Reproduction and Inheritance · 6 question types
Past paper frequency (2018 to 2024)
This topic accounts for approximately 14% of your exam marks.
Natural selection explanations and antibiotic resistance as an application are tested in almost every series.
Darwin's theory of evolution by natural selection follows a clear logical sequence. There are four key steps, and exam questions on this topic almost always ask you to list them in order.
Every population contains variation: differences between individuals. Some of this variation is genetic, caused by different alleles of the same genes. New genetic variation arises through:
This means no two individuals in a population are genetically identical (except identical twins or clones).
Members of a population have to compete for limited resources: food, water, space, mates. Not every individual survives long enough to reproduce. Some individuals happen to have genetic variations that give them an advantage in their environment:
Individuals with these advantageous alleles are more likely to survive to reproductive age than those without them. This is sometimes called "survival of the fittest", though "fittest" here means best suited to the environment, not strongest or fastest.
Survivors are more likely to reproduce and pass on their genes. Each surviving individual passes on all of its alleles to its offspring, including the advantageous ones that helped it survive.
Individuals that did not survive long enough to reproduce never pass on their alleles, no matter how good their genes might have been at other things. Evolution is shaped by which individuals leave offspring, not by which live the longest.
Over many generations, the advantageous alleles become more common in the population. Less helpful alleles become rarer because the individuals carrying them leave fewer offspring.
After enough generations, the average characteristics of the population have shifted: the population has evolved.