Hominin Evolution Chapter 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 Australopithecines The 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 Australopithecines There 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

Robust Australopithicus Homo habilis 1.5 mya Robust Australopithicus extinct Australopithecus africanus 2 mya Australopithecus afarensis 4 mya

The Robust Australopithecines The robust Australopithecines 3 – 1.5 mya Australopithecus aethiopicus Australopithecus boisei Australopithecus robustus Main features of the robust Australopithecines: Brain size around 500 mL Very large molars Bony 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 Organisation Social 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 Zygomatic Arches 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.

Diets The 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.

Diets As the species of Australopithecines were herbivorous, they had relatively large digestive tracts. In order to accommodate this, they had wider rib cages and waists.

Habitats The Australopithecines had various habitats, but these habitats were usually in or near forests. A few species of Australopithecines also lived in grassland savannahs.

Locomotion The 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 Homo The 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 teeth An increase in brain size Increase in size of the cranium (to accommodate the brain)

The genus Homo There are many features associated with the genus Homo, including: Enlargement of brain Reduction of tooth size Shortening of face Making and using fire Caring for aged and ill members Burying the dead Development of art Language Music The use and development of technology.

Homo habilis: The First Toolmaker Homo habilis had the following features: Face is much flatter Reduced brow ridge Larger 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 fire Crafting of better tools Cooperative 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 heidelbergensis Homo 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: Asia Europe Africa

Homo neanderthalensis Fossils 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 evolution Cultural evolution Technological 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 shape The 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 Evolution Cultural evolution refers to any type of learned behaviour (either learned or imitated). This can include: Making tools Learning to write Learning rules in social groupings New ideas and knowledge Customs Symbols Skills Learning to play musical instruments

Technological Evolution Technological 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 see Using various vehicles to travel Bionic 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.

Humans have a juvenile form Humans have a juvenile form. Our face is similar to a juvenile chimp; the nose is flat, as is the chin and the brow ridge has not developed. It is believed that part of our evolution has been the maintenance of the juvenile features and not developing the adult features as the other great apes do. We have lost the ability to develop these features with age.