Prehistoric Life. The Origin of Life on Earth. When? The Hunting and Gathering Period. At some point in the 4½4

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1 Prehistoric Life The Hunting and Gathering Period 1 The Origin of Life on Earth At some point in the 4½4 billion years of the Earth s s past, the environmental conditions were right for complex chemical compounds to form the organic compounds necessary necessary for life. From those compounds evolved amino acids; from amino acids, proteins; from proteins, nucleic acids; and ultimately plants, then animals. 2 When? Current estimates are that there were some life forms in the seas 3½3 billion years ago; plants emerged 400 million years ago; land animals, 360 million years ago. Life on land was well established at the time of Pangaea. When the continents separated, life evolved differently on different continents. 3 1

2 Ecosystems Photosynthesis All life depends on sun s s energy through photosynthesis the the only way that energy is introduced into our ecosystem. Only about 0.2% of sun s s energy is converted into matter. Photosynthesizers provide the basic energy input. These include: Plants, trees, grasses. This is the bottom of the food chain. 4 The Food Chain The basic food chain consists of: Photosynthesizers Herbivores Carnivores Top Carnivores Photosynthesizers are: Broken down in the soil by decomposers, e.g., fungi. They are also eaten by herbivores. Herbivores are eaten by carnivores. Top carnivores eat both herbivores and other carnivores. When these animals die, their carcasses rot and elements are recycled. 5 Hierarchy of Ecosystems The higher an animal is in the food chain, the rarer it will be. A cow can store only 0.6% of the primary production of grass. Only a small number of carnivores can exist in an ecosystem, compared with the number of primary producers. 6 2

3 The Flow of Energy Example: A deciduous forest 88% of primary production by photosynthesizers falls to the ground and decomposes. Another 8% is stored as dead wood. About 3% is available for herbivores to eat. Even less is available for the carnivores living off the herbivores. 7 The Flow of Energy in an Estuary 8 Orderly Series of Changes in Ecosystems The culmination of orderly change is a climax system with the maximum number of possible plants and animals. Thousands of years are required to go from bare rock to lichens and mosses to ferns, plants, and trees to create a climax forest, which can survive for very long periods without human interference. 9 3

4 Different Types of Ecosystems Ecosystems vary depending on temperature and rainfall. They are found in broad bands between the poles and the equator. Changes in earth s s climate cause bands to change location by hundreds of miles over several thousands of years. 10 Tundra Near the poles: low rainfall, low temperatures, permafrost. Poorly drained, acidic soils are covered in low scrub. Productivity is low because of cold and lack of sun. The food chain is short and simple. 11 Taiga Further from the pole, but only in the Northern Hemisphere (no land in the right place in the southern). Great coniferous forests. 12 4

5 Temperate Forests Further still from the poles Rich secondary flora, better soils, high leaf drop. Large quantity of decomposers. 13 Grasslands Less rain. Poorer soils. 14 Desert Confined to about 30 degrees N and 30 degrees S of the equator. Due to large masses of very dry air. 15 5

6 Tropical Rainforests High rainfall. High temperatures. Many local variations. 16 Coral Reefs The open ocean is like a desert. But coral reefs and estuaries teem with life, at levels equivalent of the tropical forests. 17 Productivity of Tropical Forests Tropical forests produce 40% of all terrestrial primary plant production. They contain about half of all the plants and animals on earth. They are remarkable for their diversity. A typical 4 sq miles of forest will contain the following numbers of species (not individuals): 1500 flowering plants, 750 trees, 125 mammals. 400 birds, 100 reptiles, 60 amphibians, 150 butterflies. 50,000 insects (probably there are 20 million species of insects in all tropical forests). 18 6

7 Poor Soil of Tropical Forests Tropical forests different from temperate forests, which have rich soils. ¾ of nutrients are held in the plants and trees. Only 8% of nutrients are in the soil. Very little rainwater runs into soil. Over ½ of this evaporates; most of rest is absorbed directly by plants and trees. 19 Vulnerability of Tropical Forests Soil is thin, acidic, and of poor quality. It contains little humus, which has most of the life-giving properties of soil. If the ecosystem is destroyed through forest clearance, most nutrients are destroyed too. Exposed ground quickly turns into hard clay. 20 What is Soil? Soil is a product of an ecosystem. Created by living plants and animals. Relies on them to remain fertile. Built up over thousands of years. Rock is weathered into minute fragments. Incorporated with remains of dead plants and animals. Forms a medium that supports bigger plants and trees. 21 7

