Natural selection Flashcards
What did Aristotle think?
Early view for 2000 years
He believed in a ladder of life showing that species were fixed in time and that there was a hierarchy of species. Species were created individually and they havn’t changed
What changes questioned Aristotle’s theory of the ladder of life around (1769–1832)
Geology
Georges Cuvier and the fossil record which showed that organisms change over time – ‘evolution’ and that organisms disappear – ‘extinction’
What was Lamarcks theory (2000 years)
Species never become extinct
Over time they become new (better) species
Offspring inherit characters acquired by their parents
‘Lineages’ improve from generation to generation in response to ‘needs’
Lineages were created separately and remain separate
Biodiversity like a series of ‘escalators’
What did Malthus say (economics)
Animal populations should outgrow limited resources but there is always a Struggle for survival
What is Darwin’s theory
Individuals with advantageous variations would do better in the struggle for survival and these individuals would produce more offspring.
Offspring share some of their parent’s features
Advantageous variations would automatically increase in the population between generations
Lineages would change over time – different from ancestors
Organisms well suited or ‘adapted’ for their environment
‘Descent with modification’ – a continuous process with no ‘end point.
Darwins theory compared to Lamarcks theory
Evolution is like a ‘bush’ not a ‘ladder’ – no ‘progression’ and does not imply ‘improvement’
‘Common descent’ of species
Explains evolution and adaptation
What were the issues with Darwins’s theory
not compatible with natural selection and misses out key aspects such as those mentioned by Mendel
What is the ‘Modern Synthesis’ or ‘Neo-Darwinian Synthesis’ :
Advantageous variations inherited genetically
Recombination and mutation provide the variation for selection to work.
What is an adaptation
Organisms appear well ‘designed’ for their environment
But the ‘designs’ are the result of chance and selection
‘Adapted’ for different environments or niches.
This is a trait that enables an organism to survive and reproduce better than if it lacked the trait
What is the definition of fitness
Reproductive success and reflects how well an organism is adapted to its environment
The average number of offspring produced by individuals with one genotype relative to the number produced by individuals with different genotypes
When the fitness of alternative genotypes varies because of differential survival:
Fitness = ƒP : ƒF1
What does function mean
The survival benefit of an adaptation
How does it improve the chances of contributing genes to the next generation (i.e. fitness)?
What is Catastrophism?
The Earth has been shaped by catastrophic events that also cause extinctions
What is the definition of natural selection ?
The differential reproductive success of different phenotypes
What causes variation?
What does selection act on?
Random mutation and sexual recombination are the sources of variation
Selection acts on alternative genotypes producing phenotypes that appear ‘well designed’, it produces adaptations that maximises an individual’s fitness.
but evolution is not a directed process that brings improvement
