1. Evolution
Year 10 Topic 4

2. Evolution
Nearly two million different kinds of plants, animals and micro-organisms are known to be currently living on Earth. More are being found each year. The average time that a species lasts on Earth is about four million years. Which means that, like the dinosaurs, many species are long extinct.

3. Evolution suggests that all forms of life stem from the same remote beginnings and that the different species we now know have developed gradually over millions of years. The fossil record clearly shows that through time, life became more complex.

4. Surviving in different environments
In order to evolve, a species must survive.

5. Adaptations
Organisms survive and breed in their environments because they have characteristics suited to that environment. Specific structures, functions and behaviours increase their chances of surviving, at least until the organism is able to reproduce. These characteristics are called adaptations. They are inherited and are passed from parents to offspring. Adaptations take many forms and can be classified as either structural (where the adaptation is physical), behavioural (where the adaptation controls the way they act).

6. Structural adaptations
Many animals blend with their background, now invisible to predators.

7. A few can change colour to blend with changing backgrounds

8. Others resemble non-living objects such as leaves, twigs etc

9. With some animals it is difficult for a predator to tell which end is which. The predator attacks the wrong end, giving the prey a chance to escape.

10. Some extremely colourful animals warn predators to stay away, because they taste bad or are poisonous.

11. A tricky variation on this is the ‘mimic’
A tricky variation on this is the ‘mimic’. The mimic is not dangerous to predators, but has copied the colourings and shape of another animal, so predators avoid it.

12. Some animals have features that make them look larger and more frightening to predators. For example, the neck frills of some lizards can be opened to make the head seem like that of a much larger lizard.

13. Behavioural adaptations
Some animals have learned to sit very still or move slowly to avoid predators.

14. Others are active only at certain times of the day or year to avoid unfavourable conditions such as extremes of heat or cold.

15. Some have learnt to use tools to access difficult food
Some have learnt to use tools to access difficult food. For example, chimpanzees commonly use broken twigs to extract termites.

16. Some collect and store food for future use.

17. Many larger animals form herds to provide protection from predators.

18. Adaptations serve many purposes
Adaptations serve many purposes. Arctic fish contain a kind of antifreeze in their blood, allowing them to survive in waters that would freeze the blood of other
fish. The long mane of a male lion makes it appear larger to opponents. This kind of adaptation for intimidation is common. Intimidation also involves behaviours such as puffing out the chest and standing up as tall as possible.

19. Plants also have adaptations
One orchid achieves pollination by imitating the shape, colour and smell of a female bee. When a male bee attempts to mate with the orchid, pollen is transferred from flower to flower.

20. The silvery coloured, narrow-shaped leaves of the wattle tree help reduce water loss by evaporation. All organisms have adaptations that assist their survival in their environment.

21. Variation
Although individuals within a species are very similar, they are not identical. Variation occurs within all species. Much of this variation comes from the differences in genes each individual inherits from their parents.
These differences are the result of the random assortment of chromosomes during meiosis, and the combination of gametes (sex cells) during fertilisation. Further genetic variation occurs as a result of mutations. Other variations come from environmental factors such as the amount of exposure to the Sun and differences in diet.

22. Variation and survival
The organisms best adapted to their environment are the most likely to produce offspring. Their offspring will inherit these characteristics. Over several generations, individuals with favourable characteristics will become the most common. In contrast, those with less favourable characteristics will find the environment inhospitable. They will be more likely to die before they get a chance to reproduce and so will become less common. We can say that favourable characteristics are ‘selected’.

23. Variation in a species is important if environmental conditions change
Variation in a species is important if environmental conditions change. Some individuals will have characteristics that are favourable, allowing the species to survive the change.

24. The Theory of Evolution
The theory of biological evolution states that life on Earth has changed over time. This gradual development of different species from a common ancestor is called evolution.
It basically states that a species has natural variation which allows it to adapt to a wider range of environments. The best suited to their environment will survive and breed the next generation, this eventually gives rise to new species.

