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J^[j^[ehoe\[lebkj_ed ‘. . . from so simple a beginning, endless forms most beautiful and most wonderful have been, and are being, evolved.’ Charles Darwin, from The Origin of Species Leaves The Origin of Species In 1858, an Englishman named Charles Darwin rocked the science world with an essay titled The Origin of Species by Means of Natural Selection. His theory was that every organism on Earth is a descendant of those that lived millions of years ago. Species change and evolve, and two different species may be related, through many, many generations, to an ancestral species (a common ancestor). This was one of the great intellectual revolutions of human history because until this time, most scientists believed the Earth’s organisms were the unchanging work of a creator, God, and that the Earth was only a few thousand years old. Darwin’s finches Darwin spent most of his life developing his theory. At the age of 22, he set sail on the HMAS Beagle, on a five-year voyage that took him to the Brazilian jungles, the Andes mountains and the Argentine grasslands. Darwin’s travels opened his eyes to the vast range of animal and plant species on Earth, and he began to question the belief that the Earth and its species were unchanging. During his journey, Darwin visited the Galapagos Islands, which are home to at least 13 species of finch. He noticed that the different finch species were similar in colour and size, but had variations in their beaks that made them suited to the food sources available on their particular island. Some used twigs to extract insect larvae from tree branches, some drank blood from seabirds, some removed ticks from tortoises, and some ate seeds, leaves and flowers. He proposed that all species were the descendants of one shared, ancestral species, a ground-dwelling, seed-eating finch, which had migrated out to all the islands from the mainland. Over many generations Insects Tool-using Darwin’s finches Grubs Buds and fruit Seeds Darwin observed that each species of finch had a beak that matched its method of obtaining food. the different groups of finches had evolved to suit their different environments and feeding habits. The groups of finches are now so different from one another that they do not interbreed. Evolution is the study of the change in inherited characteristics within a group of organisms. Darwin developed his theory while another prominent English naturalist was reaching a similar conclusion. Alfred Wallace Alfred Wallace’s writings prompted Charles Darwin to publish his Origin of Species when he did. Like Darwin, Wallace travelled extensively (in what is today known as Indonesia) and made many detailed observations of the variations between species. Wallace wrote to Darwin in 1858 from the East Indies, telling him that he had a theory about evolution 188 Science Alive for VELS Level 6 Go to worksheet 9.2 and natural selection. Darwin was shocked to realise Wallace had reached the same conclusions as himself. Darwin later described Wallace’s writings as an almost perfect summary of his own life’s work. Darwin was spurred on to submit both his paper and Wallace’s to the Linnean Society science conference held in London on 1 July 1859. Wallace is recognised as a co-founder of the theory of evolution by natural selection. Lamarck’s giraffes Jean Baptiste Lamarck (1744–1829) was one of the first scientists to suggest that evolution occurred, that is, that new species had arisen and old ones had died out. He proposed a different means of change: he suggested that changes acquired by an individual during its lifetime could be passed on to its offspring. For example, giraffes had become long necked because they had stretched towards leaves high up on trees, and this stretching had been passed on to their offspring. He also believed that if an individual did not use a particular feature, it would shrink and gradually be lost over succeeding generations. Although his theory of the inheritance of acquired characteristics is now discredited, he made many valid observations about diversity in living things. Biogeography, the study of variation in living things in relation to geographical regions, is the name given to the studies that led Darwin and Wallace to propose their evolutionary theories. They observed in their travels that species living in the same area, such as the Galapagos finches, were more similar to each other than to species living in similar habitats much further apart. If all species had been created at the same time, why would this be so? To Darwin and Wallace, this simple observation implied that such species were related; that one had evolved from another or they had both evolved from an earlier, common ancestor. 6 A scientific theory is an explanation REMEMBER 1 How old did many scientists believe the Earth to be before Darwin’s writings were published? 