Evolution of Humankind (Senior 1 History and Citizenship): free lessons | Ganzaa

Evolution of Humankind

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Senior 1 · History and Citizenship

Evolution of Humankind

5 lessons

Lesson 1 of 5

The origin of humankind

22 min

A prediction made in 1871

In 1871 the English naturalist Charles Darwin published The Descent of Man. At that time not a single fossil of an early human had been found in Africa. Yet Darwin wrote:

"In each great region of the world the living mammals are closely related to the extinct species of the same region. It is therefore probable that Africa was formerly inhabited by extinct apes closely allied to the gorilla and chimpanzee; and as these two species are now man's nearest allies, it is somewhat more probable that our early progenitors lived on the African continent than elsewhere."

Charles Darwin, The Descent of Man (1871), chapter 6. Public domain.

Words to know: "allied" means closely related; "progenitors" means ancestors.

Before reading on, answer: What does Darwin predict? What evidence does he use? Is his statement a fact, or a reasoned guess?

Worked example: analysing Darwin's statement as a source

Who? Charles Darwin (1809–1882), a British naturalist who had spent decades studying plants and animals. An expert, but not an eyewitness to human origins; no one was.
When? 1871, before any early human fossil had been found in Africa. So this is a prediction, not a report of a discovery.
Why? To argue that humans, like other living things, have evolved. He wanted to persuade, so he chose his words carefully: "probable", "somewhat more probable".
What reasoning? Living animals are usually related to extinct animals of the same region; our closest living relatives, gorillas and chimpanzees, live in Africa; so our ancestors probably lived in Africa too.
Was it confirmed? Yes, by later evidence: the Taung Child in South Africa (1924), the finds at Olduvai Gorge in Tanzania (from 1959) and "Lucy" in Ethiopia (1974).

Verdict: a valuable source for how scientists reasoned in 1871, and a prediction that later evidence supported. On its own it is not evidence of where humans began; the fossils are.

Two ways of answering "Where do we come from?"

People have always asked where humans came from. Their answers take two broad forms.

Creation accounts. Religions and cultures explain the beginning of humans through faith. The Bible and the Qur'an teach that God created the first man and woman, Adam and Eve (Hawwa). Rwandan tradition speaks of Imana as the creator of all things. These accounts answer questions of meaning and faith: why we exist and how we should live.
The scientific theory of evolution. Scientists explain how living things changed over very long periods, using evidence that can be tested: fossils, the layers of rock in which they lie, stone tools, and the DNA of living people.

Many people hold religious beliefs about creation and also study the scientific evidence, because the two answer different kinds of question. History and archaeology work with evidence, so this unit follows the scientific account.

Definition

Evolution: the gradual change in living things over many generations, as features that help survival are passed on more often. Example: over millions of years our ancestors' brains became larger and their bodies became adapted to walking upright.

Definition

Fossil: the remains or traces of a living thing preserved in rock, such as bones, teeth or footprints. Example: the footprints at Laetoli in Tanzania, left in volcanic ash about 3.66 million years ago.

Definition

Hominid: a member of the human family: modern humans and our extinct relatives who walked upright, such as Australopithecus and Homo erectus. Scientists today often use the word hominin for this group. Example: "Lucy" was a hominid.

The evidence: Africa is the cradle of humankind

Figure 1. Some of Africa's most important early human fossil sites. The oldest fossils of hominids, and of our own species, have all been found in Africa. Map drawn by Ganzaa from Natural Earth (public domain) outlines.

Evidence	What it shows
Fossils	The oldest hominid fossils, from about 7 million to 2 million years old, have been found only in Africa: in Chad, Ethiopia, Kenya, Tanzania and South Africa.
Footprints	At Laetoli, Tanzania, hominids walked upright through wet volcanic ash about 3.66 million years ago.
Stone tools	The oldest known stone tools, about 3.3 million years old, come from Lomekwi, near Lake Turkana in Kenya.
Our own species	The oldest fossils of Homo sapiens, about 300,000 years old, come from Jebel Irhoud in Morocco.
DNA	Living people in Africa have more genetic variety than everyone else in the world together, a sign that humans lived in Africa longest and that all people today share African ancestors.