25. Alternatives to Evolution
Most societies have stories about the origin and diversity of life. Creation is the view that regards the world and everything in it as having been made by supernatural means, by a god or gods. The ancient Greeks suggested that the world grew out of Chaos, a dark mass where everything was hidden. From Chaos emerged a god and/or a goddess. The ancient world was peopled by them, producing other gods and goddesses, and then mortal men and women. The Biblical account includes stories of the creation of the Earth and all life on it in six days.

26. There is also an account of the first man, Adam, being created from clay and the first woman, Eve, being created from his rib. Some people believe the events happened exactly as stated. Other people interpret these as stories with symbolic meaning, as teachings about the relationships between God or gods, the universe and humans. The whole question of the origin of life then becomes bound to religious belief.

27. Early Theories of Evolution
Until the late 1700s most scientists believed that the different types of organisms and their characteristics had been fixed for all time. This idea of the ‘fixity of species’ was questioned by the French naturalist Georges Buffon (1707–88) and. Erasmus Darwin (1731–1802), who both suggested that one species could change to another.

28. Jean Baptiste Lamarck (1744–1829)
Jean Baptiste Lamarck (1744–1829). believed that organisms were guided through their lives by a creative force that enabled them to overcome adverse environmental conditions. Organisms adapted through a struggle to survive.

29. In 1809 he stated:
‘Organs are improved with repeated use and weakened by disuse. Any changes to organs due to the environment ‘are preserved by reproduction [and pass] to the new individuals which arise’.
These changes are acquired characteristics, which Lamarck thought were then passed on to the offspring.

30. Giraffes, for example, stretched their necks to reach food high in the trees. This acquired characteristic (a longer neck) was passed on, so that offspring inherited the characteristic of a longer neck.

31. Charles Darwin aged 22, took a position as naturalist on the HMS Beagle, a ship commissioned to survey and chart the coast of South America.
For the next five years Darwin observed the geographical distribution of plants, animals, fossils and rocks in various parts of the world. He became convinced that species could develop from a common ancestral type.

32. Darwin’s Finches
The Galapagos Islands are about 1000 km off the coast of Ecuador. The islands were effectively isolated from one another by strong ocean currents and a lack of winds blowing from one island to another.
Darwin marvelled at the diversity of forms on these islands. He also noted some similarity between island organisms and mainland organisms.

33. Darwin found 14 species of finches, all with similar colourings, calls, nests, eggs and courtship displays. They differed, however, in habitat, diet, body size and beak shape. Darwin believed these 14 species had come from a common ancestor. He suggested that a few finches had arrived on the islands at some time in the past. These finches showed natural variation in their beak shape. On one island, those with beaks of one shape were better able to feed on the cacti found there. Finches with other beak shapes found it difficult to survive. On other islands, other beak shapes gave some finches a feeding advantage.

34. The birds most suited to their island survived to produce offspring, which inherited that beak shape. This is called ‘survival of the fittest’. The ‘fittest’ were the birds that were able to feed and reach breeding age. The characteristic that gave some beak types an advantage were ‘selected
for’. Over many generations, the birds on different islands became sufficiently different from each other to be recognised as a different species.

35. This shows how different beaks might have been ‘selected’ for the food available on each particular island.

36. Darwins explaination of Giraffes

37. Challenging Darwin
Darwin spent 20 years collecting and sorting evidence for his natural selection theory of evolution. It was 1858 that Darwin presented his ideas to the scientific world. He was prompted to publish his work by the publication of a paper by another naturalist, Alfred Russel Wallace (1823–1913).
Wallace had reached a conclusion similar to Darwin’s—that evolution occurs by natural selection. His second paper on evolution
was presented jointly with Darwin’s in 1858.

38. Darwin’s major work, titled On the Origin of Species by Natural Selection or Preservation of Favoured Races in the Struggle for Life, was published in Although all 1250 copies of the first edition sold out within a day, much of the reaction did not support him or his theory.

39. Throughout England, religious leaders denounced his work as heretical or against the word of God. The biblical account held that man was formed in the image of God. How then could he have apes as ancestors?
Although the Church opposed his theory, Darwin was given a state funeral in Westminster Abbey in 1882.

