Where we fit in the world

  • Concept of species 
  • Evidence in classification
  • Natural selection
  • Fossil evidence

The concept of species

Species - a group of anatomically and biochemically similar organisms that can interbreed and produce fertile offspring.

Binomial system - a system whereby living organisims are given two names based on Latin. The first is the genus and the second is the species of the organism.

  • Kingdom - Animalia
  • Phylum - Chordata
  • Class - Mammalia
  • Order - Primates
  • Family - Hominidae
  • Genus - Homo
  • Species - sapien 
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Evidence used in classification

Biochemical - analysing amino acid sequence of a common protein e.g. cytochrome c. Less amino acids in commom = less related. DNA hybridisation - single strand from different species paired up, bond where complementary. Then heated, longer time taken for DNa disassociation = more in common

Anatomical - smilar anatomical structure = more closely related. E.g. 5 digit limb common in almost all vertebrates, this is how we know dolphins are more closely related to us than fish - dolphins flippers are similar to our hands

Embryological - similar stages of pre-natal development due to common ancestor 

Immunological evidence - similarities between antibodies in one organism and the antigens in another. If your blood was injected into a genetically similar species you would expected them to have the correct antibody

Behaviour - covers a wide range of traits from courtship rituals to vocalisation, facial expressions, feeding, hunting habits etc.

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Natural selection

Natural selection - process by which the best-adapted organisms in a population survive, reproduce and pass on their alleles to their offspring.

Speciation - the development of new species. Happens when different populations of the same species evolve in different ways, speciation is normally thought to happen by a gradual process.

  • A mutation creates a variation in the 'giraffe' population. 
  • There is too much competition for food at ground level for all the organisms to survive.
  • Those giraffes with long necks have an increased chance of survival, and therefore successful reproduction. As they can avoid competition by reaching food at higher levels.
  • Offspring will inherit the allele, over many generations mutation becomes common place in the population.
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Fossil evidence

Fossil - any form of preserved remains from a living organism .

Carbon dating - a method of dating artefacts up to 50,000 years old. It measures the ratio of 14C to 12C in a sample.

Potassium-argon dating - a method of dating volcanic rocks, based on the fact that 40K decays in 40Ar at a known rate. Scientist can work out age of sample by finding out how much 40Ar it contains.

Stratigraphy - the study of layers in rocks. Generally, older rocks lie below newer ones, so this enables rock layers to be dated.

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