Richard Dawkins

Arms Races between and within Species

An adaptation in one lineage (e. g. predators) may change the selection pressure on another lineage (e. g. prey), giving rise to a counter-adaptation. If this occurs reciprocally, an unstable runaway escalation or ‘arms race’ may result. We discuss various factors which might give one side an advantage in an arms race. For example, a lineage under strong selection may out-evolve a weakly selected one (‘the life-dinner principle’). We then classify arms races in two independent ways. They may be symmetric or asymmetric, and they may be interspecific or intraspecific. Our example of an asymmetric interspecific arms race is that between brood parasites and their hosts. The arms race concept may help to reduce the mystery of why cuckoo hosts are so good at detecting cuckoo eggs, but so bad at detecting cuckoo nestlings. The evolutionary contest between queen and worker ants over relative parental investment is a good example of an intraspecific asymmetric arms race. Such cases raise special problems because the participants share the same gene pool. Interspecific symmetric arms races are unlikely to be important, because competitors tend to diverge rather than escalate competitive adaptations. Intraspecific symmetric arms races, exemplified by adaptations for male-male competition, may underlie Cope’s Rule and even the extinction of lineages. Finally we consider ways in which arms races can end. One lineage may drive the other to extinction; one may reach an optimum, thereby preventing the other from doing so; a particularly interesting possibility, exemplified by flower-bee coevolution, is that both sides may reach a mutual local optimum; lastly, arms races may have no stable end but may cycle continuously. We do not wish necessarily to suggest that all, or even most, evolutionary change results from arms races, but we do suggest that the arms race concept may help to resolve three long-standing questions in evolutionary theory.

Do digger wasps commit the concorde fallacy

Abstract The Concorde fallacy is a notorious theoretical error which tempts economists and evolutionists alike. It amounts to investing further in a project simply because one has invested in it heavily in the past, rather than because of potential future return on investment. Digger waps, Sphex ichneumoneus , disconcertingly appear to behave as if following the Concorde fallacy. Pairs of females fight over jointly occupied nests, provisioned with paralysed katydids. The prior investment by each wasp in the nest is measured as the number of katydids that she has put into it. The true value of the nest is approximated by the total number of katydids there. The evidence suggests that the wasp with the least prior investment is the one most likely to surrender. In a post-hoc attempt at rationalizing this Concordian result, we uncover some of the pitfalls of naive optimality speculations, and recommend analysis in terms of evolutionarily stable strategies.

A Cheap Method of Recording Behavioural Events, for Direct Computer-Access

A new system is described for recording behavioural events on a time scale, in a form which can be fed directly into a computer. The user presses keys on a keyboard to denote behavioural events. The number of separate events which can be distinguished depends on the quality of equipment used, and can be over 60. The main disadvantage of the system is that no two events can be recorded simultaneously. The information is coded on magnetic tape, using an unmodified single channel domestic tape recorder. The encoding unit is light and battery driven, and together with the tape recorder can easily be taken into the field. The tapes are later played back through a simple interface to a small computer. The computer decodes them, and punches out a permanent paper tape record of which behaviours occurred, and when, to the nearest tenth of a second. These paper tapes can then be fed back into the same or another computer for analysis. In addition to recording discrete events, the system can be used as a simple analogue to digital converter. The main advantage of the system is that it is extremely cheap and easy to make. This is because a very simple frequency code is used, and the computer itself is programmed to perform the whole decoding operation.

A threshold model of choice behaviour

Abstract 1. 1. Among the problems raised by choice behaviour is that of the mechanism of decisionmaking. Given that a chick pecks more often at a red spot than at a green one, but nevertheless sometimes pecks at the green one, what mechanism determines each individual choice? This paper presents a model called the choice threshold model to help answer this type of question. 2. 2. The model is initially expressed in terms, familiar from the ethological literature, of a fluctuating variable (cf. ‘drive’), interacting with thresholds. Whether expressed in this pictorial way or not, the important assumption of the model is that for any two stimuli presented together, an animal either chooses the preferred one or chooses completely indiscriminately; the less preferred stimulus can only be chosen during periods of non-discrimination. 3. 3. A precise quantitative prediction (of what psychologists call ‘strong stochastic transitivity’) is deduced from the model and named prediction 1. If any three stimuli are presented in all three possible pair combinations, and if the percentage preference for the best over the worst is called PAC, the other two percentage preferences being PAB and PBC, prediction 1 is that PAC should equal 2(PAB+PBC−PAB PBC)-I. 4. 4. Experiments on domestic chicks, and data from, other workers on a variety of species including man tend to confirm prediction 1. Other predictions will be discussed elsewhere. 5. 5. Some general properties of the model, and alternative ways in which they might be realized are discussed.