Case study: Olduvai Gorge, Tanzania

Olduvai Gorge is a steep-sided valley about 50 km long in the Great Rift Valley of northern Tanzania. For decades the archaeologists Mary Leakey and Louis Leakey searched its layers. In 1959 Mary Leakey found the skull of a robust hominid about 1.75 million years old, now called Paranthropus boisei. Soon afterwards the team found the bones of a smaller-toothed, larger-brained hominid lying among simple stone tools. In 1964 it was named Homo habilis, "handy man", because scientists believed it made those tools.

Olduvai matters for two reasons. The layers of volcanic ash can be dated scientifically, so the fossils can be given ages in years. And tools, bones and animal remains are found together, so archaeologists can study how early humans actually lived. Many Tanzanians prefer the local name Oldupai, after a wild sisal plant that grows there.

Important

Humans did not evolve from chimpanzees or gorillas. Humans and chimpanzees share a common ancestor that lived about 6 to 7 million years ago; since then each line has evolved separately.

HHMI BioInteractive: "Finding the Lucy Fossil". Watch for the clues in Lucy's knee and hip that showed scientists she walked upright.

Discussion

Think, pair, share: Most of the oldest hominid fossils have been found in the Rift Valley of East Africa. Does that prove early humans lived only there? Think about where volcanic ash preserves bones, where rivers expose old layers, and where scientists have chosen to search.

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Practice

What did Darwin predict in 1871, and why was it only a prediction at that time?
Define a fossil and give one example from East Africa.
Give two kinds of evidence showing that humans first evolved in Africa.
Who found the Paranthropus boisei skull at Olduvai Gorge, and in which year?
Why are the layers of volcanic ash at Olduvai so useful to scientists?
Explain the difference between the questions answered by creation accounts and those answered by the theory of evolution.
"Humans evolved from chimpanzees." Correct this statement.

Show answersHide answers

That humanity's earliest ancestors probably lived in Africa. It was a prediction because no early human fossils had yet been found in Africa; he reasoned from where our closest living relatives live.
The remains or traces of a living thing preserved in rock. Examples: the Laetoli footprints; Lucy; the Turkana Boy; the Olduvai skulls.
Any two: the oldest hominid fossils are all African; the oldest stone tools (Lomekwi, Kenya); the oldest Homo sapiens fossils (Jebel Irhoud, Morocco); the great genetic variety of African populations.
Mary Leakey, in 1959.
Volcanic ash can be dated scientifically, and the layers lie in order, so fossils and tools found in them can be given ages in years.
Creation accounts answer questions of faith and meaning, such as why we exist; evolution explains how living things changed over time, using evidence that can be tested.
Humans and chimpanzees share a common ancestor that lived about 6 to 7 million years ago; humans did not descend from chimpanzees.

Sources and credits

Extract from Charles Darwin, The Descent of Man (1871), via Project Gutenberg, public domain.
Photo: Olduvai gorge, gailhampshire, via Wikimedia Commons, CC BY 2.0.
Figure 1 was drawn by Ganzaa from Natural Earth outlines (public domain).
Video: "Finding the Lucy Fossil", HHMI BioInteractive, embedded from YouTube.
The rest of this lesson, the practice items and the unit exercises were written by Ganzaa.

1A prediction made in 1871

2Two ways of answering "Where do we come from?"

3The evidence: Africa is the cradle of humankind

4Case study: Olduvai Gorge, Tanzania

5Discussion

A prediction made in 1871

Two ways of answering "Where do we come from?"

The evidence: Africa is the cradle of humankind

Case study: Olduvai Gorge, Tanzania

Discussion