Evolution
(a) define the term variation
Variation is the presence of differences between individuals. This can be within a species or between species.
(b) discuss the fact that variation occurs within as well as between species
The variation that occurs between species is usually obvious as there are obvious characteristics which separate one species from another. Within species, variation also occurs. For example, humans all have different characteristics (e.g. eye colour, hair colour, skin colour, nose shape) between members of the population, showing variation between different people. There are two forms of variation within a species – continuous and discontinuous.
(c) describe the differences between continuous and discontinuous variation, using examples of a range of characteristics found in plants, animals and microorganisms
There are two types of variation within a species.
(d) explain both genetic and environmental causes of variation
There are two general causes of variation.
Genetic variation and environmental variation are linked. In the past century, humans have become taller as a result of a better diet. But however good a diet you have, you are unlikely to grow very tall if all the rest of your family are short. This is because the height you can reach is limited by your genes.
(e) outline the behavioural, physiological and anatomical (structural) adaptations of organisms to their environments
Adaptation is a characteristic that enhances survival and long-term reproductive success.
Behavioural adaptation is an aspect of the behaviour of an organism that helps it to survive the conditions it lives in.
Physiological adaptation is one that ensures the correct functioning of cell processes.
Anatomical adaptation is one that is structural.
(f) explain the consequences of the four observations made by Darwin in proposing his theory of natural selection
Darwin proposed the idea of natural selection.
Darwin made 4 particular observations:
- offspring generally appear similar to their parents
- no two individuals are identical
- organisms have the ability to produce large numbers of offspring
- populations in nature tend to remain fairly stable in size
As all of the offspring are different, some may be better adapted than others. The better adapted individuals obtain enough food and survive long enough to reproduce, passing on their characteristics to the next generation. The less well adapted individuals are likely to die before they reproduce, therefore the population does not grow indefinitely. Over a long period of time, a number of small variations may arise. Eventually, the species will accumulate many small variations and one group of organisms belonging to one species could give rise to another species. It may become so different that it is unable to interbreed with the rest of the species.
(g) define the term speciation
Speciation is the formation of a new species from a pre-existing one. This is normally a long, slow process that generally takes many generations.
How does speciation occur?
- There is a reproductive barrier, meaning that some organisms are unable to breed with others in the group. A reproductive barrier is any factor that prevents effective reproduction between members of the species.
- Allopatric speciation – geographical separation e.g. different groups of the same species living on different islands – the Galapagos Islands
- Sympatric speciation – may be due to a biochemical change that prevents fertilisation, a behavioural change (e.g. a courtship dance that is not recognised) or a physical change (e.g. sexual organs of two groups of individuals are no longer compatible and they cannot mate)
- Variation that provides a benefit spread down the generations in a population through reproduction.
- If changes occur in only part of the group, but cannot spread to the whole group, then only part of the group will benefit, meaning only some members become different from the others. They may become so different they can no longer interbreed.
(h) discuss the evidence supporting the theory of evolution, with reference to fossil, DNA and molecular evidence
(i) outline how variation, adaptation and selection are major components of evolution
(j) discuss why the evolution of pesticide resistance in insects and drug resistance in microorganisms has implications for humans
- There is genetic variation is a population of bacteria/plants as mutation has occurred spontaneously meaning some bacteria/plants are naturally resistant to antibiotics/pesticides.
- The selective pressure for the population of bacteria/plants is the antibiotic/pesticide.
- The bacteria/plants with resistance will survive.
- The resistance allele will be passed on to the next generation.
- Resistance becomes more frequent within the population over many generations.
Problems with pesticide and drug resistance:
