Chapter 14: Human Evolution

In 1924, workers blasting limestone at a quarry near Taung, in South Africa, broke open a block of rock with a small skull inside it. Rock from that quarry was being sent to Raymond Dart, an anatomist in Johannesburg. When a box reached his house, he lifted out a lump of stone with a face pressed into it, and beside it a hardened natural cast of the inside of a braincase.

Dart worked for weeks, chipping the rock away grain by grain until the face came free. What he had was a child. The milk teeth were still in place and the first molars were only just coming through. The braincase was small, not much bigger than a young ape’s. But the canine teeth were short and blunt, not the long pointed canines of an ape, and the opening where the spinal cord enters the skull sat underneath it rather than at the back — this head had been balanced on top of an upright body.

In 1925 Dart described the fossil in the journal Nature and named it Australopithecus africanus, the southern ape of Africa. Almost nobody believed him. It took over twenty years and many more African fossils before the Taung child was accepted for what it was: a creature that already walked upright, long before its brain grew large. Fig. 14.0-1 shows the skull he was looking at.

Diagram

Fig. 14.0-1 — The Taung Skull Line drawing of the young Australopithecus africanus skull from Taung in side view, with a small inset of the same skull seen from below; label the face, the braincase, the milk teeth, an erupting first molar, the short blunt canine, and the forward position of the opening for the spinal cord on the underside of the skull. Line drawing, not a photograph.

Curiosity Corner

Q1. Why do scientists measure the empty space inside a fossil skull, and what does that measurement tell them? Q2. What can the skull and the backbone of a fossil show about whether its owner walked upright or on all fours? Q3. You still grow wisdom teeth and you still carry an appendix — why would the body keep parts it hardly uses? Q4. If a giraffe stretches its neck all its life to reach high leaves, will its calf be born with a longer neck? Q5. How could soot from factory chimneys change the colour of the moths living on the trees nearby?

14.1 What Is Evolution?

Look at any patch of ground for a minute and you will find several kinds of life sharing it. Grass, an ant, a crow overhead, mould on a fallen fruit. They differ enormously in size, shape and way of living. A natural question follows from that variety: have living things always been like this, or did they arrive at these forms slowly?

Species That Never Changed

For a very long time the common answer was that they had always been like this. The earth and every living thing on it were held to have been created complete, in the forms we see today, by a divine act. This idea is called the theory of special creation, and accounts of it appear in many religious traditions, including the account of the first man and woman.

The implication of that idea mattered more than the story itself. If every species — a group of similar organisms that can breed among themselves and produce fertile young — had been present from the beginning and had never altered, then nothing about living forms was left to explain. No species could have ancestors unlike itself, and no new kind of organism could ever appear.

Life From Non-Living Matter

The scientific account begins at a different place. According to the autogenesis theory of the origin of life, life arose on the early earth from non-living organic matter, rather than being placed here ready-made.

That arising is not thought of as a single moment. It is understood as a gradual process — a long series of physical and chemical changes, running in step with the constantly changing conditions of the early earth.

Side Note

Where The Words Come From ‘Autogenesis’ is built from two Greek roots: autos, meaning self, and genesis, meaning origin — life originating of itself. ‘Evolution’ comes from the Latin evolvere, to unroll, in the way a scroll is unrolled to show what is written further along.

Once living things existed, they did not stay as they were. There is good evidence, from fossils in the rocks and from living organisms alike, that the more complex forms of life have arisen from simpler ones. This change in living things over long stretches of time is called evolution, or organic evolution.

Do Not Mix Up

Origin Of Life And Evolution The origin of life asks how living matter first appeared from non-living matter. Evolution asks what happened afterwards — how the forms of life already present changed over time. One question ends where the other begins.

What Evolution Means

Evolution is slow, and it is continuous. It works on a scale no single lifetime can display — not years or centuries, but millions of years. What alters over that time is not one individual but a whole species, generation after generation.

Definition

Evolution The slow and continuous process by which complex forms of life have emerged from simpler forms over millions of years.

That tells you what evolution is. It does not yet tell you how it happens — what actually drives a species to change. Two explanations became prominent, and both are taken up in the next section: the Theory of Inheritance of Acquired Characters, proposed by Jean-Baptiste de Lamarck, and the Theory of Natural Selection, proposed by Charles Robert Darwin.

Try Yourself

Sorting By Complexity Pick five living things you can see from where you are sitting — a plant, an insect, a bird, a fungus, yourself. Arrange them from simplest to most complex. Then write down the single feature you used to decide the order, and check whether it works for all five.

14.2 Theories Of Evolution

Saying that species change over time leaves the harder question untouched. What makes them change, and why does an organism end up so well suited to the place it lives in? A desert plant stores water, a fish is shaped like a spindle, a giraffe can reach leaves no other browser can touch. Something must account for that fit.

Two explanations became prominent, and they are quite different from each other. The French biologist Jean-Baptiste de Lamarck held that the driving force was the inheritance of acquired characters — organisms change physically as they struggle to meet the demands of a changing environment, and those advantageous changes are passed on to their offspring. The English naturalist Charles Darwin held instead that the variation already present in a species is what nature works on, and called his explanation the Theory of Natural Selection, or Darwinism.

14.2.1 Lamarck’s Theory Of Inheritance Of Acquired Characters

Lamarck (1744–1829) did not arrive at his idea by guessing. He studied fossils and compared them with living species, matching organisms to the environments they were found in. Laid out in order, the fossils formed a series running from older forms to younger ones and ending in a species alive today.

That series told him something important. A present-day species is not a fixed thing dropped into the world; it stands at the end of a line of changing ancestors. He explained how that line changed using two principles, both widely accepted in his time.

14.2.1.1 Use And Disuse Of Organs

The first principle is easy to observe in a single lifetime. A part of the body that is used a great deal becomes larger and stronger, while a part that is not used deteriorates and wastes away. This is the principle of use and disuse.

Lamarck explained the giraffe with it. He suggested that the giraffe evolved from ground-feeding herbivores. At a later stage the area fell short of ground-level vegetation, so the animals took to feeding from trees instead. Constant stretching of the neck and fore-limbs, over many generations, made these structures longer and stronger, until they could reach the higher foliage. The stages are set out in Fig. 14.2-1 and as a chain of causes in FC 14.1.

Diagram

Fig. 14.2-1 — The Giraffe As Lamarck Explained It Three panels in a row, line drawing. Panel 1: a short-necked, short-limbed ancestral browser feeding on ground vegetation. Panel 2: the same animal stretching its neck and fore-limbs upward towards the lower branches of a tree, ground vegetation shown sparse. Panel 3: a long-necked, long-limbed giraffe feeding comfortably on high foliage. Label each panel with the stage it shows and mark the neck and fore-limbs in all three.