40. Neo-Darwinism
Darwin’s explanation that evolution occurs through natural selection is one of the most important theories of science and is still regarded as being essentially correct. Darwin’s theory can be restated in terms of modern genetics. This is sometimes called neo-Darwinism.
Evolution is natural selection based upon the natural genetic variation that appears in all populations.

41. Natural selection
Is the process in which the environment ‘selects’ favourable characteristics, reducing the frequency of unfavourable characteristics. This means that after many generations of selection, a species will become better adapted to its environment. Individuals will become highly adapted if their environment doesn’t change. Except for mutations, each individual will be very similar, because the amount of variation will have declined.

42. Environments are rarely constant, however!
Suppose the environment suddenly got colder for a couple of generations of a particular animal. Some individuals within the species may naturally be better able to tolerate the cold, having thicker coats or some other favourable characteristic. They are better suited to the new, colder conditions than the rest of their species. Over time, natural selection would increase the proportion of individuals with this tolerance of the cold and decrease the proportion of those who don’t.

43. Natural selection takes several generations to become obvious and so it is extremely difficult to observe in large plants and animals. It is more obvious in organisms that reproduce quickly. Bacteria and insects are two organisms in which natural selection can occur quickly enough to be observed.

44. Selection of peppered moths
Scientists noticed that populations of the peppered moth, were changing from mostly light-coloured to mostly dark-coloured forms

45. The change occurred during the Industrial Revolution, when coal-burning factories produced a lot of pollution in the form of soot. When on the soot-darkened trees, the light-coloured form of the moth was easily seen by birds, their main predator. The dark-coloured moth blended with the blackened background,
increasing its chances of survival. The dark colour is an inherited characteristic. Hence, more dark-coloured moths survived to produce dark-coloured offspring.

46. After clean-air regulations were implemented, lichen began to regrow on tree trunks and the trees returned to their original paler colouring.
Moth populations in many of these areas have shifted back towards the light-coloured forms

47. Selection and rabbit control
In Australia, rabbits overran the land for many years. The myxoma virus, carried by fleas and mosquitoes, was released in Australia in December 1950 to control the rabbit population. Within two months, 90% of rabbits in certain areas had died. Ten years later over 99% of infected rabbits were dead. This means less than 1% of
rabbits infected with the virus survived. Ten years later, only 25% of rabbits in those same areas would die as a result of the virus, and around 40% of those infected with the virus would survive.

48. These dramatic changes were the result of natural selection acting on the rabbits. The resistant rabbits would have survived the initial myxoma spread, and produced offspring with an inherited resistance. A healthy rabbit may produce seven or more litters of
young per year, and therefore within a few years the number of resistant rabbits would have increased dramatically.

49. Selection and diseases
There have also been several well documented cases of populations acquiring resistance to introduced chemicals. Mosquitoes, which carry the diseases yellow fever and malaria, were treated with chemical pesticides.
By natural selection, populations of mosquitoes with a natural resistance to the pesticides developed over the 20-year period following the introduction of the pesticides into their environment. Similarly, many bacteria are now resistant to certain types of antibiotics.

50. Superbugs
When penicillin was first introduced it was very effective in treating infections caused by golden staph. Now, a new stain of Staph is resistant to it as well as around twenty other substances, including antibiotics, antiseptics and disinfectants. Recently, several strains of Staph have become resistant to the drug of last resort—vancomycin. If vancomycin fails, the death rate from Staph will rise dramatically.

51. Speciation
A species is defined as a group of organisms that normally interbreed in nature to produce fertile offspring. The formation of a new species is called speciation. Natural selection over long periods of time, combined with other factors such as isolation and mutations, can lead to new species forming.

52. Geographic isolation
The first step in speciation is geographic isolation of the populations. Suppose a particular population of rabbits. If the environments differed on each side of the river, each population would change through natural selection and the occasional genetic mutation. Eventually the two rabbit populations would have their own characteristics, sufficiently different from each other to be called a variety, or subspecies. Subspecies appear different but are still capable of interbreeding.

53. Reproductive isolation
If the isolation of the populations was long enough, the change might be sufficient to make them incapable of interbreeding.
They would then have reproductive isolation. At this point a new species has emerged.

