B1b - Evolution

B1b - Evolution and environment

Science AQA Biology Unit 2.

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Darwin's theory of evolution explains how species of living things have changed over geological time. The theory is supported by evidence from fossils, and by the rapid changes that can be seen to occur in microorganisms such as antibiotic-resistant bacteria. Many species have become extinct in the past and the extinction of species continues to happen. Darwin's ideas caused a lot of controversy, and this continues to this day, because the ideas can be seen as conflicting with religious views about the creation of the world and creatures in it.

Darwin's finches

Darwin studied the wildlife on the Galápagos Islands. He noticed that the finches on the different islands there were fundamentally similar to each other, but showed wide variations in their size, beaks and claws from island to island. For example, their beaks were different depending on the local food source. Darwin concluded that, because the islands are so distant from the mainland, the finches that had arrived there in the past had changed over time. Darwin studied hundreds more animal and plant species. After nearly 30 years of research, in 1858 he proposed his theory of evolution by natural selection.

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Darwin's Finches

Darwin's drawings of the different heads and beaks he found among the finches on the Galapagos Islands (http://www.bbc.co.uk/schools/gcsebitesize/science/images/bifinches.jpg) 

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Natural Selection

The theory of evolution states that evolution happens by natural selection. Here are the key points:

  • Population has variations. (because of differences in genes)
  • Some variations are favourable. (because they're more suited to the environment)
  • More offspring are produced than survive. (because of predators)
  • Those that survive have favourable traits. (because of survival of the fittest)
  • The population will change over time. (because only the best animal variations are breeding because they are the only ones that are surviving to be able to breed)
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Evolution evidence

Fossils - Most of the evidence for evolution comes from fossil records. Fossils show how much, or how little, organisms have changed over time.

One of the problems with the fossil record is that it contains gaps. Not all organisms fossilise well, and there will be many fossils that have been destroyed by the movements of the Earth, or simply not yet been discovered.(http://www.bbc.co.uk/schools/gcsebitesize/science/images/biammonite.jpg)

Rapid changes - Rapid changes in species have been observed. These support the theory of evolution. For example: Micro-organisms such as bacteria and viruses reproduce very rapidly and can evolve in a relatively short time. One example is the bacterium E. coli.

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Individuals that are poorly adapted to their environment are less likely to survive and reproduce than those that are well adapted. Similarly, it is possible that a species that is poorly adapted to its environment will not survive and will become extinct.

Some of the factors that can cause a species to become extinct are:

  • Changes to the environment, e.g. climate change 
  • New diseases
  • New predators
  • New competitors

The fossil record shows that many species have become extinct since life on Earth began. Extinction is still happening and a lot of it occurs because of human activities. We compete with other living things for space, food and water, and we are very successful predators.

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1. According to Darwin's theory of evolution, how do new species evolve?

  • Natural Selection
  • Extinction
  • Artificial Selection

2. Which individuals are most likely to survive to reproduce?

  • Individuals that are well suited to the environment
  • Individuals that have no immunity to new disease

3. Which of the following is not likely to cause a species to become extinct?

  • New disease
  • New food source

4. What sort of variation is inherited?

  • No variation is inherited at all
  • Genetic variation
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