Evolution Change Over Time Biology Essay

Published: Last Edited:

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

Natural selection: environmental conditions that favoured and therefore selected some phenotypes/varieties over others, leading to change in a population

• Theory: a coherent explanation for a group of phenomena or observations; fact: a truth that exists

• Evidence for evolution: evidence that past life is different from present life (for example, fossil evidence), and that unrelated organisms on different continents are similar in similar environments (convergent evolution), or that related organisms have similarities (divergent evolution)

• Variation is caused by mutation, by new combinations of alleles within individuals.

• Species become extinct when there is a feature in their environment they cannot adapt to (for example, traffic, introduced animals, lack of prey) or if they are unable to find mates - scarcity due to some of the listed features.

• The distribution of species is controlled by their needs. Some species of birds (for example, emus or seagulls) may not be able to find food or nesting requirements in rainforests.

• Humans and cabbages are both eukaryotes - and will therefore have many genes in common that control cell physiology (for example, genes that produce proteins for respiration, cell divisions and movement of substances across cell membranes).

• Evidence for evolution happening today: changes observed within our lifetimes (for example, in Galapagos finches, in wild guppies, in the adaptations of introduced organisms to new environments).

• New species are constantly evolving - hybridisation has resulted in new varieties of finches in the Galapagos Islands, in Australia, major highways have fragmented populations of lizards that are each developing separate characteristics, and mutations in pheromones are making some species of orchid unpalatable to the usual pollinators. If these changes are sustained, and the new varieties do not become extinct, these will become reproductively separated from the original 'stock'.

Students to work in pairs to write a six-word summary of the key elements of this task.

Invite students to share their summaries.

The key point about this assignment is that it is a fictional scenario. As students research the scientific history, they will need to interpret whether the ethical standards of today apply equally to the past (this is called an 'anachronism' - sometimes expressed as 'the past is another country'), and consider the social, economic, and/or environmental contexts in which these scientists worked.

Also, give students time to consider their preferred format.

Set a due date for the conference.

Ask students to evaluate (perhaps on a study note) how they plan to respond to this task. Spend a few moments with each student over the next month, to follow up on progress before the conference date.

You could provide an alternative culminating assessment task (and create an intra-disciplinary link with Unit 6).

Quality science fiction lasts because it tests the big questions of science seriously in hypothetical and imaginative contexts. Consider how a fictional scenario may provide solutions to this question:

Could a planet support more than one genetically related group of organisms at the same time?

Your response needs to demonstrate evidence of understanding relevant scientific ideas from Units 1 and 6. Maximum suggested length of transcript: 1200 words.

Understanding biodiversity underpins our appreciation of evolution. A highly readable and witty book, over 30 years old but still pertinent, is Paul Colinvaux's Why Big Fierce Animals are Rare - An Ecologist's Perspective (1978, Princeton Science Library).

The many thoughtful biodiversity related topics that can be linked to evolution include: what limits diversity (stability of habitat, where the risk of extinctions is low), what limits the rarity of prey (supported by the second law of thermodynamics) and how humans have changed their niche from being rare, top predators to an ingenious species that continues to turn more and more of the resources of the earth to its own end during the last 9000 years.

Of special interest in our understanding of biodiversity, is how photosynthetic efficiency, which underpins all life, is limited by the rarity of CO2, why the blueness of the oceans is an indicator of its low productivity, and why ocean plants are small, not large, compared to the water plants at the ocean's fringes. Discussing some of these ideas with students will help them look at their world with new, critical and reflective eyes.

This activity will be easy if students broaden their list of 'living things' beyond mammals, birds or reptiles. Consider the varieties of plants growing on the oval, look for arthropods in leaf litter.

The arguments supporting 'Why biodiversity is important?' include the following.

• Food webs in regions with high biodiversity are likely to be more complex - and therefore provide alternative food sources for many species, providing them with a more sustainable environment.

• There will be many species in each trophic layer, therefore providing alternatives to fill niches and acting as a 'buffer' should one species go extinct.

• In ecosystems with high biodiversity, there is likely to be many levels in the food pyramid, a requirement for supporting 'top' predators.

• High biodiversity can suggest the ecosystem is undamaged (although this may be a fallacy - introduced species may also increase biodiversity - see iScience9 Unit 4).

• High biodiversity represents a bank of 'untapped potential' for human use. Examples include new domestic animals, new crops and new medicines. (A counter argument is that biodiversity is also a source of zoonotic disease when wild organisms come into contact with humans - examples include Sars, Ebola and Lyme disease.)

Reasons for 'Humans need biodiversity to survive' (suggestions only):



Biodiversity is ethically pleasing - national parks are places for spiritual renewal.

Ethical needs are a 'moveable feast'; the sources of spiritual sustenance appreciated by humans in the past differ from those of the present, and may change again in the future.

Biodiversity can be a source of new foods and medicines.

Biodiversity can be a source of zoonotic disease (see above). Biodiversity includes diseases, and parasites like malaria, which humans could well do without.

Areas on Earth with the highest biodiversity also tend to support the highest human population density -consider Java, Indonesia as an example.

There is no evidence that the less biodiverse temperate regions support human habitation less sustainably - consider Northern Europe and Canada as examples.

Without an ecosystem, there can be no foundation to support any life on Earth, including humans. An intact ecosystem implies there is biodiversity.

Humans living in traditional hunter-gatherer societies were sustained by many hundreds of different species, but today a very much smaller range of domestic livestock and crops supports seven billion people.

Biodiversity is a function of 'lack of extinction' and therefore high biodiversity is evidence the conditions that support life/the ecosystem were sustained for hundreds of millions of years.

