Category Archives: evolution

Patterns of Evolution


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Speciation: Due to natural variation between individuals, selection pressure, “survival of the fittest” and favourable traits being passed on to offspring over many generations, new species are formed. Biologists refer to allopatric (geographical), sympatric (same location and habitat), and parapatric (habitat differences) speciation.

Divergent Evolution: Over time, due to selection pressures, sub-species or species become less and less alike, as they become better adapted to their niche. Adaptive radiation (below) is a specific type of divergent evolution. The human foot and the foot of a chimpanzee is an example – they are quite different (divergent), although they evolved from a common ancestor, due to the differing habitats of the upright walking man, compared to the knuckle-walking chimpanzee.

Adaptive Radiation: The process by which organisms change over generations to fill different niches, especially when changes in the environment make new resources available. Charles Darwin famously documented the different beak shapes of finches on the Galapagos Islands, which he postulated had arisen form a common ancestor. Above, you can see the variations of honeycreepers from the Hawaiian islands.

Convergent Evolution: In this form of change over time, different species begin to look more alike, despite having no recent common ancestor. Analogous structures develop, that have the same form and function, but were not present in the most recent common ancestor. Examples include flying insects, birds and bats, who have all developed wings as a solution to escaping from predators or finding more food and mates. Hedgehogs and echidnas are a good example of convergent evolution.

Parallel Evolution: Parallel evolution is similar to convergent evolution, in that different organisms display similar characterisitics, but tend to be more closely related. So, gliding frogs for example, evolved in parallel from multiple types of tree frog. Some examples that are closer to home include the Tasmanian tiger and the European wolf; the flying squirrel and gliding possums and marsupial and placental moles/mice.

More about patterns of evolution:

Population genetics


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Population genetics is the study of distributions and changes in allele frequency in a population, as the population is subject to the four main evolutionary processes:

  • Natural selection
  • Genetic Drift
  • Mutation
  • Gene flow (by migration or distribution of pollen and seeds)

Variation between individuals and species and polymorphism: In any normal population there is some variation between individuals – a box of apples may have individual apples that are slightly different sizes and shapes with slightly different colour variations, even when they come from the same tree. So, not all variation is caused by genetic differences. It may be environmental differences that result in the variation – for example, the amount of light, temperature or soil nutrients in the case of plants or the nutrition and experiences provided to animals. Some characteristics , such as height or wing length might show continuous variation, while other characteristics can be clearly separated into different categories (discontinuous variation). An example of discontinuous variation in humans might be the ability to roll one’s tongue – you can either do this or you can’t – there is no blending, or in-between characteristic. Polymorphism occurs when two or more clearly defined phenotypes are present in the population. A classic example is the light and dark coloured morphs of the peppered moth. The ABO blood grouping is an example in human populations.

Inherited variationsFrom our Unit 3, Area of Study 2 work, we understand that the DNA molecule, present in every cell of living organisms, codes for proteins that determine the phenotype of an organism. DNA is passed from one generation to the next through reproduction, which can occur asexually or sexually (with the production of gametes (meiosis) and fusion of sperm and egg). So, families of individuals tend to look more alike than non-related individuals due to these inherited characteristics. This was seen in our work with pedigree trees, showing how genetic diseases can be passed on through several generations.

Mutations – sources of variation: The source of these variations is genetic mutations – check pages 371-372 and 477-478 in your textbook “Nature of Biology”. Genetic mutations may be spontaneous or may be induced by exposure to mutagenic agents (X-rays and Gamma rays and some chemicals, such as benzene and mustard gas).

Gene pool, gene flow, genetic drift (by chance): The gene pool is the set of all genetic information in a population, while gene flow describes how genes leave and arrive in a population by death and emigration or births and immigration. Genetic drift is the change of gene frequencies due to random sampling.

Polygenes, polygenetic traits: Polygenes are non-allelic genes that together influence a phenotypic trait – often the precise loci of these genes is unknown to biologists. Examples of polygenetic traits in humans are height, weight and skin colour.

Mitochodrial DNA: Mitochondrial DNA is a single, circular strand of DNA found in the mitochondria of eukaryotic cells. In most species, mitochondrial DNA is inherited solely form the mother. In humans, mitochondrial DNA was the first significant part of the human genome to be sequenced.

Founder and bottleneck effects:The founder effect is the lost of genetic variation that occurs when a new population is established by a small group of individuals from a larger population. The people of Easter Island and Pitcairn Island show limited genetic variability (small gene pools) due to this effect. A similar effect is the bottleneck effect, when large numbers of a population are removed, leaving a small gene pool.  As a species, cheetahs have famously low levels of genetic variation. In fact, cheetahs are so closely related to each other that transplanted skin grafts do not evoke an immune response. This can probably be attributed to a population bottleneck they experienced around 10,000 years ago, barely avoiding extinction at the end of the last ice age. However, the situation has worsened in modern times. Habitat encroachment and poaching have further reduce cheetah numbers, consequently snuffing out even more genetic variation and leaving cheetahs even more vulnerable to extinction.



