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9.3 Blueprint of life: 1. Evidence of evolution

Extract from Biology Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW
[Edit: 12 June 08]

Prior learning: Science Stages 4 - 5 syllabus: Outcome 4.10 (content 4.10 a: ecosystems), Outcome 5.8 (content 5.8.3 a and b: the theory of evolution and natural selection) Outcome 5.9 (content 5.9.4 b and c: natural events).

Preliminary modules 8.4 and 8.5

Background: Evolution in its broadest sense means change. Biological evolution is a change to the gene pool of a population. So, evolution refers to a lasting change to a population over generations. The theory of evolution is supported by many forms of evidence. There are inherent variations in populations and not all individuals survive to reproduce. Through the mechanism of natural selection, heritable changes may occur in populations over many generations.

plan, choose equipment or resources and perform a first-hand investigation to model natural selection

• Plan a first-hand investigation to model natural selection. You need an investigation design that will allow valid and reliable data to be collected.
  
  A simple but useful investigation that you might use is 'Stick-bird': Within a hypothetical population of 'worms' (toothpicks) that inhabit a predominantly green-coloured environment (green grass), there are two colour variations; cream and green. The worms are food for a predator known as a 'stick-bird' (students).
  
  Possible hypothesis: In a predominantly green coloured environment, green worms have a greater chance of survival due to their ability to blend in with the background.
  
  
  
  Stick bird
  
  Toothpicks are mixed and scattered randomly over a measured grassed area. Stick birds (students) are later brought to that area and remain outside a 'fence'. They are told to prey on the 'worms' in the field (collect as many toothpicks as they can) in a given time. After 3 minutes, the 'stick-birds' are driven from the field by the 'farmer' (teacher). They escape back to the classroom
  
  Tally and compare the numbers of green and cream toothpicks recovered. Calculate percentages recovered of each colour.
  
  Consider the numbers of toothpicks and students that will be needed for valid and reliable data to be collected in the investigation. You may need to modify the procedure in light of your considerations.
  
  
• Choose equipment or resources by setting up the most appropriate equipment to undertake the investigation. For example, 1000 toothpicks; 500 coloured green with food dye and 500 left natural (cream).
  
• Perform the planned procedure to model natural selection. You need to be able to identify and explain how the activity models natural selection. Consider what aspects of the activity do not represent natural selection well. This may lead you to recognise any modifications that need to occur to the activity.

analyse information from secondary sources to prepare a case study to show how an environmental change can lead to changes in a species

• A case study here would need to describe the Australian example (a report) and would need to explain how environmental pressures can change species over time (an explanation). Assess a range of resources including popular scientific journals, CD-ROM encyclopaedias and the Internet. You will need to extract information, and summarise and collate your data. Some starting information for some good subjects to use for this investigation is provided below.
  
  
• Analyse the information to make and justify generalisations that have led to changes in species.

outline the impact on the evolution of plants and animals of:

• changes in physical conditions in the environment
• changes in chemical conditions in the environment
• competition for resources

Changes in physical conditions in the environment

• These include natural conditions, such as temperature and the availability of water.
  
  
• The Australia landmass has become drier over time and this has lead to changes in the species of kangaroos that are present today. Approximately 25 million years ago, Australia was considerably wetter than today with large areas of rainforest. During this time, kangaroos were small and omnivorous, with unspecialised teeth, eating a variety of foods from the forest floor. Food was nutritious and abundant; there was no need for specialised grinding teeth.
  
  
• As Australia became more arid and grass became the dominant vegetation in some areas, environmental selective pressure resulted in larger kangaroos favouring teeth suitable for grass. These teeth, high-crested molars, efficiently grind low-nutrition grass into a more easily digestible paste. Slicing pre-molars are of little use and so became much reduced from the ancestral kangaroos.

Changes in chemical conditions in the environment

• Chemicals that can affect the evolution of species include salts and elements, such as iron. For example, many parts of Australia have soils that have a high salinity. There are a range of salt tolerant plants that have evolved to inhabit those areas. The animals that feed from these plants have also evolved to inhabit those areas.
  
  
• The sheep blowfly, Lucilia cuprina, is a major problem to the Australian sheep industry. It stresses, weakens and can be lethal to sheep when larvae, laid by females, burrows into wounds and wet wool. Chemicals, such as dieldrin and organophosphates, have been used extensively to control the blowfly. However, genetic resistance has occurred within the fly population that has made these chemicals ineffective. Withholding a particular insecticide for a time allowed the resistance of this particular blowfly population to drop. Continued use of the insecticide has resulted in the mutation of a modifier gene that increases and maintains the resistance. Thus, the insecticides can never be effective again, regardless of the number of blowfly generations that pass.

Competition for resources

• This occurs within a species and between species. If a new species is introduced into an area then the competition may lead to different species using different resources.
  
  
• Resources can include food, space or mates. If populations that live in the same area could specialise on slightly different resources or breed at different times, they would avoid direct competition.
  
  
• Some species of fruit fly have evolved into different species with each confined to a different type of fruit tree. This is possible if there are different flowering and fruiting times on each tree type suited for different breeding cycles in the fruit flies. Eventually, two distinct species can result.

perform a first-hand investigation or gather information from secondary sources (including photographs/ diagrams/models) to observe, analyse and compare the structure of a range of vertebrate forelimbs

• Perform a first-hand investigation by observing a range of vertebrate forelimbs to compare their structures. Use at least three different types of vertebrates.
  
  OR
  
  
• Gather information from secondary sources to observe a range of vertebrate limbs. Use biology references and look for terms such as homology and vertebrate limb. You can try the same words in a search engine on the Internet. The sites below are a starting point.
  