Biodiversity is a function of 'lack of extinction', and past ice ages caused repeated mass extinctions in Earth's polar regions. The lower biodiversity in these biomes today is evidence that evolution hasn't had time to generate the same numbers of new species as are found in the tropics.

An example could include: Biodiversity will be sustained when habitats are large enough to maintain the genetic diversity of species.

An example of justification: Many Australian species are endemic; therefore their loss is a loss to global biodiversity. A refutation example: Many species fill similar niches, therefore replacing fussy native species with more ecologically efficient introduced species is inevitable anyway.

A brilliant examination of the importance of islands, their relative size and the relationship of their biodiversity to the nearest large landmass can be read in David Quammen. (1996). The Song of the Dodo. Island biogeography in the age of extinctions, Hutchinson.

Part travelogue, part discussion of the methodology of famous experiments, part history and part debate, nearly every chapter of this book filled with stimulating ideas that will challenge students with dilemmas. Our world is in pieces. 'Island biogeography is no longer an offshore enterprise…It's everywhere.'

A contemporary ecological study to find on the critical size of rainforest ecosystems needed to sustain biodiversity is currently underway in Malaysia. Here, the global pressure to produce biofuel is replacing thousands of square kilometres of virgin rainforest in Sarawak with massive oil palm plantations. Species at risk of extinction include Orang-utans, a rare species of rhinoceros, a pygmy elephant and many hornbills (birds with large colourful beaks). What is the solution to this dilemma?

In Australia, habitat fragmentation caused by urbanisation is contributing to the worrying collapse of koala populations all along the Australian East coast. A recent ABC 4 Corners programme ('Koala Crunch Time') about this can be viewed at .

Geological periods are named after the location of rocks where their distinctive fossils are first discovered. The most recent period to be ratified (in 2004) is the Ediacaran Period. It is named after some unusual multicellular fossils found by Australian geologist Reg Sprigg in 1946, in the Ediacara Hills in the Flinders Ranges, South Australia. To this date, no one knows whether the organisms were plants, animals, fungi, or something else.

Here are some additional activities you could pose to the class.

How would students interpret these images of Ediacaran fossils?

Read about Reg Sprigg's adventurous life and discuss the questions below.

What are some of the ways in which Sprigg was a pioneer scientist and thinker?

Which other famous Australians did Sprigg know and work with?

How does the following extract makes you feel about scientists and scientific work?

Reg was not a brilliant academic scholar, but he was driven by an overwhelming intellectual curiosity about the world around him. He was a lateral thinker full of new ideas and new ways of looking at the old scientific truths.

Add to the table by finding additional images of examples of each type of fossil, and sharing these on the class wiki.

This activity can best be considered as a formative task. Students may enjoy eating some of the results.

Consider eating these in a location other than a science laboratory, or be scrupulous about covering the benches.

This refers students to two activities on the same website. Both activities are interactive and enables students to work their way through Burying bodies and Making fossils. These interactives could be completed for homework.

The following link provides many additional activities for students to explore their understanding of fossilisation - making moulds and casts, modelling replacement fossils, carbonised fossils, and inferences from partial skeletons or teeth.

The word fossil comes from the Latin fossilis meaning 'dug up'. Can you think of any fossils to which 'digging' doesn't apply, exactly?

• Oil and gas are mixtures of hydrocarbons. An animation of the drilling process can be seen at

• Crude oil processing - this video clip briefly shows a rig, then fractional distillation: • Gas - methane hydrate exploration in deep oceans - the suggested extraction technique proposes replacing one gas with another:

To explore this WOW! fully, students will need to know what an isotope is, and understand the notation. This revises content in the iScience9 Unit 5.

As a 'thought experiment', investigate the relationship between the spatial distance in a ribbed structure (such as the teeth of a comb, or across the mesh of a screen) and the pitch of the sound produced by rubbing rate.

Discuss how scientists may have inferred the original stridulation of the Jurassic cricket, given that there are at least two variables involved.

The original source of the information on the fossil cricket song can be found at For students interested in the technical aspects, and other species (living and extinct) to which this technology has been applied, the original free source of this information is

Science provides a more readable version, but only the abstract of this article is free: .

This technique is now also being used to resolve a long-standing debate about whether dinosaurs were warm or cold blooded. Results based on analysis of fossil teeth, were that Brachiosaurus brancai had a body temperature of 38.2°C, and Camarasaurus a temperature of 35.7°C, which is more than found in crocodiles and alligators, but cooler than birds.

Watch a 5:17 minute video with the writers of the original paper about the technique, the information it provides, and what motivated them to study palaeontology: .

Riversleigh is in Western Queensland (source of image: ), a site particularly rich in fossil mammals.

Student responses will vary, but this is an invitation for critical thinking. For example, when a complete image of a dinosaur is reconstructed on the basis of a few leg bones, there is an assumption the reptile is anatomically homologous (refer to Comparative anatomy on page 50). When dinosaurs are coloured (for example, Rhoetosaurus brownei) the artist has drawn on knowledge that many modern reptiles such as snakes and lizards can be brightly coloured, although often there may be no real scientific evidence for this (and many modern mammals that fill similar niches, are not coloured). Why was the decision made to show the dinosaurs like that?

In NSW, fossils can be collected manually (no digging or excavation tools) provided the owner of the land has given permission. In the ACT, fossils can only be collected legally when the site will be destroyed; for example, a building excavation or at road works.

Fossils are part of our natural heritage, and could be of great scientific value. Responsible collecting would include carefully identifying the site where the fossil is collected, targeting specimens likely to be at risk of being destroyed by weathering, and those that are close to the surface.

