Altruism

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Biological Altruism

 

In evolutionary biology, an organism is said to behave altruistically

when its behaviour benefits other organisms, at a cost to itself. The

costs and benefits are measured in terms of reproductive fitness, or

expected number of offspring. So by behaving altruistically, an

organism reduces the number of offspring it is likely to produce

itself, but boosts the number that other organisms are likely to

produce. This biological notion of altruism is not identical to the

everyday concept. In everyday parlance, an action would only be called

& #8216;altruistic & #8217; if it was done with the conscious intention of helping

another. But in the biological sense there is no such requirement.

Indeed, some of the most interesting examples of biological altruism

are found among creatures that are (presumably) not capable of

conscious thought at all, e.g. insects. For the biologist, it is the

consequences of an action for reproductive fitness that determine

whether the action counts as altruistic, not the intentions, if any,

with which the action is performed.

 

Altruistic behaviour is common throughout the animal kingdom,

particularly in species with complex social structures. For example,

vampire bats regularly regurgitate blood and donate it to other

members of their group who have failed to feed that night, ensuring

they do not starve. In numerous bird species, a breeding pair receives

help in raising its young from other & #8216;helper & #8217; birds, who protect the

nest from predators and help to feed the fledglings. Vervet monkeys

give alarm calls to warn fellow monkeys of the presence of predators,

even though in doing so they attract attention to themselves,

increasing their personal chance of being attacked. In social insect

colonies (ants, wasps, bees and termites), sterile workers devote

their whole lives to caring for the queen, constructing and protecting

the nest, foraging for food, and tending the larvae. Such behaviour is

maximally altruistic: sterile workers obviously do not leave any

offspring of their own -- so have personal fitness of zero -- but

their actions greatly assist the reproductive efforts of the queen.

 

From a Darwinian viewpoint, the existence of altruism in nature is at

first sight puzzling, as Darwin himself realized. Natural selection

leads us to expect animals to behave in ways that increase their own

chances of survival and reproduction, not those of others. But by

behaving altruistically an animal reduces its own fitness, so should

be at a selective disadvantage vis- & #224;-vis one which behaves selfishly.

To see this, imagine that some members of a group of Vervet monkeys

give alarm calls when they see predators, but others do not. Other

things being equal, the latter will have an advantage. By selfishly

refusing to give an alarm call, a monkey can reduce the chance that it

will itself be attacked, while at the same time benefiting from the

alarm calls of others. So we should expect natural selection to favour

those monkeys that do not give alarm calls over those that do. But

this raises an immediate puzzle. How did the alarm-calling behaviour

evolve in the first place, and why has it not been eliminated by

natural selection? How can the existence of altruism be reconciled

with basic Darwinian principles?

 

1. Altruism and the Levels of Selection

 

The problem of altruism is intimately connected with questions about

the level at which natural selection acts. If selection acts

exclusively at the individual level, favouring some individual

organisms over others, then altruism cannot evolve, for behaving

altruistically is disadvantageous for the individual organism itself,

by definition. However, it is possible that altruism may be

advantageous at the group level. A group containing lots of altruists,

each ready to subordinate their own selfish interests for the greater

good of the group, may well have a survival advantage over a group

composed mainly or exclusively of selfish organisms. A process of

between-group selection may thus allow the altruistic behaviour to

evolve. Within each group, altruists will be at a selective

disadvantage relative to their selfish colleagues, but the fitness of

the group as a whole will be enhanced by the presence of altruists.

Groups composed only or mainly of selfish organisms go extinct,

leaving behind groups containing altruists. In the example of the

Vervet monkeys, a group containing a high proportion of alarm-calling

monkeys will have a survival advantage over a group containing a lower

proportion. So conceivably, the alarm-calling behaviour may evolve by

between-group selection, even though within each group, individual

selection favours monkeys that do not give alarm calls.

 

The idea that group selection might explain the evolution of altruism

was first broached by Darwin himself. In The Descent of Man (1871),

Darwin discussed the origin of altruistic and self-sacrificial

behaviour among humans. Such behaviour is obviously disadvantageous at

the individual level, as Darwin realized: & #8220;he who was ready to

sacrifice his life, as many a savage has been, rather than betray his

comrades, would often leave no offspring to inherit his noble nature & #8221;

(p.163). Darwin then argued that self-sarcrificial behaviour, though

disadvantageous for the individual & #8216;savage & #8217;, might be beneficial at

the group level: & #8220;a tribe including many members who...were always

ready to give aid to each other and sacrifice themselves for the

common good, would be victorious over most other tribes; and this

would be natural selection & #8221; (p.166). Darwin's suggestion is that the

altruistic behaviour in question may have evolved by a process of

between-group selection.