Flowchart

FC 14.1 — Lamarck’s Account Of The Giraffe’s Long Neck Ground vegetation becomes scarce → animals reach upward to feed on tree foliage → neck and fore-limbs are stretched constantly during life → these parts become longer and stronger through use → the lengthened neck and limbs are passed on to the offspring → repeated over many generations → the long-necked giraffe of today

14.2.1.2 Inheritance Of Acquired Characters

The second principle is what carries the change forward. Lamarck stated that an organism can pass on to its offspring the modifications it picks up during its own lifetime. A character gained in this way, after birth and through the organism’s own activity, is called an acquired character.

Applied to the giraffe, this is what the principle claims. The long, muscular neck and fore-limbs of the living giraffe were passed to it by ancestors that had stretched them, and the same characters will continue to appear generation after generation. Notice that the two principles must work together: use and disuse produces the change, and inheritance of acquired characters preserves it. Without the second, every generation would have to start again from the beginning.

Do Not Mix Up

Acquired And Inherited Characters An inherited character comes from the parents through the reproductive cells and is present from birth — eye colour, blood group. An acquired character is gained during life, through use, injury or habit — a scar, a swimmer’s shoulders. Lamarck’s theory rests on the claim that acquired characters can become inherited ones.

14.2.2 Vestigial Organs In Humans

The disuse half of Lamarck’s first principle has a striking illustration in your own body. Some organs have shrunk so far that they no longer do the work they once did, yet they have not disappeared. They still appear, in reduced form, generation after generation. These are the vestigial organs.

Definition

Vestigial Organs Organs that have ceased to be of any use to their possessor but still persist, generation after generation, in a reduced form.

Put the other way round, a vestigial organ is the remnant of a feature that served an important function in the organism’s ancestors. That is exactly why it is evidence for evolution: a structure with no present use is hard to explain unless it was inherited from an ancestor in which it did work. Many such structures have been described in the human body. Three of them are easy to point to.

Wisdom Teeth

The wisdom teeth are the last molars on each side of both the jaws. They are so called because they appear last, at an age of about 17 to 20 years. They are smaller and less complex than the other molars, and we hardly use them for chewing our food.

Vermiform Appendix

The vermiform appendix projects from the blind end of the caecum — the pouch at the beginning of the large intestine — as a narrow, worm-like tube. Its position is shown in Fig. 14.2-2. In humans it does no digestive work, although the small amount of lymphoid tissue in its wall plays a minor part in defence.

Diagram

Fig. 14.2-2 — Position Of The Vermiform Appendix Simplified front view of the human digestive tract within the outline of the abdomen; label the stomach, small intestine, large intestine, caecum and vermiform appendix, and show the appendix arising from the blind end of the caecum. Line drawing.

The comparison that makes it a vestigial organ is with other mammals. In herbivorous mammals such as the sheep, the corresponding organ is large and is quite helpful in digesting cellulose, the tough carbohydrate that makes up plant cell walls. The same structure that does real work in a plant-eater has dwindled to a tube in us.

Real-World Application

When Vestigial Organs Cause Trouble The modern human jaw often has too little room for the wisdom teeth. They may erupt at an angle or stay partly buried in the gum, which can be painful, and a dentist may then remove them.

The appendix can become inflamed and swollen, a condition called appendicitis, which causes severe pain in the abdomen and is usually treated by surgery. A person lives normally afterwards — which is itself a measure of how little the organ now does.

Pinna Of The Ear

The pinna is the projecting, lobe-like part of the external ear, shown in Fig. 14.2-3. In other mammals its main function is to gather sound waves and direct them into the auditory canal, which leads to the ear drum, and the animal turns it towards whatever it wants to hear.

You cannot do that. The muscles that would move the pinna are present in human beings and are complete, but they are poorly developed and functionless. A structure kept, with its machinery kept alongside it, but no longer worked — the pinna is another clear example of a vestigial organ.

Diagram

Fig. 14.2-3 — The Pinna Of The Human Ear Side view of the external ear on the side of the head; label the pinna, the lobe, and the opening of the auditory canal. Line drawing.

Structure and Function

A Dog’s Pinna Large, funnel-shaped and worked by well-developed muscles → can be swivelled towards a sound → collects sound waves from one direction and funnels them into the auditory canal → the animal locates the source without turning its head.

Curiosity Corner

Q3. You still grow wisdom teeth and you still carry an appendix — why would the body keep parts it hardly uses?

A. Because the body does not build itself afresh each generation. These structures were inherited from ancestors in which they did useful work, and they are still inherited now, reduced but not erased.

14.2.3 Darwin’s Theory Of Natural Selection

Charles Darwin (1809–1882) worked from what he had seen. Travelling from one island to another he found great diversity among closely related forms, and he spent years turning those observations into an explanation of how evolution might have occurred in nature.

That is worth stating carefully. Darwinism is not a statement of what evolution is; it is a proposed mechanism for how it happens. Darwin built the mechanism out of four facts that anyone can check, and the argument is set out step by step in FC 14.2.

Real Incident / Discovery

The Voyage Of The Beagle In December 1831 Darwin, then twenty-two, sailed from England on the survey ship HMS Beagle as its naturalist. The voyage lasted almost five years and took him along the coasts of South America and across the Pacific.

Wherever the ship stopped he collected specimens and wrote notes, and he kept noticing the same thing: closely related animals and plants differed slightly from one island or valley to the next, in ways that seemed to match where they lived.

He worked on the problem for more than twenty years after coming home. In 1859 he published his famous book On the Origin of Species, in which he proposed the idea of natural selection.

Flowchart

FC 14.2 — Darwin’s Argument For Natural Selection Organisms produce far more offspring than can possibly survive → food, space and shelter remain limited → struggle for existence → individuals of the same species differ from one another (variations) → individuals with favourable variations survive and reproduce more often → favourable variations become commoner generation after generation (natural selection) → such variations accumulate over a long period → a new species arises (speciation)

14.2.3.1 Overproduction

Living things produce far more offspring than can ever grow up. This is overproduction, and the numbers are easy to see in animals that reproduce in bulk.

An oyster releases tens of millions of eggs at a single spawning — by some counts sixty to eighty million. Paramecium, a single-celled pond organism, divides again and again, a few times a day in good conditions, so one cell can give rise to millions within a few weeks. Even the slowest breeders make the point. Darwin calculated that a pair of elephants, producing about six young over a breeding life of some ninety years, would after roughly 750 years have around nineteen million living descendants if all of them survived.

