humans have bigger brains (than other primates) and thus there is a selection pressure for increased size of pelvic inlet to allow for bigger brains and higher intelligence......BUT a larger pelvic inlet affects locomotion negatively so there is also selection pressure for decreased size of pelvic inlet as it allows for more efficient locomotion.So there is a trade-off between having as large a possible pelvic inlet to allow birth of larger brained infants and keeping the pelvic inlet small enough for efficient locomotion.Due to changes in the pelvis, childbirth became much more difficult and painful.
Slipped discs in spines – S-shaped spine makes humans more prone to back pain and back problems– load carried by 2 instead of 4 limbs.
Hard work returning blood to the heart – varicose veins can result
Hernias – intestine may bulge through weakened abdominal wall as gut is no longer hung from spine by broad ligament as in quadrupeds
Flat feet – feet sometimes suffer strain because body rests on just 2 limbs. Arches of feet collapse producing flat footedness.
A human child takes about a year to walk. Quadrupedal mammals often walk within a few hours of birth.
How analysis of fossils provided evidence of how Ardipithecus ramadus transitioned into bipedalism in a changing environment.
Comparing the locomotion and skeletal features of quadrapedal chimpanzees, intermediate Australopithecus afarensis, and habitual bipedal modern human. No sound.
Page updated
Google Sites
Report abuse