Trends in Human Evolution

Question 1

Define ‘Apes’

Answer 1

The family name for the group of primates that do not have tails (humans are part of this grouping).

Question 2

What does ‘Arboreal’ mean?

Answer 2

Living in/relating to trees.

Question 3

What is ‘Brachiating’?

And what adaptations do ‘Brachiators’/primates typically possess in order to do this?

Answer 3

A form of locomotion involving movement through arboreal environments via swinging from branch to branch.

Brachiators typically have:

• A short lumbar spine
• Long Curved Fingers
• Reduced Thumbs
• Long Forelimbs
• Flexible Shoulder Joints
• Freely Rotating Wrists

Question 4

What is ‘Knuckle-Walking’?

And what main adaptation/trait do ‘Knuckle-Walkers’/primates typically possess?

Answer 4

This is a form of quadrupedal locomotion in which the forelimbs hold the fingers in a partially flexed posture that allows the primate’s body weight to press down on the ground through the knuckles as they walk.

• Bones around the knuckle joints are enlarged to enhance stability and weight-bearing (presence of this is used to identify Knuckle-Walking in fossils)

Question 5

State the types of locomotion typically observed in arboreal primates:

Answer 5

• Brachiation (swinging through the branches)

- Knuckle-Walking (quadrupedal walking)

Question 6

Suggest two possible advantages of ‘Brachiating’:

Answer 6

Allows for effecient travel through trees from branch to branch, thus allowing primates to adopt an arboreal niche:

Thus;
1) Increased likelihood of avoiding ground-dwelling predators

2)Ability to access otherwise unobtainable food sources

Question 7

Suggest two possible advantages for ‘Knuckle-Walking’:

Answer 7

1) Allows primates to efficiently travel in terrestrial niches/ground environments during times when ‘Brachiation’ is perhaps not possible (thus expanding range of niches/environments they may occupy)
2) Allows primates to grasp and carry objects while travelling from one location to another

Question 8

Briefly describe the ‘Cranium/Brain-Case’:

Answer 8

This is the part of the skull that encloses the brain and protects it from injury.

Question 9

Briefly describe the ‘Brow Ridge’:

Answer 9

These are well-developed bony ridges above and around the eyes.
They help protect the eyes by reinforcing against the powerful forces generated by chewing/biting.

Question 10

Briefly describe ‘Canine Teeth’:

Answer 10

Large pointed teeth used for holding/killing prey, as weapons, or for aggressive displays.

Question 11

Briefly describe the ‘Zygomatic Arch’:

Answer 11

This is the ‘arch’ in the ‘cheekbone’ where important muscles utilised for chewing pass through;
(These muscles are then attached to the mandible and skull).

Question 12

Briefly describe the ‘Nuchal Crest’:

Answer 12

This is an extension towards the base of the skull to which (thick) neck muscles attach.
(These muscles position, move, and stabalise the head and cervical vertibrae).

Question 13

Briefly describe the ‘Sagittal Crest’:

Answer 13

This is a ridge bone running lengthwise along the midline of the top of the skull.
(Strong jaw muscles attach to it, and thus it reinforces the skull against powerful forces generated by chewing/biting).

Question 14

Briefly describe the ‘Premolars’ and ‘Molars’:

Answer 14

These are the large flat teeth that are used for shearing and crushing food during chewing.

Question 15

Briefly describe the ‘Foramen Magnum’:

Answer 15

This is a large hole at the base of the skull through which the spinal cord and spinal arteries enter the skull.

(For Bipeds, it is located centrally at the base of the skull)
(For Quadrupeds, it is located further back at the base of the skull).

Question 16

Briefly describe a ‘Diastema’:

Answer 16

This is a space between the teeth for which large canines may fit into so that the teeth can come together fully when the mouth closes.

Question 17

Briefly describe a ‘Prognathism’:

Answer 17

This is a feature when the lower portion of the face markedly projects forward (at an angle).