 

The concept of group selection has a chequered and controversial

history in evolutionary biology. The founders of modern neo-Darwinism

-- R.A. Fisher, J.B.S. Haldane and S. Wright -- were all aware that

group selection could in principle permit altruistic behaviours to

evolve, but they doubted the importance of this evolutionary

mechanism. Nonetheless, many mid-twentieth century ecologists and some

ethologists, notably Konrad Lorenz, routinely assumed that natural

selection would produce outcomes beneficial for the whole group or

species, often without even realizing that individual-level selection

guarantees no such thing. This uncritical & #8216;good of the species & #8217;

tradition came to an abrupt halt in the 1960s, due largely to the work

of G.C. Williams (1966) and J. Maynard Smith (1964). These authors

argued that group selection was an inherently weak evolutionary force,

hence unlikely to promote interesting altruistic behaviours. This

conclusion was supported by a number of mathematical models, which

apparently showed that group selection would only have significant

effects for a limited range of parameter values. As a result, the

notion of group selection fell into widespread disrepute in orthodox

evolutionary circles. In recent years the position has changed

somewhat; a number of biologists have argued that group selection was

wrongly rejected in the 1960s, and that it is an important explanatory

principle after all, though this is still probably a minority view.

See Sober and Wilson (1998) for further details of this fascinating

controversy.

 

The major weakness of group selection as an explanation of altruism,

according to the consensus that emerged in the 1960s, was a problem

that Dawkins (1976) called & #8216;subversion from within & #8217;; see also

Maynard

Smith (1964). Even if altruism is advantageous at the group level,

within any group altruists are liable to be exploited by selfish

& #8216;free-riders & #8217; who refrain from behaving altruistically. These

free-riders will have an obvious fitness advantage: they benefit from

the altruism of others, but do not incur any of the costs. So even if

a group is composed exclusively of altruists, all behaving nicely

towards each other, it only takes a single selfish mutant to bring an

end to this happy idyll. By virtue of its relative fitness advantage

within the group, the selfish mutant will out-reproduce the altruists,

hence selfishness will eventually swamp altruism. Since the generation

time of individual organisms is likely to be much shorter than that of

groups, the probability that a selfish mutant will arise and spread is

very high, according to this line of argument. & #8216;Subversion from

within & #8217; is generally regarded as the major stumbling block for

group-selectionist theories of the evolution of altruism.

 

If group selection is not the correct explanation for how the

altruistic behaviours found in nature evolved, then what is? In the

1960s and 1970s two alternative theories emerged: kin selection or

& #8216;inclusive fitness & #8217; theory, due to Hamilton (1964), and the theory

of

reciprocal altruism, due primarily to Trivers (1971) and Maynard Smith

(1974). These theories, which are discussed in detail below,

apparently showed how altruistic behaviour could evolve without the

need for group selection; they quickly gained prominence among

biologists interested in the evolution of social behaviour. However,

the precise relation between these theories and the older idea of

group selection is a source of ongoing controversy. Some authors argue

that kin selection and evolutionary game theory are in fact special

cases of group selection, rather than alternatives to it, and that the

widespread dismissal of group selection in the 1960s was therefore

mistaken (Sober and Wilson (1998); see Maynard Smith (1998) for an

alternative view.) Whatever the correct resolution of this issue, the

fact remains that kin selection and reciprocal altruism were widely

seen as alternatives to group selection, rightly or not, and their

success contributed to the fall from grace of the latter.

