What are 5 pieces of evidence that helped Darwin and Wallace to propose the theory of evolution by natural selection?
- Observations of artificial selection
- Fossil record
- Biogeography
- Homologies
- Adaptions to environment
How did observations of artificial selection help Darwin and Wallace propose the theory of evolution by natural selection?
- Humans had selectively bred plants and animals to produce desired traits
- If humans could selectively breed organisms, nature could also select for advantageous traits
How did observations of fossil record help Darwin and Wallace propose the theory of evolution by natural selection?
- Different layers of rock contained different kinds of fossils
- Life has changed over time
How did observations of biogeography help Darwin and Wallace propose the theory of evolution by natural selection?
- Species on different continents often had similarities, however were also different in significant ways
- Suggests that they share a common ancestor, but after continents split apart they evolved separately
How did observations of homologies help Darwin and Wallace propose the theory of evolution by natural selection?
- Different species have similar structures, such as bones in wings of birds and human arms
- Similarities due to common ancestry
How did observations of adaptions help Darwin and Wallace propose the theory of evolution by natural selection?
- Organisms are well-suited to their environments
- Example being finches on Galapagos Islands
- Indicated that natural selection had acted to produce adaptions that helped them survive in particular environments
What is Lamarckian evolution?
- The idea that organisms can pass on acquired traits to their offspring
- Discredited by modern science
What is evolution by natural selection?
- Proposed by Darwin and Wallace
- Suggests that species change over time due to natural selection acting on variation within populations
- Widely accepted scientifically
What are the 5 main mechanisms that cause evolution in populations?
- Mutations
- Gene flow
- Genetic drift
- Natural selection
- Non-random mating
How do mutations cause evolution?
- Spontaneous changes in DNA sequence can introduce/change particular phenotypic traits
- Can increase/decrease likelihood of survival
What is gene flow?
- Movement of alleles from one population to another
- Result of migration, interbreeding or other forms of genetic exchange
What is genetic drift?
- Random fluctuation of allele frequencies in a population due to chance events
- E.g. founder effect or bottleneck effect
What is the founder effect?
Where a small fraction of the population becomes geographically isolated from the rest, causing a reduced genetic diversity in that group
What is the bottleneck effect?
Where only a small fraction of the population survives (e.g. a natural disaster), causing a reduced genetic diversity in that group
What is non-random mating?
Individuals with particular traits are more likely to mate
What is natural selection?
The process by which certain traits that give a selective advantage are more likely to be passed on to future generations, while traits that are disadvantageous are less likely to be passed on
What is directional selection?
When individuals with traits on one side of the mean in their population survive better or reproduce more than those on the other
What is disruptive selection?
When more extreme phenotypes (or genotypes) within a population have a fitness advantage over intermediate individuals
What is continuous variation?
- Continuous variation refers to characteristics that can have many different values a range (e.g. height)
- Majority of continuous traits are around the mean
What is discrete variation?
- Discrete variation refers to characteristics that fit into distinct categories (e.g. colour)
- Discrete traits will be shown as multiple peaks
What is ‘fitness’ in natural selection?
- Fitness refers to an organisms’ ability to survive and reproduce
- It is often used as a measure of how well adapted an organism is to its environment
What is sexual selection?
- A type of natural selection that occurs when individuals within a population differ in their ability to attract mates
- Traits such as courtship displays or physical characteristics that indicate genetic quality to mates are more likely to be passed on
What are biological species?
Defined based on their ability to breed and produce fertile offspring
What are morphospecies?
Defined based on observable physical characteristics
