PAST’s Tools4Schools series provide educators with powerful teaching tools
The Palaeontological Scientific Trust’s commitment to education in the origin sciences is being significantly expanded with the launch of PAST’s new Tools4Schools – an initiative to provide tools for learners and teachers online.
Welcome to PAST’s Walking Tall Video Trilogy, a series of three video performances by PAST’s award-winning Walking Tall Educational Theatre Project! The three videos tell the amazing story of the shared origins of humankind and of all living things. Ten short messages highlight the most important information contained in each video. These should be read after watching each video.
Titled African Homeland, the first video tells the story of human evolution. In just under six minutes, it reminds viewers that all the things that make us human started in Africa, from bipedalism and technology, to art, intelligence and language. This is why Africa is known as the Cradle of Humankind.
- All people belong to a species called Homo sapiens. Our species belong to a group of mammal species called primates. Other primate species include monkeys, gorillas and chimpanzees. Chimpanzees are the living species most closely related to us. Many people think we evolved from chimpanzees, but this is not true.
- Instead, humans and chimpanzees both evolved from the same common ancestor. This species lived in Africa between 6 and 7 million years ago and gave rise to two new lines of evolving species. One line eventually evolved into the chimpanzees we see today. The other line includes a group of species called hominids that eventually gave rise to us.
- The first species to evolve from the common ancestor on the hominid line was called Sahelanthropus. Sahelanthropus lived in Africa 6 million years ago. It was the first human ancestor to walk upright on two legs. Called bipedalism, upright walking allowed Sahelanthropus to more easily carry food, other objects, and their babies.
- Sahelanthropus was a biped, but it also climbed trees to eat fruit and other plant foods. Sahelanthropus probably also slept in trees to stay safe from large predators such as the ancestors of lions and leopards. Little else is known about Sahelanthropus, but palaeontologists are searching rock layers of its age to find more of its fossil remains.
- Many hominid species evolved after Sahelanthropus, including Ardipithecus and a group called the australopithecines that appeared 4 million years ago. These include the Taung Child from South Africa, the first hominid found in Africa and the first fossil evidence that human ancestry lay on this continent. Other famous australopithecines are South Africa’s “Little Foot,” Ethiopia’s “Lucy,” and Tanzania’s “Zinjanthropus.”
- One of the australopithecines gave rise to Homo habilis in Africa about 2.5 million years ago. Homo habilis was the first hominid to make tools from stone. The tools were simple knives and pounders used to extract meat and marrow from large animals scavenged from lions and other big cat kills. Homo habilis was also the first hominid to have a brain larger than that of apes, but it was still only half the size of ours.
- Homo erectus evolved from Homo habilis by 1.5 million years ago. Homo erectus had a larger brain than Homo habilis, but it was still three-quarters the size of ours. Homo erectus made complex stone tools, but its greatest invention was controlling fire. Fire allowed Homo erectus to expand out of Africa into cooler Europe and Asia. Fire also allowed Homo erectus to cook food, greatly expanding the variety of plant and animal foods in their diet.
- Our species, Homo sapiens, evolved in Africa 200,000 years ago. Although physically like us, with a large brain, early Homo sapiens hunted animals, fished, and gathered wild plant foods. They made very complex tools from stone, bone and other materials and they had the same intelligence and cognitive abilities as we do. In fact, they created the first art and ornamentation by 90,000 years ago, and spoke the first languages.
- We hope you can now see how Africa is humankind’s birthplace. Our earliest bipedal ancestors arose in Africa, as did every species that led to us. This means that the fossil heritage of every person in the world today lies in Africa.
- We are an African species, because everything that makes us human arose in Africa. All of humankind’s greatest accomplishments were made possible by our 6 million years of evolution in Africa.
Human Unity amid Diversity
Now that you know we are an African species, you can explore how our ancestors expanded out of Africa to populate the rest of the world. The second Walking Tall video, called Human Unity amid Diversity, will guide you on this journey. You will discover when humans first populated other continents and learn about some of the physical differences that arose. Among these are skin colour differences.
- Our species, Homo sapiens, arose in Africa 200,000 years ago, but it was not until 60,000 years ago that the ancestors of all non-Africans living today expanded out of Africa. From one generation to the next, populations grew and spread into Europe, Asia and Australasia by 45,000 years ago. Later, global sea levels fell during a cold period, allowing some groups to cross the now submerged land bridge from Siberia into North and South America by 15,000 years ago.
- Homo sapiens adapted to the new environments encountered during their global expansion by relying on their African-grown intelligence and Stone Age technology. Only a few of the adaptations were genetic, and these led to regional differences we see today in traits such as hair type, nose shape and skin colour. Skin colour differences are important to understand, because these have been repeatedly but mistakenly used to divide people into races.
- Your skin colour is determined by the amount and type of melanin, a natural pigment, made in a layer of your skin cells called melanocytes. The more melanin these cells make, the darker your skin. Melanin production is controlled by about ten genes. Differences in these genes between you and others are due to mutations and result in different skin colours.
- Melanin acts as a natural sun block by controlling the amount of the sun’s ultraviolet radiation (UVR) penetrating your skin. The more melanin you make, the more UVR you block. People with darker skin usually come from equatorial areas, where the sun’s UVR is strong. People with lighter skin come from areas further from the Equator where UVR is weaker. We see this pattern because skin colour is an adaptation UVR levels.