2. Kin Selection and Inclusive Fitness

 

The basic idea of kin selection is simple. Imagine a gene which causes

its bearer to behave altruistically towards other organisms, e.g. by

sharing food with them. Organisms without the gene are selfish -- they

keep all their food for themselves, and sometimes get handouts from

the altruists. Clearly the altruists will be at a fitness

disadvantage, so we should expect the altruistic gene to be eliminated

from the population. However, suppose that altruists are

discriminating in who they share food with. They do not share with

just anybody, but only with their relatives. This immediately changes

things. For relatives are genetically similar -- they share genes with

one another. So when an organism carrying the altruistic gene shares

his food, there is a certain probability that the recipients of the

food will also carry copies of that gene. (How probable depends on how

closely related they are.) This means that the altruistic gene can in

principle spread by natural selection. The gene causes an organism to

behave in a way which reduces its own fitness but boosts the fitness

of its relatives -- who have a greater than average chance of carrying

the gene themselves. So the overall effect of the behaviour may be to

increase the number of copies of the altruistic gene found in the next

generation, and thus the incidence of the altruistic behaviour itself.

 

Though this argument was hinted at by Haldane in the 1930s, it was

first made explicit by William Hamilton (1964) in a pair of seminal

papers. Hamilton demonstrated rigorously that an altruistic gene will

be favoured by natural selection when a certain condition, known as

Hamilton's rule, is satisfied. In its simplest version, the rule

states that b > c/r, where c is the cost incurred by the altruist (the

donor), b is the benefit received by the recipients of the altruism,

and r is the co-efficient of relationship between donor and recipient.

The costs and benefits are measured in terms of reproductive fitness.

The co-efficient of relationship depends on the genealogical relation

between donor and recipient -- it is defined as the probability that

donor and recipient share genes at a given locus that are & #8216;identical

by descent & #8217;. (Two genes are identical by descent if they are copies of

a single gene in a shared ancestor.) In a sexually reproducing diploid

species, the value of r for full siblings is & #189;, for parents and

offspring & #189;, for grandparents and grandoffspring & #188;, for full cousins

1/8, and so-on. The higher the value of r, the greater the

probability that the recipient of the altruistic behaviour will also

possess the gene for altruism. So what Hamilton's rule tells us is

that a gene for altruism can spread by natural selection, so long as

the cost incurred by the altruist is offset by a sufficient amount of

benefit to sufficiently closed related relatives. The proof of

Hamilton's rule relies on certain non-trivial assumptions; see Frank

(1998), Grafen (1985) or Michod (1982) for details.

 

Though Hamilton himself did not use the term, his idea quickly became

known as & #8216;kin selection & #8217;, for obvious reasons. Kin selection theory

predicts that animals are more likely to behave altruistically towards

their relatives than towards unrelated members of their species.

Moreover, it predicts that the degree of altruism will be greater, the

closer the relationship. In the years since Hamilton's theory was

devised, these predictions have been amply confirmed by empirical

work. For example, in various bird species, it has been found that

& #8216;helper & #8217; birds are much more likely to help relatives raise their

young, than they are to help unrelated breeding pairs. Similarly,

studies of Japanese macaques have shown that altruistic actions, such

as defending others from attack, tend to be preferentially directed

towards close kin. In most social insect species, a peculiarity of the

genetic system known as & #8216;haplodiploidy & #8217; means that females on

average

share more genes with their sisters than with their own offspring. So

a female may well be able to get more genes into the next generation

by helping the queen reproduce, hence increasing the number of sisters

she will have, rather than by having offspring of her own. Kin

selection theory therefore provides a neat explanation of how

sterility in the social insects may have evolved by Darwinian means.

(Note, however, that the precise significance of haplodiploidy for the

evolution of worker sterility is a controversial question; see Maynard

Smith and Szathmary (1995) ch.16.)

 

Kin selection theory is often presented as a triumph of the

& #8216;gene's-eye view of evolution & #8217;, which sees organic evolution as the

result of competition among genes for increased representation in the

gene-pool, and individual organisms as mere & #8216;vehicles & #8217; that genes

have

constructed to aid their propagation (Dawkins (1976), (1982)). The

gene's eye-view is certainly the easiest way of understanding kin

selection, and was employed by Hamilton himself in his 1964 papers.