In NSW, fossils are part of landownership.

Student responses will vary, but most students are likely to favour collecting fossils at sites that are at risk of weathering and erosion, or other situations in which they are likely to be destroyed.

This is an open-ended investigation. Here are some pointers to drive the 'this might help' section.

Help students by suggesting limbs often move in groups: insects, for example, often move their legs in two groups of 'tripods' for stability, and millipedes control their legs by moving them in a 'wavelike' motion, from which underlying nerve connections that stimulate this movement may be inferred. Many animals (well studied in horses) have different gaits depending on the speed they move.

Some studies, often including tall animals like giraffes, analyse leg movement as an example of pendulum motion.

Look at the s on this activity sheet and brainstorm strategies for investigations. Perhaps students could build puppets or construct models. Perhaps they will analyse actual gaits using time-lapse photography, or measuring the depth of imprints on a sandy surface.

This simple and engaging interactive introduces students to the science of cladistics, and then demonstrates how cladistics can be used to infer information that can never be derived from fossils.

Spindle diagrams pack a lot of information. Ask students to consider the scale (for 50 families) to infer the size of relative biodiversity at different geological time periods.

Questions for discussion include the following.

• What happens to biodiversity in all the families at the horizontal lines defining the change to a new geological era? (Answer: Collapses - evidence of a mass extinction.)

• Does mass extinction seem to be a prerequisite for the evolution of new biodiversity? Why is this? (Answer: Yes. After a mass extinction, the surviving organisms experience 'ecological release', where most phenotypes are able to take advantage of unoccupied niches, to which they evolve specialised adaptations. This would not have been possible in stable ecosystems.)

• Are there any examples where biodiversity seemed suddenly to decline which cannot be linked with a new geological time period or era? (Answer: No. A decline always signals a local or global mass extinction.)

Find more information about the Gogo fish at .

This clip runs for 4:10 minutes and is about 'living fossils' and the discovery of the Wollemi pine:


As an extension activity, students could investigate how to grow a Wollemi pine in a garden.

• Where could you buy one? (Many Australian nurseries now sell them.)

• How big a space would you need to grow one? (It will eventually be a large tree, up to 100&&m high, so as a guide you would need an area of at least 100&&m2.)

• Would you be adding to the species biodiversity by growing one? (No: they are clones or so genetically similar they are the equivalent of laboratory mice. This is because they have been genetically isolated for a long time, and may have gone through a 'genetic bottleneck' - where the species may once have been represented by a single individual.)

• Would you be helping global biodiversity by growing one? (Yes, every additional specimen is a buffer against extinction.)

Observation: Galapagos finch species seemed very similar; Prediction: Galapagos finches (and other groups of similar-looking species) shared common ancestors; Evidence: Fossil organisms with features that are intermediate to groups of living species would provide evidence of common ancestors.

The heat and pressure in metamorphic rock formation from sedimentary rock destroy fossils, and the heat from volcanic rock formation, would usually destroy living organisms trapped in lava flows (the casts of victims covered in volcanic ash, such as the Pompeii eruption of AD 79 are exceptions). Sedimentary rocks form from silt, mud, sand or larger rocks settling in lakes and oceans, and then becoming compacted and concreted. These conditions often trap dead organisms at the same time.

Possible answers include the following.

• Oceans cover a greater proportion of the Earth's surface.

• Oceans and other deep water bodies are places where sedimentary rocks form - protected from other forms of damage.

• Some marine species that were very common also had persistent hard parts - for example, shells and corals.

• Some marine species that are very common moulted, so a single individual could leave many trace exoskeletons during its lifetime (for example, trilobites, which are arthropods).

Fossils of soft bodied organisms are rare because they are (i) often small, which means the entire specimen can be destroyed easily and are (ii) physically more fragile.

Darwin realised that if evolution had taken place, this would require vast amounts of time, and that fossils provided the evidence of past life forms.

Possible answers include the following.

• The organism had four forward-pointing toes (no evidence of the backward-pointing toes).

• The organism was relatively large (there is no scale, but the sand grains suggest each foot was several centimetres across)

• The organism was a quadruped - walked using four feet

• The organism was probably not running (size of the feet relative to the distance between backward and forward-facing paws)

Acids (including those found in peat bogs) react with carbonates to produce a salt, carbon dioxide and water.

Australia has relatively few peat bogs, and very little surface water. Cultural features found with 'bog bodies', including evidence of garrotting and ritual murder, and these are not typically associated with Australian Aboriginal cultures. If an Australian 'bog body' is ever to be found, it will more likely be the result of an accident, which will always be rarer than deliberate disposal.

Shells are made of calcium carbonate and this preserves well in dry alkaline conditions.

Placoderms - armoured fish

Spiny sharks - a group that had features in common with cartilaginous and bony fish

Bony fish (≈&&275 families based on using the scale with diagram 2.15)

Mammals (≈&&165), Birds (≈&&135), Reptiles (≈&&45), Amphibians (≈&&25), Jawless fish (<5)


The late Permian Period

Bony fish (≈&&100 families based on using the scale with the diagram)

Reptiles (≈&&65 - this was the 'Age of dinosaurs')

At different times:

Amphibians (≈&&38 families based on using the scale with the diagram), Jawless fish (≈&&35), Placoderms (≈&&33), Bony fish (≈&&30), Reptiles (≈&&25).

Key information should include biodiversity and fossils.

Sample responses below.

• Yes: tuataras are small reptiles on a New Zealand island that are related to dinosaurs.