Question 18

Give a brief comparison of a Chimpanzee’s jaw area to that of a Modern Human:

Answer 18

1) Chimpanzee:
- More robust/rectangular-shaped jaw
- Narrow ‘U-Shaped’ Dental Arcade
(Post-canine teeth either side of jaw are parallel to each other)

2) Modern Human:
- Wider, Parabolic/’V-shaped’ Dental Arcade
- Smaller teeth
- Less robust/more gracile mandibles

Question 19

Compare the ‘Sagittal Crest’ for Chimpanzees and Humans, giving a reason for the difference:

Answer 19

• Chimpanzee: Present
• Human: No Sagittal Crest
• Substantial jaw muscles are needed to move a large/robust mandible attach to this skull component. As such muscles are reduced in humans, no crest is necessary.
• Most likely brought about by change in diet over time.

Question 20

Compare the ‘Relative Size of Canines’ for Chimpanzees and Humans, giving a reason for any difference:

Answer 20

• Chimpanzee: Larger (with associated larger Diastema)
• Human: Smaller/reduced
• Canine Teeth predominantly utilised in aggressive displays, and thus trend of Modern Humans toward less overt displays (ie increased use of language/vocalisations) reduced the need for intimidating dental features

Question 21

Compare the ‘Shape of Jaw’ for Chimpanzees and Humans, giving a reason for any difference:

Answer 21

• Chimpanzee: ‘U-shaped’, no chin, and presence of Simian Shelf
• Human: ‘V-shaped’, protruding chin, NO Simian Shelf
• Trend towards Modern Humans follows reduction in size and specialisation of human teeth as our diet evolved.
• Less musculature required in Humans, so bone structure could be reduced/become more gracile

Question 22

Compare the ‘Zygomatic Arch’ and ‘Brow Ridge’ of Chimpanzees and Modern Humans, giving a reason for any differences:

Answer 22

• Chimpanzee: Thick/prominent Zygomatic Arch and Brow Ridges
• Human: Less thick/prominent and more gracile
• Chimpanzees have a ‘tougher’ diet, requiring greater chewing forces to process fibrous plant material, and so need more robust structures for reinforcement/muscle attachments to prevent fractures.
• Humans’ shift toward diet with higher content of ‘softer’/cooked foods meant a removed need for ‘Biologically Expensive Butressing’, and so evolved more gracile structures.

Question 23

Compare the ‘Foramen Magnum’ of Chimpanzees and Modern Humans, giving a reason for any difference:

Answer 23

• Chimpanzee: Positioned toward rear of skull and angled backwards.
• Human: Centrally located and vertically aligned.
• Humans evolved to be bipedal, and so mostly upright positioning involves skull being situated directly above spinal cord, thus requiring a centrally located Foramen Magnum.
• Chimpanzees are quadrupeds who mostly knuckle-walk as a means of locomotion, so their skulls project forward from a relatively horizontal spine, requiring a Foramen Magnum located more towards rear of skull for support.

Question 24

Contrast the main ‘Differences in Hand Structure’ for Quadrupeds and Bipeds:
(According to LearnCoach)

Answer 24

Quadrupeds:

• Curved Fingers for Brachiating
• Power Grip (fingers and thumb wrap around an object)
• Less Fine Motor Skills

Bipeds:

• Straight Fingers
• Precision Grip (thumb and finger grip object)
• More Fine Motor Skills
• Better Tool-Use Ability (and ability to acquire food)
• Opposable Thumb!

