Gizmo: Human Evolution PDF

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Student Exploration: Human Evolution - Skull Analysis Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes.Complete the lab Assessment Define Each Vocabulary Word: bipedal-an organism that moves by means of its two rear limbs or legs canine-relating to or characteristic of dogs cranial capacity- the volume of the interior of the cranium of vertebrates that possess a cranium and a brain cranium-the skull, especially the part enclosing the brain evolve-develop gradually, especially from a simple to a more complex form foramen magnum-the hole in the base of the skull through which the spinal cord passes hominid-the group consisting of all modern and extinct Great Apes hominin-the group consisting of modern humans, extinct human species and all our immediate ancestors index-a scale for showing the quality of an environment by indicating the types and abundances of organisms present in a representative sample of the environment maxilla-the jaw in vertebrates that is fused to the cranium orbit- the bony cavity that contains the eyeball palate-the roof of the mouth skull-the bones of the head collectively Prior Knowledge Questions (Do these BEFORE using the Gizmo.) 1. Label one of the skulls below as human and the other as a chimpanzee skull. Human

Chimpanzee

2. What features did you use to identify which skull was human and which was chimpanzee? The chimpanzee has a longer skill and larger jaw bone.

Gizmo Warm-up In 1924, a fossilized skull that looked very similar to a chimp skull was discovered. But the skull most definitely did not belong to a chimp. The location of the foramen magnum—a hole in the skull where the spinal cord exits—indicated that the individual was bipedal, or walked on two legs. This fossil was some of the earliest evidence of human evolution. Using the Human Evolution – Skull Analysis Gizmo, you will discover some of the ways that skulls can be used to learn about human evolution. Start by comparing two modern hominids: a human and a chimpanzee. 1. Examine the Front view of the Homo sapiens (modern human) skull. use the Select skull menu to examine the same view of the Pan troglodytes (chimp) skull. How do the skulls compare? The human skull has a smaller jaw, smaller teeth, and a larger forehead. Chimpanzees also have a larger nose.

Then,

2. Now, examine the Bottom view of the two skulls. How do they compare?

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The mouth of a chimpanzee is larger.

Activity A: Foramen magnum

Get the Gizmo ready: ● Select the Homo sapiens (modern human) skull.

Introduction: Skulls, even from the same species, can have a wide variety of shapes and sizes. To compare skulls, scientists use measurements of certain features to calculate indexes. An index is a ratio of one measurement to another. An important index for measuring hominid skulls is the opisthion index. This index indicates the position of the foramen magnum in the base of the cranium. The opisthion index can indicate whether a hominid species was bipedal or not.

Question: How does the location of the foramen magnum indicate if a species was bipedal? 1. Measure: Select the Bottom view. To determine the opisthion index for humans and chimps, follow the steps below and complete the table. ● Turn on Click to Measure Lengths. Measure the distance from the opisthocranion to the opisthion, as shown at top right. Record the opisthocranion-opisthion distance in the table below. ● Measure from the opisthocranion to the orale, as shown at bottom right. Record the opisthocranion-orale distance in the table. ● To calculate the opisthion index, divide your first measurement by your second measurement. Multiply this number by 100. Species

Homo sapiens

Opisthocranion opisthion distance (cm) 6.80

Opisthocranion orale distance (cm)

Opisthion index

20

34

Pan troglodytes

1.80

18.60

9.18

2. Analyze: The opisthion index is an indicator of where the foramen magnum is situated. The greater the opisthion index, the closer the foramen magnum is to the center of the cranium. This position is usually found in species that stand upright. A low value for the opisthion index occurs when the foramen magnum

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is situated in the rear of the cranium. This may indicate that the species walked on its knuckles or on four legs. Using the index values you calculated, what can you conclude about humans and chimps? Humans are bipedal and chimpanzees walk on their knuckles.

3. Gather data: Humans, chimpanzees, and the other great apes are hominids. Hominids evolved from a common ancestor that lived about 13 million years ago. Hominins are hominids that belong to the lineage that led to humans. Measure the opisthion index of the other hominids available in the Gizmo. (Note: the foramen magnum was not preserved in the Homo naledi skull.) Species

Opisthocranion opisthion distance (cm)

Opisthocranion orale distance (cm)

Opisthion index

A. afarensis

2.62

16.10

16.3

A. africanus

3.50

18.10

19.3

P. boisei

4.63

20.10

22.9

H. habilis

4.91

17.50

28.1

H. erectus

5.21

20.00

26.1

H. heidelbergensis

6.61

22.80

29.0

H. sapiens neanderthalensis

6.93

24.70

28.1

H. floresiensis

4.10

16.70

24.6

4. Analyze: Hominins are characterized by bipedalism. A. Based on their opisthion indexes, which of the hominids in the Gizmo are hominins? All except for chimpanzees.

B. Based on opisthion indexes, which hominin skulls are most similar to human skulls? All the homo skulls except naledi.

4. Explain: Why do you think the foramen magnum is positioned near the rear of the cranium for knuckle walking species and near the center of the cranium for bipedal species?

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I think the foramen magnum is positioned in the rear of the cranium for knuckle walking species because of the angle in which their head is in. For bipedal species it is near the center because for the most part their head is level.