- Dark skin is beneficial in equatorial areas because it protects a vitamin called folate from being broken-down by UVR. Folate is important for many body functions and is essential for normal brain and spinal cord growth in unborn children. Because of this, you can see that individuals with genes for dark skin are better adapted to the high UVR near the Equator. But if dark skin is so beneficial, why don’t all people have dark skin?
- The benefit of dark skin declines further north and south of the Equator. This is because everyone needs some UVR to make another important vitamin, vitamin D, which is essential for normal bone growth. Vitamin D deficiency can result in the deformities seen in people with rickets, and can prevent normal childbirth by deforming the birth canal. Because of this, you can see that individuals with genes for lighter skin are better adapted to places like Europe.
- In summary, skin colour of people from different regions balances the need to protect the body’s folate from too much UVR with the need to produce Vitamin D in low UVR environments. UVR levels change gradually across the earth, and as a result skin colour of indigenous people also changes gradually from one place to another. In fact, skin colours blend into one another, forming a continuum, or range, of darker to lighter skin tones that lacks sharp breaks.
- Because skin colour differences in people form a continuum without breaks, it impossible to divide people into races based on skin colour in anything but an arbitrary way! Where does “black” end and “white” begin? What about “coloured?” You can see these are false categories. In fact, the whole idea of race has no biological reality!
- The physical differences that emerged since humans first spread out of Africa are greatly outnumbered by our similarities. For example, the nucleotide sequences in the genomes of any two people are 99.9% alike. And, the different appearances of Africans, Europeans, Asians and others arose only in the last 1% of the six million-years since our first bipedal ancestor, Sahelanthropus, lived. The prior 99% of that time is when our shared humanity was forged in Africa.
- Because we cannot be divided into races, and we have more similarities than differences, we should all be able to celebrate our shared African origins and our common humanity.
Tree of Life
In the first two videos, you have learned about our zoological family, the hominids. The third video, entitled The Tree of Life, tells the story about how hominids are one branch among thousands on the Great Tree of Life.
- Think of hominid evolution as a tree’s branch that sprouted 6 million years ago with Sahelanthropus. The branch grew to include our direct ancestors such as Homo habilis and Homo erectus before giving rise to us. Other twigs that sprouted on the branch are our hominid cousins like the australopithecines that eventually died out. The hominid branch has only one surviving species, Homo sapiens.
- Hominids are one branch on what you can think of as the Great Tree of Life. Each leaf on the tree represents one of the millions of species living today. The tree has many leafless twigs, each an extinct species. It also has dead, leafless branches, each a group of related species that all died out.
- The Tree of Life sprouted at least 3.8 billion years ago, when the Earth was 800 million years old. The earliest species that lived when the tree was still a seedling were microscopic single-celled organisms. One of these was called LUCA, the Last Universal Common Ancestor. All living species, from bacteria to plants and animals, including humans, are descendants of LUCA. Each can retrace its ancestry down its twig and branches to LUCA near the base of the tree’s trunk.
- Bacteria were the first group of living things to branch off the Tree of Life. More than 3 billion years later, the bacteria branch has many leaves and is still growing. Single-celled organisms called Archaea were the next group to branch off. Plants appeared and branched-off about 1.6 billion years ago, followed by amoebae, fungi and then the earliest animals by about 800 million years ago. All of these branches are still sprouting new species today.
- Sponges were the first animals on the Tree of Life. Then a new branch for corals and jellyfish started to grow, followed about 540 million years ago by three new branches. One grew to include the spiders, insects and crabs. A second became earthworms, leeches, clams, squid and snails. The third is for starfish and vertebrates, animals with backbones such as fish, frogs, reptiles and mammals. Humans are one leaf on a branch of the mammals called hominids.
- The Tree of Life suffered severe damage five times over the last 540 million years from events that cause mass extinctions. During each, 75% or more of plant and animal species went extinct in a brief period of time. The most recent, Fifth Mass Extinction occurred 66 million years ago. Among the animals that died out were all of the dinosaurs except those ancestral to today’s birds. Except for the ancestors of crocodiles, no land animals larger than 25 kg survived.
- The five mass extinctions had natural causes. For example, the Fifth Mass Extinction resulted from a massive asteroid impacting the Earth. This threw enough dust into the atmosphere to block sunlight needed for plant growth, reducing food supplies globally. After the dust settled, mammals started to evolve into many forms to fill the niches left vacant by dinosaurs, but species diversity was not fully restored for more than five million years after the impact event.
- Today, a Sixth Mass Extinction in underway due to human activities. Species are going extinct faster than in the last 66 million years. The extinctions began with farming 10,000 years ago, but have quickened since the industrial revolution began. If we continue destructive activities such as cutting down forests, polluting the land, water and air, and overfishing, we will kill off 75% of species in 250 years from now, causing the Sixth Mass Extinction.
- Mass extinctions kill whole branches on the Tree of Life. The species affected disappear forever. Many of these species contribute to our well-being. If too many go extinct, our survival as a species will be threatened. It is up to you, your family members and your friends to do what you can to protect the environment, conserve resources, and recycle the waste you produce. Only in this way will the Tree of Life continue to flourish and sustain us.
- We hope you have enjoyed and learned from the Walking Tall Video Trilogy. Please share the link to this webpage with your friends. Your school and neighbourhood will be better places if everyone knows that all people and all living things share the same origins.