DNA evidence for evolution

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Last week we had another opportunity to connect with the Gene Technology Access Centre to learn about how biologists use genetic information to discover more about evolutionary relationships. Tony discussed some of the features of the ‘old world’ monkeys and the hominids – including opposable thumbs and the presence or absence of a tail. We then used a computer program, the Biology Work Bench, to compare the similarities and differences of DNA sequences between the different species. The fewer differences in DNA base pairs, the greater the similarities between species and therefor it is assumed that they are more closely related, with a more recent common ancestor.

Evolutionary biologists have been investigating the existence of a ‘molecular clock‘ for the past 40 years – the theory is that some evolutionary changes (mutations) occur at a regular rate, which gives us a powerful tool to estimate how long since different species diverged from a common ancestor. Using molecular clocks to estimate divergence dates depends on other methods of dating. In order to calculate the rate at which a stretch of DNA changes, biologists must use dates estimated from other relative (stratigraphy) and absolute dating techniques (radiometrics). There are many different methods that scientists can use to estimate the age of fossils. Read more at the Smithsonian National Museum of Natural History.

Evidence for Evolution



Image Source – Haeckel’s drawings

What evidence supports the theory of evolution? – some good questions here!

This interactive animation, “Evolution in Action” outlines the evidence for evolution and gives an opportunity for students to particpate in a simulated natural selection experiment.

Origins of Life

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1. Download the student worksheet from Ages 16-19: Highlighting Important Stages in Evolution

2. Watch the “Tree of Life” video, narrated by David Attenborough

3. Click on “Interactive” to view the “Tree of Life” Interactive timeline

4. Answer the questions on the student worksheet.

Other Resources:

What does it mean to be human?


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Have you ever wondered what makes us different from other animals? Why Homo sapiens appear to dominate the earth, altering the landscape and using vast amounts of energy compared to other species? The story might have began around six million years ago, when the primate lineage between humans and chimpanzees branched; in other words, we didn’t evolve from chimpanzees, they are like distant cousins, with a common ancestor six million years ago. A recent non-fiction book by psychologist Thomas Suddendorf, “The Gap – The science of what separates us from other animals” distills two traits that appear to account for most of the ways in which our minds appear quite different from other animals – the ability to cast our mind back and forward, imagining different scenarios and our drive to communicate with others, linking our minds together. I have only just started it, but so far it is fascinating and easy to read.

On Monday we had another terrific Polycom session with Tony and Frazer from the Gene Technology Access Centre. The session focussed on the characteristics of seven fossil skulls – in fact, half-scale models of skulls, including:

  • Homo sapiens (human)
  • Homo habilis
  • Homo erectus
  • Homo neanderthalensis
  • Australopithecus afarensis (also known as ‘Lucy’)
  • Gorilla gorilla
  • Pan troglodytes (chimpanzee)

We looked carefully at the models and tried to order and classify them based on the following characteristics:

  • Presence or absence of pronounced canine teeth
  • Presence or absence of a sagittal crest (presence indicates exceptionally strong jaw muscles)
  • Protruding jaw
  • Brow ridges (subtle or pronounced)
  • Presence of temporal lines
  • Cranium capacity (an indication of brain size – measured in millilitres)
  • Location of the foramen magnum – where the spinal cord passes through the skull to attach to the brain (using a ratio) – this indicates if the specimen is quadrupedal or bipedal.

If we consider the Homo sapien skull to be most advanced, it appears that the brain case has increased in size and become smoother, with a more rounded forehead and the face has become flattened, with a less pronounced jaw.

Habitats, Environment and Survival

Otway forest

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This chapter of work is about habitats and the factors that affect the survival of organisms in their environments. You will learn about biotic (living) factors – predators, competitors, pathogens, parasites – and abiotic (non-living) factors – temperature, wind speed, pH, atmospheric gases, turbidity, salinity, solar radiation etc. You will also learn about niches and resource use graphs. Match some Australian species to their habitats at DECC.

Living organisms survive in their environments due to structual, functional and behavioural adaptations. Evolution is the process by which living organisms have changed over thousands of years to become more suited to their environments. Google ‘evolution’ and you will find an enormous selection of contradictory articles confirming or condemning “The Theory of Evolution”, first proposed by Charles Darwin in 1859.

To summarise Darwin’s Theory of Evolution;
1. Variation: There is variation in every population.
2. Competition: Organisms compete for limited resources.
3. Offspring: Organisms produce more offspring than can survive.
4. Genetics: Organisms pass genetic traits on to their offspring.
5. Natural Selection: Those organisms with the most beneficial traits are more likely to survive and reproduce.

Natural Selection Animations

peppered moth

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Natural selection is the important process that results in changes in populations over time. All the structual, functional and behavioural adaptations we have discussed over the past few months have evolved as a result of natural selection. However, because the effects of natual selection can only be seen over many generations, it is difficult to visualise. There are a number of computer simulations that allow us to visualise natural selection. The Peppered Moth Simulation, from the Biology Corner, uses a well known example of a case study of natural selection. The Biology in Motion lab uses more stylized images for it’s Evolution Lab.