The attention threshold model

Abstract 1. 1. The attention threshold model is a modified version of a previously proposed choice model called the choice threshold model. It arose as an attempt to explain a puzzling feature of the original model. 2. 2. The assumptions of the attention threshold model are listed. These seem quite complex, but the complexity is needed to preserve the predictive properties of the original model. 3. 3. The assumptions of the attention threshold model are given formal algebraic expression with respect to a particular hypothetical example. 4. 4. Predictions which follow from this algebraic treatment are discussed and compared with experimental evidence, mostly taken from the literature. These are: (a) a prediction about the effect of irrelevant cues on preference strength; (b) a prediction about additivity of cues (‘heterogeneous summation’); (c) a prediction about opposition of cues (‘heterogeneous subtraction’); and (d) various predictions about response latency. 5. 5. The model is assessed according to the success of its predictions.

The ‘peck/no-peck decision-maker’ in the black-headed gull chick

Abstract 1. 1. In companion papers a model called the Choice Threshold Model was described, and its applicability to percentage preference data tested. The present paper extends the treatment to absolute numbers of responses in a choice situation. 2. 2. It is postulated that while the Choice Threshold Model functions as a ‘directing’ decision-maker, determining how choices are to be directed, the determination of when and how often such choices shall occur may be the function of a separate ‘go/no-go decision-making mechanism’, the rate of whose activity is represented by the symbol K. 3. 3. Data on rates of pecking at coloured stimuli by black-headed gull chicks Larus ridibundus , are used to determine the relationship between K and the stimulus situation. 4. 4. It is found that K is determined only by the most preferred stimulus available. 5. 5. Thus a stimulus affects the animal in two different ways. By influencing the ‘directing decision-maker’ (the Choice Threshold Model), it affects the relative number of times it is chosen compared with other simultaneously available stimuli. By influencing the ‘go/no-go decision-maker’, which it only does when it is the most preferred of the available stimuli, it affects the absolute rate of choosing regardless of which stimulus is chosen. This dichotomy is reminiscent of that of classical ethology between ‘directing’ and ‘releasing’ roles of stimuli. 6. 6. Paradoxically it is found that stimuli which are preferred with respect to their ‘directing’ function tend to have low ‘releasing’ value and vice versa. 7. 7. A quantitatively precise prediction concerning the relative merits of two methods of studying selective responsiveness, simultaneous or successive presentation of stimuli, can be derived from the model if it is assumed that K is constant. In the light of the findings about the dependence of K on the stimulus situation, this prediction has to be modified. The present data are used in an indirect way to verify the modified prediction. 8. 8. The actual values of K (i.e. ‘releasing’ value) for each colour are estimated from the data, and are plotted graphically against the corresponding threshold values (i.e. ‘directing’ value). The inverse relationship appears to be a regular one, for the points all fall on a smooth curve. 9. 9. These findings can all be explained by a Lorenzian hydraulic type of model. Various versions of the model have been simulated, and the parameters of one version adjusted to achieve a precise fit to the gull data.

Voltage-Controlled Oscillators: Inexpensive Alternative to Analog-to-Digital Converters

We describe a simple software mimic of an analog-to-digital (A/D) converter that is suitable for most laboratory applications requiring A/D. The routine samples output from a voltage-controlled oscillator that can be built for around

The evolution of altruism – what matters is gene selection

6. Results of proving trials show the output to be linear and sampling rates of up to 50/sec are possible.

Die unsterblichen Spiralen

Edward Wilson is the worlds leading expert on social insects, but he errs when he discards kin selection as an explanation for sociality

Nette Kerle kommen zuerst ans Ziel

Wir sind Uberlebensmaschinen, aber mit dem Wort „wir“ sind nicht nur wir Menschen gemeint. Es umfast alle Tiere, Pflanzen, Bakterien und Viren. Die Gesamtzahl der Uberlebensmaschinen ist schwer zu zahlen, und selbst die genaue Zahl von Arten ist unbekannt. Nehmen wir nur allein die Insekten: die Zahl der rezenten Arten ist auf ungefahr drei Millionen geschatzt worden, und die Zahl der einzelnen Insekten betragt vielleicht eine Trillion.