They do not survive. Under natural conditions, and whatever the rate of reproduction, the number of individuals of a species stays roughly constant over long periods in a fairly stable environment. That gap — between the offspring produced and the adults that actually appear — is the fact everything else in the argument rests on.

14.2.3.2 Struggle For Existence

Numbers multiply in a geometric ratio, doubling and redoubling, while space and food remain almost constant. The result is a struggle for existence among the organisms, in which every individual is in effect competing for a place.

The competition is for whatever is in short supply: favourable shelter, climate, food supply and breeding places. It may be between members of the same species, which is called intraspecific competition, or between members of different species, which is called interspecific competition. Intraspecific competition is usually the fiercer of the two, because members of one species need exactly the same things.

14.2.3.3 Variation

Struggle would decide nothing if all individuals were identical. They are not. Even the progeny of the same parents are not exactly alike in all respects, and it is difficult to find any two individuals that are. Such differences between individuals are called variations.

Without variations there would be nothing for the struggle to sort, no change could occur, and evolution would be impossible. Certain variations that appear in the parent generation continue to appear in the progeny, generation after generation.

Variations are not all of one kind. A harmful variation makes its possessor unfit in the struggle for existence and leads to its being weeded out. An advantageous variation does the opposite: the individual carrying it is more successful in the struggle, and lives to leave offspring.

14.2.3.4 Survival Of The Fittest And Speciation

Put the last three sections together and the outcome follows on its own. During the struggle for existence, only those individuals survive which have advantageous adaptations or variations; those without them are routed out. This is survival of the fittest.

Nature, in effect, does the choosing. The environment allows only suitable variations to be carried forward, and this is what Darwin termed natural selection. No one selects; the surroundings simply make some variations useful and others useless.

As the environment changes, new advantages get selected in nature. After many generations, sufficient characters would alter so as to change the species into a new one. This is how new species originate.

Definition

Speciation The origin of a new species by gradual modification of an existing one.

14.2.4 Industrial Melanism In The Peppered Moth

A classical example of natural selection is provided by the peppered moth, Biston betularia. This moth rests by day on tree trunks and walls, in full view of birds, so how well it is hidden decides whether it lives.

Its light-coloured wings, dotted with dark spots, blended well with the lichens growing on the houses and tree trunks it rested on. There was also another variety, with much darker wings. In 1850, in the Manchester area, this dark variety was rare — resting on pale lichen it was easily visible to birds and was eaten up, while the light form was well concealed and was seen in large numbers.

Then the industrial revolution changed the surface the moths rested on. Pollution in the area caused the death of the lichens and the darkening of the tree trunks with soot. The dark variety was now better hidden and was not easily picked out, and the light-coloured moth easily became the prey. Natural selection here acted through the agency of the birds. The dark variety survived better, left more offspring and almost entirely replaced the light form. This phenomenon has been called industrial melanism, and it is shown in Fig. 14.2-4 and traced step by step below.

Diagram

Fig. 14.2-4 — Industrial Melanism In Biston betularia Two panels side by side. Panel (a): a section of lichen-covered tree trunk with a light-coloured peppered moth almost invisible against it and a dark moth clearly visible. Panel (b): a section of soot-blackened trunk with the dark moth almost invisible and the light moth clearly visible. Label the light form, the dark form, the lichen cover and the soot cover.

Trace It

Before the factories, tree trunks and walls near Manchester carry a pale crust of lichen.
A light moth resting on that crust is very hard to see; a dark moth stands out against it.
Birds hunting by sight take mostly the dark moths, so in 1850 the dark form is rare.
Coal smoke from the factories kills the lichens and blackens the bark with soot.
The same two moths now sit on a dark surface: the light one stands out, the dark one is hidden.
Birds now take mostly the light moths.
More dark moths than light ones survive to breed, so each generation contains a larger share of dark moths.
Within a few decades the dark form has almost replaced the light form in the polluted area.

One point in that sequence is worth being exact about. No moth changed colour. Both forms were present all along; what changed was which of them the birds could see, and therefore how many of each survived to breed. Natural selection did not create the dark variety — it only altered how common it was.

Curiosity Corner

Q5. How could soot from factory chimneys change the colour of the moths living on the trees nearby?

A. It changed the background, not the moths. Soot blackened the bark the moths rested on, so the dark form became the hidden one, survived the birds and left more offspring until it was the commoner form.

14.2.5 Lamarck’s Theory Compared With Darwin’s Theory

Both theories set out to explain the same thing, and both allow long periods of time and many generations. They part company over where the new character comes from. Table 14.1 sets the two side by side.

Compare Table

Table 14.1 — Lamarck’s Theory Compared With Darwin’s Theory

Basis of difference	Lamarck’s theory	Darwin’s theory
Name of the theory	Known as the theory of inheritance of acquired characters	Known as the theory of natural selection
Main belief	Believes in the use and disuse of an organ; parts used, or changes acquired during life, get transmitted to the next generation	Believes that since variations already exist among individuals, only the fittest survive in the struggle for existence
Origin of new species	New species evolve after a long period of time, after many generations acquire new characters	New species evolve due to the accumulation of favourable variations over a long period of time

The difference in the middle row decides everything. For Lamarck, the environment produces the new character and heredity then carries it; for Darwin, the variation is there first and the environment merely decides which variations are passed on.

Side Note

A Test Of Lamarck’s Idea In the 1880s the German biologist August Weismann removed the tails of mice and bred them, repeating this for many generations. Every generation was still born with a normal tail. A character forced on the body during life did not reach the offspring.

Curiosity Corner

Q4. If a giraffe stretches its neck all its life to reach high leaves, will its calf be born with a longer neck?

A. On Lamarck’s theory, yes. On the evidence, no — a calf inherits what is carried in its parents’ reproductive cells, not what their necks did. Darwin’s account needs no such inheritance: calves already differ in neck length, and the longer-necked ones feed better.

14.2.6 Neo-Darwinism

Darwin’s argument had one gap in it, and he knew it. He could explain what happens to variations once they exist, but he was unable to explain where the variations came from in the first place.

Modern genetics has revealed those sources — chiefly sudden changes in the genetic material, and the reshuffling of parental genes that happens in sexual reproduction. With this added, Darwin’s original theory of natural selection was modified, and the new theory is termed Neo-Darwinism.

The correction takes nothing away from him. Darwin is still regarded as the Father of Evolution, because the mechanism he proposed survived the discovery of everything he did not know.

14.3 Human Evolution

The same reasoning that explains a giraffe’s neck or a moth’s colour must also apply to us. Human beings are living organisms, and if species change over time then so did ours. This section follows that change from an ape-like ancestor to the human beings alive today.

