HSC - Stage 6 2 Unit Biology
9.3 – Blueprint of Life:
1. Evidence of evolution suggests that the mechanisms of inheritance, accompanied by selection, allows change over many generations:
- Outline the impact on the evolution of plants and animals of:
- Changes in the physical conditions in the environment:
- Changes in the chemical condition in the environment:
- Competition for resources:
- Evolutionary theory states that all organisms have developed from previous organisms and that all living things have a common ancestor in some initial form of primitive life.
- It also states that all organisms are fundamentally similar because their basic chemistry was inherited from this very first organism.
- Changes in the Physical Environment:
- The Earth has continually changed since life first evolved.
- Various changes in sea levels, the splitting of the continents and great changes in climate are just some of the environmental changes that life on Earth have had to cope with, or become extinct.
- Changes in the environment force species to either die out, or survive and diversify.
- An Example - The Peppered Moth:
- Prior to the Industrial Revolution of the late 18th Century, the majority of the Peppered moths were light coloured. They survived better as they could camouflage against the white lichen on the trees.
- Post-revolution, the pollution caused the trees to blacken with soot. The trees could no longer hide white moths. The darker variant of the moth was better able to hide, and so the population of the Peppered moth shifted from mainly white to mainly dark.
- This is how a change in the environment can affect the evolution of an organism.
- Changes in the Chemical Environment:
- In the early years of life, the environment on earth was chemically unable to support life as we know it today
- An anaerobic atmosphere prevented the growth of any aerobic organisms
- However, as organisms evolved special pigments that allowed them to exploit the carbon dioxide in the atmosphere, many organisms appeared.
- Chemical changes in the environment impact on the evolution of organisms
- An Example - Mosquitoes and DDT:
- When DDT (dichloro-diphenyl-trichloroethane) was first used as an insecticide to kill malarial mosquitoes, low concentrations were effective.
- In subsequent doses, higher concentrations were needed and the sprayings became less effective.
- The few DDT-resistant mosquitoes that had survived passed on their genes to their offspring, and now the mosquito population is mainly resistant.
- Competition for Resources:
- Competition for resources affects evolution because the survival of a species relies heavily on its ability to obtain the resources needed for life.
- For example, when the dinosaurs were the dominant life form on Earth, mammals were very scarce
- The dinosaurs had access to most of the resources and so mammals were unable to proliferate into different niches.
- When the mass extinction of the dinosaurs occurred, the mammals that so scarcely populated the planet quickly diversified to take advantage of all the available resources, such as plants, or other organisms.
- Competition for resources, and changes in the physical and chemical environment influence the evolution of plants and animals
- Throughout the history of evolution, there have been several periods of mass extinctions.
- These are followed by periods of rapid diversification of surviving populations.
- Describe, using specific examples, how the theory of evolution is supported by the following areas of study:
- Palaeontology; including fossils that have been considered to be transitional forms:
- Biogeography:
- Comparative embryology:
- Comparative anatomy:
- Biochemistry:
- RECALL:
- Fossils are any preserved remains or traces of past life found in sedimentary rocks of different ages
- Palaeontology is the study of fossils.
- Fossils found in rocks lower down are older than fossils found closer to the surface (unless folding has occurred)
- Because fossils can be aged, the sequence from the very earliest life to the present can be observed
- Fossils show a clear change from simple to very complex organisms.
- This suggests a change over time, which is evidence for evolution
- Transitional Forms:
- Transitional forms are examples of organisms that indicate development from one group of organisms to another
- They help biologists to understand how evolution may have come about
- Eg 1: Crossopterygian (lobe-fin) Fish:
- Fish that could absorb oxygen from air appeared 40 mya
- It is thought that amphibians developed along this line of descent
- A special feature is that it had bones in its fins, which suggests it could drag itself on the land.