54. Factors that might cause reproductive isolation are:
• a change in colour patterns so that mates are no longer recognised
• seasonal differences in mating times
• a changed chromosome which prevents the sperm of one group from fertilising eggs of the other.

55. Types of evolution

56. Divergent evolution
The Galapagos Island finches and the geographically isolated rabbits illustrate the idea that many new forms can evolve from a single ancestor. This is known as divergent evolution.

57. The idea is that new environments are inhabited, causing the evolution of new species. Divergent evolution results in a phenomenon known as adaptive radiation. As the ancestral organisms adapt and evolve in their different environments, they take on new forms. Australia’s marsupial ancestors have evolved and radiated into many different forms, from tree-dwelling, fruit-eating possums to blind, meat-eating underground moles, and the more familiar kangaroos and koalas.

58. Convergent evolution
Or convergence, occurs when organisms evolve and end up having similar adaptations. This is due to:
• living in similar environments, and
• having similar habitats and lifestyles.
In similar habitats the same types of characteristics are ‘selected for’, resulting in organisms that look similar despite having very different genes. These organisms may have analogous structures, structures that look similar but which have come from different ancestors. One example is the gliding membrane found between the limbs of Australia’s gliding possums and also found in the flying squirrels of North America, Europe and Asia.

59. Parallel evolution
A third type of evolution is parallel evolution, which occurs where related species evolve similar features while separated from each other. The result is organisms that look alike and have common ancestry, but are found in different locations.
Old and New World monkeys share many features. New World monkeys like the vervet (bottom left) have prehensile tails to hold onto branches, whereas Old World monkeys lack prehensile tails since they have evolved to live on the ground.

60. Evidence for Evolution

61. The fossil record
Direct evidence for evolution comes from palaeontology, the study of fossils. The fossil record from all over the world provides evidence of continual changes in life forms from over 3500 million years ago until the present. Fossils are the preserved evidence of past life usually found in sedimentary rocks.

62. Fossils may be the:
• actual remains of organisms (e.g. mammoths frozen in ice, insects trapped in a type of sap called amber)

63. hard parts of organisms (e.g. shells, teeth and bones)

64. impressions of organisms (e. g
impressions of organisms (e.g. hollowed casts, moulds where substances have replaced the organism)

65. evidence of the presence of organisms (e.g. footprints).

66. The ages of fossils, and the rocks in which they are found, can be estimated using radioisotope-dating techniques. These techniques have enabled scientists to devise a geological time scale, dividing the history of the Earth into eras. These eras are subdivided into periods, which are further subdivided into epochs.

67. Using the fossil record
The fossil record allows us to trace major events in the history of life on Earth. Life seems to have begun around 3500 million years ago. The first organisms were probably simple, single-celled, anaerobic (no oxygen was available) bacteria which fed on organic compounds in the primitive seas. Later, photosynthetic bacteria and blue-green algae appeared, releasing oxygen into the atmosphere. This oxygen release allowed ozone (O3) to form and accumulate, screening out some of the ultraviolet (UV) radiation. This gave some safety to the newly evolving organisms.

68. An explanation for the appearance of life?
One hypothesis to explain the initial appearance of life was put forward by a Russian scientist, A.J. Oparin, in The early atmosphere is thought to have consisted of gaseous methane (CH4), ammonia (NH3), hydrogen (H2) and water vapour (H2O). Energy from lightning, ultraviolet rays or gamma rays split some of these gas molecules. New bonds formed
to create complex organic molecules, which collected in pools to form an ‘organic soup’. Over millions of years this ‘organic soup’ became concentrated, more complex molecules formed and the first cells appeared.

69. In 1953, S. Miller and H. Urey tested the idea in a laboratory experiment at the University of Chicago. Electric sparks were passed into a gas mixture that was thought to be similar to the early atmosphere of the Earth. Organic molecules were produced! No experiments, however, produced a living cell.
The Miller/Urey experiment. Given suitable conditions molecules can combine to form organic molecules.