14.3.1 Humans Among The Primates

Carl Linnaeus (1707–1778), who built the system of two-word scientific names, gave our species the name Homo sapiens. Within the animal kingdom, Homo sapiens belongs to the order Primates, along with the monkeys and the apes. FC 14.3 shows where that places us.

Flowchart

FC 14.3 — Where Modern Man Sits In The Animal Kingdom Kingdom Animalia → Phylum Chordata → Class Mammalia → Order Primates → branches to monkeys, apes and human beings (Homo sapiens)

Being placed in one order with monkeys and apes is not a casual grouping. It is based on shared features — grasping hands, forward-facing eyes, nails instead of claws, a large brain for body size — which is exactly the kind of evidence that points to a shared ancestor.

Do Not Mix Up

Monkeys And Apes Monkeys have tails and are generally smaller, with the body held more horizontally. Apes — the gibbon, orangutan, gorilla and chimpanzee — have no tail, have longer arms and a broader chest, and are larger-brained. Human beings are neither, but share the order Primates with both.

Human evolution began against a changing background. Forests had dwindled because of glaciation — a period of ice age marked by colder temperatures and the formation of glaciers. The common ancestors of apes and primitive humans, which had lived in the trees, had to come down from them, and they began by walking on the ground on all four limbs.

14.3.2 The Fossil Record Of Human Origins

The story of our origin was not written down by anyone. It is recorded in the rocks, in the form of fossils — the preserved remains or impressions of organisms that lived long ago, buried in layers of sediment that later hardened into rock. Fig. 14.3-1 shows why the arrangement of those layers matters.

Diagram

Fig. 14.3-1 — How Rock Layers Record Time Vertical section through several horizontal layers of sedimentary rock; label the deepest layer as the oldest and the top layer as the youngest, and show simple fossil remains (a shell, a bone, a skull fragment) embedded at different depths, with an arrow at the side marked ‘increasing age downwards’. Line drawing.

Because sediment settles layer upon layer, the deeper a fossil lies the older it usually is. Comparing fossils from different depths therefore gives an order in time, and this is the scientific basis on which human origin and evolution is studied. The fossils used have been obtained primarily from Asia and Africa.

The record is not complete. Fossilisation is a rare accident, and most individuals leave no trace at all. What survives is enough, however, to construct the evolutionary path that man has followed, even though gaps remain in it.

14.3.3 Changes From An Ape-Like Form To A Human Form

Human beings are supposed to have originated from some ape-like ancestors about 15 to 20 million years ago, during the Miocene period. These ape-like ancestors serve as a common ancestor for both apes and humans — which means apes are not our ancestors but our cousins, sharing an ancestor with us.

Going from an ape-like form to the human form required many major changes. The important ones are these.

Bipedal locomotion, and the freeing of the forelimbs from the ground.
Increase in the cranial capacity.
Reduction in the size of the canines, due to omnivorous feeding habits.
Loss of jaw power.
Development of a chin.
Development of a forehead, with reduction of the brow ridges.
Increase in height.
Erect posture, through the development of the lumbar curve.
Reduction in body hair.

That list is worth reading as a set of linked consequences rather than nine separate items. Once the hind limbs alone carried the body, the forelimbs were free to carry, throw and make things. Hands that could handle food and, later, tools meant the jaws no longer had to tear and hold, so jaw power was lost, the canines shrank, and the snout flattened into a face with a chin. Meanwhile the skull could grow larger, because it was now balanced on top of the vertebral column instead of being slung in front of it.

Bipedalism — walking upright on two legs — is therefore the change that made the others possible. Fig. 14.3-2 shows what it took.

Diagram

Fig. 14.3-2 — The Evolution Of Bipedalism Two skeletons side by side in the same scale, line drawing. Left: an ape skeleton in the four-limbed walking posture, with long forelimbs reaching the ground, a C-shaped vertebral column, a long narrow pelvis and the skull slung forward. Right: a human skeleton standing upright, with shorter forelimbs held clear of the ground, an S-shaped vertebral column with the lumbar curve marked, a short broad bowl-shaped pelvis, and the skull balanced on top of the vertebral column. Label the vertebral column, lumbar curve, pelvis and skull position in both.

Standing upright is not simply a matter of straightening. The vertebral column had to take on curves — the lumbar curve above all — so that the weight of the trunk falls in a line over the hip joints. The pelvis had to become short and broad, like a bowl, to support the organs from below and give the hip muscles a grip that holds the body erect at each step.

Curiosity Corner

Q2. What can the skull and the backbone of a fossil show about whether its owner walked upright or on all fours?

A. In an upright walker the skull sits on top of the vertebral column, so the opening for the spinal cord faces downwards, and the column carries a lumbar curve with a short broad pelvis below it. In a four-limbed walker the skull is slung in front, the column is a single arch, and the pelvis is long and narrow.

Real-World Application

The Price Of Standing Up Upright posture stacks the weight of the head, arms and trunk onto the lowest few vertebrae of the lumbar curve. Those vertebrae and the discs between them take a load no four-limbed animal’s backbone has to bear.

This is one reason low back pain is so common in people, and why lifting a heavy load with a bent back — rather than with bent knees and a straight back — so often injures it. An evolutionary change can leave a weakness behind as well as an advantage.

14.3.4 Ramapithecus, The Prehuman Ancestor

Before the human ancestors proper, it helps to start from a prehuman form, Ramapithecus. It is known only from a few teeth and some fragments of jaw, obtained as fossils in Asia, and for many years these were treated as belonging to an early man-like primate standing at the head of the human line.

Teeth and jaws are useful evidence, because the flat grinding teeth and small canines of a fossil tell you about its diet. They cannot, however, tell you how their owner walked — that needs limb and hip bones, which have not been found for Ramapithecus. Later fossil finds have placed it closer to the Asian apes than to us, and the sequence that follows is best read as the chapter’s ordered set of stages rather than as a chain in which each form is the parent of the next.

14.3.5 Human Ancestors

Over about the last hundred years, fossils of man have been reconsidered in the light of modern biological principles. The different stages of human ancestors during evolution are termed as: Australopithecus, Homo habilis, Homo erectus, Neanderthals, Cro-Magnon and Homo sapiens sapiens (modern man). The stages are shown in Fig. 14.3-3 and listed in order in FC 14.4.

Diagram

Fig. 14.3-3 — Stages In The Evolution Of Man A row of seven full-length figures walking left to right in the same scale, line drawing, each labelled: Ramapithecus, Australopithecus, Homo habilis, Homo erectus, Neanderthal man, Cro-Magnon man, modern man. Show the posture becoming progressively erect, the body hair decreasing, the forehead rising and the height increasing from left to right.

