1. The five different types of explanation are described in Section 1.1.1 (pp. 6-7).
2. Literally = "present at birth". The term is fully defined in the Glossary and explained on p.14.
3. See above and also Section 5.4 (p.118).
'Instinctive' is a rather vague and imprecise term with a variety of meanings,
including 'innate'. It is not used in the scientific literature.
4. It is useful in that many animals display rather fixed, specific behaviour in response to a particular stimulus (section 2.4.1, p.21). It is wrong because such behaviour is not always exactly the same each time it occurs - it is not 'fixed' (2.4.1, pp. 22-23).
5. Probably - see definitions in Glossary. The term 'reflex' is used by physiologists to describe responses that ethologists call fixed action patterns! (see Section 2.2).
6. Hormones are chemicals used for communication within an animal; pheromones are chemicals used for communication between animals (see definitions in Glossary).
7. Stimulus filtering may be due to limited responsiveness ("tuning") of receptors to a narrow range of stimuli (peripheral filtering). Information from 'broad band' receptors may be filtered centrally (in the brain) to elicit different behaviour patterns (e.g. toads - Fig. 2.19), or can be further processed to produce 'search images'. Selective attention allows a particular signal to be identified against a background of otherwise indistinct (and uninteresting) 'noise': e.g. you become alert when your name is mentioned amongst the general hubbub of conversation at a party.
1. Its genes (chromosomes) - half of them from Mum's egg and half from Dad's sperm. Unlike most cells, eggs and sperm contain only single (rather than paired) chromosomes (i.e. haploid rather than diploid). (See Introduction & Guide Section 6.4; Book 1, sections 3.2.1 and 3.2.4, especially foot of p. 56 and top of p. 58.)
2. All body cells (except eggs and sperm) contain all the organism's chromosomes and genes, but not all the available genes are used (expressed) in a given cell. In order to display their potential (be expressed) the genes need to be switched/turned on by some stimulus, e.g. genes controlling secondary sexual characteristics are turned on by hormones at puberty. Once switched on, a gene can also be 'turned off', thus terminating its action.
3. Proteins are important in many ways. They can be part of a cell's structure, or its chemical machinery, e.g. enzymes etc. (See section 3.2.2 and also Intro. & Guide.)
4. Usually because different genes have been expressed ('turned on') in the different cells. (See Section 3.2.2.)
5. It means they can do different things: muscle cells can contract, glands secrete, nerves transmit electrical signals, etc. (See above and Intro. & Guide section 6.4)
6. There are several aspects to this:-
(a) Genes code for proteins and thus determine the properties of cells,
tissues and organs. They determine the 'machinery' that an animal uses
to perform its behaviour.
(b) Even in individuals with very similar genes there can be a lot of variation
- this would not be so if genes determined behaviour.
(c) The effects of some genes, e.g. PKU, may not be evident unless a particular
diet is consumed.
(d) Genes can be influenced by the environment: e.g. the sex of reptiles
is dependent upon the temperature at which the eggs are incubated.
1. See Section 4.2.1. Characters exhibiting continuous variation can have any value over a certain range, e.g. height, body temperature, blood pressure, etc. With discontinuous variation it is possible to identify distinct categories, e.g. blood groups, sex, etc. To put it simply: continuous variables can be measured, whereas discontinuous variables (categories) tend to be counted.
2. Variety is the spice of life! If there was no variation between animals, i.e. they were all the same, none would have an advantage over the others. Natural selection works on the principle that small differences (variations) in character increase the fitness of particular individuals, who will leave offspring possessing that character (See 4.3.3.).
3. Possible causes of variation (e.g. genetic or environmental effects) are given in sections 4.1, 4.2.1.
4. If we consider the heights of individuals in a 'normal' adult population, the majority of individuals will have heights close to the 'average condition'. There will also be many individuals with heights just below or just above the average. Moving progressively away from the average (above or below) there are fewer and fewer individuals; very short and very tall people do occur but they are very rare. When some continuous variable is plotted as a graph against frequency of occurrence, a symmetric bell-shaped curve results; an example is shown in Fig. 4.6. This type of symmetrical bell-shaped curve is called a 'normal distribution'. Curves where the average is shifted (skewed) to one side or other are not normal. This can have important implications when statistical tests are used.
5. If they shared the same genes and environment - e.g. identical twins.
6. The flaws in the notion of group selection (for the good of the species) are outlined in Section 4.3.7. Most examples of altruistic behaviour occur between relatives (kin selection), but it can occur between non-relatives and is usually reciprocated. (You scratch my back...)
7. If it increases total fitness (benefits greater than costs) - see Section 4.4. Sections 4.4.1 - 4.4.4 provide examples, which are summarised at the top of page104.
8. No, it can be influenced by external stimuli as well as genes. The reasons are given in Section 5.4, but a summary of the points is provided in the final paragraph of page 121.
9. On balance, neither! There are instances where one is more influential than the other, but the message we want you to remember is that both influence behaviour.