Question 25

List the main points of difference for Quadrupeds and Bipeds in the Environment (after it evolved from Arboreal to Savannah-type):
(According to LearnCoach)

Answer 25

Quadruped:

• Look Smaller to Predators
• Can’t See as Far
• More of Body-Surface/Back Exposed to Sun (more prone to overheating)
• Can’t Carry Food/Infants/Tools/Defend Selves when Travelling
• Less Efficient Mode of Locomotion

Biped:

• Look Larger/More Intimidating to Predators
• Greater Range of Sight
• Only Top of Head Exposed to Direct Sun (better Thermoregulation)
• Ability to Carry Food/Infants/Tools/Defend Self while Travelling
• More Efficient Form of Locomotion

Question 26

Explain what is meant by the ‘Obsterical Dilemma’:

Answer 26

The ‘Obsterical Dilemma’ is a hypothesis surrounding the conflicting evolutionary trends of Homo sapiens, in which from our development of bipedalism we required narrower pelvises for, and thus there was a resulting decrease in the size of the bony birth-canal, However, bipedalism also led to increased intelligence/brain size, which required a larger cranium/cranial capacity, which would also need a wider pelvic area and birth canal.

All of this explains why human births are particularly long, painful, and risky to both the mother/child when compared to other primates.

Question 27

Define ‘Hominid’:

Answer 27

The group consisting of all extant and extinct Great Apes, Modern Humans, Chimpanzees, Gorillas and Orangutans and their immediate ancestors.

Question 28

Define ‘Hominin’:

Answer 28

A sub-group of the ‘Hominids’ consisting of Modern Humans, extinct Human Species, and all immediate ancestors.

(including so-called ‘dead-ends’, ie ancestral lines that became extinct after diverging from the direct line between humans and even earlier lines).

Question 29

List the main ten hominin species in order from oldest to most recent:

Answer 29

• Ardipithecus ramidus (4.4 mya)
• Australopithecus afarensis (3.7 - 2.9 mya)
• Australopithecus africanus (3.3 - 2.1 mya)
• Paranthropus boisei (2.3 - 1.2 mya)
• Homo habilis (2.4 - 1.6 mya)
• Homo ergaster (1.9 - 1.5 mya)
• Homo erectus (1.9 mya - 30 kya, unknown though)
• Homo heidelbergensis (600 - 200 kya)
• Homo neanderthalensis (350 - 28 kya)
• Homo sapiens (200 kya - now)

Question 30

List the 6 Key Aspects of Ardipithecus ramidus, and any additional notes:

Answer 30

• Age: 4.4 mya
• Height: 1.2 m
• Cranial Capacity: 300 - 350 cm3
• Locomotion: Climber/Brachiator capable of Bipedalism
• Habitat: Lush, humid Woodlands
• Diet: Omnivorous and not entirely dependent on foliage
• Extra Notes:
• Reduced aggression/inter-male and inter-group aggression compared to Chimpanzees, reflected in dentition
• NOT sexually dimorphic, unlike Chimpanzees

Question 31

List the 6 Key Aspects of Australopithecus afarensis, and any additional notes:

Answer 31

• Age: 3.7 - 2.9 mya
• Height: F 1.05m M 1.51m
• Cranial Capacity: 350 - 600 cm3
• Locomotion: Mostly climbing/brachiation but also adapted to Bipedalism
• Habitat: Wooded-Savannah
• Diet: Largely Plant-based, similar to modern gorillas
• Extra Notes:
• Famous specimen ‘LUCY’
• Extreme sexual dimorphism observed

Question 32

List the 6 Key Aspects of Australopithecus africanus, and any additional notes:

Answer 32

• Age: 3.3 - 2.1 mya
• Height: F 1.10m M 1.35m
• Cranial Capacity: 420 - 625 cm3
• Locomotion: Habitual Biped, but spent some time in trees
• Habitat: Wooded-Savannah
• Diet: Mainly Vegetarian/Fruit and Leaves, with some Scavenged Meat
• Extra Notes:
• Small-bodied compared with later hominins
• First specimen found that proved human evolution started in Africa
• Significant sexual dimorphism present

Question 33

List the 6 Key Aspects of Paranthropus boisei, and any additional notes:

Answer 33

• Age: 2.3 - 1.2 mya
• Height: F 1.24m M 1.37m
• Cranial Capacity: 475 - 550 cm3
• Locomotion: Mostly Quadrupedal/Climber with inconclusive indications of some Bipedalism
• Habitat: Wooded-Savannah
• Diet: Primarily Plant Matter, i.e. nuts, seeds, fruit, and addition of tubers
• Extra Notes:
• Robust Herbivores
• One of many side-branches of human evolution, i.e. did not lead on to H. sapiens
• High degree of sexual dimorphism present

Question 34

List the 6 Key Aspects of Homo habilis, and any additional notes:

Answer 34

• Age: 2.4 - 1.6 mya
• Height: F 1.10m M 1.35m
• Cranial Capacity: 600 - 700 cm3
• Locomotion: Obligate Bipeds
• Habitat: Wooded-Savannah
• Diet: Better Quality Plant Material, i.e. softer, and some Meat
• Extra Notes:
• Fossil specimens are highly variable; some show evidence of endocranial bulge in Broca’s area, which indicates some level of capacity for speech perhaps
• Remains often accompanied by primitive stone tools, hence ‘Handy Man’
• Thought to coexist with P. boisei

Question 35

List the 6 Key Aspects of Homo ergaster, and any additional notes:

Answer 35

• Age: 1.9 - 1.5 mya
• Height: F 1.45m M 1.85m
• Cranial Capacity: 600 - 910 cm3
• Locomotion: Upright, Bipedal (efficiently)
• Habitat: Savannah
• Diet: Omnivorous/Higher Quality Foods, eg. Meats, Underground Tubers, other Proteins
• Extra Notes:
• Sometimes considered subspecies of H. erectus
• Sparked migration of the Homo genus to other continents
• First Hominin with human-like shape, stature, and stride
• Sexual dimorphism still present
• Innovator of ‘Acheulian Stone Tools’

Question 36

List the 6 Key Aspects of Homo erectus, and any additional notes:

Answer 36

• Age: 1.9 mya - 30 kya, but unknown
• Height: 1.6 - 1.8m
• Cranial Capacity: 750 - 1300 cm3
• Locomotion: Upright, Bipedal (efficiently)
• Habitat: Open/Grasslands
• Diet: Omnivorous, with large amounts of Meat, i.e. similar to early Modern Humans
• Extra Notes:
• ‘Upright Man’
• Undetermined on how recent they are
• ‘Side-branch of the Family Tree’
• First Hominin to live in Hunter-Gatherer Societies

Question 37

List the 6 Key Aspects of Homo heidelbergensis, and any additional notes:

Answer 37

• Age: 600 - 200 kya
• Height: 1.45 - 1.85m
• Cranial Capacity: 1280 cm3
• Locomotion: Efficient Bipedalism
• Habitat: Varied; in Africa and Eurasia
• Diet: High Quality Omnivorous
• Extra Notes:
• ALLOPATRIC SPECIATION:
• African Populations evolved to H. sapiens
• European Populations evolved to H. neanderthalensis
• More Advanced Stone Tools, i.e. multiple materials and parts

Question 38

List the 6 Key Aspects of Homo neanderthalensis, and any additional notes:

Answer 38

• Age: 350 - 28 kya
• Height: F 1.56 M 1.68m
• Cranial Capacity: 1200 - 1750 cm3
• Locomotion: Efficient Bipedalism
• Habitat: Varied; Colder, Drier Climates of Europe and the Middle East
• Diet: High Quality Omnivorous; Large Game supplemented by Vegetation, and including Seafood
• Extra Notes:
• Thought to have evolved from H. heidelbergensis populations located in Europe and Asia
• Controlled Use of Fire Evidenced

Question 39

List the 6 Key Aspects of Homo sapiens, and any additional notes:

Answer 39

• Age: 200 kya - now
• Height: F 1.6 M 1.75m
• Cranial Capacity: Archaic 1500 cm3 - Modern 1350 cm3
• Locomotion: Efficient/Full Bipedalism
• Habitat: Highly Varied; World-Wide
• Diet: High Quality Omnivorous; Meat, Seafood, Vegetables, Fruit, Grains etc.
• Extra Notes:
• Only surviving member of Hominin Family
• Thought to have evolved from African H. heidelbergensis Populations