8 Fertility in an Ecosystem An ecosystem develops toward a climax. Fertility is an active process through the interaction of plant cover, existing soil, decomposers, rainfall, and temperature. One acre of soil from a temperate region will contain 125 million small invertebrates. 30 grams of that soil will contain 1 million bacteria of just one type, 100,000 yeast cells, and 50,000 fungus mycelium. Soil creation is so slow that it is, in effect, a non-renewable resource. 22 Fragility of Ecosystems Ecosystems develop naturally in a way that protects the soil they depend on. On dry grasslands, roots of grass hold together a poor soil In temperate forests, leaf drop in the autumn and large number of decomposers maintain fertile soil. In tropical forests, ecosystem protects the poor soil. Once an ecosystem is destroyed or damaged the underlying soil is easily destroyed or eroded. 23 Feedback Loops in an Ecosystem If one species of animal is wiped out, there are ramifications up and down the food chain. Population of plants and animals forming its diet will increase. Population that hunted it will decrease. This will bring further disruption at other levels. Disruption of primary producers, e.g. through forest fire or deliberate clearance, is an attack on the base of the food chain, with disastrous effects. Ecosystems themselves are part of a greater whole the earth itself. 24 8

9 The Earth is a Closed System Resources are finite. Nothing gets out. Waste products must go somewhere. Recycling is essential. Problems arise when artificial wastes are disposed of in ecosystems, e.g. dumping at sea or into the air. 25 Humans in Ecosystems Two factors distinguish humans from other members of ecosystems. We are the only species capable of endangering and/or destroying ecosystems on which we depend. We are the only species to have spread into every terrestrial ecosystem, and then dominated it. The problem for human society is to balance our various demands against the ability of ecosystems to withstand pressures. 26 Human Origins The dinosaurs all died out about 65 million years ago. When then did, there were already some small mammals that had found an ecological niche that supported them. The mammals became dominant and evolved into many different forms. 27 9

10 Primates From within the order of mammals, a particular group developed with grasping hands and stereoscopic vision, the primates. Out of the primates, developed the monkey, about 50 million years ago. The monkey developed differently in different parts of the world. Out of the African monkeys came the apes, about 30 million years ago. 28 Apes The apes are our direct ancestors and have many anatomical features in common with humans. At right is a chimpanzee, the closest living relative to humans. 29 Homonids Out of the apes evolved a series of species with features more and more human-like. As a group, we call these homonids,, meaning simply human-like. There are several stages of homonids.. Of greatest interest are those that developed anywhere from 5 million to 1 ½ million years ago. This is the species we call Homo erectus, or upright man

11 Homo erectus Fossils of Homo erectus date from about million years ago. These are the direct ancestors of modern humans. The possible appearance of Homo erectus. 31 Traits of Homo erectus Earlier fossil remains show human traits: Upright posture (up to 3.5 million years ago hard to date) Toolmaking in stone. Homo erectus had an enlarged brain capacity (1,100 cc = ¾ modern brain size) Probably emerged in Africa. Survived until 100,000 years ago. 32 Homo sapiens Anatomically modern skeletons, from 100,000 years ago. Homo sapiens lived in camps and hunted in groups

12 Homo sapiens sapiens From 30,000 years ago. Widespread through the world. These are essentially anatomically identical to ourselves. 34 Almost all of our Past Humans (including Homo erectus) go back 2 million years. In all but the last few thousand years, humans have subsisted by hunting and gathering. They lived in small mobile groups. They had minimal effect on the environment. During this time humans spread all over the globe and into every terrestrial ecosystem. Evidence is scanty, hence interpretations disputed. 35 Hunting and Gathering This has been the universal human way of life for 99% of human history. It is now restricted to a handful of groups such as, The San, or Bushmen, of SW Africa. Pigmy groups in equatorial Africa. Hadza of east Africa. A few groups in India and SE Asia. Aborigines in Australia, Inuit. Native groups in tropical S. America. All these groups are now marginal, having been pushed aside by agriculture

