Explaining Evolution
Below is a brief timeline of the different concepts Scientists proposed about our changing world.
Below is a brief timeline of the different concepts Scientists proposed about our changing world.
Natural Selection
Charles Darwin proposed the idea of natural selection in 1859. His theory of evolution is based on the following assumptions -
Charles Darwin proposed the idea of natural selection in 1859. His theory of evolution is based on the following assumptions -
- Variation exists in populations.
- More offspring are produced than can possibly survive to reproduce in a population.
- In the struggle for survival, those organisms better suited to their environment survive in greater numbers than those less suited.
- Surviving organisms breed and pass on the genes that helped them survive to the next generation.
- Over time, the population is dominated by those organisms with the genes best suited to surviving in the current environment.
New species can arise by this process. In order for this to happen, there needs to be - variation within species; isolation and competition; selection and speciation.
Variation with species
If you look closely at the members of the same species, you will notice differences in their appearance. For example, skin, hair and eye colour, height and foot size are obvious differences in the human species. Humans also have different blood types or most have wisdom teeth (some don't). These represent naturally occuring variation among members of the same species.
Much more variation exists within sexually reproducing species than those that reproduce asexually. This is because both asexual processes produce offspring genetically identical to their parents. Whereas, sexually reproducing organisms, have two parents contributing to each new offspring. This produces an individual with DNA that contains a unique set of of DNA and codes for a distinctive set of proteins.
Isolation and Competition
Members of the same species can interbreed naturally to produce viable (healthy and able to reproduce) offspring. As long as a male and a female are brought together and still able to reproduce, they are considered to be the same species.
However, what if two populations of the same species were isolated from each other? This could be physical isolation due to an earthquake, volcanic eruption, the building up of mountain ranges, a drying river or continental drift.
Each environment provides only a limited number of places in which organisms can live. These places, or niches, include physical resources and biological resources. However, every generation adds new members to the population. All these organisms must compete with one another for the limited number of available niches.
Selection and speciation
Natural selection can explain how the volcanic islands of the Galapagos Archipelago came to have such a variety of finch species.
Originally, a few lost South American finches arrived on one of the remote islands of the Galapagos Archipelago. These finches had a variety of naturally occurring genetic variations, such as colour, beak size and leg length. The descendants of these birds gradually populated the other islands, each with different environmental conditions.
Variation with species
If you look closely at the members of the same species, you will notice differences in their appearance. For example, skin, hair and eye colour, height and foot size are obvious differences in the human species. Humans also have different blood types or most have wisdom teeth (some don't). These represent naturally occuring variation among members of the same species.
Much more variation exists within sexually reproducing species than those that reproduce asexually. This is because both asexual processes produce offspring genetically identical to their parents. Whereas, sexually reproducing organisms, have two parents contributing to each new offspring. This produces an individual with DNA that contains a unique set of of DNA and codes for a distinctive set of proteins.
Isolation and Competition
Members of the same species can interbreed naturally to produce viable (healthy and able to reproduce) offspring. As long as a male and a female are brought together and still able to reproduce, they are considered to be the same species.
However, what if two populations of the same species were isolated from each other? This could be physical isolation due to an earthquake, volcanic eruption, the building up of mountain ranges, a drying river or continental drift.
Each environment provides only a limited number of places in which organisms can live. These places, or niches, include physical resources and biological resources. However, every generation adds new members to the population. All these organisms must compete with one another for the limited number of available niches.
Selection and speciation
Natural selection can explain how the volcanic islands of the Galapagos Archipelago came to have such a variety of finch species.
Originally, a few lost South American finches arrived on one of the remote islands of the Galapagos Archipelago. These finches had a variety of naturally occurring genetic variations, such as colour, beak size and leg length. The descendants of these birds gradually populated the other islands, each with different environmental conditions.
Plants growing on the these islands are more likely to produce seeds with thick coats. This is an adaptation often associated with the survival of seeds in these circumstances. In turn, this seed feature provides a selection pressure on the finches, where natural selection will favour birds with larger, stronger beaks capable of eating these seeds and selects against those birds with smaller, shorter beaks. The larger, stronger-beaked birds are able to survive, breed and pass on the larger, stronger beak genes to their offspring. Over time, the whole population of finches has the larger, stronger beaks. If these finches reunited with the smaller, shorter-beaked finches, they were still able to interbreed and produce viable offspring - otherwise they wouldn't be classified as the same species.
Questions
1. Natural selection is often described as 'survival of the fittest'. Is this an accurate description? Explain.
2. How would you test whether two isolated populations were different species.
3. Charles Darwin investigated the finches and used this as an example that demonstrated natural selection. What are some other examples that demonstrate natural selection?
Task 1
Create a species that will survive one million years in a particular environment. Use 'Switcheroo Zoo' to create an animal that is very well adapted to a particular environment. Describe the environment.
Visit http://www.sciencechannel.com/games-and-interactives/charles-darwin-game.htm and play!
Artificial Selection
Every domestic organism - plant and animal - is the result of sustained selection by humans. Artificial
selection differs from natural selection in that it is not random. Once humans deliberately began selecting organisms with desirable traits, species of plants and animals changed rapidly, generating new and distinct varieties.
Questions
1. Natural selection is often described as 'survival of the fittest'. Is this an accurate description? Explain.
2. How would you test whether two isolated populations were different species.
3. Charles Darwin investigated the finches and used this as an example that demonstrated natural selection. What are some other examples that demonstrate natural selection?
Task 1
Create a species that will survive one million years in a particular environment. Use 'Switcheroo Zoo' to create an animal that is very well adapted to a particular environment. Describe the environment.
Visit http://www.sciencechannel.com/games-and-interactives/charles-darwin-game.htm and play!
Artificial Selection
Every domestic organism - plant and animal - is the result of sustained selection by humans. Artificial
selection differs from natural selection in that it is not random. Once humans deliberately began selecting organisms with desirable traits, species of plants and animals changed rapidly, generating new and distinct varieties.
Task 2
Choose an organism that was artificially created (using artificial selection) and explain why the organism was created. For example, the Australian cattle dog has been bred for toughness and hard work.
Choose an organism that was artificially created (using artificial selection) and explain why the organism was created. For example, the Australian cattle dog has been bred for toughness and hard work.