Flowchart

FC 14.4 — Stages In The Evolution Of Modern Man Ramapithecus → Australopithecus → Homo habilis → Homo erectus → Neanderthal man → Cro-Magnon → Homo sapiens sapiens (modern man)

As you read about each stage, watch the same seven features: bipedalism, cranial capacity, size of the canine teeth, forehead and brow ridges, development of the chin, body hair, and height and posture. They are what the whole comparison rests on.

Memory Aid

The Order Of The Stages Really Ancient Humans Ever Needed Clever Minds — Ramapithecus, Australopithecus, Homo habilis, Homo erectus, Neanderthal, Cro-Magnon, Modern man.

14.3.5.1 Australopithecus

Australopithecus was small statured, averaging about 120 centimetres (cm) tall, with a cranial capacity ranging from 450 to 600 cubic centimetres (cm³). It walked nearly straight: the vertebral column had a distinct lumbar curve, and the pelvis was broad. Its head is shown in Fig. 14.3-4.

Diagram

Fig. 14.3-4 — Australopithecus Skull in side view beside a head reconstruction of the same form in side view, line drawing; label the low forehead, the projecting eyebrow ridges over the eyes, the prognathous face and the absence of a chin.

The teeth were strikingly man-like. The dental arch was a smoothly rounded parabola rather than the long U of an ape, the canines did not project beyond the level of the other teeth, and the simian gap — the gap present in apes between the incisors and canines on each side of the jaw, into which the opposing canine fits — was absent. A jaw without that gap is a jaw whose canines have stopped working as weapons.

The face, however, was still prognathous, that is, protruding outwards, and the chin was absent. Eyebrow ridges projected over the eyes.

14.3.5.2 Homo habilis

Homo habilis represented the first man-like ancestor, and is the first of these forms placed in our own genus, Homo. They were about 150 cm tall, with a cranial capacity ranging from 680 to 735 cm³.

They showed bipedal locomotion, slightly more erect than Australopithecus, with a large head and a less protruding face. The body was still covered with hair, and the dentition showed small canines like that of modern man. The forehead was still receding, and there was almost no chin.

14.3.5.3 Homo erectus

Homo erectus was named for the way it stood. They stood erect, and the proportion of the arms to the legs resembled that of the modern man — shorter arms, longer legs, a body built for walking rather than climbing. They walked fully upright, and their pelvis was more bowl-shaped. Their head is shown in Fig. 14.3-5.

Their body size had increased to about 120 to 150 cm, and the cranial capacity ranged between 800 and 1125 cm³. The forehead was receding, the jaws were still projecting and the chin was absent, but the size and arrangement of their teeth resembled those of humans rather than those of apes.

Diagram

Fig. 14.3-5 — Homo erectus Skull in side view beside a head reconstruction in side view, line drawing; label the receding forehead, the prominent brow ridges, the deep-set orbits, the projecting jaws and the absence of a chin.

Homo erectus were the first ancestors to hunt animals and to use fire, as shown in Fig. 14.3-6. Both matter more than they may seem to. Hunting means cooperating and planning; fire means warmth in cold country, protection at night, and cooked food, which is softer and easier to chew — one more reason for heavy jaws and teeth to become unnecessary.

Diagram

Fig. 14.3-6 — Homo erectus At A Cave Scene showing a group of Homo erectus outside a cave shelter: one tending a fire, one carrying a hunted animal, one working a stone tool. Line drawing.

Real Incident / Discovery

The Fossils From Java In 1891 Eugène Dubois, a Dutch physician who had gone to the East Indies deliberately to look for fossils of an early human ancestor, was digging on the bank of the Solo River at Trinil in Java. He found a thick skullcap with heavy brow ridges. The next year, close by, he found a thigh bone.

The skullcap was small-brained and low; the thigh bone was straight and built for walking upright. Dubois named the find Pithecanthropus erectus, the erect ape-man, and it became known as Java Man.

His claim was disputed for decades, until similar fossils were found elsewhere in Asia and Africa. Today they are all classified as Homo erectus.

14.3.5.4 Neanderthal Man

Neanderthal men were successors of Homo erectus. They had a height of about 160 cm and a cranial capacity of about 1450 cm³ — as large as our own, and a reminder that brain size alone does not settle everything about a form.

Neanderthal man exhibited characteristics like absolute bipedalism, a large head, a broad, flat and sloping forehead, prominent brow ridges, almost no chin and less hair on the body. Fig. 14.3-7 shows the skull and head. The classical Neanderthals were found in Western Europe, North Africa and Asia.

Diagram

Fig. 14.3-7 — Neanderthal Man Skull in side view beside a head reconstruction in side view, line drawing; label the low sloping forehead, the prominent brow ridges, the large braincase and the almost absent chin.

Neanderthals are best understood as a closely related group of the genus Homo that lived at the same time as early modern human beings rather than as a step our own ancestors passed through. They buried their dead and made tools, and they died out while our species continued.

14.3.5.5 Cro-Magnon Man

During the last 30,000 years or even more, human beings very close to modern man lived mainly in Europe and were known as Cro-Magnons. They were much more advanced than the Neanderthals, and are shown in Fig. 14.3-8.

Cro-Magnons were about 180 cm in height, with a cranial capacity of about 1450 to 1600 cm³. They had a large skull, a broad face, a rounded forehead and a prominent chin, and they lacked eyebrow ridges. The body was less hairy and the face was perfectly orthognathous, that is, straight-jawed, with strong jaws and man-like dentition.

Diagram

Fig. 14.3-8 — Cro-Magnon Man Skull in side view beside a head reconstruction in side view, line drawing; label the high rounded forehead, the absence of brow ridges, the straight orthognathous face and the prominent chin.

They were swift footed and cave-dwelling. Cro-Magnon made tools from finely chipped stones, of the kinds shown in Fig. 14.3-9. They were good hunters and knew how to use the hide of animals, but did not know agriculture and domestication — so they had to follow their food rather than grow it.

Diagram

Fig. 14.3-9 — Tools Made By Cro-Magnon Man Five chipped stone tools drawn separately and labelled: hand-axe, microliths, blades and spear points, scraper, points. Show the chipped working edge on each. Line drawing.

The Cro-Magnon man possibly represented the transition between the Neanderthal man and the modern man, Homo sapiens sapiens. Further evolution of man after Cro-Magnon involves the evolution of culture rather than of anatomy.