• Yes: the discovery of the Wollami pine compares with finding a 'dinosaur' - huge organisms can remain undiscovered.

• No: Wollami pines are plants and therefore don't move - an animal would be detectable, including from space.

• No: other reptiles are now taking their niche, and also birds have taken their niche.

Analogous structures are only superficially similar to homologous structures. They are evidence for evolution because they demonstrate there are many different 'solutions' to the problem of adapting to the same niche, such are living in flowing streams or being able to fly. You can investigate and compare homologous bone arrangements at this.

How to read a cladogram. As with all diagrams and figures, students need to recognise how efficient these are at presenting information visually, and be sensitive to the nuances. Questions that could be asked to check their understanding include the following.

• What is the significance of the horizontal lines starting at different positions? (This indicates the 'split' occurred at different times in the past. There is an inferred independent variable, time, along the bottom axis of this diagram.)

• How are decisions made to include organisms in a 'clade' or group? (This is based on common features. Echinoderms, with their 'loss of pharyngeal gill slits', must therefore have many other characteristics in common with the Hemichordates.)

• Apart from Vertebrates and Echinoderms, students are unlikely to be familiar with all the groups in this figure. They might be interested to find images of examples online, and consider the evidence for the way they have been classified.

A useful book is Neil Shubin. (2009).Your Inner Fish: A journey into the 3.5 billion year history on the human body,Vintage. Neil Shubin is the palaeontologist who in 2004 discovered Tiktaalik in the Arctic. Tiktaalik is an important and famous fossil 'missing link' which shares characteristics with fish as well as amphibians.

The book assembles a jigsaw of stories about evolution (anatomical and genetic): how the bones in shark's jaw became the incus of the human inner ear, how the gene responsible for the multiple eyes in Box jelly fish (some of these eyes have corneas and lens-like structures similar to ours) subsequently split into two, Pax 6 and Pax 2, which in humans are responsible for the ontology of ears and eyes, respectively. The examples are supported by excellent diagrams, all available in the online teacher resource at .

Another feature of the book is the Science as a Human Endeavour stories, which can always be shared with students in the 'five minutes before the bell', so they leave class buzzing with questions and arguments.

Fifty years before Haeckel (of 'ontology recapitulates phylogeny'), and decades before Darwin, Karl Ernst von Baer uncovered the three-layered tissue organisation common to all developing vertebrate embryos. Why was the significance of this discovery not understood at the time?

In 1935 the German embryologist Hans Spermann won the Nobel Prize for 'his discovery of the organiser and its effect on human development', but the technically finicky experimental research was actually done by his gifted student, Hilde Mangold, who was killed by an exploding stove before she could write her thesis! What does this example tell students about gender relationships of the time?

DNA strands are held together by H-bonds, which is why gentle heating, or immersion in a weak acid, will separate them. The A-T nucleotides are held together with two H-bonds, and the G-C nucleotides with three H-bonds.

For an extension activity, students could consider these questions.

• Would you expect the proportion of C-G pairs and A-T pairs to be the same in every species? (No - it can vary by many per cent)

• If you were heating the strands to separate them, which pairs would take longer to separate? (The G-C pairs, because more energy is needed to 'break' three bonds compared to two.)

• In a hybridisation experiment, how would the results be affected if the strands are not heated for long enough? (They may not separate entirely in G-C rich sections, therefore hybridised strands could be A-T rich, or perhaps not much would hybridise, suggesting the two species are not as closely related as they in fact are.)

• In a hybridisation experiment, how could you be sure that all DNA was separated before you mixed it? (You would need to conduct a controlled study of the effect of heating time on hybridisation.)

• Could you do a DNA-DNA hybridisation test with mixtures of more than three species? (The results could be more difficult to distinguish, because of the numbers of combinations between sections from different organisms, as some hybridised combinations could involve all three species.)

Closely related - chimpanzee. The amino acids in the section of protein shown are all identical.

Least related - yeast. 11/22 (50%) of the amino acids in the section of protein shown, are different.

Positions 1,6 and18-20 all have the same amino acid at each of these locations, for this section of the protein. Folding may bring them together to create an active site.

Yes - chimpanzees look most like humans; the pig is at least a mammal, and the chicken is a terrestrial vertebrate.

Homology: developmental and structural patterns. Examples: embryonic similarity, anatomical similarity (pentadactyl limb), and molecular similarity (DNA, proteins, RNA) between species.

Closely-related species have more in common and fewer differences. The general picture of relationships by different methods provides a similar story.

Proteins are translated from DNA templates, therefore similar proteins suggest similarity of genetic information.

If DNA 'hybridises', this means a strand from one species complements a strand from another. The base pairing of large sections of DNA from the different species must therefore be identical, and this is only likely if they share an ancestor.

Humans have pharyngeal gill slits during the embryonic stage (and they share the genes for their gill-slit development with fish in which they go on to develop into actual gills). In humans, different developmental processes have evolved to develop the gill slits into the incus bone in the middle ear. Because the ancestors of humans breathed oxygen from air there would have been selective pressure not to develop fragile structures like gills, which when exposed to a dry terrestrial environment, would cause water loss and perhaps introduce pathogens.

Academic honesty and integrity are essential to scientific endeavour because (i) dishonesty defeats the purpose of testing hypotheses and providing answers to curiosity; (ii) scientists are part of a community, so false results would mislead others, waste their research funds, and possibly also endanger lives; (iii) it will only be a matter to time before inaccuracies and exaggerations will be identified by further research (as has happened in Haeckel's case), tarnishing reputations forever.