70. More complex life evolves
Around 1500 million years ago, organisms with more complex cellular structure appeared. Sexual reproduction appears to have begun at around this time. Organisms recognisable as animals appeared around 600 million years ago. Thousands of specimens of these invertebrates have been collected from sandstone deposits at Ediacara, in the hills north of Adelaide. They are possibly related to present-day jellyfish and earthworms

71. From bacteria to humans
An abundance of fossils from the Palaeozoic era (570 to 248 million years ago) show the existence of bacteria, algae, soft-bodied invertebrates and representatives from
all the major animal groups we know today. Characteristic organisms from the earliest Palaeozoic era were the trilobites. The earliest known land organisms (vascular plants) appeared around 400 million years ago.

72. The first land vertebrates (amphibians) appeared slightly later
The first land vertebrates (amphibians) appeared slightly later. At this time the greatest diversity and number of species lived in the sea. The Mesozoic era (248 to 65 million years ago) is often called the age of the reptiles because of the abundance and diversity of reptilian forms (including dinosaurs) that lived in this era. The earliest mammals, flowering plants and birds also appeared in this era.

73. Fossils from the most recent era, the Cenozoic era (from 65 million years ago), show the increasing dominance of mammals and the appearance of humans ( years ago).

74. A changing record
The fossil record provides evidence of continual change. A vast number and variety of species have emerged from the earliest life forms. Whole groups of organisms have appeared, become abundant and then disappeared.

75. Some of these changes include:
Dramatic climate change and altered sea levels may have caused the disappearance of 50% of all shallow-water marine invertebrates around 225 million years ago.

76. The impact of a large asteroid, and consequent dust storms, are thought to have caused the extinction of the dinosaurs around 65 million years ago.

77. Other organisms, like club mosses and jawfish, have appeared, been abundant, but now survive in small numbers only.

78. Others, like the flowering plants, insects, mammals and birds, were present in small numbers for some time, then became abundant.

79. Mammals increased dramatically after the demise of the dinosaurs.

80. An incomplete record?
The fossil record is, however, far from complete. Only a small proportion of the plant and animal species thought to have existed are preserved as fossils. While the fossil history of aquatic organisms is extensive and detailed, the fossil history of land animals is far less so. Fossilisation is a rare occurrence. Organisms must ‘fall’ into conditions where decay does not occur. The soft tissues of organisms usually do not form fossils.

81. Fossilisation is more likely in seas, lakes, swamps and caves, but unlikely on land. Geological processes, and human activity, are constantly moving and destroying the sedimentary rocks that contain fossils.

82. Fossil evidence shows an excellent record for the evolutionary development of some organisms such as the horse.

83. Transitional forms
Provide the links between the major groups, such as the air-breathing crossopterygian fish, and the bird-like reptile, Archaeopteryx.
For many groups of organisms there are large gaps in the fossil record, often with no transitional forms being found.

84. Anatomical studies
Comparisons of the anatomy of various plants and animals provide indirect evidence of their evolution from common ancestors. The front flipper of a seal, a cat’s paw, a horse’s front leg, a bat’s wing and your own hand all look different and perform different functions.

85. However, they all consist of the same number of bones, muscles, nerves and blood vessels arranged in a similar basic pattern. The basic pentadactyl limb (a limb with five digits) can be traced back to
the fins of certain fish from which the first amphibians are thought to have evolved. These fundamentally similar structures are called homologous structures. The differences seen in the structures may reflect adaptations to different environmental conditions. Their similarity strongly suggests a common ancestor.

86. The distribution of plants and animals
Biogeography is the study of the distribution of plants and animals, both now and in the past. As Darwin saw in the Galapagos Islands, the organisms found on oceanic islands resemble those living on the nearest mainland, yet include species found nowhere else. As oceanic islands have never been attached to the mainland, their inhabitants are thought to have somehow arrived from the mainland, to then evolve in isolation.

87. Genetic evidence
The structure of DNA and the genetic code provide us with more evidence for evolution. Comparisons of DNA are used to provide evidence of how closely different species are related. For example, the genetic make-up of a chimpanzee is 98.5% identical to that of a human. Gorilla DNA matches human DNA except for the last 2.6%. The genetic make-up of other primates is also similar to our own.

