Date post: | 14-Dec-2015 |
Category: |
Documents |
Upload: | leslie-stevens |
View: | 223 times |
Download: | 3 times |
Hominin EvolutionChapter 15 – Part 2
Hominin Species: When Did They Live?
The oldest hominin fossil that has been found would have lived between 6-7 million years ago.
Early hominins shared some of the derived characteristics of humans.
E.g.: they had reduced canine teeth, and some fossils suggest that they had relatively flat faces. They also show signs of having been more upright and bipedal than other apes.
One clue to their upright stance can be found in the foramen magnum, the hole at the base of the skull through which the spinal cord exits.
In chimpanzees, the foramen magnum is relatively far back on the skull, in early hominins (and in humans), it is located underneath the skull.
This position allows us to hold our head directly over our body.
The AustralopithecinesThe fossil record indicates that hominin diversity
increased dramatically between 4 million and 2 million years ago.
Many of the hominins from this period are collectively called Australopiths.
The AustralopithecinesThere appear to have been several species of
Australopithecus.
Some of these are likely to have been in the human line.
There are two general types of Australopithecines:Robusts Graciles
Australopithecus afarensis
Australopithecus africanus
Robust Australopithicusextinct
Homo habilis
4 mya
2 mya
1.5 mya
The Robust AustralopithecinesThe robust Australopithecines 3 – 1.5 mya
Australopithecus aethiopicusAustralopithecus boiseiAustralopithecus robustus
Main features of the robust Australopithecines:Brain size around 500 mLVery large molarsBony crest on top of the skulls of males.Males range from 1.3-1.4 m tall and females
range from 1.0-1.3 m
Robust Australopithecines
The Gracile Australopithecines
The gacile Australopithecines were ancestral to the first Homo species
Some examples of gracile Australopiths: Australopithecus anamensis Australopithecus afarensis (Lucy) Australopithecus africanus (Taung Child)
Some of the main features of the gracile Australopithecines include: Brain size around 400 mL Large molars Rounded top skull Males range from 1.4-1.5 m in height and the females range
from 1.0-1.2 m in height
Lucy Lucy is the most complete skeleton of an early hominid.
Found in Hadar, Ethiopia (1974). Dated at 3.2 million years old 40% of her skeleton was found. Bipedal
Australopithecus afarensis Found in many areas of East Africa. 4.0 – 3.0 mya.
Lucy was a small-brained biped. Small brain 380 – 500 mL Lucy was 3’6” tall 50 lb Dates to 3.2 mya
Sexual dimorphism in Australopiths
Australopithecus individuals displayed sexual dimorphism.
This is when the male and female of the species look different to each other.
E.g.: in the case of the Australopithecines, the males are much larger than the females.
Social OrganisationSocial organisation amongst species determines
the degree to which sexual dimorphism is displayed.
Species who form monogamous pairs show little dimorphism, whereas polygamous spices show significant differences between males and females.
Diets
Studying fossilised skulls can provide us with evidence of the diet of a particular species.
For example studying the zygomatic arches , the muscles that run through them and the jaw (including teeth).
The size of the zygomatic arches indicates the size of the muscles associated with the movement of the jaw.
Zygomatic Arches
DietsThe robust Australopithecines had diets which
included mainly tough and fibrous vegetable matter.
This is evidenced by large jaws and jaw muscles Flat, large molars provide
The gracile Australopithecines also had a diet mainly consisting of vegetable matter, however, their smaller jaws and jaw muscles suggest that the food they ate was of a less fibrous nature.
DietsAs the species of
Australopithecines were herbivorous, they had relatively large digestive tracts.
In order to accommodate this, they had wider rib cages and waists.
HabitatsThe Australopithecines had various habitats, but
these habitats were usually in or near forests.
A few species of Australopithecines also lived in grassland savannahs.
LocomotionThe Australopithecines had skeletons which
were capable of bipedal locomotion.
However, they were also capable of life in trees (arboreal) as they had long digits on their hands and feet, as well as long arms for swinging in between branches.
It is thought that these hominins hunted out in open landscapes during the day and then retreated into the forest at night for shelter and protection.
The genus HomoThe first members of the genus Homo were
found in Africa, dating back to 2.4 million years ago.