  Comparative vertebrate anatomy Eastern Kentucky University, USA.
  Scroll down to Limbs.
  
  
• Analyse the information by comparing the collected data and looking for trends and patterns. A table like the one below is a suitable way to organise information.

describe, using specific examples, how the theory of evolution is supported by the following areas of study:

• palaeontology, including transitional forms
• biogeography
• comparative embryology
• comparative anatomy
• biochemistry

Palaeontology

• The fossil record provides a time line of evolution of life engraved in the order in which the fossils appear in rock layers. Some parts of the fossil record show a gradual change in life forms over millions of years.
  
  Of particular interest are transitional fossils that have characteristics belonging to ancestral and descendant groups. The most famous transitional form is Archaeopteryx. This is a fossil first thought to be a therapsid reptile. Its reptilian features include teeth and a reptilian-like skeleton. However, Archaeopteryx also had feathers and a wishbone sternum used to attach flight muscles. This provides evidence of an evolutionary pathway from dinosaurs to birds.
  
  Transitional Fossils Archaeopteryx: an early bird, Museum of Paleontology, University of California, Berkeley, California, USA

Biogeography

• Charles Darwin and Alfred Russell Wallace both observed the distribution of species into different biogeographic regions and saw this as major evidence to support the theory of evolution. They argued that animals in different regions had come from ancestors in that region and had adapted over time to the conditions there. Special Creation, the prevailing religious-based explanation of the time, did not explain why islands with similar conditions did not contain the same flora and fauna. Darwin proposed that migration and evolution were much more satisfactory explanations for the unique flora found in places such as Australia.

Comparative embryology

• There is an obvious similarity between embryos of fish, amphibians, reptiles, birds and mammals. A comparison of embryos of vertebrates shows that all have gill slits, even though they do not remain later in life, except in fish. This indicates a fundamental step that is common to all vertebrates and supports the idea of a common ancestor.
  
  Embryonic Development Animations of embryos, NOVA Online PBS Broadcasting, USA

Comparative anatomy

• Anatomical structures on different organisms that have the same basic plan but perform different functions are called homologous structures. Homologous structures are evidence for evolution. The structures are shared by related species because they have been inherited in some way from a common ancestor.
  
  An example of an homologous structure is the pentadactyl limb found in amphibians, reptiles, birds and mammals. The basic plan consists of one bone in the upper limb, two in the lower limb leading to five fingers or toes. In bats, the limb is modified to form a wing with the fingers extended and skin stretched between each finger. Whales have within their single paddle-like fin a fully formed pentadactyl limb.
  
  Homologous structures BioWeb 9-12, USA

Biochemistry

• Recent advances in technology have allowed comparison of organisms on a molecular basis rather than simply comparing structures. This was previously impossible between such distantly related organisms as an orchid and a mouse.
  
  The study of amino acid sequences shows that more closely related species share more common sequences than do unrelated species. Particular evidence has been derived from the amino acid sequence in haemoglobin, showing that humans and rhesus monkeys share all but eight amino acid sequences whereas there are 125 amino acid differences between humans and lampreys. This supports the fossil, embryological and anatomical evidence that humans are more closely related to rhesus monkeys than they are to lampreys.

analyse information from secondary sources on the historical development of theories of evolution and use available evidence to assess social and political influences on these developments

• Analyse information you gather to make and justify a generalisation about the influences on the theories of evolution.
  
• Use the evidence you have collected to make a judgement about the influences of the social and political pressures of the time on the theories of evolution.
  The following reference is provided as a starting point.
  
  History of evolutionary thought University of California Berkeley, USA.

explain how Darwin/Wallace's theory of evolution by natural selection and isolation accounts for divergent evolution and convergent evolution

Divergent evolution occurs when closely related species experience quite different environments and as a result vastly different characteristics will be selected. The species, over time, will evolve differently and will eventually appear quite different. For example, elephants are large plains-dwelling animals that are closely related to a small guinea pig-like animal called a hyrax. Hyraxes live amongst rocky outcrops on mountains. Comparison of skeletons indicates the close relationship between the two groups.

Convergent evolution occurs when two relatively unrelated species develop similar structures, physiology or behaviours in response to similar selective pressures from similar environments. For example, dolphins (mammals) and sharks (cartilaginous fish) have evolved a streamlined body shape and fins that enable them to move efficiently through their aquatic environment, yet they are only remotely related as vertebrates. Communal social behaviour has developed independently in ants, termites and bees.

use available evidence to analyse, using a named example, how advances in technology have changed scientific thinking about evolutionary relationships

• Use the available evidence to analyse how advances in technology have changed scientific thinking. You should consider how the results of investigations that use new technology support previously available evidence and theories. Use this to justify the conclusions that indicate changes in scientific thinking about evolutionary relationships.
  
  For example, biochemical taxonomy and gene mapping has changed the relationship of the primate groups.
  
  The web pages below will give you some starting points.
  • Evidence Supporting Biological Evolution
    Extracts from Science and Creationism: A view from the National Academy of Sciences, Second Edition. Steering Committee on Science and Creationism, National Academy of Sciences. National Academy Press, USA. See New Evidence from Molecular Biology (about two-thirds down the page).
  • The modern view of evolution
    M.J. Farabee, Estrella Mountain Community College, Avondale, Arizona, USA
  (These websites last updated June 2008.)
  
  
• You may identify or encounter mass media information when studying this syllabus point. Where that occurs, process the information to assess the accuracy of scientific information presented by comparing it with similar information presented in scientific journals.

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