What fossils such as Ardi, Lucy and the Turkana fossils and stone tools tell us about how humans evolved, and how the evidence is dated.
Objectives
Describe the evidence for human evolution from the fossils Ardi, Lucy and the fossils found by Richard Leakey.
Describe how stone tools changed over time and how they can be dated.
Say why the fossil evidence is incomplete and why ideas about human evolution can change.
Specification references this topic covers: AQA 4.6.3; Edexcel B4.4, B4.5.
Evidence for human evolution explained
Start here
Humans are part of the same tree of life as all other animals. Over millions of years our ancestors changed. Scientists build up the story from clues: fossil bones, and the tools our ancestors made.
This matters because it shows how evolution can be studied when no one was there to watch. It also shows how scientists use evidence, and how ideas change when new fossils are found.
By the end you will be able to describe three important fossils, say how stone tools changed, and explain how the evidence is dated.
Fossil evidence
Fossils form when parts of an organism are buried in sediment and replaced by minerals, or when the shape is left as an imprint. Bones and teeth fossilise best because they are hard.
By studying fossil bones, scientists work out how tall an individual was, how it moved, how big its brain was and what it ate. The skull shows brain size. The pelvis, leg bones and the position of the hole where the spine joins the skull show whether it walked upright.
Putting fossils in order of age shows how features changed. Over about 4.4 million years our ancestors became more upright, with larger brains and smaller teeth and jaws.
Ardi: 4.4 million years ago
Ardi is a fossil skeleton of an early human ancestor, Ardipithecus ramidus, found in Ethiopia and about 4.4 million years old. Ardi had a small brain, about the same size as a chimpanzee's.
Ardi could walk upright on two legs, but the foot still had a big toe that stuck out sideways and could grip branches. So Ardi was adapted both for walking and for climbing in trees.
Ardi shows that walking upright started very early, before the human brain became large.
Lucy: 3.2 million years ago
Lucy is a fossil skeleton found in Ethiopia and about 3.2 million years old. She belongs to a species called Australopithecus afarensis. Lucy stood about 1.1 m tall.
The shape of her pelvis and leg bones show that she walked upright on two legs. Her brain was still small, about 400 cm³. Her arms were long and she may have climbed trees too.
Lucy and Ardi together show that our ancestors walked upright long before they had large brains. Walking on two legs frees the hands and helps an animal to see over long grass.
Richard Leakey's fossils: 1.6 million years ago
Richard Leakey and his team found fossils around Lake Turkana in Kenya, including a nearly complete skeleton of a young person about 1.6 million years old. It is a Homo erectus fossil and is often called the Turkana Boy.
The skeleton shows a tall body with long legs, built much more like a modern human than Lucy. The brain was much larger than Lucy's, at about 900 cm³, though still smaller than ours, which is about 1350 cm³.
Fossils such as these show that over time our ancestors became taller, longer-legged and bigger-brained. They were also able to make better tools.
Stone tools
Stone tools are another kind of evidence. The oldest tools are simple stones with a few flakes knocked off to make a sharp edge, used for chopping and cutting meat. Later tools, such as hand axes, were shaped on both sides into a regular teardrop shape.
Over time tools became more complicated and better made. This suggests that our ancestors were getting better at planning and using their hands, and that their brains were developing. Later still there were tools of bone and finely worked stone blades.
Tools tell us what our ancestors could do. For example, cut marks on animal bones show that they used tools to butcher meat.
Dating the evidence
Tools and fossils can be dated from where they are found. Layers of rock build up over time, so deeper layers are usually older. Tools or bones found in the same layer are about the same age.
Layers of volcanic ash or lava above and below a find can be dated using radioactive decay, because the half-life of the radioactive elements in them is known. This puts an age range on the layer. Material such as bone or charcoal found with the tools can be dated by its radioactive carbon, for more recent finds.
The fossil record is incomplete. Most organisms never fossilised, and fossils can be destroyed by erosion, or not yet found. So scientists have to work out the story from limited evidence, and new discoveries can change ideas about human evolution.
Recap
Ardi (4.4 million years ago) and Lucy (3.2 million years ago) walked upright but had small brains. The fossils from 1.6 million years ago are taller with a larger brain.
Stone tools became more complex over time. They are dated from the age of the rock layers they are found in.
The fossil record is incomplete, so ideas can change when new evidence is found.
Key points
Ardi (4.4 million years ago): upright, grasping toe, small brain. Lucy (3.2 million): upright, small brain. Leakey's fossils (1.6 million): tall, bigger brain.
Upright walking evolved before big brains.
Stone tools became more complex and skilled over time.
Dating: age of the rock layer, radioactive decay of layers above and below. The fossil record is incomplete.
Worked examples
Example 1
Ardi and Lucy both walked upright. Give one piece of evidence from their skeletons that shows this.
Scientists look at the shape of the bones.
The pelvis and leg bones are built for walking on two legs.
So the shape of the pelvis and legs shows upright walking.
Answer: The shape of the pelvis and leg bones
Common slips
Slip: The colour of the bones. The colour comes from the minerals in the rock.
Slip: They were found in Ethiopia. The place where a fossil is found does not show how it moved.
Slip: The size of the skull. The skull shows brain size, not how the animal moved.
Example 2
Lucy's brain volume was about 400 cm³. Modern human brains are about 1350 cm³. Calculate how many times bigger a modern brain is, to 2 significant figures.
Divide the modern brain size by Lucy's brain size.
