Human evolution from ape- like ancestors (3)

Question 1

The story of human evolution began in Africa
about __ million years ago and where it continued
until about __ million years ago.

Answer 1

6
2

Question 2

Which forces have directed human evolution?

Answer 2

The forces of natural selection have directed it. Environmental factors such as climate change causing alterations in habitat and food supply, as well as fast-running prey and fierce predators, acted on the gene pool.

Question 3

Those hominins with adaptations that allowed

them to survive to breed successfully over time

formed new _____.

Answer 3

species

Question 4

True or false, for much of the first 4 million years there were NO more than one hominin species living in Africa at the same time.

Answer 4

False, for much of the first 4 million years there were more than one hominin species living in Africa at the same time.

Question 5

The main sources of evidence to show humans

have evolved from an ape-like ancestor are: (3)

Answer 5

A. Fossil evidence, i.e. the fossil record of early hominins

B. Genetic evidence, specifically analysis of mitochondrial DNA (mtDNA)

C. Cultural evidence such as tool-making

Question 6

How many human fossils have been found worldwide?

Answer 6

A large number, approximately seven thousand,

hominin fossils have been found worldwide. These

represent about 6 million years of evolution.

Question 7

What are the most common fossils?

Answer 7

The most common fossils are teeth and lower jaws,

and the facial and upper cranial bones of the skull.

Question 8

Skulls are almost never found intact but can be

reconstructed from ____. Femurs are the next

most common, while remains of the feet, hands,

pelvis or spine are very rare.

Answer 8

fragments

Question 9

What do scientists learn by studying fossilised bones?

Answer 9

By studying fossilised bones, scientists learn about the physical appearance for example of earlier hominins and how they changed over time.

Question 10

____, ____ and ____ left by muscles show how hominins moved around and held tools.

Answer 10

Bone size

shape

markings

Question 11

To try and work this out, palaeontologists look at the following key features of the fossils: (6)

Answer 11

• Bipedalism (spine and pelvic girdle)
• Brain size
• Teeth (dentition)
• Prognathism (having a jaw that sticks out markedly)
• Palate shape (roof of the mouth)
• Cranial (sagittal) and brow ridges

Question 12

As mentioned earlier _____ ______ , walking

upright was the most important adaptation

that started humans on their evolutionary path. It

is therefore very important to be able to trace the

gradual transition from walking on four legs to

walking on two legs.

Answer 12

habitual bipedalism

Question 13

Some of the early hominids (hominins and African apes) were probably pre-adapted to bipedalism; they had freed arms that they used for ____ ____ and stretching for fruit.

Answer 13

climbing trees

Question 14

About ten million years ago, when the climate changed and Africa was drying up, the habitat changed from near-continuous forest to wooded savannah. What consequence did this have?

Answer 14

This had great consequences for human evolution as our ancestors would have been forced to move partially upright across open ground to find new sources of food. With time those early hominids that could successfully move about upright on the ground survived to breed and in time formed a new species.

Question 15

Bipedalism, therefore, gave them a crucial advantage in the struggle for survival. It enabled early hominins to:

Answer 15

• live in a greater variety of areas, e.g. forested areas, open savannah, deserts and coastal areas.
• see danger from predators.
• gather food and make and use tools with their completely free arms and more erect stance.
• reduce the risk of overheating as a large surface area is exposed for losing heat to the surroundings.

Question 16

What are the disadvantages of bipedalism? (3)

Answer 16

• The backbone no longer acts like a cantilever bridge between the hind and forelimbs and is put under a lot of stress.
• Bipedalism removes the shock-absorber function of the shoulder blade that front-legged animals benefit from when they take a leap.
• The reshaping of the pelvis narrows the birth canal, so children are born when they are smaller and relatively helpless.

Question 17

Discuss whether this premature birth was an advantage or disadvantage in hominin evolution.

Answer 17

Perhaps it compelled more parental care and opened opportunities for learning from parents during the long childhood.

Question 18

How do we know if a fossil was bipedal?

Generally, palaeontologists decide if a fossil hominin was bipedal by looking for the following: (3)

Answer 18

• a foramen magnum that is positioned further forward; the skull weight is born by the shoulders while walking upright with the skull balanced on a vertical spine.

Under-surface of hominid skulls Foramen magnum is positioned: near the back of the skull in apes (left) under the skull in humans (right) in intermediate position in fossil hominids (two middle)

• a shorter, broader pelvis; allows for efficient weight distribution in an upright position.
• an S-shaped spine; this acts like a spring enabling an upright posture to be easily maintained.

Question 19

Throughout human evolution, there were drastic climate changes. This caused the environment to alter and be unpredictable. What did our ancestors do to survive?

Answer 19

To enable our ancestors to survive, a larger, more complex brain, capable of processing new information, was selected. This trend of an increase in braincase size (and bigger brain) over time can be observed in fossils.

Question 20

The average brain _____ of African apes (395 cc) is close to that of very early hominins (435 cc). Brain size continued to increase in the later hominins (700 cc then 850 cc), and finally Homo sapiens ( ____ c).

Answer 20

Capacity

(1 350 c)

Question 21

What did the larger brain make possible? (3)

Answer 21

• better coordination of movement.
• large amount of information could be processed.
• the development of speech and ultimately a written language for communication.

Question 22

Why are fossil teeth important?

Answer 22

Fossil teeth are important as they give an indication of which specific hominin species one is looking at, what they ate, and in what type of environment they might have lived.

Question 23

What do the teeth remains show?

Answer 23

The tooth remains show a general decrease in size, particularly of molars and canines, through the ages. There is an exception, Paranthropus robutus that had massive grinding teeth (molars and premolars) in its large lower jaw when compared to the incisors and canines. This would indicate that its diet probably would have been mostly coarse, tough food that needed a lot of chewing.

Question 24

The tooth enamel, ___ in African apes, gradually thickens in early and later hominins until in humans it is ___.

Answer 24

thin

thick

Question 25

In African apes and early hominins, the ____ are larger and project above the tooth row. Over time they have gradually got smaller until in humans they are the same size as the other teeth and no longer stick above the others.

Answer 25

canines

Question 26

Why are the canines of the African apes so large?

Answer 26

The canines of the African apes are so large that a gap (the diastema) develops between the canine and incisors to make room for the opposing canine so the jaw can close. In early hominins this can still be seen. However, in the later hominins it disappeared.

Question 27

African apes have large and ______ jaws, i.e jaw sticks out beyond the upper part of the face. This condition is still seen in the early hominins, the __________. Partly because the teeth and the muscles for chewing become smaller the trend is towards a smaller and less sloping face until finally in humans the face is small and flat.

Answer 27

prognathous

Australopithecines

Question 28

What is the function of the palate?

Answer 28

The palate, sometimes called the dental arch, is the bone separating the mouth and nasal cavities. The chewing trend is away from crushing and tearing to crushing and grinding For this to happen, the palate shape changed from a roughly rectangular palate in African apes to u-shaped in early hominins (australopithecine) and finally, in Homo sapiens, to a parabolic curve.

Question 29

____ _____ (sagittal crest), found on the top of

the skull, can be seen in hominids that have

protruding (prognathous) jaws and well-developed

chewing muscles, e.g. gorillas.

Answer 29

Cranial ridge

Question 30

Brow ridges, i.e. bony ridges over the eye sockets, are very ___ in African apes (see the gorilla skull alongside) and are also well developed in some early hominins. They get smaller in later hominins until in humans they are greatly reduced or usually absent. They may have served as ____ against the stress exerted by jaw muscles or protection for the eyes.

Answer 30

big

buttresses