Major phases in hominin evolution from 6 mya to present (7) Flashcards
(32 cards)
The first 4 million years or so of human evolutionary history took place exclusively on the ____ continent.
African
Over the passage of time, from the common ancestor of the hominids to modern humans there have been jumps in human evolution. What caused these?
A current hypothesis is that extreme shifts of climate where it swung wildly from hot and wet to dry and cold were a key factor in driving human evolution. These dramatic changes presented powerful
selection pressures for all living organisms. Many plants and animals became extinct.
Which hominins survived?
However, hominins survived mainly as nature selected for survival those variants with the ability to walk upright and with larger brains. These hominins being more intelligent and physically adaptable could deal with different environments and changing food sources. The successful hominins were then bred to form populations of new species.
The Tribe ____ (humans and fossil hominins) and the African apes separated about ___ mya in Africa. By comparison, dinosaurs died out 65 mya, the earth was formed about 4 600 mya and the universe was born about 14 000 mya.
Hominin
6
What are the genera of Tribe Hominin? (3)
A. Orrorin and Ardipithecus the earliest hominins, from Ethiopia
B. Australopithecus, from East and South Africa
C. Homo, from various sites in and out of Africa
All members of the hominini tribe walked habitually on ___ ___, i.e. they were (or still are) bipedal. When tracing the changes over time, one will see a great transition from an arboreal, long-armed, short-legged, small-brained creature to a terrestrial one with short arms, long legs and a big brain.
two legs
Within these genera, there are ___ to ___ different
species of early hominins. There is no agreement
on how these species are related but there is only
one living hominin species, i.e. us humans, H.
sapiens.
15
20
The large amount of fossil evidence shows that: (3)
- humans were preceded for millions of years by other hominins.
- at times many hominin species coexisted. See time-line graph below.
- there was no ladder-like progression in which one species gave rise to the next.
A. Ardipithecus
In this genus bipedalism is evident. _______ is the earliest major trait of hominins and the single most important difference between humans and apes.
Bipedalism
What is Ardipithecus ramidus?
Ardipithecus ramidus is one of the earliest examples of what one would expect the most recent common ancestor of humans and African apes to be like. It lived in North-East Ethiopia.
Diagnostic features - Ardipithecus (6)
- Height is 1.2 m high, weight about 50 kg.
- Braincase is small (350 cc)
- Arms and fingers long. Similar to African apes.
- Foramen magnum more forward than apes, therefore, could walk upright. Divergent big toe helped grasp branches therefore could move through trees.
- Skull has brow ridges and lower face projects.
- Has ape-like teeth but molars are smaller and narrower and canines reduced.
Between ___ and ___ million years ago, several different species of ape-men, the ________, inhabited the African landscape - in the Rift Valley (Ethiopia, Kenya and Tanzania) and in South Africa. While there was much variation in different areas two dominant australopithecine forms emerged, probably as a result of ____ and ____ changes.
4
1
australopithecines
habitat
dietary
What are the two forms of australopithecines?
- A gracile (thin/slender) form, with smaller teeth and chewing muscles, is likely to have led to the first humans. Examples of these were Australopithecus africanus and Au. sediba.
- A robust form, with very large jaws and teeth, which became extinct about 1 million years ago. It is now more commonly placed in the genus Paranthropus. Paranthropus (Australopithecus) robustus is a well-known example of this form.
Diagnostic features - australopithecines (8)
- Quite short (1 m - 1.5 m) and upright.
- Face strongly projecting (prognathic), low sloping forehead, large brow ridges, sometimes cranial ridges, no chin.
- Palate is u-shaped. The trend is for a reduction in canine size in later australopithecines and the disappearance of the diastema.
- Brain capacity is small, 435 cc to 530 cc.
- Walked bipedally - main way of moving.
- Position of foramen magnum (more forward), human-like pelvis and leg and foot bones confirm this.
- Arms long and strong, hands curved, legs relatively short, feet short with long toes. All suggest they still climbed trees.
- Probably omnivores, scavenging food from carcasses killed by lions and other predators and feeding off fruits and leaves. Why do you think they scavenged rather than hunted? And, why would meat-eating be important in the evolution of hominins?
What is Australopithecus afarensis?
Australopithecus afarensis is key species in human evolution as it had both ape and human characteristics and is probably ancestral to the Homo genus.
Why are Australopithecus afarensis one of the best understood hominins?
They are one of the best understood of the early hominins as hundreds of fossils from dozens of individuals have been found.
Why do the adaptations of Australopithecus afarensis enable them to do?
Their adaptations for living both in the trees and on the ground helped them survive for almost a million years as the climate and environments changed. They lived for over four times as long as our own species has been around.
Diagnostic features - Australopithecus afarensis (7)
- Short, about 1.0 - 1.5 m tall.
- Small cranial capacity (435 cc), about 1/3 that of a modern human brain.
- Light build, long arms, curved fingers and toes.
- Ape-like features - skull has low forehead, brow ridge, flat nose, sloping face, no chin.
- Dentition primitive with a diastema and canines sticking beyond other teeth.
- Sexual dimorphism evident, males 45 kg and females 29 kg.
- Has only been found in Ethiopia, Kenya and Tanzania.
Name two well-known examples of Australopithecus afarensis: (2)
- Lucy’ (3.2 mya) - a fossil that started major revisions in the understanding of human evolution.
- Laetoli fossil footprints (3.7 mya) - trace fossils that show bipedal walking as the big toe is in line with the other toes.
Between 2 and 3 million years ago, a hominin with a mixture of ape and human characteristics lived in the Gauteng highveld. Which hominin was this?
This ape-man, Australopithecus africanus (the ‘southern ape of Africa’), was less ape-like than earlier australopithecines. It may well have been the ancestor of our own genus Homo.
Diagnostic features Australopithecus africanus (2)
- Quite short, about 1.1 - 1.4 m.
- Brain capacity of 450 cc. See skull on p 278.
- Slight build, probably with long arms and shorter legs.
- Skull with less prominent brow ridges, higher forehead and shorter face than earlier australopithecines.
- Teeth and jaws much larger than humans, a u- shaped palate, reduced canine teeth and no diastema.
- Has only been found in South Africa.
- Lived in small social groups and ate fruits and leaves and probably scavenged on the remains of animals killed by predators. Why do you think they scavenged rather than hunted? And, why would meat-eating be important in evolution of hominins?
Name two well-known examples of Australopithecus africanus.
- ‘Taung Child’ (2.5 mya) a remarkably well-preserved 3-year-old child’s skull and an endocranial cast of its brain. Found in 1924, but it took over 20 years before scientists accepted that Africa was the major place of human evolution.
- ‘Mrs Ples’ (2 mya) the most complete skull ever found in South Africa of an Au. africanus specimen.
- ‘Little Foot’ (2.2-3.3 mya) - an amazingly complete fossil of an australopithecine.
What features of Australopithecus africanus show evolution towards Homo?
- A larger brain than A. Afarensis (450 cc)
- Upright and fully bipedal, as evidenced by the position of the foramen magnum
- Human-like teeth (no large canines and no diastema between canines and incisors)
- Rounded dental arch
- Recent isotope studies of teeth have suggested they ate quite a lot of meat, which they probably scavenged. Why do you think they scavenged rather than hunted? And why would meat-eating be important in the evolution of hominins?
- Larger body, 45 kg - heavier than A. Afarensis
According to archaeological evidence, this species (Australopithecus africanus) might have made primitive stone tools such as stone _____. he first stone tool used and made was at least 2.6 mya; such tools have been discovered at sites that are the same age as these Australopithecus africanus ____.
choppers
fossils