Question 40

Summarise the General Trend from ‘Ardipithecus to H. sapiens’ for the ‘Relative Size of Cranium’:

Answer 40

Cranium size/capacity increased, reflecting an increase in brain size over time

Question 41

Summarise the General Trend from ‘Ardipithecus to H. sapiens’ for the ‘Sagittal Crest’:

Answer 41

Presence reduces (eventually disappearing) as muscles associated with chewing also decrease, coinciding with diet changes (from tough plant material to softer/cooked foods etc.)

Question 42

Summarise the General Trend from ‘Ardipithecus to H. sapiens’ for the ‘Slope of Forehead’:

Answer 42

Reduces in its backwards-angle over time/becomes more vertical in appearance (reflects increasing cranial capacity)

Question 43

Summarise the General Trend from ‘Ardipithecus to H. sapiens’ for the ‘Brow Ridge’:

Answer 43

Large/Prominent brow ridge continually reduces in size and prominence as muscles associated with chewing reduce/as amount of pressure/force from biting decreases due to diet change

Question 44

Summarise the General Trend from ‘Ardipithecus to H. sapiens’ for the ‘Slope of Face’:

Answer 44

Becomes more vertical as robustness of jaw simultaneously decreases; all coinciding with increases to cranial capacity

Question 45

Summarise the General Trend from ‘Ardipithecus to H. sapiens’ for the ‘Foramen Magnum Location’:

Answer 45

Becomes more centrally located as reliance upon vertical/upright bipedal locomotion increases

Question 46

Summarise the General Trend from ‘Ardipithecus to H. sapiens’ for the ‘Presence of Diastema’:

Answer 46

Disappears as diet changes from tougher to softer foods, and as social behaviour develops to be less aggressive and more focused around cooperation and language (rather than aggressive displays)

Question 47

Summarise the General Trend from ‘Ardipithecus to H. sapiens’ for the ‘Degree of Prognathism’:

Answer 47

Significantly reduces over time as face becomes more vertically aligned and ‘snout’ significantly reduces; follows reduction in size of teeth and chewing muscles due to diet evolution

Question 48

Summarise the General Trend from ‘Ardipithecus to H. sapiens’ for the ‘Shape of Chin’:

Answer 48

Becomes a forward, pointed chin present only in H. sapiens (perhaps to reinforce very gracile mandible developed)

Question 49

Summarise the General Trend from ‘Ardipithecus to H. sapiens’ for the ‘Size and Shape of Mandible’:

Answer 49

General trend of size decrease, prominence of Simian Shelf reduces until disappearance in H. sapiens, and U-shaped dental arcade becomes V-shaped/Parabolic

Question 50

Summarise the General Trend from ‘Ardipithecus to H. sapiens’ for the ‘Presence of Nuchal Crest’:

Answer 50

Reduces in size and prominence as species become more and more reliant on vertical, bipedal locomotion

Question 51

Summarise the General Trend from ‘Ardipithecus to H. sapiens’ for the ‘Curvature of Dental Arcade’:

Answer 51

U-shaped/Parallel alignment becomes V-shaped/Parabolic

Question 52

Summarise the General Trend from ‘Ardipithecus to H. sapiens’ for the ‘Shape of Incisors’:

Answer 52

Reduction in size and ‘sharpness’ coinciding with dietary and social changes.
(Generally small in all species though, and becoming more vertical over time)

Question 53

Summarise the General Trend from ‘Ardipithecus to H. sapiens’ for the ‘Relative Size of Canines’:

Answer 53

Initially smaller than P. troglodytes and decreasing further over time; likely reflecting changing diet and social behaviour

Question 54

Summarise the General Trend from ‘Ardipithecus to H. sapiens’ for the ‘Shape of Canine Teeth’:

Answer 54

Becomes less pointed, and instead more blade-like

Question 55

Summarise the General Trend from ‘Ardipithecus to H. sapiens’ for the ‘Relative Size of Molars’:

Answer 55

Decrease in size over time coinciding with gradual change in diet from tough, raw plant material to softer foods, cooked meats, etc.