Responses will vary but reactions are likely to span the 'Hello! Meet my (very distant) cousin' to 'Yuck, that 1.8% DNA difference that separates me from this hairy animal is really important!'

The same way that the finches across an island archipelago inspired Darwin's thoughts on evolution in 1835-1836, birdwing butterfly species across an island archipelago which are now part of Indonesia inspired the younger Wallace in 1857. The once very rare butterflies are now bred commercially on butterfly farms in Indonesia and Malaysia. Preserved in resin, they are for sale to tourists and collectors.

There are a great many books and articles discussing the Wallace-Darwin controversy.

One of the most readable is:

• Arnold C Brackman. (1980). A Delicate Arrangement - the Strange Case of Charles Darwin and Alfred Russel Wallace, Times. This book quotes many contemporary passages for its narrative and speculates how complex was the relationship between Darwin and Wallace, based on mutual friendship and also Darwin's guilt (for Darwin was essentially a decent gentleman scientist). After Darwin's death, letters to Bates make apparent that Wallace became aware that his theory had been gazumped, yet the bond of respect, friendship and a government pension for life ensured these complaints remained private.

More scholarly books on the topic include:

- Gondwana features a slider that moves the positions of continents against geological time.

During the Cretaceous Period 100 million years ago, land masses that are now South America, Antarctica and Australia were just in contact. Africa and Asia had already 'drifted' away.

This Venn diagram suggests that Australia and America were physically linked at the time Orites and Lomata diversified.

All the other genera are probably all younger/more recent.

Wallace's original paper noting the distribution of 'an animal so large, so peculiar and of such a high type and form as the orang-utan' can be read at

Wallace's writing, often written in tents or while recovering from malaria, is all the more impressive for being succinct, yet clearly communicating complex ideas.

Biogeography is the study of the geographical distribution of living things.

When organisms are separated in time and space, you would expect recent events (for example, volcanic islands in the Galapagos Archipelago, or rivers cutting through landscapes) to separate more closely related species than distant events (for example, continents drifting). This is the case: Darwin commented on similarity of the finches, and Wallace identified two differently coloured monkeys on opposite banks of a tributary of the Amazon.

The continents that separated last - South Africa, Antarctica (where they are preserved as fossils) and Australia - have more species in common that with those that separated early - Asia and Africa. Common species include examples of marsupials and Protecaea.

The edges of two continental plates (the Indo-Australian and Eurasian plates) are near to the Wallace line. A particularly clear image can be seen at , but the boundaries do not exactly match its position. An explanation could be that in the distant past, species dispersal populated islands that were once geographically close to each other (New Guinea and Sulawesi, for example), but now continental drift is bringing these once distant groups of islands closer together.

Suggested Habits could include striving for accuracy and persistence.

This suggests animals evolve more quickly. One reason for this may be dispersal - if animals can disperse more widely, this helps them reach a more diverse range of environments.

Lamarck's idea can be related to WOW! The case of the Midwife toad on page 64. Some species do apparently seem to acquire characteristics during their lifetimes that they pass on, provided the genes responsible for the adaptation were already present. During the 1920's, Darwinian evolution was so popular with scientists that Kammerer found no one was prepared to believe his results. Today, a new branch of genetics is beginning to explain how this could happen: epigenetics.

Further information about epigenetics can be viewed on:

This is a fun activity that takes the new technology of social networking (tweeting) back into history. Students need to summarise Darwin's theory into 140 characters so they can tweet the information to their colleagues back in England. Some students might realise that they can use more than one tweet to get their message across.

Discuss this figure with the following questions.

• What do the circles represent? (Answer: Species)

• What do the crosses represent? (Answer: Extinction)

• Can a new species ever arise from a 'line' that has gone extinct? (Answer: No)

• How do new species arise? (Answer: By the process of speciation - gradual change to fit new environmental niches.)

• Does existing biodiversity prevents speciation? (Two possible types of answers: Yes, because existing niches will already have been filled with very well adapted species and No, because evolution is a function of time, and lucky mutations may discover new niches.)

Speculate on the types of organisms that might not be able to cross this type of barrier (non-flying invertebrates like earthworms, some types of amphibians).

What else would be needed for organisms to evolve into new species with this type of barrier? (They would have to be rare, and their movement should not be able to be assisted with vectors like birds.)

These islands are a focus in contemporary research evolution, including by the Grants (also discussed on page 60-61). Jigsaw one of the following papers, as appropriate to the level of your class:

This is a fun low-level activity. It requires students to go to - Switcheroo Zoo and create their own species by using parts of other species. It reinforces the idea of adaptation to an environment.

Darwin was a brilliant observer and synthesiser of ideas, more than a critical thinker. He did not reject any ideas that supported his theory, nor did he always fully understand them (for example, he backtracked on some of the ideas around the mechanism of natural selection in later editions of On the Origin of Species), and he certainly did not understand the mechanism of genetics (although an unread copy of Mendel's paper was actually found in a book in his study after his death). He built is ideas through copious note taking.

Selection can only act on the phenotypes exposed by genetic combinations.

'Survival of the fittest' is an apt description of natural selection if the term 'fitness' is seen as a 'best fit' for any particular environment, rather than a 'best physical fitness'.

The usual test is whether two species from different islands can interbreed. However, barriers to natural breeding do not have to be genetic: they can include behaviours like mating displays and songs, which are more easily changed or can to be learnt from parents. Therefore, a true test may need to involve the use of artificial fertilisation.