2 What did Darwin observe about the beaks of finches in the Galapagos Islands? 3 In your own words, what is: (a) common ancestry? (b) evolution? THINK 4 How was Darwin’s theory different from Lamarck’s? 5 August Weismann (1834–1914) did an experiment in which he measured and cut off the tails of mice and then bred the mice for many generations. If Lamarck’s theory of the inheritance of acquired characteristics was correct, what would you expect to observe in the later generations? based on evidence that accounts for observations made. (a) What observations does the Theory of Evolution account for? One requirement of a good scientific theory is that scientists should be able to make accurate predictions based on the theory. (b) Think of some predictions based on the theory of evolution. INVESTIGATE 7 Alfred Wallace was one of the founders of biogeographical studies. He divided the Earth into six major biogeographical zones, each with its own characteristics. • Nearctic: USA and Canada, home to many reptiles and other vertebrates • Palaearctic: Europe and Asia, features many deciduous forests • Neotropical: South America, 16 of the 32 families of mammals are restricted to this region 189 9. Evolution • Ethiopian: Africa, a land of tropical forest, savannah, grasslands and desert • Oriental: Indonesia, rich in primate species like monkeys and lemurs • Australian: Australia, where marsupials are dominant. Use the internet to find out more about these zones: (a) What are the dominant types of fauna and flora in each zone? (b) What are some of the unique species in each zone? (c) Include any other interesting facts about the types of living things in each zone. Present your results as a poster. �learning Biogeography I CAN: describe the observations from which Darwin and Wallace developed the theory of evolution explain the idea of evolution from a common ancestor explain the concept of biogeography describe the theories of Lamarck. M^[h[Z_Zm[Yec[\hec5 W hen Darwin published The Origin of Species in 1858, one sentence on the last page caused a sensation. It read: ‘Much light will be thrown on the origin of man and his history’. Darwin reached the conclusion that humans had evolved from the same family as the great apes. People found it very hard to believe our ancestors were apes! In 1871, Darwin published The Descent of Man, describing the relationship between men and other species, including monkeys. In 2005, scientists were able to compare the sequence of complete human DNA with the chimpanzee; they found them 96% identical! Other studies have shown close relationships between the DNA of humans and gorillas, orang-utans and other primates. This genetic evidence points to very close links between humans and the great apes. Monkey business Human beings are mammals of the Primate Order, which is estimated to have evolved about 65 million years ago. Beginning as small-brained, fruit-eating treedwellers, similar to the modern day lemur, these creatures evolved over millions of years into monkeylike animals. At some point in time, probably between five and 15 million years ago, the humans and apes of today began to evolve separately. There are many theories about where, when and how modern humans evolved. The Hobbit In 2004, scientists were stunned by the discovery of a fossil of a one-metre high Homo floresiensis among the remains of dwarf elephants, giant rodents and Komodo dragons on the Indonesian island of Flores. Scientists believe it is a previously unknown human species that lived about 95 000 to 13 000 thousand years ago, at the same time as modern humans — and it’s very likely that they met! From monkey to you! At first Darwin’s suggestion that humans were descended from apes was laughed at. First hominid, Australopithecus The Handyman, Homo habilis DATED: 3–7 MYA FOUND: Africa Australopithecus was the first group classed as hominid (i.e. one of the group of human-related species that walked on two legs). It is believed to be a common ancestor of both humans and living apes. The first remains of this species were found in northern Ethiopia in 1974 and named ‘Lucy’. DATED: 2.2–1.6 MYA FOUND: South and east Africa Homo habilis is known as the first member of the genus Homo (of which humans are the only living species today). The ‘handyman’ used some of the earliest known examples of stone tools, and had a brain much larger than Lucy’s. The Workman Homo ergaster DATED: 1.8–1.2 MYA FOUND: Africa Homo ergaster could represent a different population of Homo erectus (meaning ‘upright man’). This species migrated out of Africa into Asia at least 1.8 million years ago. 200 Science Alive for VELS Level 6 Upright man, Homo erectus DATED: 1.8 million–20 000 years ago FOUND: Africa, Asia, possibly Europe The most famous fossil remains of Homo