- FISH Features: scales, fins, gills
- AMPHIBIAN Features: lobe-fins, lungs
- Eg 2: Archaeopteryx:
- This was a small flying dinosaur with feathers
- It appeared in the late Jurassic
- It shared features with both birds and reptiles, suggesting that birds evolved from these reptiles
- REPTILE Features: long-tail, claws, no keel, solid bones, teeth
- BIRD Features: wish-bone, feathers
- Biogeography:
- Biogeography is the study of the distribution of living things
- Basic principle is that each plant and animal species originated only once
- This is called the centre of origin (or the common ancestor)
- Regions that have separated from the rest of the world, e.g., Australia and NZ, often have organisms that are distinctive and found no where else (endemic)
- General principles of dispersal and distribution of land animals:
- Closely related organisms in different geographical areas probably had no barrier to dispersal in the past
- The most effective barrier to distribution is the oceans and seas
- By looking at the pattern of distribution today plus its fossil distribution in the past, we are able to reconstruct its evolutionary history
- For Example - Waratahs:
- 3 genera of waratahs; distribution spans southern pacific ocean
- The present-day distributions of these closely related species in the eastern parts of Aus, and New Guinea and the Western part of South America suggest that the 2 regions may have been connected in the past
- Comparative Embryology:
- The embryos of different vertebrates are very similar
- The embryos of many different vertebrates all have gill pouches at some stage of development.
- This suggests that these vertebrates evolved from a common aquatic ancestor, such as the crossopterygian fish.
- Comparative Anatomy:
- Comparative anatomy is the study of the differences and similarities in structure between different organisms.
- The structures they have in common are evidence of similar inherited characteristics from a common ancestor.
- For Example - Pentadactyl Limb:
- The pentadactyl limb is a 5-digit limb
- It is a structure of bones that is found in many vertebrates
- It is believed that this limb was inherited from an aquatic ancestor
- Xylem is found in almost all plants. This suggests a common ancestor
- Biochemistry:
- All organisms share the same basic biochemistry. They all:
- Consist primarily of organic compounds
- Share a common genetic code of DNA or RNA
- Rely on enzymes to control chemical reactions
- Share the same cell membrane structure
- Rely on cellular respiration to make energy for cell processes (except chemosynthetic bacteria)
- Similarities in the base-pairing of DNA strands have been analysed to show evolutionary links between organisms
- The amino-acid sequence of certain proteins found in many organisms (such as haemoglobin and cytochrome-c) has been analysed across a range of organisms, and similarities provides evidence for evolution in general
- Explain how Darwin/Wallace’s theory of evolution by natural selection and isolation accounts for divergent and convergent evolution:
- Natural Selection:
- There are variations within every population of species
- Organisms that don’t reproduce have their genes removed from the population
- Organisms that survive and reproduce are well suited to their environments
- Favourable variations are passed onto offspring and become common
- The Role of Isolation:
- For a new species to evolve, groups of organisms need to become isolated from each other
- Usually the organisms become separated by a physical barrier
- Within each separate population, different mutations occur, and therefore, different variations are produced
- Natural selection acts differently on each isolated population, as there are different environmental conditions and selection pressures
- Over time the populations differ so much that they no longer interbreed, and as such, a new species was produced
- Isolation can be created by a difference in food preference, to the splitting of the continents.
- Divergent Evolution:
- Also known as adaptive radiation
- It is the process whereby one species radiates out into different environments and as a result produces organisms that look different from each other, and may have many other differences.
- One of the best known examples are Darwin’s finches
- 14 different species where described; all with similar greyish-brown to black feathers and all had similar calls, nests eggs and courtship displays
- However, their habitats, diets, body size and beak sizes differed throughout
- Darwin believed that they had all evolved from a common ancestor
- Convergent Evolution:
- Natural selection over many generations can result in similar adaptations in species that live in similar environments, even though they may be unrelated
- This is called evolutionary convergence
- For example, the seal and the dolphin both live in the ocean
- They have flippers as limbs, they are strong swimmers, can hold their breath longer than most mammals, and they have a layer of fat under their skin.
- But they belong to different orders of mammals and are unrelated.
