Who was Lamarck?
Lamarck proposed one of the earliest theories of evolution.
Describe Lamarck’s theory of evolution.
- Lamarck proposed that organisms could change over time due to changing environmental conditions.
- His theory proposed changes could occur within an organisms lifetime and be passed on to offspring.
What was the power of the Darwin-Wallace theory of evolution by natural selection.
- identified a mechanism or cause of evolution.
- mechanism was testable by observation and experimentation.
- identified that individual organisms do not evolve in their life - but evolutionary changes occurs over many generations in populations.
Describe the Darwin-Wallace theory of evolution by natural selection.
- Organisms produce more offspring than can survive.
- Offspring have variation, some variations are more suited to environments than others.
- Individuals with favourable characteristics are more likely to survive and reproduce.
- Successful generations will become modified over time - eventually becoming a new species.
Define allele frequency.
How common an allele is in a population.
Define gene pool.
The combination of different genes present in an interbreeding population.
Define mutation.
A change in an organism that occurs when DNA is changed.
Define natural selection.
The mechanism for evolution in which individuals with traits the best adapted to selection pressures in their environment survive and pass on their genes. Also known as ‘survival of the fittest’.
Outline the steps of natural selection.
- Variation - there is a variation in phenotypes between individuals in a population.
- Selection Pressure - a specific selection pressure exists that causes a struggle for survival.
- Adaptations - individuals with the advantageous phenotype overcome the selection pressure, survive and reproduce. Individuals with unfavourable phenotypes decrease in number.
- Selection - organisms with the advantageous phenotype pass on their genes to the next generation. Successive generations will be genetically more like them and better adapted to the environment.
Define speciation.
The process by which one species splits into two or more seperate species through evolutionary changes that can no longer produce fertile offspring.
Describe the process of speciation.
- Variation - there must be variation in the population.
- Isolation - different groups are prevented from interbreeding, preventing gene flow.
- Selection - natural selection affects the genotype and increasing frequency of mutations that prevent the groups breeding even if they got back together.
Define genetic isolation.
Factors that prevent gene flow or mating between two populations.
Identify types of genetic isolation.
- Geographical barrier - separation by physical barriers, e.g., mountains.
- Ecological - different niches.
- Temporal - different breeding cycles.
- Behavioural - different courtship behaviours.
- Structural - differences in reproductive organs.
Define homologous structures.
Structures in organisms that have a similar structure and provide evidence of a recent evolutionary relationship.
- Similar structure
- Different function
- Closely related
Define analogous structures.
Structures in organisms that perform a similar function but are structurally different, suggesting no recent common ancestor. Structures have been developed due to similar environments and selection pressures.
E.g. Butterfly and bat wings.
Define divergent evolution.
Process by which two or more species evolve from a common ancestor, forming new species due to change in environment.
E.g., Finches on Galapagos Islands created different species due to different foods.
Define convergent evolution.
Process by which two of more unrelated species adopt similar adaptations (analogous structures) in response to common environmental conditions.
E.g., Sharks and dolphins are similar in appearance but not related.
Define fossils.
The preserved remains of ancient life.
Define transitional fossils.
A fossil that shares characteristics of both its ancestral group and existing descendant group. ‘Missing link’ between related species.
E.g., archaeopteryx is the transitional fossil between velociraptors and chickens.
Describe the process of fossilisation.
- The remnants of an organism are covered in sediment.
- Layers of sediment build up and pressure pushes these layers together forming sedimentary rock.
- In the absence of oxygen, microorganisms and other disturbances, the remains are preserved.
Conditions for fossilisation.
- conditions that reduce the rate of decomposition.
- areas of rapid sediment accumulation.
- constant cool temperatures.
- low light availability.
- protection from scavengers and decomposers.
Describe fossil dating techniques.
- Absolute dating - determines an age (range) of a fossil using the breakdown of radioisotopes such as carbon-14.
- Relative dating - uses the position of fossils in strata (layers of sedimentary rocks) to indicate a fossils age in comparison to other fossils.
Define biogeographical distribution.
- The study of how the continents move across Earth and how this directly affects the location of organisms.
- Continents now separated by oceans and containing identical fossil species were once connected in the past.
Define vestigal structures.
- Structures and organs that have no apparent function and appear to be residual parts from a past ancestor.