13 A Better Life in the Past Before being pushed to marginal land, hunting & gathering was a much easier way of life. Food could easily be extracted, taking only a small part of the day. Generally the diet was nutritionally adequate and varied. Personal possessions were few. There was no concept of food ownership. 37 E.g., the San, or Bushmen, of SW Africa The San, or Bushmen, of the Kalahari Desert in South West Africa is one of the world s oldest human groups, going back long before the invention of agriculture. 38 The San (Bushmen) They have remained a hunting and gathering culture, and preserve as much as possible of their traditional way of life. Anthropologists trying to reconstruct the past will often study such cultures for indications of how all humans must have lived thousands of years ago

14 The Mongongo Nut The mainstay of their diet is the mongongo nut, from a drought resistant tree. It is a reliable source of food that keeps for over a year. It contains 5x the calories and 10x the protein of an equivalent amount of cereal crops. ½ lb of nuts has the calories of 2 ½ lbs of cooked rice and the protein of 1 lb of beef. San women gathering mongongo nuts. 40 The San Diet The San use 23 of the 84 edible plants available. There are 54 edible animals. 17 are regularly hunted. This diet is more than adequate. It requires on average 2 ½ days a week in food obtaining & production. Work is steady throughout year (unlike agriculture). It rarely involves traveling more than 6 miles a day. 41 Gathering Women gather nuts and berries and roots. Women and men devote the same amount of time overall to food. Women, who do the gathering, bring in twice the amount of food as men, who hunt. Women work about 1-31 hours a day

15 Hunting Men do the hunting Hunting more intermittent. A week of hunting is often followed by no activity for 2-33 weeks. Hunting is less successful than gathering, especially with primitive weapons, but can provide superior nutrition. 43 Leisure About 40% of the population are not involved in food production: 1 in 10 are over 60. The young do not participate until marriage (20 for a woman, 25 for a man). Leisure time is valued highly. 44 Where Gathering Fails A Hunting and Gathering group spearing fish. In ecosystems farther from equator, plant food needs to be supplemented, often by fishing

16 Hunting as the Sole Source of Food Only in Arctic areas where there is little plant food does hunting dominate. 46 Population Control All hunting & gathering groups tried to control their numbers. Infanticide was one method. Twins, the handicapped, and a proportion of female offspring were killed. Inuit killed about 40% of female children. Protracted weaning provided birth control. Abandonment of old people was accepted. Thus demand on resources was kept at manageable levels. Total population about 10,000 years ago was less than 4 million. The size of the Greater Toronto Area population. 47 Causes of the Spread of Humanity cross the Globe 1. Brain size Power of abstract thought, required for technology

17 Causes of the Spread of Humanity Across the Globe 2. Bipedalism Walking upright on two legs freed hands to, e.g., make tools. 49 Causes of the Spread of Humanity Across the Globe 3. Speech Increased cooperation. Social organizations. 50 Causes of the Spread of Humanity Across the Globe 4. Tool making Stone tools-choppers, pebbles, hand ax. Wooden spears. Bolas. Wood, skins, fire

18 Out of Africa Home erectus had spread out of Africa by 1½1 million years ago. The first migrations were to the Middle-East, India, south China, and parts of Indonesia. 52 Limitations on Migration At first migration was very restricted. Survival was only possible in semi- tropical areas with a variety of easily gathered vegetable materials given the tools they had. In other climates hunting would be more important, but they did not have sufficient weaponry. 53 Migration to Europe Settlement from 730,000 to 350,000 years ago. Often intermittent and only in interglacial periods. Permanent settlement only during last glacial period, 80,000 to 12,000 years ago. Marked a major advance in human ability to adapt to harsh environment

19 Ice Age Inhabitants of Europe Living off of animals The usual view is that humans hunted animals randomly. But this is too erratic. Success rate would be too low. Instead, humans were dependent upon animal herds. The herds were managed with minimum disturbance. Herds were followed and culled selectively. This could only support a small number of people. E.g reindeer would support 3 families of 15 each. 55 Example: France and Spain at height of Ice Age Subsistence was based on large herds. Dense human populations managed without migrating with herds. Hunting was supplemented by fishing. Great cave paintings. 56 Way of Life Dependent on the Ice When the ice age subsided, the herds migrated north and the basis of human subsistence collapsed

