Terminology: learn these definitions!
Evolution: Change in the genetic composition of a population during successive generations, which may result in the development of new species.
Microevolution: Small-scale variation of allele frequencies within a species or population, in which the descendant is of the same taxonomic group as the ancestor.
Macroevolution: The variation of allele frequencies at or above the level of species over geological time, resulting in the divergence of taxonomic groups, in which the descendant is in a different taxonomic group to the ancestor.
Determining episodes of evolutionary radiation and mass extinctions
Evolutionary history shows that biodiversity has gone through several mass extinctions. These tend to tend to be followed by periods of rapid evolutionary radiation in the form of an increase in taxonomic diversity or morphological disparity.
This is due to the opening up of previously occupied niches, and the most common example given for this is the Cretaceous/Tertiary (K/T) global mass extinction event that caused 76% of life on Earth to go extinct. The survivors included birds, crocodiles, lizards, snakes and turtles and they largely remained the same and we still see the same body forms today.
However, for the pre-existing mammals that survived, this became the Age of the Mammal. The mass extinction provided the opportunity for mammals to start to occupy different niches and increase rapidly in size.
Previously small nocturnal creatures diversified into a wide range of mammals that dominated all parts of the Earth. The Eutherians (placentals) mainly dominated in the northern hemisphere and the Metatherians (marsupials) in the southern hemisphere.
You will have to use data to determine when episodes of mass extinctions and evolutionary radiation occurred. Mass extinctions are when the population crashes, and then you’re looking for a very quick and huge increase in diversity for evolutionary radiation.
State in which geological period reptiles first appeared.
Calculate how many families of mammal were present five million years ago.
Infer when a mass extinction occurred.
Interpreting data to reveal phylogenetic relationship
You can look at the degree of DNA similarity to compare genomic features to provide evidence for the theory of evolution.
Samples of DNA werre removed from three species of Fucus. The DNA in each sample was separated into its two strands. The single stranded DNA was then mixed with single-stranded DNA from another sample (either the same species or different). This allowed sections of DNA with complemetary base sequences to join together to form a new double helix. The results are shown to the left.
Which two species seem to be the most closely related?
Scientists analysed the sequence of amino acids in one polypeptide chain in the haemoglobin of four different ape species. The only differences they found occurred at three positions in the chain. The results are shown to the left, with the letters abbreviating amino acids.
What information do the data in the table suggest about the relationships between the chimpanzee, bonobo and gorilla?