Major phases in hominin evolution from 6 mya to present (7)

Question 1

The first 4 million years or so of human evolutionary history took place exclusively on the ____ continent.

Answer 1

African

Question 2

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?

Answer 2

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.

Question 3

Which hominins survived?

Answer 3

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.

Question 4

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.

Answer 4

Hominin
6

Question 5

What are the genera of Tribe Hominin? (3)

Answer 5

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

Question 6

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.

Answer 6

two legs

Question 7

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.

Answer 7

15
20

Question 8

The large amount of fossil evidence shows that: (3)

Answer 8

• 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.

Question 9

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.

Answer 9

Bipedalism

Question 10

What is Ardipithecus ramidus?

Answer 10

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.

Question 11

Diagnostic features - Ardipithecus (6)

Answer 11

• 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.

Question 12

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.

Answer 12

4

1

australopithecines

habitat

dietary

Question 13

What are the two forms of australopithecines?

Answer 13

• 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.

Question 14

Diagnostic features - australopithecines (8)

Answer 14

1. Quite short (1 m - 1.5 m) and upright.
2. Face strongly projecting (prognathic), low sloping forehead, large brow ridges, sometimes cranial ridges, no chin.
3. Palate is u-shaped. The trend is for a reduction in canine size in later australopithecines and the disappearance of the diastema.
4. Brain capacity is small, 435 cc to 530 cc.
5. Walked bipedally - main way of moving.
6. Position of foramen magnum (more forward), human-like pelvis and leg and foot bones confirm this.
7. Arms long and strong, hands curved, legs relatively short, feet short with long toes. All suggest they still climbed trees.
8. 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?

Question 15

What is Australopithecus afarensis?

Answer 15

Australopithecus afarensis is key species in human evolution as it had both ape and human characteristics and is probably ancestral to the Homo genus.

Question 16

Why are Australopithecus afarensis one of the best understood hominins?

Answer 16

They are one of the best understood of the early hominins as hundreds of fossils from dozens of individuals have been found.

Question 17

Why do the adaptations of Australopithecus afarensis enable them to do?

Answer 17

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.

Question 18

Diagnostic features - Australopithecus afarensis (7)

Answer 18

1. Short, about 1.0 - 1.5 m tall.
2. Small cranial capacity (435 cc), about 1/3 that of a modern human brain.
3. Light build, long arms, curved fingers and toes.
4. Ape-like features - skull has low forehead, brow ridge, flat nose, sloping face, no chin.
5. Dentition primitive with a diastema and canines sticking beyond other teeth.
6. Sexual dimorphism evident, males 45 kg and females 29 kg.
7. Has only been found in Ethiopia, Kenya and Tanzania.

Question 19

Name two well-known examples of Australopithecus afarensis: (2)

Answer 19

• 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.

Question 20

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?

Answer 20

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.

Question 21

Diagnostic features Australopithecus africanus (2)

Answer 21

1. Quite short, about 1.1 - 1.4 m.
2. Brain capacity of 450 cc. See skull on p 278.
3. Slight build, probably with long arms and shorter legs.
4. Skull with less prominent brow ridges, higher forehead and shorter face than earlier australopithecines.
5. Teeth and jaws much larger than humans, a u- shaped palate, reduced canine teeth and no diastema.
6. Has only been found in South Africa.
7. 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?

Question 22

Name two well-known examples of Australopithecus africanus.

Answer 22

• ‘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.

Question 23

What features of Australopithecus africanus show evolution towards Homo?

Answer 23

• 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

Question 24

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 ____.

Answer 24

choppers

fossils

Question 25

A. africanus also has some ape-like features; longer ____ relative to legs, _____ nose and forward projecting ___.

Answer 25

arms

flattened

jaws

Question 26

What is Australopithecus sediba?

Answer 26

Australopithecus sediba is a proposed new species of Australopithecus, which lived at about the same time as the oldest Homo ergaster fossils. It is an odd blend of primitive and modern hominin traits that makes it a possible candidate for the immediate ancestor of Homo sapiens.

Question 27

Diagnostic features - Australopithecus sediba (5)

Answer 27

• Height 1.2 m.
• Skull has brow ridges, no cranial ridge.
• Less prognathous.
• Australopithecine traits small brain capacity, long arms, short strong hands suitable for climbing.
• Homo traits wider and shallower pelvis, long legs capable of striding and possibly running like a human and relatively small premolars and molars, short canines.

Question 28

Two partial skeletons of a new australopithecine species, Australopithecus sediba (2 mya) were found Malapa in the ____ of _____ and identified by Professor Lee Berger of the University of the Witwatersrand in 2008. The skeletal remains of one, an 11 to 12 year old boy, includes the most compete undistorted pelvis and ___ hand ever yet found.

Answer 28

Cradle of Humankind

Ancient

Question 29

What is Au. Sediba often described as?

Answer 29

Au. sediba may be a key transitional species’ between Au. Africanus and the early Homo species.

Question 30

Why is Au. Sediba is described as a transitional species?

Answer 30

This is because it is more similar to Homo than to any other australopithecine, which makes it a possible candidate for the ancestor of Homo. If this is correct, these fossils could yield a great deal of information about the origins and ancestor of the genus Homo.

Question 31

What is Australopithecus (Paranthropus) robustus?

Answer 31

These bipedal, small-brained australopithecines are not regarded as ancestral to humans. They are now usually called Paranthropus.

Question 32

Diagnostic features - Paranthropus robustus (6)

Answer 32

• Height 1.1 - 1.3 m.
• Brain capacity of about 530 cc.
• Face long, broad and flat with very small forehead, heavy brow ridges and sagittal crest (for the attachment of chewing muscles).
• Heavy build with relatively long arms.
• Small incisors and canines, huge molars in a large, lower jaw. Indicates a vegetarian diet. Possibly an adaptation to the drier African environment.
• The most common hominin fossil in southern Africa.