erectus were found in the late 1800s: the Java man (Indonesia), and Peking man (China). H. erectus was very similar to H. ergaster, but with a flatter skull. H. erectus is believed to have evolved in Asia then spread back to Africa and possibly Europe. Homo heidelbergensis DATED: 900 000–100 000 years ago FOUND: Europe Homo heidelbergensis is considered the first European hominid, and a common ancestor of Neanderthals and Homo sapiens. A famous discovery in 1907, in Germany, was the Mauer mandible (jawbone), found with the remains of sabretoothed tigers, hippopotamuses and rhinoceroses. Believed to be more intelligent than Homo erectus, it used advanced tools, including spears. Go to worksheet 9.5 Piecing it together Palaeontologists have different opinions about new fossil discoveries, and whether they are on the direct line of ancestry to humans. They look at such features as brain size, skull and jaw shape, and other features of the skeleton. When considering the variation between humans today, it isn’t surprising there are disputes! DNA studies provide powerful evidence of relationships. A study in 1987 supported the theory that modern humans evolved in Africa and migrated out from there. It is believed humans reached the Near East at least 90 000 years ago, Australia by at least 60 000 years ago, Europe around 40 000 years ago, and the Americas by 12 000 years ago. Other evidence conflicts with this ‘Out of Africa’ hypothesis (see Mungo mania below). Theories will remain tentative and limited as long as new evidence continues to emerge. Mungo mania! The discovery of ‘Mungo Man’ in 1974 at Lake Mungo in New South Wales cast doubt on the ‘Out of Africa’ theory. DNA tests show Mungo Man did not have a direct African ancestor, suggesting more than one Homo species or subspecies contributed their genes to modern Homo sapiens. Neanderthal man, Homo neanderthalensis DATED: 230 000–29 000 years ago FOUND: many locations in Europe, western Asia DNA evidence suggests the Neanderthal was not an ancestor of modern humans. Neanderthals were short and stocky, and adapted to the very cold climate of Earth at that time. Their brains were larger than modern humans, and it is likely they used basic words, used spears, sharp stone tools and clubs. Early Homo sapiens DATED: 100 000 years ago Cro-Magnon man is believed to be our direct descendant. Cro-Magnons were tall, had similar-sized brains to humans, and they could probably speak. They used complex stone and bone tools, made jewellery from shells and ivory, and produced paintings on cave walls. RESEARCH 9 Use internet research to REMEMBER 1 How closely related is the DNA of chimpanzees and humans? 2 When did the original primates evolve and which of today’s species were they similar to? 3 What activities did Cro-Magnon man undertake that were similar to those of a modern human? 4 What kinds of studies are made of human fossil finds, in order to determine whether they come from separate species? THINK 5 Create a timeline showing when the different Homo species were alive on Earth. Use this timeline to suggest some alternative evolutionary relationships between the species. 6 Why are there different theories of human evolution? How are the competing theories in science often resolved? Why can’t this approach be taken to human evolution? COMPARE 7 Obtain a study set of hominid skulls or research them using the internet. Make drawings of each and take notes about their differences. What changes have occurred over time? IMAGINE 8 Imagine you are a Cro-Magnon and your tribe encounters a H. floresiensis tribe. How do you attempt to communicate? What kinds of technology do you each use? Can you live together peacefully? 201 9. Evolution complete a table comparing the species below with respect to: • relative brain size • height • posture • shape of skull • teeth. Australopithecus Homo habilis H. ergaster H. erectus H. heidelbergensis H. neanderthalensis H. sapiens 10 Investigate the controversy surrounding the ‘Out of Africa’ theory. Obtain several copies of a world map and mark on it the possible movements of the Homo species. Which case do you think is most convincing? 11 For a long time it was believed Neanderthals were not particularly intelligent. Search the internet or library and find out: (a) why this was first proposed (b) why it might not have been the case. FIELD TRIP 12 Take a trip to the zoo and observe the primates. Make notes of the behaviour and physical similarities to each other, and to humans. �learning I CAN: recall the scientific names of the species of the genus Homo, the early fossil evidence of the evolution of the species understand that evolutionary theories will remain tentative and limited as long as new evidence continues to emerge recall that DNA studies provide powerful evidence for the many evolutionary theories that exist.