Altruism seems anomalous from the individual organism's point of view,

but from the gene's point of view it makes good sense. A gene wants to

maximize the number of copies of itself that are found in the next

generation; one way of doing that is to cause its host organism to

behave altruistically towards other bearers of the gene, so long as

the costs and benefits satisfy the Hamilton inequality. But

interestingly, Hamilton showed that kin selection can also be

understood from the organism's point of view. Though an altruistic

behaviour which spreads by kin selection reduces the organism's

personal fitness (by definition), it increases what Hamilton called

the organism's inclusive fitness. An organism's inclusive fitness is

defined as its personal fitness, plus the sum of its weighted effects

on the fitness of every other organism in the population, the weights

determined by the coefficient of relationship r. Given this

definition, natural selection will act to increase the inclusive

fitness of individuals in the population. Instead of thinking in terms

of selfish genes trying to maximize their future representation in the

gene-pool, we can think in terms of organisms' trying to maximize

their inclusive fitness. Most people find the & #8216;gene's eye & #8217; approach

to

kin selection heuristically simpler than the inclusive fitness

approach, but mathematically they are in fact equivalent (Michod

(1982), Frank (1998), Hamilton (1996)).

 

Contrary to what is sometimes thought, kin selection does not require

that animals must have the ability to discriminate relatives from

non-relatives, less still to calculate coefficients of relationship.

Many animals can in fact recognize their kin, often by smell, but kin

selection can operate in the absence of such an ability. Hamilton's

inequality can be satisfied so long as an animal behaves

altruistically towards others animals that are in fact its relatives.

The animal might achieve this by having the ability to tell relatives

from non-relatives, but this is not the only possibility. An

alternative is to use some proximal indicator of kinship. For example,

if an animal behaves altruistically towards those in its immediate

vicinity, then the recipients of the altruism are likely to be

relatives, given that relatives tend to live near each other. No

ability to recognize kin is presupposed. Cuckoos exploit precisely

this fact, free-riding on the innate tendency of birds to care for the

young in their nests.

 

Another popular misconception is that kin selection theory is

committed to & #8216;genetic determinism & #8217;, the idea that genes rigidly

determine or control behaviour. Though some sociobiologists have made

incautious remarks to this effect, evolutionary theories of behaviour,

including kin selection, are not committed to it. So long as the

behaviours in question have a genetical component, i.e. are influenced

to some extent by one or more genetic factor, then the theories can

apply. When Hamilton (1964) talks about a gene which & #8216;causes & #8217;

altruism, this is really shorthand for a gene which increases the

probability that its bearer will behave altruistically, to some

degree. This is much weaker than saying that the behaviour is

genetically & #8216;determined & #8217;, and is quite compatible with the existence

of strong environmental influences on the behaviour's expression. Kin

selection theory does not deny the truism that all traits are affected

by both genes and environment. Nor does it deny that many interesting

animal behaviours are transmitted through non-genetical means, such as

imitation and social learning (Avital and Jablonka (2000)).

 

The importance of kinship for the evolution of altruism is very widely

accepted today, on both theoretical and empirical grounds. However,

kinship is really only a way of ensuring that altruists and recipients

both carry copies of the altruistic gene, which is the fundamental

requirement. If altruism is to evolve, it must be the case that the

recipients of altruistic actions have a greater than average

probability of being altruists themselves. Kin-directed altruism is

the most obvious way of satisfying this condition, but there are other

possibilities too (Hamilton (1975), Sober and Wilson (1998)). For

example, if the gene that causes altruism also causes animals to

favour a particular feeding ground (for whatever reason), then the

required correlation between donor and recipient may be generated. It

is this correlation, however brought about, that is necessary for

altruism to evolve. This point was noted by Hamilton himself in the

1970s: he stressed that the coefficient of relationship of his 1964

papers should really be replaced with a more general correlation

coefficient, which reflects the probability that altruist and

recipient share genes, whether because of kinship or not (Hamilton

(1970), (1972), (1975)). This point is theoretically important, and

has not always been recognized; but in practice, kinship remains the

most important source of statistical associations between altruists

and recipients.

3. Reciprocal Altruism and the Prisoner's Dilemma

 

Though much altruism in nature is kin-directed, not all is: there are

also many examples of animals behaving altruistically towards

non-relatives, and indeed towards members of other species. Kin

selection theory cannot help us understand these behaviours. The

theory of reciprocal altruism, developed by Trivers (1971), is one

attempt to explain the evolution of altruism among non-kin. The basic

idea is straightforward: it may benefit an animal to behave

altruistically towards another, if there is an expectation of the

favour being returned in the future. ( & #8216;If you scratch my back, I'll

scratch yours & #8217;.) The cost to the animal of behaving altruistically is

offset by the likelihood of this return benefit, permitting the

behaviour to evolve by natural selection. For obvious reasons, this

evolutionary mechanism is termed & #8216;reciprocal altruism & #8217;.

