10.4 Evidence for evolution Flashcards
What’s evolution
The theory that describes the way in which organisms evolve or change over a period of time as a result of natural selection
What’s natural selection
An organisms best suited to their environment are more likely to survive and reproduce, passing on their advantageous alleles onto their offspring. Gradually the species changes over time to have a more advantageous phenotype for the environment in which it lives
Wallace and Darwin’s developments on the theory of evolution
Observations on finches by Darwin: in the different Galápagos Islands the beaks and claws of the finches were different shapes due to the different foods available on each island
- Alfred Wallace also was developing his theory of evolution at the same time
- Darwin and Wallace presented their findings in a joint paper
Three main pieces for evidence for evolution
-Palaeontology (study of fossils)
- Comparative anatomy (similarités and differences in organisms anatomy)
- Comparative biochemistry (similarities and difference in chemical make up of organisms)
The process of natural selection
Within a population, there is variation due to mutation and sexual reproduction
- Those best adapted to the environment or a specific selection pressure are more likely to survive
- Those with favourable traits will survive and reproduce with organisms with similar traits
- Over long periods, the frequency of the advantageous characteristic will increase and the nature of the organism will gradually change
Comparing organisms through comparative biochemistry
The base sequence is compared for two different organisms
The number of differences that exist are plotted against the rate the molecule undergoes neutral base pair substitutions
From this information scientists can estimate the point at which the two species last shared a common ancestor
Species that are closely related have more similar DNA and proteins whereas those who are distantly related have far fewer similarities
Ribosomal RNA has a very slow rate of substitution so it’s commonly used with fossil information to determine relationships between ancient species
Cytosine c is also used as it’s a protein involved in respiration
Problems with fossil records
Many organisms are soft bodied and decompose quickly before the have a chance to fossilise
The conditions needed for fossils to form are not often present
Many fossils have been destroyed by the earths movements (e.g. volcanoes) or are still undiscovered
Evidence proved by fossil records
- Fossils of the simplest organisms are found in the oldest rocks and more complex organisms are found in more recent rocks, supporting the evolutionary theory that simple life forms gradually evolved over a long period of time
- The sequence in which organisms are found matches their ecological links to each other
- Allow relationships between extinct and living organisms to be investigated
- Can show how closely related organisms have evolved from the same ancestor
whats divergent evolution
how from a common ancestor different species have evolved each with a different set of adaptive features evidence for this is homologous structures