Isolation separates gene pools. Small populations (for example, less than 100 individuals) lose rare alleles quite quickly, often for reasons which have nothing to do with natural selection (examples are death by accidents, or the alleles simply not being passed on to the next generation). This mechanism will quite quickly make isolated populations different from each other. Secondly, the isolated environments are likely to be subtly different. As new alleles (caused by mutations) emerge, their impact will be much greater than in a large population, and they will be selected for if they are advantageous. (Advice: Activity sheet - Modelling selection pressure on page 62, will help students understand these subtleties.)

An example response could be: what causes species to change?

Darwin was persistent, a keen observer, and also scientifically ambitious, realising early in his career what the impact of his theory would be. He was independently wealthy and understood his relationship to his class, which included influential clergymen (Darwin himself had studied theology before geology). He was also considerate about those he loved (including his religiously devout wife), and this may explain his endless procrastination because he felt he needed yet more, and more detailed evidence to support his theory.

Take some time to reproduce the beetle cards on coloured card and prepare laminated sets will provide a long-lasting resource for your school. Students enjoy the random element of the activity, and the discussion questions integrate Units 1 and 2, but this is to some extent a 'recipe activity'. Inquiry skills are not developed to the highest levels; therefore, this activity sheet is not challenging enough as a culminating task for gifted and talented students.

Black: homozygous BB; Cream: homozygous bb; Brown: heterozygous Bb.

Responses will vary. Most students will lose the black phenotype first, then brown.

The results will vary, but the general pattern will be similar.

Changes will usually be faster in the smaller populations (simulating the effect of isolation on the speed of evolution). Islands are famous for their endemic species.

The chance of survival of any individual phenotypes remains the same (the model suggests black beetles are consistently three times more attractive to predators than cream beetles, for example.)

The chance of survival of the species does not change from year to year, because the populations remain constant.

Predator pressure on black beetles could change if (i) the background foliage or sand changed or (ii) the predator changed, for example a new species was introduced to the island).

The simulation would change if the probability of selection by the predator was the same for each phenotype by keeping the numbers of each colour more or less the same.

Phenotype ratios could still change if a particular allele was not passed on in a generation. This could be tested by running the simulation with different population sizes.

For the population was to become a homogenous black or cream, either cream or black beetles, as well as brown, would need to be strongly predated? For a population to become homogenous brown, exactly half the individuals in the previous generation should be either cream or black, and mate with the other phenotype. (Theoretically possible, but not likely.) The following generation would have a Mendelian ratio of phenotypes again.

Assumptions include: there is only one factor involved in selection pressure and it is constant (in reality, there will be many, often acting in opposing ways. Examples include intraspecific competition and environmental effects) and that populations remain constant. Improvement responses will vary but could include introducing subtleties such as the effect of a second predator or twinning effects for certain phenotypic mating combinations - what if black Ã- black crosses result in three times as many offspring, for example? These types of effects keep deleterious alleles in populations.

The interactive model is self-explanatory. Worksheets that can be used with this popular simulation of a famous experiment include:

• sex and the single guppy lab report (rubric included):

• how females choose their mates - literacy development:

Class discussion questions (including answers) and a link to a video clip of sexual selection in peacocks can be found on .

That he was modest, careful, observant and adventurous.

Beak size, the types of bushes they live in, and how they feed

Perhaps you could carry the information as a link to a database in a satellite-connected phone.

An excellent memory and attention to detail continues to be important to scientists; modern scientists have access to additional technologies and a larger community.

Wallace's paper from Ternate is a first draft, but succinct and clear. The original has never been found. Darwin's letter is only an excerpt but evidence that he had been thinking about the origin of species before Wallace. (Darwin's book was finished over 14 months following receipt of Wallace's paper, but worked on over 20 years prior to that and is brimming with detail. It continued to be revised many times after its first publication). In the 21st century, precedence is determined from the date of a peer-reviewed paper in a reputable journal.

The first selection pressure (leading to larger beaks) was a drought; later the second selection pressure (leading to smaller beaks) was intraspecific competition - small beaks require fewer resources to grow than large beaks, therefore birds with smaller beaks were able to raise more offspring.

Islands are different environments from large land masses. They tend to be windy, but animals blown offshore are likely to die, therefore one outcome is that birds become flightless. Islands are less likely to have large permanent water bodies, and this puts pressure on species to develop characteristics for drought resistance. Secondly, the starting populations on islands tend to be small; therefore the numbers of alleles will be small. Any advantageous genetic mutation will have a proportionally larger effect on the gene pool, therefore will spread quickly through the population, leading to 'faster' change.

Batesian mimicry could evolve if a species had a mutation that gave it a phenotype which resembled a toxic organism in its environment. Selection would then favour these phenotypes.

An example: Why are do animals of particular sex (usually male) have features that seem to disadvantage their survival?

Amphibians cannot cross a salty sea - as would be necessary on long voyages.

The size suggests a reservoir - these animals have been selected to survive for months without food. Perhaps the islands selected animals that were bigger than average, to survive voyages on mats of vegetation, and these are the descendants. Consider Komodo dragons (on Rinci and Komodo, Indonesia) and Galapagos tortoises as examples.

The islands protected them against their usual predators (removing a selection pressure) and strong winds may have caused a different kind of selection pressure. Consider the dodo of Madagascar and other pigeons, and New Zealand's kakapo as an example.

Unlike reptiles, homoeothermic animals (animals that maintain their body temperature) need to eat constantly. Islands have smaller reservoirs of food, therefore small size is easier to maintain. Consider quokkas off Western Australian's Rottenest Island as an example.

Predators will be reminded frequently that the wasps are poisonous or bad tasting, therefore the flies are safe.

The reverse situation: predators will take longer to learn, and may keep taking their chances with likely meals. Neither flies, nor wasps are as safe. This would weaken the selection pressure on both organisms.

