Sequence of human evolution & Evidence for a common ancestor for living hominids (2)

Question 1

Humans belong to the order primates, which is divided into two super families. Which are… (2)

Answer 1

• Hominoidea

* Prosimians

Question 2

Due to differing characteristics, homininae has been further divided into two tribes. Which are? (2)

Answer 2

• Gorillini (gorillas)

* Hominini – Hominins (living humans and their extinct ancestors) and Pan (chimpanzee and bonobos

Question 3

Genetic analysis combined with fossil evidence indicates that:
• Hominidae family split (speciated) into the subfamilies, homininae and ponginae about ___.
• Homininae subfamily split into two tribes, hominini and gorillini about ___.
• Hominini tribe split into the genera, Homo, australopithecines and Pan about ___.

Answer 3

15 mya
7.5 mya
6 mya.

Question 4

What does a phylogenetic tree depict?

Answer 4

A phylogenetic tree depicts a hypothesis about evolutionary relationships among organisms. The tree is based upon similarities and differences in their physical or genetic characteristics.

Question 5

Why do we want to show that hominids

have a common ancestor?

Answer 5

If there is a common ancestor, we will be able to trace the evolution of humans from this ancestor through the series of early hominin species to today’s humans.

Question 6

To try and find the common ancestor, scientists
use the ____ ___ and _____ (chromosomal
DNA and mitochondrial DNA).

Answer 6

fossil record

genetics

Question 7

What traits should the common ancestors have?

Answer 7

The common ancestors should have traits that are found in both African apes and humans.

Question 8

What is the benefit of knowing the similarities and differences of apes and humans?

Answer 8

Knowing the similarities and differences of African apes and humans will give us a starting point when
looking at fossils of early man and enable us to
follow the trend in human evolution. This is done
below.

Question 9

Physical and genetic similarities show that the modern human species, Homo sapiens, very closely resembles……..

Answer 9

the African apes, i.e. chimpanzees,

bonobos and gorillas

Question 10

What must be stressed about humans?

Answer 10

However, it must be stressed that humans did not evolve from African apes. Rather the two groups evolved from a common ancestor.

Question 11

Based on the
estimated rates of genetic change, this common
ancestor is thought to have existed about 6 million
years ago. After splitting into two lineages, one that
led to the _____ (an African ape) and the
other to _____ both species have undergone 6
million years of separate evolution.

Answer 11

chimpanzee

humans

Question 12

What are their anatomical similarities?

All living hominins: (10)

Answer 12

• have an upright posture
• lack of external tails.
• have freely rotating arms
• have hands with an opposable thumb that, with the other fingers, allows them to grasp and handle objects. The thumb sticks out sideways.
• have digits (fingers and toes) with flat nails. All other mammals have claws or hooves on their digits. Nails probably allowed for manipulation that is more sensitive.
• have eyes that face forward so that the eyes’ visual fields overlap to give stereoscopic vision. What is the value of this? This feature is a general feature of all predators.
• have molar and premolar teeth with low and rounded cusps. Other placental mammals have high cusps. Look at those of a cat or dog. Where fossil teeth are found, this feature makes it very easy to identify the fossil as a hominin or not.
• have eyes with cones for colour vision.
• are sexually dimorphic (male and female vary in some physical trait), e.g. males are about 5 to 10% larger and have an upper body with larger muscles
• have a large brain compared to body mass

Question 13

As mentioned before humans and African apes
have been evolving separately for about 6 million
years. During that time, humans experienced
different selection pressures, such as…. (3)

Answer 13

• climate change
• different diet
• effect of bipedal locomotion.

Question 14

What did these selection pressures result in?

Answer 14

These different pressures resulted in
various physical differences developing.

(It is the physical differences that one must be
aware of when looking at hominin fossils. They
will help trace the evolution of humans.)

Question 15

What are the anatomical differences between humans and African ape related to?

Answer 15

The anatomical differences between humans and
African apes are largely related to the evolution of
habitual bipedalism in humans.

Question 16

The African apes are ____ ____, but when on the ground, they are _____ knuckle-walkers. Apes can, however, walk briefly on two legs but humans do so habitually.