 

For reciprocal altruism to work, there is no need for the two

individuals to be relatives, nor even to be members of the same

species. However, it is necessary that individuals should interact

with each more than once, and have the ability to recognize other

individuals with whom they have interacted in the past.[1] If

individuals interact only once in their lifetimes and never meet

again, there is obviously no possibility of return benefit, so there

is nothing to be gained by behaving altruistically. However, if

individuals encounter each other frequently, and are capable of

identifying and punishing & #8216;cheaters & #8217; who have refused to behave

altruistically in the past, then reciprocal altruism can evolve. A

non-altruistic cheater will have a lower fitness than an altruist

because, although he does not incur the cost of behaving

altruistically himself, he forfeits the return benefits too -- others

will not behave altruistically towards him in the future. This

evolutionary mechanism is most likely to work where animals live in

relatively small groups, increasing the likelihood of multiple

encounters and making cheating harder to get away with.

 

The concept of reciprocal altruism is closely related to the

Tit-for-Tat strategy in the well-known & #8216;Prisoner's Dilemma & #8217; game

from

game theory. In this game, players interact in pairs and may adopt one

of two possible strategies: cooperate © or defect (D). The payoffs

to each player, which in this context can be thought of as increments

of reproductive fitness, depend not only their own strategy but also

on their opponent's. Payoff values are shown in the matrix below. (The

actual numbers used in the payoff matrix are not important; it is only

the inequalities that matter.)

 

Player 1

Cooperate Defect

Player 2 Cooperate 11 0

Defect 20 5

Payoffs for Player 1 in units of reproductive fitness

 

If players are pitted against each other only once, then the optimal

strategy is obviously to defect -- whatever one's opponent does,

defecting pays better than cooperating (20 versus 11 if one's opponent

cooperates, 5 versus 0 if he defects). So if players meet only once,

there is no way that cooperative behaviour can evolve -- natural

selection will favour the defectors and any co-operators will

eventually be eliminated from the population. However, if players are

pitted against each many times over, and can adjust their strategy

depending on their opponent's past behaviour, things are more

complicated. In this so-called & #8216;iterated Prisoner's Dilemma & #8217;, always

defecting is not necessarily the best option. Indeed, Axelrod and

Hamilton (1981) have shown that the Tit-for-Tat strategy in fact

yields the highest payoff, so long as the probability of future

encounters is sufficiently high. In Tit-For-Tat, a player follows two

basic rules: (i) on the first encounter, cooperate; (ii) on subsequent

encounters, do what your opponent did on the previous encounter. If

all the individuals in a population play Tit-for-Tat, then no

alternative strategy, such as & #8216;always defect & #8217;, will be able to

invade;

Tit-for-Tat is therefore an & #8216;evolutionarily stable strategy & #8217;

(Maynard

Smith (1982)).

 

The relevance of this result for the evolution of reciprocal altruism

is readily apparent. Co-operating in the Prisoner's Dilemma game

corresponds to behaving altruistically, while defecting corresponds to

behaving selfishly. The Axelrod and Hamilton result provides a

rigorous foundation for the intuitive idea that behaving

altruistically may be selectively advantageous for an organism where

there is an expectation of return benefit in the future. So long as

organisms interact with each other on multiple occasions, and are

capable of adjusting their behaviour depending on what other organisms

have done in the past, reciprocal altruism can in principle evolve.

 

Theoretical considerations therefore show that reciprocation of

benefits is a possible mechanism for the spread of altruism, but what

about the empirical evidence? A well-known study of blood-sharing

among vampire bats by G. Wilkinson suggests that reciprocation does

indeed play a role in the evolution of this behaviour (in addition to

kinship) (Wilkinson (1984), (1990)). It is quite common for a vampire

bat to fail to feed on a given night. This is potentially fatal, for

bats die if they go without food for more than a couple of days. On

any given night, bats donate blood (by regurgitation) to other members

of their group who have failed to feed, thus saving them from

starvation. Since vampire bats live in small groups and associate with

each other over long periods of time, the preconditions for reciprocal

altruism -- multiple encounters and individual recognition -- are

likely to be met. Wilkinson's study showed that bats tended to share

food with their close associates, and were more likely to share with

others that had recently shared with them. These findings provide a

striking confirmation of reciprocal altruism theory.