Some suggestions are could include the following.

• Snip off the ocelli (the coloured spots on the tail) of different birds and watch the peahen's reaction, particularly compared to control peacock.

• Spots can be added (and this can be done to test the method).

• Different coloured spots can be added (with the same number of spots). The tail can be shortened (with the same number of spots).

• An ethical consideration is that the birds should not suffer distress - rival birds should be removed if, as a result of treatments, a formerly dominant individual gets bullied.

This is an example of the compromise by conflicting selection pressures (like the male guppy and predator interactive).

• Without human hunters, elephants prefer to have big tusks.

• With human hunters, those with shorter tusks preferentially survive because hunters don't select them.

• These elephants may have invested their resources in larger muscles (not recorded in results) and were better adapted for avoiding hunters.

Example Habits could include: managing impulsivity, striving for accuracy, persistence, gathering data through all senses or questioning and posing problems.

The modern explanation is that Hox genes (see page 66) are involved. This is an opportunity for a class discussion on the value of 'open mindedness' to scientific endeavour.

• In what ways do prevailing beliefs limit insight? (By 1926, a new kind of orthodoxy had developed in scientific circles - Darwinism.)

• Was Kammerer a victim of academic prejudice? (Although many scientists enjoy involvement in music as a hobby, Kammerer was unusual in being a musician and composer whose hobby was science!)

• Was Kammerer a victim of racism? (Kammerer was a Jewish. When he died the pistol was found in his non-dominant hand, suggesting his death was murder, not suicide. AC History National Socialism began emerging in Austria from 1918-1920. 'Social Darwinism' was used to by Nazis to justify their extermination of Jews, gypsies, albinos, disabled people and others. )

The domestic organism that is most like its wild ancestors is the mushroom. How can this observation be related to the way it reproduces? (Answer: fungi often have long phases during which they only reproduce asexually, or exist as dormant spores.)

A brief explanation (4:49 minutes running time) with excellent graphics about Hox genes can be viewed on

Evolution genetic toolkit at .

How can Hox genes explain this story?

A long-term Russian breeding experiment on fur trade foxes has revealed how the wolf may have become a dog. Every generation, only the 'least timid' 1-10% of Dmitry Belyaev's silver foxes were allowed to breed. Selecting this one feature has changed wild foxes in many different ways. Within 10 generations they were tame. After 20 generations they had upturned tails, floppy, puppy-like ears, and barked. Now, after 35 generations, they whine for attention and lick their masters' faces.

Several of these dog-like traits have a single cause: immaturity. Domestication of animals often required the species to retain immature features throughout their life.

• The silver fox experiment, from Horizon programme - The Secret Life of the Dog:

• Belyaev Experiment: Docile Foxes: .

Below are some ideas for discussion and extension.

• Bacteria (and other prokaryotes) have an unusual genome: a single loop of DNA. This means that they are genetically haploid. Whatever alleles they have will be seen in their phenotype. Disadvantageous alleles cannot be hidden as recessive alleles in a heterozygous organism, and advantageous alleles multiply quickly when the organisms reproduce with binary fission.

• Question: What effect does a haploid genome have on an organism's rate of evolution? (Answer: It should be much faster. And as a corollary, this applies even more when the nucleic acid is single stranded - RNA viruses like colds mutate at 10&&000 the rate compared to double stranded DNA viruses.)

• Bacteria have another source of mutation: plasmids are small rings of DNA which can be physically passed on to other, quite unrelated microbes. This mode of transmission is known as 'horizontal gene transfer'. Many of the known plasmids carry genes for antibiotic resistance. Question: Why do you think that is? (Answer: An environment filled with antibiotics provides the selection pressure to share genes for antibiotic resistance.)

• The first person treated with an antibiotic was Albert Alexander, a policeman who had developed a bad infection from a rose thorn scratch in 1941. Over five days of treatment, he became much better, but then the penicillin ran out. His health deteriorated, and he died a few weeks later. Question: How can we explain this sad event in terms of natural selection? (Answer: The treatment selected an antibiotic-resistant strain.)

• Frightening examples of diseases that were once easily treated with antibiotics, but are now developing widespread resistance, include tuberculosis and the venereal disease gonorrhoea. However, the slight increase in DNA caused by carrying extra plasmids slow down the rate it can reproduce asexually. Question: What type of environment would select for bacteria that do not carry antibiotic resistant plasmids? (Answer: An environment where antibiotics are rare.)

Deliberate selection of desirable characteristics in individuals of domestic species (usually animals and plants) which will be bred by humans.

Artificial selection is sustained and directed, unlike natural selection, which can reverse selective pressures if the climate cycles. Artificial selection does not necessarily improve survival, except in a domestic setting.

Examples include sheep, goats, horses, cattle, alpacas. Characteristics for these: for mild behaviour and tractability (notice that these are all herd animals, the selection took advantage of the natural social behaviour of these animals) and a source of food, natural fibres and also, often, transport; guinea pigs (size, used as a food source in South America), poultry (size, egg laying capacity); grains (selected for seed size, yield and harvesting methods); fruit (size, sweetness, yield).

Examples include blind eyes in cave fish; nipples in male humans; wings in emus. These organs will not be bred out unless they have a selective disadvantage.

Supergenes control the overall pattern of development, and this can result in vastly different phenotypes without affecting actual genes.

Because technology (and the built environment generally) is a human artifact, any changes are the result of artificial selection (for example, for efficiency or appearance).