The defining features of the Homo genus were:Reduction in size of teethAn increase in brain size Increase in size of the cranium (to accommodate
the brain)
The genus HomoThere are many features associated with the genus
Homo, including:Enlargement of brainReduction of tooth sizeShortening of faceMaking and using fireCaring for aged and ill membersBurying the deadDevelopment of artLanguageMusicThe use and development of technology.
Homo habilis: The First Toolmaker
Homo habilis had the following features:Face is much
flatterReduced brow
ridgeLarger cranial
capacity (680 mL)
Homo habilis also used tools in order to strike things, such as nuts.
Homo erectus
Homo erectus evolved from Homo habilis about 2 million years ago.
It is widely believed that Homo erectus was the first species to venture out of Africa.
This is evidenced fossils of Homo erectus being found in continents out side of Africa.
Larger brained and smarter
The brain size of Homo erectus was between 900 and 1,000 mL.
As a result of the increased brain size (and intelligence), Homo erectus displayed some new skills:Use of fireCrafting of better toolsCooperative hunting
The Hobbit: Homo floresiensis
In 2004, a number of fossilised remains were found in Indonesia of a new hominin species.
It has been estimated that this species existed around 18,000 years ago.
Until the discovery of these fossils it was believed that Homo sapiens were the only hominin species after the Neanderthals became extinct.
The discoveries of these fossils suggest that Homo floresiensis and Homo sapiens would have existed alongside each other.
Homo heidelbergensisHomo heidelbergensis was an intermediate species
between Homo erectus and Homo sapiens.
Their brain capacity is between 1,100 and 1,200 mL
The fossils that have been found have been dated between 400,000 and 40,000 years ago.
These fossils have been found on a number of continents including:AsiaEuropeAfrica
Homo neanderthalensisFossils of Neanderthals have been found all over the
world.
These individuals had large brains (1,400 mL).
They were built strongly, with larger bones.
It is thought that the Neanderthals may have buried dead individuals.
They existed between 150,000 and 35,000 years ago.
This species existed at the same time as Homo sapiens and therefore they are NOT our ancestors.
Modern Humans: Homo sapiens
Evolved in eastern Africa.
Appeared 100,000 years ago.
Highly complex weapons and tools.
Brain capacity around 1,400 mL
Agriculture and the first villages
Evidence has indicated that Homo sapiens had set up agricultural farms and tended to domestic animals around 10,000 to 12,000 years ago.
This was mainly in the Middle East in what is known as the “fertile crescent”
The first plants to be cultivated were wheat, barley and pea plants.
Changes in human population
Changes in human populations have been driven by a number of factors, including:Biological evolutionCultural evolutionTechnological evolution
Human biological evolution
Biological evolution refers to the changes in human populations that has resulted from natural selection.
This allows the population to adapt to their particular geographic area.
Some of the traits that have been selected for in different human populations include:Physical traits: such as variation in skin colour and hair
texture.Biochemical traits: such as ABO and Rhesus blood types.Physiological traits: such as tolerances to non-human
milk, extreme temperatures, etc.
Climate and body shapeThe climate of regions have major effects on body shape.
For example, people living in hotter areas are generally thinner and taller, those living in colder environments are shorter and wider.
This difference can be explained by comparing the surface area to volume ratio of individuals from hot and cold climates. Individuals from hotter climates have a high surface area to
volume ratio, allowing them to lose heat more rapidly when they sweat.
Individuals from colder climates have a low surface area to volume ratio, allowing them to retain heat more efficiently.
Human Cultural EvolutionCultural evolution refers to any type of learned
behaviour (either learned or imitated).
This can include:Making toolsLearning to writeLearning rules in social groupingsNew ideas and knowledgeCustomsSymbolsSkillsLearning to play musical instruments
Technological EvolutionTechnological evolution refers to changes over
time in technology that give humans increased control over their environment.
Technology extends capabilities
Humans have developed and used technology to allow us to achieve things beyond our physical capabilities.
For example:Using glasses to seeUsing various vehicles to travelBionic Ear
Biology, culture and technology interact
It is important to remember that biology, culture and technology are interrelated.
Biological evolution created larger brains in the Homo sapiens, this allowed them to develop the technology of tool use, and developed their culture so they hunted in cooperative groups.