genetics and evolution

• The idea behind the theory of evolution through the process of natural selection is that all species of living things have evolved from simple life forms over a period of time. 
• . The Earth is about 4.5 billion years old and there is scientific evidence to suggest that life on Earth began more than three billion years ago.
• Charles Darwin is recognised as the scientist most associated with the theory of evolution, however, a number of other scientists were influential in this field.
• At the beginning of the 19th century Jean-Baptiste Lamarck was a French scientist who developed an alternative theory of evolution before Charles Darwin.
• Lamarck's theory involved two ideas:

  • a characteristic which is used more and more by an organism becomes bigger and stronger, and one that is not used eventually disappears
  • any feature of an organism that is improved through use is passed to its offspring
• Lamarck's theory cannot account for all the observations made about life on Earth. For instance, his theory implies that all organisms would gradually become complex, and simple organisms disappear.
• Lamarck's theory suggested that the giraffe's original short-necked ancestor repeatedly stretched its neck to reach the higher branches to eat. Lamarck believed that the stretching elongated the giraffe's neck, which became a useful characteristic and was passed onto future generations. This resulted in the length of the giraffe's neck increasing over time.
• It is now commonly accepted that Lamarck's ideas were wrong. For example, simple organisms are still detected in all varieties of life, plus it is now known that mutations can create variation such as neck length.
• Charles Darwin was an English naturalist who studied variation in plants, animals and fossils during a five-year voyage around the world in the 19th century. Darwin visited four continents on the ship HMS Beagle.
• Darwin observed many organisms including finches, tortoises and mocking birds, during his five week visit to the Galapágos Islands, near Ecuador in the Pacific Ocean. He continued to work and develop his ideas once he returned from his voyages.
• Darwin's theory of evolution challenged the idea that God made all the animals and plants that live on Earth, which contradicted the commonly held Christian views of his era. He did not publish his scientific work and ideas until 28 years after his voyage.
• as a result of Darwin's world expedition and observations, which were backed by many years of experimentation; his discussions with like-minded scientists and his developing knowledge of geology and fossils; he proposed the theory of evolution by natural selection.
• Darwin proposed that:

  • individual organisms within a particular species show a wide range of variation for a characteristic
  • individuals with characteristics most suited to the environment are more likely to survive to breed successfully
  • the characteristics that have enabled these individuals to survive are then passed on to the next generation
• darwins theory is called natural selection
• Darwin ideas were documented in the book On the Origin of Species, which was published in 1859. The naturalist's ideas created controversy in Victorian society.
• The theory of evolution through the process of natural selection was only gradually accepted because:

  • the theory challenged the idea that God made all animals and plants that live on Earth (creationism)
  • there was insufficient evidence when the theory was published to convince many scientists
  • the mechanism of inheritance and variation was not known until 50 years after the theory was published
• Some scientists were reluctant to change their minds about the ideas of creationism, even when new evidence was discovered that contradicted their ideas.
• Darwin's book, On the Origin of Species, was a world best seller and is still in print today. With every new edition of his book, more evidence was discovered to support Darwin's ideas. This led to the development of his theory over time. In a later edition, he introduced the famous term 'Survival of the fittest'.
• Alfred Russel Wallace was a great admirer of Darwin and a fellow naturalist, who independently proposed the theory of evolution by natural selection.
• Wallace produced scientific journals with Darwin in 1858, which prompted Darwin to publish On the Origin of Species the following year.
• Wallace worked around the world gathering evidence to support his evolutionary theory. He is best known for studying warning colouration in animals, and examples include the Golden Birdwing Butterfly (Ornithoptera croesus) and his theory of speciation.
• After a variety of zoological discoveries Wallace proposed a theory of evolution, which matched Darwin's unpublished ideas that he had kept secret for nearly 20 years. This encouraged Darwin to collect his scientific ideas and collaborate with Wallace. They published their scientific ideas jointly in 1858.
• Alfred Russel Wallace created pioneering work in speciation; however, additional evidence over time has led to our current understanding of the theory of speciation.
• A species is a group of organisms able to interbreed and produce fertile offspring.
• • genetic variation - each population has a wide range of alleles that can control their characteristics
• • natural selection - the alleles which help an organism to survive are selected in each population
• • speciation - the populations become extremely varied and successful interbreeding cannot happen anymore
• New species can also arise as a result of isolation
• • two populations of a species can become geographically separated because of the environment
• • isolation can prevent interbreeding and the combination of genes within a species
• • different mutations can take place in the isolated groups and create different phenotypes within a particular location
• • over time species may evolve to be different to each other, and they will not be able to interbreed
• A fossil is the preserved remains of a dead organism from millions of years ago
•  Fossils are found in rocks and can be formed from:

  • hard body parts, such as bones and shells, which do not decay easily or are replaced by minerals as they decay
  • parts of organisms that have not decayed because one or more of the conditions needed for decay are absent. For example, dead animals and plants can be preserved in amber, peat bogs, tar pits, or in ice
  • preserved traces of organisms, such as footprints, burrows and rootlet traces - these become covered by layers of sediment, which eventually become rock
• Fossil remains have been found in rocks of all ages. 
• Fossils of the simplest organisms are found in the oldest rocks, and fossils of more complex organisms in the newest rocks. This supports Darwin's theory of evolution, which states that simple life forms gradually evolved into more complex ones.
• Evidence for early forms of life comes from fossils. By studying fossils, scientists can learn how much (or how little) organisms have changed as life developed on Earth.
• There are gaps in the fossil record because many early forms of life were soft-bodied, which means that they have left few traces behind. What traces there were may have been destroyed by geological activity. This is why scientists cannot be certain about how life began.
• Fossils provide a snap shot of the past and allow us to study how much or how little organisms have changed as life developed on Earth.
• Evolutionary trees are used to represent the relationships between organisms. Branches show places where speciation has occurred, and a new species has evolved.