1350 ÷ 400 = 3.375.
To 2 significant figures this is 3.4.
Answer: 3.4 times bigger
Common slips
Slip: 400 ÷ 1350 = 0.30 That is Lucy's brain as a fraction of ours. The question asks how many times bigger ours is.
Slip: 1350 − 400 = 950 That is the difference, not how many times bigger.
Slip: 3.375 × 100 = 337.5% The question asks for how many times bigger, not a percentage.
Example 3
A stone hand axe is found in a layer of rock between two layers of volcanic ash. The lower ash layer is 1.7 million years old and the upper layer is 1.5 million years old. Explain what this tells you about the age of the axe and how the dates of the ash are found.
Layers lower down were laid down earlier, so the axe layer is younger than the lower ash and older than the upper ash.
The axe is between 1.5 and 1.7 million years old.
The ash layers can be dated using radioactive decay, because the half-life of the radioactive elements in the ash is known.
Measuring how much of the radioactive element has decayed gives the age of the layer.
Answer: The axe is between 1.5 and 1.7 million years old, found by dating the ash layers using radioactive decay
Common slips
Slip: The axe is exactly 1.6 million years old. You can only say it lies between the two dates.
Slip: The axe is older than 1.7 million years. It is above the lower layer, so it is younger than 1.7 million years.
Slip: The ash is dated by its colour. It is dated by radioactive decay.
Slip: The axe is younger than 1.5 million years. It is below the upper ash layer, so it is older than 1.5 million years.
Questions and answers
Evidence for human evolution practice questions for GCSE Combined Science Biology. Try each one, then open the answer. Easy questions come first.
Question 1 Easy
How many million years old is Ardi?
Show answer
Answer: 4.4
Ardi lived 4.4 million years ago.
Ardi is 4.4 million years old.
Question 2 Easy
How many million years old is Lucy?
Show answer
Answer: 3.2
Lucy lived 3.2 million years ago.
Lucy is 3.2 million years old.
Question 3 Easy
What word means walking on two legs?
Show answer
Answer: bipedal
Bi means two and ped means foot.
The word is bipedal.
Question 4 Easy
Which bones show that Lucy walked upright: the pelvis and leg bones or the finger bones?
Show answer
Answer: the pelvis and leg bones
Walking depends on the pelvis and legs.
So it is the pelvis and leg bones.
Question 5 Easy
Are older rock layers usually higher or lower down?
Show answer
Answer: lower
New layers are laid on top of old ones.
So older layers are lower down.
Question 6 Medium
Did upright walking evolve before or after large brains?
Show answer
Answer: before
Ardi and Lucy walked upright but had small brains.
So walking came first.
Question 7 Medium
Lucy's brain was about 400 cm³. A modern human brain is about 1350 cm³. How many times bigger is the modern brain? Give your answer to 2 significant figures.
Show answer
Answer: 3.4
Divide 1350 by 400.
1350 ÷ 400 = 3.4 (2 s.f.).
Question 8 Medium
Ardi is 4.4 million years old and Lucy is 3.2 million years old. How many million years separate them?
Show answer
Answer: 1.2
Subtract the two ages.
4.4 − 3.2 = 1.2 million years.
Exam-style questions
Longer questions in the style of a written paper, with the marking points. These are Yumio practice questions.
Exam-style question 14 marks
(a) Ardi and Lucy are fossils of early human ancestors. Describe two features that show they were able to walk upright. [2 marks] (b) State what the sizes of their brains tell us about the order in which features evolved. [2 marks]
Show answer and marking points
Answer: (a) the shape of the pelvis and the shape of the leg bones (b) their brains were small compared with modern humans, so walking upright evolved before large brains
(a) shape of the pelvis (1)
(a) leg bones or foot or position of the skull joint (1)
(b) their brains were small (1)
(b) so upright walking evolved before large brains (1)
Exam-style question 24 marks
(a) Describe how stone tools changed over time. [2 marks] (b) Explain how the age of stone tools can be found. [2 marks]
Show answer and marking points
Answer: (a) the oldest tools were simple stones with a sharp edge and later tools were shaped and more complex (b) the age of the layer of rock they are found in, which can be found by dating volcanic ash layers above and below using radioactive decay
(a) early tools were simple or crude (1)
(a) later tools were more complex or shaped (1)
(b) the tools take the age of the rock layer (1)
(b) dated using radioactive decay of rock or ash above and below (1)
Common mistakes
Saying Lucy had a large brain
Lucy had a small brain, about 400 cm³. She walked upright.
Saying humans evolved from chimpanzees
Humans and chimpanzees share a common ancestor. We did not evolve from chimpanzees.
Mixing up the ages of Ardi and Lucy
Ardi is 4.4 million years old, Lucy is 3.2 million years old and the Leakey fossils are 1.6 million years old.
Saying the fossil record is complete
Most organisms never fossilised, so it has gaps.
Saying a tool is exactly as old as one ash layer
A tool between two layers is between their ages.
Questions students ask
Is Evidence for human evolution on the Foundation or Higher tier?
Evidence for human evolution is on both Foundation and Higher papers for GCSE Combined Science Biology, aimed at around grade 6.
What is a common mistake on Evidence for human evolution?
Saying Lucy had a large brain. Lucy had a small brain, about 400 cm³. She walked upright.
Where are the answers to the Evidence for human evolution questions?
Open Show answer under each question on this page. The questions are Yumio practice questions, not past exam questions.