Side Note

Where The Names Come From Both are named after the places their first fossils were found. Neanderthal man is named from the Neander valley in Germany, where quarry workers uncovered bones in 1856. Cro-Magnon man is named from the Cro-Magnon rock shelter at Les Eyzies in France, where skeletons were found in 1868.

14.3.6 Homo sapiens sapiens (Modern Man)

Modern man evolved from Cro-Magnon man towards the end of the last Glacial period. Fossils of modern man have been found in deposits in France, Java and South Africa, and on present evidence people anatomically like us had appeared in Africa at least two hundred thousand years ago, spreading from there across the world.

Modern human beings possess the following main characteristics.

Bipedal locomotion, with four curves in the spine that bend alternately forwards and backwards.
Upright head, with the skull on top of the vertebral column; eyes facing in front, giving binocular vision; and a more mobile neck able to rotate the head for vision in different directions.
Cranial capacity ranging from 1450 to 1600 cm³, with a much enlarged cerebrum.
Straight limbs, with the hindlimbs longer and the forelimbs shorter; fingers and toes with flat nails.
Steep forehead with reduced brow ridges.
Well developed and prominent chin.
Thoracic region flattened into a broad chest by the flattening of the sternum.
Hair on the limbs and body highly reduced.
Entirely erect posture.

Two of these repay a second look. Binocular vision means both eyes look forward at the same object from slightly different positions, which is what gives judgement of distance — essential for an animal that reaches for branches, and later for one that throws. And the enlarged cerebrum is the part of the brain concerned with reasoning, memory and speech, so the growth in cranial capacity is not merely a growth in size.

From Anatomy To Culture

The evolution of the modern human being has been a continuous process, but after a point what changed was no longer the body. Modern man developed a logical and syllabic speech in order to communicate, which allowed one generation to hand on what it had learnt instead of each starting afresh.

He used metals to prepare metallic tools, ornaments and utensils by smelting ores. He cultivated plants and domesticated animals of economic importance. Cities developed on river banks, and as agriculture advanced, humans vastly expanded their numbers, moved to permanent settlements, and civilisations flourished.

The Scientific Revolution came about, and as of today humans have altered the world in ways that benefit them greatly. But with the unintended consequences of this transformation, humans have also created new survival challenges, not only for themselves but for other species as well.

14.3.7 Stages Of Human Evolution Compared

Table 14.2 sets the seven features side by side across all six forms, so that the direction of change in each can be followed across the row.

Compare Table

Table 14.2 — Different Stages Of Human Evolution And Their Major Characteristics

Feature	Australopithecus	Homo habilis	Homo erectus	Neanderthal	Cro-Magnon man	Modern man / Homo sapiens sapiens
1. Bipedalism	Walked nearly straight; vertebral column had a definite lumbar curve	Bipedal gait; slightly more erect than Australopithecus	Walked fully erect	Absolute bipedalism	Perfect bipedalism	Perfect bipedal locomotion
2. Cranial capacity	450 to 600 cm³	680 to 735 cm³	800 to 1125 cm³	About 1450 cm³	1450 to 1600 cm³	1450 to 1600 cm³
3. Size of canine teeth	Almost the same as modern man; did not project above the level of the other teeth	Small canines, almost like those of modern man	Canines of the lower jaw larger; arrangement closer to that of modern man	Small canines, heavier than those of modern man; wisdom teeth present	Small canines; teeth closer to each other; wisdom teeth present	Small canines; teeth closer to each other; wisdom teeth present
4. Forehead and brow ridges	Low forehead; eyebrow ridges projecting over the eyes	Forehead receding, with an ape-like head	Forehead receding and low; prominent brow ridges; deep-set orbits; prognathous face	Forehead low and slanting, broad and flat; prominent eyebrow ridges	Broad arched forehead; moderate brow ridges; orthognathous face	Steep forehead; reduced brow ridges; flattened face
5. Development of chin	Lack of chin; prognathous face	Almost no chin	Almost no chin	Strong lower jaw with almost no chin	Well developed chin	Prominent chin; snout disappeared
6. Body hair	Body covered with hair	Hair on body reduced	Hair on body reduced	Reduced hair on body	Body less hairy	Highly reduced body hair
7. Height and posture	About 120 cm; nearly upright	120 to 150 cm; bent-kneed posture	120 to 150 cm; straight-legged, upright stance	About 160 cm; fully erect	About 180 cm; fully erect	Up to 190 cm; fully erect

The cranial capacity row is the one that can be plotted, and Fig. 14.3-10 does so.

Diagram

Fig. 14.3-10 — Cranial Capacity Across The Stages Of Human Evolution Vertical bar chart. Horizontal axis: the six forms in order — Australopithecus, Homo habilis, Homo erectus, Neanderthal, Cro-Magnon man, modern man. Vertical axis: cranial capacity in cm³, scaled 0 to 1800 with gridlines every 200. Draw each bar to span the range given in Table 14.2: 450–600, 680–735, 800–1125, about 1450, 1450–1600, 1450–1600. Label both axes with quantity and unit.

Interpret Data

Reading Fig. 14.3-10 1. Check the axes first. The horizontal axis is not a scale of years; it is the six forms placed in their order. The vertical axis is a true scale, in cm³. 2. Each bar spans a range, not a single value, because the fossils of one form differ from one another. 3. Read the first three steps. From about 450–600 to 680–735 is a rise of roughly 200 cm³. From there to 800–1125 is a larger rise, and the bar is also much taller, showing a wider spread among the fossils. 4. Read the fourth step. From 800–1125 to about 1450 is the largest single jump in the chart. 5. Read the last two steps. The bars for Neanderthal, Cro-Magnon and modern man are at nearly the same level. The rise has stopped. 6. Draw the conclusion the chart supports: cranial capacity roughly trebled over the earlier stages and then levelled off. What changed after that was culture, not brain size — which is exactly what the last section said. 7. Note one caution. Neighbouring bars overlap, so a single skull of 1500 cm³ could belong to any of the last three forms. A chart of ranges cannot identify an individual fossil.

Curiosity Corner

Q1. Why do scientists measure the empty space inside a fossil skull, and what does that measurement tell them?

A. The space inside the braincase is the cranial capacity, and it gives the volume the brain filled. Measured across fossils in order, it shows the brain roughly trebling from Australopithecus to modern man — and then stopping, which is why the later changes are cultural rather than anatomical.