20 Developments in Technology New tools and new materials from 40-30,000 years ago. Thin parallel sided blades, and small light blades for projectiles. More complicated manufacturing and heat treatment. 58 Australia and the Boat The settlement of Australia required boats. 59 Settlement of Australia, 2 It was settled 40,000 years ago when sea levels were at their lowest. A voyage of 60 miles would have been needed (from Asia). Tasmania was linked to Australia until 15,000 years ago. New Guinea became an island 8000 years ago

21 Settlement of Australia, 3 The environment was more benign than Europe. To live here did not require technological sophistication. Initial settlement was maybe 25 people. Population grew rapidly to 300,000. Settlement here did not lead to more complex social organization as was common elsewhere. 61 America Almost the last stage. Migration to American depended on the ability to survive the harsh climate of Siberia and then advance to the Bering Strait. The crossing made at the height of ice age, when the Bering Strait was a land bridge. 62 Settlement of America Migration out of Alaska to the south could have taken place either 30-23,000 years ago or 13,000 years ago Once into the south, the living was easy. Compared to the climate of Siberia and then across the Bering Strait, the environment to the south in America was enormously rich. The population multiplied rapidly. It spread all the way to the southern tip of South America in a few thousand years

22 Adaptations for Life in America On the plains of North America there were few large plants to be gathered. Subsistence depended on hunting. Exploitation of herds of bison resulted. The animals were often killed in a crude and highly wasteful way, such as driving them into narrow canyons or over cliffs. 64 Adaptations for Life in America, 2 A single kill in Caspar,, Wyoming about 10,000 years ago involved 74 animals. Another in Colorado set off a stampede resulting in 200 corpses, most of which could not be used. 65 Final Phase: Pacific and Indian Oceans Migration here was carried out by groups who had a primitive form of agriculture and also relied on occasional hunting. Polynesians undertook the most extensive voyages. People travelled from New Guinea to Tonga and Samoa about 1000 BC, to Marquesas about 300 AD, and Easter Island years later

23 Humans Across the Globe All major areas of the world were settled by humans (except Antarctica). They adapted to every environment, from semi- tropical in Africa to ice-age Europe, from Arctic to SW African deserts. 67 Living in Harmony with the Environment? The usual assumption: These groups lived in close harmony with the environment and did minimal damage to natural ecosystems. 68 Arguments in Favour: They required detailed knowledge of where resources were found and habitats of animals. Some of these groups tried to conserve resources to maintain subsistence over a long period of time

24 Efforts of Primitive Cultures to Preserve the Environment Totemic restrictions on hunting particular species at certain times of year. Only hunting an area every few years. Sacred areas where hunting was forbidden. E.g. Cree in Canada, used rotational hunting: returning to an area after a considerable length of time, allowing animal populations to recover. But the main reason why they avoided over exploiting is that their numbers were small. 70 Damage to the Environment from Hunters and Gatherers Many activities did alter the environment and cause damage. Examples from present day hunter- gatherer societies: The Hadza of Tanzania Aborigines of Tasmania Maoris of New Zealand 71 The Hadza A (male) Hadza hunter and a (female) Hadza gatherer digging for roots

25 The Hadza,, 2 The modern Hadza of Tanzania are careless about their environment. The hunters destroy wild beehives to obtain a small amount of honey, instead of resealing the honeycomb. The women digging for tubers pull up the whole plant, leaving no part to regenerate. 73 Deliberate Intervention The Hadza approach is careless rather than deliberate. They are highly nomadic, moving on at short notice to wherever better hunting and gathering seems available. More settled hunter-gatherer societies intervene in their environment deliberately to produce some favoured benefit. They can do this by burning areas. Fire alters habitat by favouring annual plants that grow well in new ground. 74 Australian Aborigines Aborigines use fire regularly to encourage an edible bracken on Tasmania. (Maoris did the same.) They also set fires to drive kangaroos when hunting