Answer 16

tree climbers

quadrupedal

Question 17

What is the most important adaptation that started humans on their evolutionary path and why?

Answer 17

Habitual bipedalism is the most important adaptation that started humans on their evolutionary path. It has resulted in many differences between the skeletons of humans and the African apes.

Question 18

Compare the arms of humans and apes.

Answer 18

Apes have arms that are usually longer than the legs.

Humans have arms that are shorter and weaker than the legs. If long arms were no longer needed for climbing they would not have been selected.

Question 19

Compare the fingers and toes of humans and arms.

Answer 19

Apes have fingers and toes that are long and curved for grasping branches.

Humans have fingers and toes that are short and straight.

Question 20

Compare the thumbs of humans and apes.

Answer 20

Apes have big toes that are divergent.

Humans have thumbs that can grasp objects precisely and firmly between the tips of the fingers and thumb. This has greatly increased humans ability to manipulate objects. The African apes do not have this advanced manipulating ability. They can only grasp between the thumb and sides of the other fingers.

Question 21

Compare the hip bones of apes and humans.

Answer 21

Apes have ilia (hip bones) that are large, elongated and parallel to the spinal column. This is to support the legs and trunk in the bent-over posture necessary for quadrupedal knuckle-walking.

Humans have a shorter, broader and more bowl-shaped pelvis, which supports the legs and trunk in an upright position. Thus provides greater stability for walking and running. See alongside and below.

Question 22

Compare the spines of humans and apes.

Answer 22

Apes have a bow-shaped (less curved) spine.

Humans have a spine curvature that has two major curves, the thoracic (where the back curves away from the chest) and the lumbar (where the spine curves towards the stomach). ‘These S-shaped curves keep the trunk of the body, and the weight of it, centred above the pelvis, which is crucial for efficient upright walking.

Question 23

Compare the thigh bones of humans and apes.

Answer 23

Longer femurs (thighbones) that are set farther apart at the hips than they are at the knees and slant toward the midline to keep the knees close together. This angle allows anthropologists to diagnose bipedalism even if the fossil is only the knee end of a femur. The femur arrangement makes walking and running more efficient.

Question 24

Compare the feet of humans and apes. (3)

Answer 24

feet that have:

• a large strong heel.
• tiny toes with the large big toe moved into line with the others, i.e. convergent.
• longer feet with a stable arch, which supports the body better. An African ape’s foot is mobile. The human foot is adapted to support the whole weight of the body and for walking or running.

Question 25

Humans have a much larger brain than that of the
African ape, especially the _____ ____ . The average capacity of an adult chimpanzee brain is
____ cc while that of a modern human brain is ___ cc.

Answer 25

cerebral cortex
395 cc
1350 cc

Question 26

True or false
Humans have relatively far more white
matter in the cortex than chimpanzees.

Answer 26

True, this means that there are more connections between nerve cells and therefore a greater ability to process information.

Question 27

The larger more complex brain is responsible for
the development of the unique behavioural
qualities of humans, which include: (3)

Answer 27

• using their hands with greater dexterity to make simple tools. After bipedalism, tool-making was the next major evolutionary step in human development.
• the use and control of fire.
• the use of a highly developed language.

Question 28

Humans do not have the pronounced ____ ___ of an African ape.

Answer 28

brow ridges

Question 29

What is the significance of the foramen magnum in humans?

Answer 29

The foramen magnum in humans is found centrally under the skull, unlike apes that have it at the rear of the skull. Therefore the spine of a human connects with the skull underneath and near the centre so that the head is held firmly upright and the body’s centre of gravity is directly over the legs. This reduces the energy needed to balance.

Question 30

However, the spine of an African ape connects
with the skull at the back to allow for the
attachment of strong neck muscles and to place
the head at an angle; the proper position for
walking on all ____.

Answer 30

Fours

Question 31

Which features suggest that the cranial capacity of the African apes is smaller than that of humans and that their diet is different?

Answer 31

Humans have a large braincase, small jaws, a nearly vertical face and chin, but African apes have a small braincase, large jaws, a sloping face but no chin.

Question 32

The _____ teeth of humans are relatively small, whereas those of apes are large and pointed and project beyond the other teeth.

Answer 32

canine