14.4 Summary

Evolution is the slow and continuous process by which complex forms of life have emerged from simpler forms over millions of years.
The theory of special creation held that every species was created in its present form and never changed.
According to the autogenesis theory, life arose on the early earth from non-living organic matter, through a gradual series of physical and chemical changes.
A species is a group of similar organisms that can breed among themselves and produce fertile young. What changes during evolution is the species, not the individual.
Jean-Baptiste de Lamarck proposed the theory of inheritance of acquired characters, after comparing fossil forms with living species arranged from older to younger.
By the principle of use and disuse, body parts used extensively become larger and stronger, while parts not used deteriorate.
By the principle of inheritance of acquired characters, modifications gained during an organism’s life are passed on to its offspring. Lamarck explained the giraffe’s long neck and fore-limbs by these two principles together.
Vestigial organs are organs that have ceased to be of any use to their possessor but still persist, generation after generation, in a reduced form. They are remnants of features that worked in the organism’s ancestors.
Wisdom teeth, the vermiform appendix and the pinna of the ear are vestigial organs in human beings. The organ corresponding to the appendix helps herbivorous mammals such as the sheep to digest cellulose.
Charles Darwin proposed the theory of natural selection, or Darwinism. It does not state what evolution is; it explains how evolution might have occurred in nature.
Overproduction: organisms produce far more offspring than can survive, yet the number of individuals of a species stays roughly constant in a stable environment.
Struggle for existence: numbers multiply while food and space remain limited, so individuals compete — within the same species (intraspecific) or between different species (interspecific).
Variation: no two individuals are exactly alike. Harmful variations lead to their possessor being weeded out; advantageous variations make their possessor more successful.
Survival of the fittest: only individuals with advantageous variations survive and reproduce. Nature allows only suitable variations to be carried forward, and this is natural selection.
Speciation is the origin of a new species by gradual modification, as favourable variations accumulate over a long period.
Industrial melanism in the peppered moth, Biston betularia, is a classical example of natural selection. Soot killed the lichens and blackened the tree trunks, birds acted as the selective agent, and the dark form almost replaced the light form.
Lamarck and Darwin differ over the source of the new character: for Lamarck the environment produces it and heredity carries it, while for Darwin the variation exists first and the environment decides which variations are passed on.
Darwin could not explain where variations come from. Modern genetics supplied the answer, and the modified theory is called Neo-Darwinism. Darwin is still regarded as the Father of Evolution.
Carl Linnaeus gave man the scientific name Homo sapiens, which belongs to the order Primates along with monkeys and apes.
Human origin and evolution is studied from fossils, obtained primarily from Asia and Africa. The fossil record is incomplete but is enough to construct the path that man has followed.
Human beings originated from ape-like ancestors about 15 to 20 million years ago, and these ancestors are common to both apes and humans.
The major changes from an ape-like form to the human form were bipedal locomotion with freeing of the forelimbs, increase in cranial capacity, reduction of the canines, loss of jaw power, development of a chin and a forehead with reduced brow ridges, increase in height, erect posture through the lumbar curve, and reduction of body hair.
Ramapithecus, known only from teeth and jaw fragments, is taken as the prehuman form standing before the human ancestors.
The stages of human ancestors are Australopithecus, Homo habilis, Homo erectus, Neanderthals, Cro-Magnon and Homo sapiens sapiens.
Cranial capacity rises across these stages — about 450 to 600 cm³ in Australopithecus, 680 to 735 cm³ in Homo habilis, 800 to 1125 cm³ in Homo erectus, about 1450 cm³ in Neanderthal man, and 1450 to 1600 cm³ in Cro-Magnon and modern man — and then levels off.
Homo erectus were the first ancestors to hunt animals and to use fire. Cro-Magnon made finely chipped stone tools and used animal hide, but did not know agriculture and domestication.
Modern man shows entirely erect posture, a spine with four alternating curves, the skull balanced on top of the vertebral column, binocular vision, an enlarged cerebrum, a prominent chin, a steep forehead and highly reduced body hair.
Evolution after Cro-Magnon has been of culture rather than of anatomy — speech, metal working, agriculture, domestication, settlements and civilisations — and this transformation has created new survival challenges for human beings and for other species.

Flowchart

FC 14.5 — The Chapter End To End Non-living organic matter → origin of simple forms of life → variations among individuals → overproduction and struggle for existence → natural selection of favourable variations → accumulation over long periods → speciation → ape-like ancestors of the Miocene → Ramapithecus → Australopithecus → Homo habilis → Homo erectus → Neanderthal man → Cro-Magnon → Homo sapiens sapiens, in whom further change is cultural rather than anatomical

14.5 Key Terms

Autogenesis theory — The idea that life arose on the early earth from non-living organic matter, through a gradual series of physical and chemical changes.
Bipedalism — Walking upright on the two hind limbs, leaving the forelimbs free.
Cranial capacity — The volume of the space inside the braincase, measured in cubic centimetres, and taken as a measure of brain size.
Darwinism — Darwin’s explanation of how evolution occurs, that is, the theory of natural selection.
Evolution — The slow and continuous process by which complex forms of life have emerged from simpler forms over millions of years.
Fossil — The preserved remains or impression of an organism that lived long ago, buried in sediment that later hardened into rock.
Glaciation — A period of ice age, marked by colder temperatures and the formation of glaciers.
Industrial melanism — The replacement of a light-coloured form of an organism by a dark form in a soot-polluted area, seen in the peppered moth, Biston betularia.
Inheritance of acquired characters — Lamarck’s claim that modifications gained by an organism during its own lifetime are passed on to its offspring.
Natural selection — The process by which the environment allows only individuals with suitable variations to survive and reproduce.
Neo-Darwinism — Darwin’s theory of natural selection as modified by modern genetics, which supplies the sources of variation he could not explain.
Orthognathous — Having a straight, flat face with jaws that do not project forward.
Overproduction — The production by organisms of far more offspring than can possibly survive.
Primates — The order of mammals that includes the monkeys, the apes and human beings.
Prognathous — Having a face with the jaws protruding outwards, as in apes.
Simian gap — The gap present in apes between the incisors and the canines on each side of the jaw, absent in human beings.
Special creation — The idea that the earth and every living thing on it were created complete, in their present forms, and have never changed.
Speciation — The origin of a new species by gradual modification of an existing one.
Species — A group of similar organisms that can breed among themselves and produce fertile young.
Struggle for existence — The competition among organisms for food, space, shelter and breeding places, which are limited while numbers multiply.
Survival of the fittest — The survival, during the struggle for existence, of only those individuals that carry advantageous variations.
Use and disuse — Lamarck’s principle that a body part used extensively becomes larger and stronger, while one that is not used deteriorates.
Variations — The differences that exist between individuals of the same species, including between offspring of the same parents.
Vestigial organs — Organs that have ceased to be of any use to their possessor but still persist, generation after generation, in a reduced form.