Question 56

How does the ‘Bowl-Shape’ of the Hominin pelvis provide an Adaptive Advantage?

Answer 56

The ‘Bowl-Shape’ to the pelvis results in the internal organs and spine being positioned over the leg bones, and thus the centre of gravity, helping make bipedal locomotion more energy efficient.

Question 57

Which Hominin species was considered the first to walk Bipedally as its Primary Locomotion?

Answer 57

Australopithecus afarensis

ie Lucy

Question 58

What are the ‘Ilium’?

Answer 58

The upper-portion of each hip bone (which are wider in Bipeds).

Question 59

What are the Two Main Selection Pressures that acted on the Pelvis?

Answer 59

• Childbirth (increased brain size led to larger-headed offspring, and so wider birth-canal required)
• More efficient Bipedal Locomotion

Question 60

What are the Three Main Adaptative Advantages of the evolved short and wide pelvis in the Hominin species?

Answer 60

1) The spine and internal organs are placed over the centre of gravity
2) The ‘bowl-shape’ accommodates the muscles associated with bipedalism
3) Femoral attachment is angled, creating ‘Valgus Angle’

Question 61

What is the ‘Valgus Angle’?

Answer 61

This is the angle the femur bone makes relative to the knee.

In Bipeds, the Valgus Angle is larger than in Apes, due to the femur being angled inward, rather than straight down.

Question 62

What change was seen in the ‘Lateral Femoral Condyle’?

Answer 62

The Lateral Femoral Condyle enlarged to aid the knee to withstand the stress of standing and walking upright.

Question 63

State and Explain the Three Main Differences in the Feet of Apes and Hominins:

Answer 63

1) Apes have a diverging large toe, which aids climbing and an arboreal lifestyle. Whereas the hominin toe is elongated and in-line with the other toes. This provides the forward thrust necessary for bipedal locomotion, as well as aiding with balance.
2) Hominin feet have an arch, whereas ape feet are flat footed. The arch of the foot acts as a spring, reducing the shock from striding out and enabling the hominin to travel long distances.
3) The calcaneus (heel bone) is enlarged in bipedal hominins to accommodate the “heel-toe” locomotion.

Question 64

What is Spinal Lordosis?

Answer 64

The curvature of the lumbar and cervical regions of the spine.

Question 65

Briefly Summarise the Key Suggestion of the ‘Out of Africa Theory’:

Answer 65

The Out of Africa Theory (also known as the replacement hypothesis), suggests that modern humans evolved in Africa, and migrated into the rest of the world, replacing existing hominin species which had descended from Homo erectus.

Question 66

Briefly Summarise the Key Suggestion of the ‘Multiregional Hypothesis’:

Answer 66

The Multiregional Hypothesis theorises that Homo erectus migrated from Africa around 1.8 million years ago, into Asia, Europe and Australia, and so all living humans derive from H. erectus.

But some level of gene flow remained between the populations.

Question 67

Why is Mitochondrial DNA a significant piece of the puzzle in terms of evidence for the ‘Out of Africa Theory’?

Answer 67

• mtDNA is only passed down through the maternal lineage (mother to child), meaning that it is easier to trace it’s origins as it does not undergo independent assortment and recombination as our DNA does.
• The mutation rate of mtDNA is steady and so can be used as a biological clock.
• Modern African mtDNA has the greatest variation, suggesting that all human populations descended from a common ancestor in Africa approximately 200 000 years ago.

Question 68

What is ‘Mitochondrial DNA’ or ‘mtDNA’?

Answer 68

Mitochondrial DNA (mtDNA) is the DNA present in the mitochondria of our cells, which is separate from our main genetic sequence in the nucleus.