Activity B: Cranial capacity

Get the Gizmo ready: ● Select Side view. ● Turn off Ruler, and turn on Click to measure area.

Introduction: The brain is housed inside the cranium. The internal volume of the cranium is called the cranial capacity. The larger an organism’s cranial capacity is, the larger its brain tends to be. Question: How does the cranial capacity compare amongst hominids? 1. Measure: To estimate the cranial capacity of each skull in the Gizmo, measure the area of the part of the cranium that houses the brain. This part of the cranium is roughly behind the red line in the diagram at right. You can also use the three skull images below as a guide for measuring the rest of the skulls in the Gizmo. After you measure the area of each cranium, multiply the result by 5. This will give you a very rough estimate of the species’ cranial capacity.

Homo sapiens 200 cm^2

Species

Pan troglodytes 90 cm^2

Australopithecus afarensis 85 cm^2

Area of cranium (cm2)

Estimated cranial capacity (cm3)

Pan troglodytes

87

435

A. afarensis

78

390

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1A. africanus

91

455

P. boisei

109

545

H. habilis

117

585

H. erectus

155

775

H. heidelbergensis

198

990

H. s. neanderthalensis

228

1140

H. floresiensis

125

625

H. naledi

204

1020

H. sapiens

204

1020

2. Analyze: Examine the estimated cranial capacities you calculated. A. Which species probably had the largest cranial capacities? Homo neanderthalensis, Homo sapiens, and Homo naledi.

B. What do you think cranial capacity is a good indicator of? Cranial capacity is a good indicator of intelligence.

C. Did any hominids have a larger cranial capacity than humans? If so, which species? Yes, Homo neanderthalensis.

3. Compare: Turn off the Area tool. Using the Front view, compare the size and shape of the forehead of a chimpanzee and the forehead of a modern human. How are they different? A. How are they different? The forehead of the human skulls are taller and wider than the forehead of the chimpanzee skull.

B. Why do you think humans have such large foreheads in comparison to chimps? Humans have such large foreheads in comparison to chimpanzees because of the shape and size of our brain. We have a rounded forehead and our head has been shaped like that.

5. Draw conclusions: Compare the data you collected in activity A with the data you collected in this activity. Which evolved first in hominins: bipedalism or large brains? Explain.

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Bipedalism evolved first in hominins. We know this because the foramen magnum moved toward the front of the skull to accommodate the bipedal walking and this happened before cranial capacity.

Activity C:

Get the Gizmo ready: ● Select Side view. ● Turn on Click to measure angles.

Maxilla and mandible

Introduction: Teeth and the bones around the mouth give a great deal of information about both a species’ diet and how it eats. Take a look at the skull features below.

Question: How do the mouths of hominids compare? 1. Measure: As shown at right, place one of the protractor’s circles on the top of the zygomatic process. Place the vertex of the protractor at the top of the nasal opening (Hint: You may have to look at the Front view in order to see where the top of the nasal opening is in relation to the orbit). Place the other circle on the edge of the maxilla. The resulting angle is the maxillary angle. Complete the table. (Note: You will not be able to do this measurement on incomplete skulls.) Species

Maxillary angle

Species

Maxillary angle

Pan troglodytes

109.52

Homo erectus

Australopithecus afarensis

102.74

Homo heidelbergensis

—

Australopithecus africanus

116.83

Homo sapiens neanderthalensis

—

Paranthropus boisei

92.77

Homo floresiensis

59.04

Homo sapiens

97.51

Homo habilis

—

59.52

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2. Observe: Select the Bottom view and look at the size and shape of each species’ palate. How does the maxillary angle and palate shape relate to the size of each species’ mouth? The shape of and size of the mouth depends on the maxillary angle.

3. Compare: Compare the human’s and chimp’s teeth. A. How many teeth are found in each species’ maxilla? Pan troglodytes:

16

Homo sapiens:

16

B. How do the size and shape of human canines compare with chimp canines? Humans are more circular and wide, while chimpanzees are longer and skinnier.

4. Form hypothesis: Chimps and humans eat similar foods. What do you think could explain the differences between the maxillary angle, teeth, and palate of these two species? The difference is the result of their stance and the angle of their head when eating. Humans are more upright while chimpanzees are hunched and leaning forward mostly.

5. Infer: What is the relationship between the evolution of bipedalism, the increase in cranial capacity, and the decrease in tooth and mouth size of hominins? (Hint: As cranial capacity increased, the use of sophisticated stone tools became more common.) Bipedalism organisms have a smaller maxillary angle and this increases the cranial capacity and decreases the mouth size.

6. Summarize: On a separate sheet of paper, record the age of each fossil. Then, look over all the data you collected. Summarize how hominins changed as they evolved. Over time hominis posture has become more upright and the brain size has increased. This resulted in humans becoming more intelligent.

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7. Evaluate: Of the fossils presented in this Gizmo, Homo floresiensis is the youngest. In what ways does this

species NOT follow the pattern of human evolution you described above? It doesn't follow the pattern because it is a fully evolved human skull.

Complete the lab Assessment

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