Ch.4 - The Origins of Living Things (Evolution)

• Biodiversity

  Means there are many different types of living things
• Fossils

  the remains of very ancient living things
• Evidence from fossils tells us that some types of living things have been wiped out. Also there are no fossils of some modern living things. this suggests that some living things become extinct and new types of living things emerge, i.e. that life on Earth changes.
• There are a number of suggestions as to how the variety of living things have arisen. However, the most widely accepted explanation based on evidence is the theory of evolution by natural selection. This theory was put forward by Charles Darwin (in association with Alfred Russel Wallace) in 1859.
• Evolution

  The process by which different kinds of living things develop from earlier forms by genetic changes over long periods of time.
• Species

  A group of living things that can reproduce together to produce offspring which themselves can reproduce.
• Examples of Species

  • Humans
  • Dogs
  • Daffodils
  • Cabbages
  • Cats
  • Rabbits

  A cat and a rabbit cannot reproduce together, which is how you know they are different species.
• Mutation

  a change in a gene
• Example of a Gene Mutation


  While humans are similar in having two eyes, they show variations in eye shape and eye colour. These variations are passed on to the next generation because they are inherited, or gene-controlled, variations.
• Theory of Evolution

  Darwin’s theory of evolution is based on three things he noticed (observations), and from these he made two predictions (hypotheses).
• Observation 1


  Living things produce huge numbers of offspring.

  For example, a tree may produce thousands of seeds or a fly may lay thousands of eggs.
• Observation 2


  The environment (or surroundings) can support only a limited number of living things.

  For example, there is not enough space for all the seeds to grow or there may not be enough food for all the flies to live.

  Observations one and two led to hypothesis one.
• Hypothesis 1


  if more living things are produced than can survive, they will struggle to get scarce resources. Darwin called this the struggle for existence. It is now often called competition for scare resources.

  For example, seeds may struggle to get enough space and light to grow; the flies may struggle for food and water.
• Observation 3


  Darwin studied animals such as pet pigeons and cows on farms. Also, on his voyage around the world he noticed that species showed inherited variations. He realised that species could have differences that they would pass on to their offspring.

  Observation three leads to hypothesis two.
• Hypothesis 2 - Suitable Variations


  Darwin realised that some of the variations would help the living things to survive better.

  For example, if some seeds produce longer or bigger roots, those seeds would grow better; if some flies developed wings more quickly, they could fly away to get more food.

  Living things that are best suited, or adapted, to their environment survive more easily. If they survive, they have a better chance of reproducing and passing on their genes (and their suitable variations) to the following generations.
• Adaptation


  a characteristic that helps an organism to survive and reproduce
• Hypothesis 2 - Unsuitable Variations


  However, some variations do not help living things to survive better. These living things are not adapted to their environment and so may die. This means they do not pass their genes (and unsuited variations) on to the next generations.
• Natural Selection

  The way in which organisms whose variations are suited to their environment survive and reproduce
• Nature selects those organisms that are best suited (or adapted) to their environment.
• Evolution and the diversity of life

  Evolution by natural selection has given rise to all of the different types of living things on earth today.

  This happens when a single species evolves to form two (or more) different species. These two species then evolve to form even more species. In time, huge numbers of species may develop from the original species.
• New Species

  The finches on the Galápagos Islands is an example of how new species form. Darwin studied these birds on his voyage on HMS Beagle. He noticed that the finches on the different islands were similar in many ways, but they showed differences in many features, especially their beak shapes.
• Darwin concluded that the original finches must have got to the islands from the mainland of South America. On each island, the conditions were different. This meant that:


  • Where hard seeds were available, those birds with a short, strong beak were better suited to feeding e.g. Ground Finch
  • If there were many insects, birds with a sharper and more slender beak were better suited to feeding e.g. Warbler Finch
  • On an island with many cactus plants, finches with a long, pointed beak were better suited to getting cactus seeds e.g. Cactus Finch
• Finch evolution on islands

  1. Finches with beaks not suited to feeding on island get less food and die out

  2. Finches with beaks most suited to available food survive

  3. Surviving birds pass on beak shape to next generation
• From a single species of Finch, many different types of finch evolved
• New beak shapes arose

  When genes became altered, or mutated
• This type of process has happened all over the world to different living things over very long periods of time
• This has produced the wide range of species or biodiversity found on earth today
• Timeline for Biodiversity

  The planet Earth formed about 4.6 billion years ago. The first forms of life on Earth appeared about 3.8 billion years ago. They were tiny, single-celled bacteria that lived in the sea. For about 90% of Earth's history, living things were found only in the sea or in watery environments.

  About 500 million years ago the first plants and fungi grew on land. It is only since then that all the modern life forms have developed.
• Example - Timeline for Biodiversity

  For example, dinosaurs first appeared about 220 million years ago, birds 140 million years ago, and humans only 200 000 years ago. The examples given show that evolution normally takes place over long periods of time.