88. Human Evolution
Evidence from the fossil record and other studies supports the theory that modern humans evolved from a common ape-like ancestor. The evidence suggests that there have been many species of humans, some of which have become extinct, while others evolved into modern humans.

89. Humans belong to the order Primates and have many of the features of the primate group. Primates (including us) have:
• forward-facing eyes that allow binocular vision
• pentadactyl digits (five fingers/toes on each limb)
• four upper and four lower incisor teeth
• opposable thumbs (for grasping things)
• nails (not claws) on the fingers and toes
• large brains for their body size
• a flexible skeleton, with arms that rotate in the shoulder socket to allow them to reach behind their body

90. Humans are unusual, as we also:
• walk upright (are bipedal)
• have fewer and smaller teeth than the apes
• have a flattened face
• have a very large skull capacity, and large brain, about three times larger than that of apes
• make and use tools
• use various verbal and visual languages to communicate
• are self-aware.

91. Evolution of humans Our distant relatives
Dryopithecus, an ape-like animal that first appeared 25 million years ago. Ramapithecus, another ape-like animal, appeared 14–16 million years ago and lasted another 6 million years. Some believe Ramapithecus to be the ancestor of the Asian orang-utan, while others see a relationship to other apes and humans.

92. The first true ‘human-like’ fossils belong to the genus Australopithecus (meaning ‘southern ape’, after the first fossils found in South Africa). They are around 4–5 million years old.. These species were fully bipedal, walked on two legs, and had a brain size of 400 cm3, less than one-third that of modern humans.
All fossil australopithecines have been found in Africa. One of the most famous is a 40% complete skeleton of a female named Lucy.

93. More recent ancestors
The first clear representation of the Homo line is Homo habilis (‘handy man’). Fossils found in East Africa dating to 1.5–2 million years ago reveal major anatomical and behavioural changes from Australopithecus afarensis. The brain size was 50% larger, and they used tools.

94. Homo erectus (‘upright man’) came next
Homo erectus (‘upright man’) came next. Although fossils have been found in Europe, China and Africa, Homo erectus is often called ‘Java man’, after the initial discovery site. The oldest fossils are 1.5 million years old. Homo erectus had an average brain size of 1000 cm3, lived in caves and used fire.

95. The evolution of Homo erectus into Homo sapiens (‘intelligent man’) is the subject of considerable debate. Some maintain that Homo erectus evolved worldwide into Homo sapiens but retained local features. This gave rise to different forms in different areas, such as Asia and Africa. Others maintain that Homo sapiens evolved in Africa, and spread from there some years ago. This would mean that all present-day variation in humans has arisen in the past years.

96. Other fossil humans
Homo neanderthalensis (‘Neanderthal man’), is thought to be approximately – years old. The Neanderthals were cave dwellers who used tools and buried their dead, indicating some religious beliefs. They are thought to have become extinct due to a change in climate or through competition with other human species in Europe. The common ancestor of humans and Neanderthals probably lived in Europe around years ago.

97. ‘Cro-Magnon man’ (10 000– years old) was a nomadic hunter-gatherer who used tools and developed art. Anatomically Cro-Magnons were similar to modern humans, but more robust. Cro-Magnons lived in Europe and the exact reasons for their extinction are not known.

99. Cultural evolution
Humans have changed in many non-physical ways. We have learned how to use tools, and have developed speech, forms of writing, artistic creativity, reasoning powers and a sense of right and wrong. It is these changes that most distinguish modern humans from their ancestors. Humans have highly complex social structures, and an accumulation of learning and knowledge. This stored experience is passed from generation to generation, and affects survival—that is, a type of cultural evolution occurs.

100. It is estimated that of all the animal species that have ever existed, only 1% are alive now.
The ultimate fate of most species appears to be extinction. Homo habilis lasted for around 1 million years, Homo erectus around 1.5 million. Modern humans have existed for about years. With cultural evolution, humans continue to acquire knowledge, enabling them to exert more control over their environment than any other species ever has, but we have probably done more damage also.