Bacteria are living organisms and populations will develop variability through mutation. If the mutations are advantageous in an environment where antibiotics are present, the surviving bacteria will be the ones that reproduce - and quickly, with binary fission.

Organisms are considered to belong to the same species if they can interbreed naturally to produce viable offspring.

The fossil record is incomplete because (i) original sedimentary rocks may have been destroyed over vast amounts of time, and (ii) the chances of any individual, even any species, being preserved after death is extremely rare and requires special conditions that avoid decay, scavengers or physical destruction.

The rarest fossil organisms are small and lacking hard structures (such as jellyfish) because these are fragile or are destroyed entirely during the fossilisation process. Another group of rare fossil organisms are large, whole animals, because it takes time to bury them or cool them to a point where decomposition ceases.

Absolute dating - by considering the age of decay of the most appropriate radioactive isotope either in the remains themselves (for example, Carbon-14 for fossils less than 50 000 years old, has a half life of 5700 years); or in nearby igneous rocks (Uranium-235 for fossils up 4.6 million years old, has a half-life of 704 million years). Relative dating - by identifying marker fossils of known age in the stratum.

Prey - camouflage - colour and behaviour would help them avoid predation. Predators - camouflage - colour and behaviour would help them avoid early detection.

Students would need to name the order in which the layers were poured - the top layer is placed there last, therefore the most recent.

Natural causes include continental drift, a sudden event like an earthquake or volcanic eruption, a drought drying a river into isolated ponds, or individuals being dispersed to offshore islands. Artificial causes include a major highway being built (in Australia, this has been linked to changes in populations of small lizards called skinks), urbanisation isolating patches of reserves, and keeping animals in artificial conditions including zoos.

The genes are still there - but Hox genes either don't force the development for very long (so they are small), or actually suppress development.

These wings are still useful - for 'flying' underwater. The body plan of penguins is still tetrapod, like all vertebrates.

Simple answer: no. However, variation does not only have to be genetic. It is possible to adapt to changing conditions by changing behaviour - think of how humans vary their housing in the Arctic circle in winter (igloos) and in deserts (by living underground in Cooper Pedy). This has effectively happened with very ancient organisms (such as extremophiles - that once lived all over the Earth, but now only in thermal springs and salt lakes, and stromatolites (Figure 2.6 on page 46) which can only live in highly saline, shallow seas.

This is an example of evolution in human life spans: the antibiotic resistant microbes have been selected for. The situation is also exacerbated by the ability of unrelated bacteria to swap genes using plasmids.

You would need to evaluate and define intelligence; for example, sense of humour, creativity, dancing ability, being able to be a good provider (high income) which might imply certain organisation skills. Then you would need to design an intelligence test to investigate a population. For example, it has been found the IQ scores of most married couples are within 15 IQ points of each other - IQ tests one kind of intelligence. Is any group likely to have larger families?

No, its rapid emergence in humans is considered an example of 'positive feedback'. Prehistoric intelligence (ability to hunt, teamwork, avoid death) is likely to have been positively correlated with survival. In addition, intelligence may have been positively selected for by females as part of the cultural environment. All the selective pressures were working together then created a 'runaway effect'.

Biodiversity is a function of natural selection. Extreme environments such as deserts, coral reefs or rainforests (which are low in essential components like water or nutrients) tend to have high biodiversity because they put selective pressure on species to specialise and take advantage of subtle differences. Biodiversity is also a function of time; places on Earth which recently experienced extinctions (for example, were affected by Ice Ages) tend to have less biodiversity.

Examples of inferences could include the following.

The animal had large eye sockets - this suggests good vision.

It has large openings for its nostrils - perhaps this indicates a good sense of smell, an ability to detect infrared radiation (like boa constrictors), represents an adaptation to a desert like environment (similar to camels) or was used to amplify sounds it made to communicate.

Its teeth are small and sharp - not adapted for grinding - which suggests a carnivore. Because of the large eye sockets, it was probably a predator, not a scavenger.

The jaw is unhinged (like a snake) so it could swallow large prey.

Examples of recently extinct Australian mammals are (i) Thylacine (could have resisted extinction if it reproduced more quickly and learnt to avoid humans), and (ii) Lesser Bilby, Macrotis leucura, thought to have become extinct in the 1950s (might have survived if it could defend itself from foxes and feral cats, and reproduced quickly enough not to be affected by habitat fragmentation due to fires).

Student responses will vary, though the essay needs to explain the lack of sunlight - with possibilities of photosensitive smog, fog or dust. The essay needs to explain the lack of other species - soil microbes, protozoans, fungi and animals - because plants are at the base of the food chain and all species (including plants) respire. Perhaps plants survived a catastrophe in the form of buried seeds.

Student responses will vary but bioinformatic evidence - is among the most compelling because it is the 'most complete', in the sense that it shows all living organisms are related.

Student responses will vary but some considerations include (i) we are looking at an anachronism - there was no established system of peer-reviewed papers at the time; (ii) social class was important - Darwin may have delayed publication of his radical ideas because he feared being ostracised by his peers and his wife (and her family) but working-class Wallace had little to lose; (iii) exaggeration may have been considered justifiable to emphasise the point (Haeckel drew the embryos in similar postures, some of which were not unnatural for the species, and omitted the yolks from his drawings).

Possible ethical positions: some people argue that biodiversity acts as a buffer - provides extra links to the food web, and loss of biodiversity therefore damages the web that supports all organisms, including humans. The rate some groups (large mammals, birds, frogs) are going extinct is caused by human activity - this does put the onus on the one species that is conscious of its impact.

Considering the rate of growth of scientific knowledge, how might your opinion in look 100 or 200 years from now?