14.6 Points To Ponder

The dark peppered moth existed before the factories did. If natural selection can only work on variations that are already present, what happens to a species when its environment changes faster than variation can supply anything useful?
A vestigial organ counts as evidence of ancestry precisely because it is useless. Is a structure that still works well — the human hand, say — weaker evidence of shared ancestry, or stronger? Give your reasoning.
Cranial capacity stopped rising after the Neanderthal stage, yet what human beings are able to do has expanded enormously since then. Where must that expansion be coming from, if not from the brain getting bigger?
Lamarck’s mechanism turned out to be wrong, but his central claim — that living species descend from earlier and different ones — turned out to be right. Is a theory that gets the mechanism wrong of any use to science?
The fossil record is admitted to be incomplete. On what grounds, then, can anyone claim it is enough to construct an evolutionary path? What would make you confident about an order you can only sample in places?
Bipedalism freed the forelimbs but loaded the lower vertebrae. Find one more change described in this chapter that brought a cost along with its advantage, and consider whether natural selection has any way of avoiding such costs.

14.7 Objective Questions

Multiple Choice Questions

A fossil skull with a cranial capacity of 900 cm³ would belong to: (1 mark)
1. Australopithecus
2. Homo habilis
3. Homo erectus
4. Cro-Magnon man
The principle of use and disuse forms a part of: (1 mark)
1. the theory of natural selection
2. the theory of inheritance of acquired characters
3. Neo-Darwinism
4. the theory of special creation
In the peppered moth, the selective agent that decided which form survived was: (1 mark)
1. the soot on the bark
2. the lichens on the bark
3. the birds that fed on the moths
4. the temperature of the air
The first human ancestors to hunt animals and use fire were: (1 mark)
1. Ramapithecus
2. Australopithecus
3. Homo erectus
4. Cro-Magnon man
Which one of the following is not a vestigial organ in human beings? (1 mark)
1. Vermiform appendix
2. Sternum
3. Pinna
4. Wisdom teeth

Assertion–Reason Questions

For each of the following, choose the correct option: (a) Both A and R are true, and R is the correct explanation of A. (b) Both A and R are true, but R is not the correct explanation of A. (c) A is true but R is false. (d) A is false but R is true.

Assertion (A): The vermiform appendix is regarded as a vestigial organ in human beings. Reason (R): The corresponding organ in herbivorous mammals such as the sheep is quite helpful in digesting cellulose. (1 mark)
Assertion (A): Natural selection created the dark variety of the peppered moth in the Manchester area. Reason (R): After the industrial revolution the dark variety survived better than the light variety. (1 mark)

Match The Following

Match each item in Column A with the correct item in Column B. (2 marks)

Column A	Column B
a. Biston betularia	i. Known only from teeth and jaw fragments
b. Ramapithecus	ii. Gave man the name Homo sapiens
c. Carl Linnaeus	iii. Industrial melanism
d. Neo-Darwinism	iv. Supplies the sources of variation

Fill In The Blanks

Fill in the blanks with a suitable word. (2 marks)
1. The order of mammals to which monkeys, apes and human beings belong is ____.
2. A period of ice age marked by colder temperatures and the formation of glaciers is called ____.
3. The gap present in apes between the incisors and the canines is called the ____ gap.
4. The origin of a new species by gradual modification is called ____.

True Or False

State whether each statement is true or false. (2 marks)
1. Homo habilis is regarded as the first man-like ancestor.
2. The muscles connected with the pinna are well developed and fully working in human beings.
3. Cro-Magnon man knew agriculture and the domestication of animals.
4. The fossils used in the study of human evolution were obtained primarily from Asia and Africa.

Name The Following

Name the following. (5 marks)
1. The theory according to which life arose from non-living organic matter.
2. The type of vision produced by both eyes facing forward.
3. The competition that takes place between members of the same species.
4. The human ancestor about 180 cm tall that made tools from finely chipped stones.
5. The scientist who could not explain the sources of variation.

Odd One Out

Pick the odd one out from each group and give a reason for your choice. (2 marks)
1. Wisdom teeth, vermiform appendix, sternum, pinna.
2. Homo habilis, Australopithecus, Homo erectus, Homo sapiens sapiens.

14.8 Check Your Concepts

Define vestigial organs, and name any two found in human beings. (2 marks)
State the two principles through which Lamarck explained his ideas. (2 marks)
What is meant by speciation? (2 marks)
Differentiate between intraspecific and interspecific competition, stating the basis of difference. (2 marks)
Give a reason why the pinna is regarded as a vestigial organ in human beings. (2 marks)
Explain, using the giraffe, how Lamarck accounted for its long neck and fore-limbs. (3 marks)
Differentiate between an acquired character and an inherited character, stating the basis of difference. (3 marks)
Differentiate between Lamarck’s theory and Darwin’s theory on any three bases. (3 marks)
Why does overproduction lead to a struggle for existence, even though the number of individuals of a species stays roughly constant in a stable environment? (3 marks)
Darwin’s original theory had to be modified. Why, then, is he still regarded as the Father of Evolution? (3 marks)
Describe how the industrial revolution altered the peppered moth population near Manchester, and state the part played by the birds. (4 marks)
What would happen to evolution in a species whose individuals were all exactly alike? Explain your answer. (4 marks)
Explain why bipedalism is regarded as the change that made several of the other human changes possible. (4 marks)
Explain Darwin’s theory of natural selection, taking its four observable facts in the correct order. (5 marks)
Describe any five characteristics of Homo sapiens sapiens (modern man). (5 marks)

14.9 Figure-Based Questions

Study Fig. 14.2-2. (3 marks)
1. Name the vestigial organ shown and the part of the gut from which it arises.
2. State the condition of the corresponding organ in a sheep, and the use it is put to.
With reference to Fig. 14.2-4: (4 marks)
1. Give the common name and the scientific name of the insect shown.
2. Name the phenomenon the two panels illustrate.
3. State which form is at an advantage in panel (b), and give a reason.
With reference to Fig. 14.3-2: (4 marks)
1. State two differences between the vertebral column of the ape and that of the human being.
2. Explain how the shape of the human pelvis helps in maintaining erect posture.
Redraw the outline of the skull shown in Fig. 14.3-7 and label the brow ridges, the forehead and the chin region, using straight, non-crossing lead lines. Name the human ancestor to which it belongs. (4 marks)
Study Fig. 14.3-10. (3 marks)
1. Between which two stages does the largest single increase in cranial capacity occur?
2. State what the level portion at the right-hand end of the chart indicates about human evolution after that point.
Fig. 14.3-9 shows articles made by one of the human ancestors. Name the ancestor, and state two things that this ancestor did not know how to do. (2 marks)