\documentclass[a4paper,10pt]{article}


%opening
\title{From the "Selfish Gene" by Richard Dawkins}
\author{archive.org/stream/TheSelfishGene/RichardDawkins-TheSelfishGene-$djvu.txt$}

\begin{document}

\maketitle


................

Suppose a species of bird is parasitized by a particularly nasty kind of 
tick which carries a dangerous disease. It is very important that these 
ticks should be removed as soon as possible. Normally an individual bird 
can pull off its owns ticks when preening itself. There is one place, 
however-the top of the head -which it cannot reach with its own bill. The 
solution to the problem quickly occurs to any human. An individual may 
not be able to reach his own head, but nothing is easier than for a friend 
to do it for him. Later, when the friend is parasitized himself, the good 
deed can be paid back. Mutual grooming is in fact very common in both 
birds and mammals. 


This makes immediate intuitive sense. Anybody with conscious foresight 
can see that it is sensible to enter into mutual back-scratching 
arrangements. But we have learnt to beware of what seems intuitively 
sensible. The gene has no foresight. Can the theory of selfish genes 
account for mutual back-scratching, or 'reciprocal altruism', where there 
is a delay between good deed and repayment? Williams briefly discussed 
the problem in his 1966 book, to which I have already referred. He 
concluded, as had Darwin, that delayed reciprocal altruism can evolve in 
species that are capable of recognizing and remembering each other as 
individuals. Trivers, in 1971, took the matter further. When he wrote, he 
did not have available to him Maynard Smith's concept of the 
evolutionarily stable strategy. If he had, my guess is that he would have 
made use of it, for it provides a natural way to express his ideas. His 
reference to the 'Prisoner's Dilemma'-a favourite puzzle in game theory- 
shows that he was already thinking along the same lines. 

Suppose B has a parasite on the top of his head. A pulls it off him. Later, 
the time comes when A has a parasite on his head. He naturally seeks 
out B in order that B may pay back his good deed. B simply turns up his 
nose and walks off. B is a cheat, an individual who accepts the benefit of 
other individuals' altruism, but who does not pay it back, or who pays it 
back insufficiently. Cheats do better than indiscriminate altruists 
because they gain the benefits without paying the costs. To be sure, the 
cost of grooming another individual's head seems small compared with 
the benefit of having a dangerous parasite removed, but it is not 
negligible. Some valuable energy and time has to be spent. 


Let the population consist of individuals who adopt one of two strategies. 
As in Maynard Smith's analyses, we are not talking about conscious 
strategies, but about unconscious behaviour programs laid down by 
genes. Call the two strategies Sucker and Cheat. Suckers groom anybody 
who needs it, indiscriminately. Cheats accept altruism from suckers, but 
they never groom anybody else, not even somebody who has previously 
groomed them. As in the case of the hawks and doves, we arbitrarily 
assign pay-off points. It does not matter what the exact values are, so 
long as the benefit of being groomed exceeds the cost of grooming. If the 
incidence of parasites is high, any individual sucker in a population of 
suckers can reckon on being groomed about as often as he grooms. The 
average pay-off for a sucker among suckers is therefore positive. They all 
do quite nicely in fact, and the word sucker seems inappropriate. But 
now suppose a cheat arises in the population. Being the only cheat, he 
can count on being groomed by everybody else, but he pays nothing in 
return. His average pay-off is better than the average for a sucker. 

Cheat 
genes will therefore start to spread through the population. Sucker genes 
will soon be driven to extinction. This is because, no matter what the 
ratio in the population, cheats will always do better than suckers. For 
instance, consider the case when the population consists of 50 per cent 
suckers and 50 per cent cheats. The average pay-off for both suckers and 
cheats will be less than that for any individual in a population of 100 per 
cent suckers. But still, cheats will be doing better than suckers because 
they are getting all the benefits-such as they are-and paying nothing 
back. When the proportion of cheats reaches 90 per cent, the average 
pay-off for all individuals will be very low: many of both types may by 
now be dying of the infection carried by the ticks. But still the cheats will 
be doing better than the suckers. Even if the whole population declines 
toward extinction, there will never be any time when suckers do better 
than cheats. Therefore, as long as we consider only these two strategies, 
nothing can stop the extinction of the suckers and, very probably, the 
extinction of the whole population too. 


But now, suppose there is a third strategy called Grudger. Grudgers 
groom strangers and individuals who have previously groomed them. 
However, if any individual cheats them, they remember the incident and 
bear a grudge: they refuse to groom that individual in the future. In a 
population of grudgers and suckers it is impossible to tell which is which. 
Both types behave altruistically towards everybody else, and both earn 
an equal and high average pay-off. In a population consisting largely of 
cheats, a single grudger would not be very successful. He would expend a 
great deal of energy grooming most of the individuals he met- for it would 
take time for him to build up grudges against all of them. On the other 
hand, nobody would groom him in return. If grudgers are rare in 
comparison with cheats, the grudger gene will go extinct. Once the 
grudgers manage to build up in numbers so that they reach a critical 
proportion, however, their chance of meeting each other becomes 
sufficiently great to off-set their wasted effort in grooming cheats. When 
this critical proportion is reached they will start to average a higher pay- 
off than cheats, and the cheats will be driven at an accelerating rate 
towards extinction. When the cheats are nearly extinct their rate of 
decline will become slower, and they may survive as a minority for quite 
a long time. This is because for any one rare cheat there is only a small 
chance of his encountering the same grudger twice: therefore the 
proportion of individuals in the population who bear a grudge against any given cheat will be small. 

archive.org/stream/TheSelfishGene/RichardDawkins-TheSelfishGene-djvu.txt





\end{document}
