Flashcards in 5. Natural Selection Deck (13):
Who is usually given the credit for being the first to realise that species evolve by natural selection?
Charles Darwin - he was the first to publish a detailed account of it
How many years of research did Darwin do? Why did he delay publication? What eventually spurred him to publish?
- more than 20 years
- feared a hostile reaction (creationist backlash)
- Alfred Wallace, another biologist, wrote to him in 1858 suggesting very similar ideas
When was 'On The Origin of Species' published?
What did 'On The Origin of Species' change?
- the way biologists think about the living world and the place of humans in it
Explain the theory of evolution through a series of observations and deductions. (7 steps)
- species tend to produce more offspring than the environment can support
- there is a struggle for existence in which some individuals survive and some die
- in natural populations there is variation between the individuals
- some individuals are better adapted than others. An adaption is a characteristic that makes an individual suited to its environment and way of life.
- individuals that are better adapted tend to survive and produce more offspring, while less well adapted individuals tend to die or produce fewer offspring so each generation contains more offspring of better adapted than less well adapted individuals.
- the frequency of characteristics that make individuals better adapted increases and the frequencies of other characteristics decrease, so species change and become better adapted.
What do living organisms acquire during their lifetime?
characteristics - e.g. an amputated leg
Why are characteristics not passed on to offspring?
characteristics are not heritable so they are lost when an individual dies. This also means, therefore, that characteristics cannot increase in a species by natural selection
Give an example of characteristics not being passed on.
- right handed tennis players develop bigger muscles in their right arms
- genes that influence muscles have not been altered
- so children of right handed tennis players do not have a bigger right arm
When, and only when, can natural selection occur?
- if there is variation among members of a species
- if the environment cannot support
Name three sources of variation.
- Sexual reproduction
Explain 'mutation' as a source of variation.
- the original source of variation
- new alleles are produced by gene mutation, which enlarges the gene pool of a population
Explain 'meiosis' as a source of variation.
- produces new combinations of alleles by breaking up existing combinations in a diploid cell
- every cell produced in meiosis is likely to carry a different combination of alleles, because of crossing-over and the independent orientation of bivalents