26 Prehistoric Uses of Fire Early hunter-gatherer groups used fire frequently to clear areas for plants. Evidence remains from, for example: In New Guinea from 30,000 years ago Forest clearing by felling, ring barking, and fire. Done to encourage food plants: yams, bananas, taro. Also the sago tree. In post-glacial Britain Patches of woodland cleared by fire to encourage forage for red deer. Most groups also transplanted wild plants and weeded. Even some irrigation. 76 Effect of Hunting on the Environment The most dramatic intervention of hunter- gatherers was through hunting wild animals: It is much easier to damage this part of an ecosystem since numbers are smaller and populations of larger animals take a long time to recover from over-hunting. There is some evidence of attempts not to over- hunt, but there is far more evidence of uncontrolled hunting and extinction of species. 77 Bison Bison hunts in North America could kill hundreds when only a few were required. The bison population was huge (50-60 million), so it could sustain very large hunts. However, it was nearly wiped out

27 Sea Otter Effect made worse by tendency to concentrate on one species to the exclusion of others. On the Aleutian Islands in the north Pacific the population concentrated on killing sea otter for over 1000 years from settlement in 500 BC until they were virtually extinct and the subsistence base of the community was wiped out. 79 Flightless Birds Large flightless birds were common on islands where there were no large mammals. They were defenseless against humans. An Australian emu. 80 Large Unusual Mammals Madagascar Within a few hundred years of human settlement, many of the larger animals, including a big flightless bird and a pigmy hippopotamus were extinct

28 The New Zealand Problem Maoris could not grow their traditional crops in the temperate environment of New Zealand. The traditional Polynesian crops included banana, breadfruit, and coconut. These would not grow in the colder temperate climate of New Zealand. Even yams and taro grew only on the North Island. They had to shift to other foods, such as: Wild plants, such as bracken fern, for which they cleared large areas of forest by setting fires. They also fished and hunted. 82 The Moa Artist s reconstruction of extinct Moas. 83 The Moa, 2 The moa was a huge flightless bird native to New Zealand The Maori settlers hunted them to extinction. In 600 years, 24 species of moa were extinct plus 20 other birds

29 The Moa, 3 A large number of flightless birds: Kiwi, weka,, and many species of moa were hunted ruthlessly and their eggs eaten too. Most moa were 6 ft high, one type was 12 feet tall if it stood erect. 85 Continental Impact Even on land masses as large as continents, hunting and gathering can have major impact. In Eurasia, 5 large animals became extinct in a few thousand years. This was partly due to climate change, as the ice age receded, but hunting may have helped to push them to extinction. The woolly mammoth, the woolly rhinoceros, the giant Irish elk, the musk ox, the steppe bison, as well as other large carnivores were destroyed. 86 Large Animal Extinctions in Eurasia, 1 Woolly mammoth. Recreated museum model

30 Large Animal Extinctions in Eurasia, 2 Wooly rhinoceros. Artist s s recreation. 88 Large Animal Extinctions in Eurasia, 3 Giant Irish Elk. Artist s s recreation. 89 Large Animal Extinctions in Eurasia, 4 Musk Ox. Driven to extinction in parts of the world

31 Large Animal Extinctions in Eurasia, 5 Steppe Bison. Artist s s recreation. 91 Far worse in Australia and the Americas But extinction of species in Europe and Asia were relatively small compared to Australia and the Americas. 92 Australian Extinctions Over the last 100,000 years, 86% of the large animals have become extinct. This happened in an area where climatic impact was minimal. The most likely explanation is: Hunting by Aborigines in the last 40,000 years. Even if not hunted to death, human disruption of the ecosystem could have led to extinction: By killing smaller herbivores, or destroying habitats

32 The Americas Large animal extinction: South America: 80% loss. North America: 73% loss. Extinctions in every type of ecosystem. These happened well after the ice age so climatic changes could not be the cause. E.g. the plains camel (found only in North America), other giant species: 3 genera of elephant, 6 of giant edentates, 15 ungulates, many rodents and carnivores disappeared. The first American settlers left a trail of destruction across the continent. 94 Summary By 10,000 years ago, humans had spread from southern and eastern Africa to every continent. This migration depended on: Growth in brain size allowing for abstract thought and technological solutions. E.g., fire, clothing. As humans moved away from tropics, new techniques had to be developed. More intensive hunting and herding. Better tools. Complex food processing. 95 Change of Pace 40,000 years ago: The pace quickened. Humans had become the only animals to dominate and exploit every niche. Overall impact was still small because of low population and limited technology. But human presence was already felt in: Extinctions of animals. Subtle modifications of the environment. Then, about 10,000 years ago, the most fundamental change of all: Agriculture