 

Trivers (1985) describes a remarkable case of reciprocal altruism

between organisms of different species, a phenomenon known as

& #8216;mutualism & #8217; or & #8216;synergism & #8217;. On tropical coral reefs,

various species

of small fish act as & #8216;cleaners & #8217; for large fish, removing parasites

from their mouths and gills. This is not pure altruism on the part of

the cleaners, for they feed on the parasites which they remove. So the

interaction is mutually beneficial -- the large fish gets cleaned and

the cleaner gets fed. However, Trivers notes that the large fish

sometimes behave altruistically towards the cleaners. If a large fish

is attacked by a predator while it has a cleaner in its mouth, then it

waits for the cleaner to leave before fleeing the predator. This is

clearly altruistic -- surely the large fish would be better off just

swallowing the cleaner and fleeing straight away? Trivers explains the

larger fish's behaviour in terms of reciprocal altruism. Since the

large fish often returns to the same cleaner many times over, it pays

to look after the cleaner's welfare, i.e. not to swallow it, even if

this increases the chance of being wounded by a predator. In short,

the larger fish behaves altruistically towards the cleaner, by

allowing him to escape before fleeing, because there is an expectation

of return benefit -- getting cleaned again in the future. As in the

case of the vampire bats, it is because the large fish and the cleaner

interact more than once that reciprocal altruism can evolve.

4. But is it & #8216;Real & #8217; Altruism?

 

The theories of kin selection and reciprocal altruism together go a

long way towards reconciling the existence of altruism in nature with

Darwinian principles. Indeed kin selection theory, in particular, is

generally regarded as one of the triumphs of 20th century evolutionary

biology. However, some people have felt these theories in a way

devalue altruism, and that the behaviours they explain are not

& #8216;really & #8217; altruistic. The grounds for this view are easy to see.

Ordinarily we think of altruistic actions as disinterested, done with

the interests of the recipient, rather than our own interests, in

mind. But kin selection theory explains altruistic behaviour as a

clever strategy devised by selfish genes as a way of increasing their

representation in the gene-pool, at the expense of other genes. Surely

this means that the behaviours in question are only & #8216;apparently & #8217;

altruistic, for they are ultimately the result of genic self-interest?

Reciprocal altruism theory also seems to & #8216;take the altruism out of

altruism & #8217;. Behaving nicely to someone in order to procure return

benefits from them in the future seems in a way the antithesis of

& #8216;real & #8217; altruism -- it is just delayed self-interest.

 

This is a tempting line of argument. Indeed Trivers (1971) and,

arguably, Dawkins (1976) were themselves tempted by it. But it should

not convince. The key point to remember is that biological altruism

cannot be equated with altruism in the everyday vernacular sense.

Biological altruism is defined in terms of fitness consequences, not

motivating intentions. If by & #8216;real & #8217; altruism we mean altruism done

with the conscious intention to help, then the vast majority of living

creatures are not capable of & #8216;real & #8217; altruism nor therefore of

& #8216;real & #8217;

selfishness either. Ants and termites, for example, presumably do not

have conscious intentions, hence their behaviour cannot be done with

the intention of promoting their own self-interest, nor the interests

of others. Thus the assertion that the evolutionary theories reviewed

above show that the altruism in nature is only apparent makes little

sense. The contrast between & #8216;real & #8217; altruism and merely apparent

altruism simply does not apply to most animal species.

 

To some extent, the idea that kin-directed and reciprocal altruism are

not & #8216;real & #8217; altruism has been fostered by the use of the

& #8216;selfish gene & #8217;

terminology of Dawkins (1976). As we have seen, the gene's-eye

perspective is heuristically useful for understanding the evolution of

altruistic behaviours, especially those that evolve by kin selection.

But talking about & #8216;selfish & #8217; genes trying to increase their

representation in the gene-pool is of course just a metaphor (as

Dawkins fully admits); there is no literal sense in which genes

& #8216;try & #8217;

to do anything. Any evolutionary explanation of how a phenotypic trait

evolves must ultimately show that the trait leads to an increase in

frequency of the genes that code for it (presuming the trait is

transmitted genetically.) Therefore, a & #8216;selfish gene & #8217; story can by

definition be told about any trait, including a behavioural trait,

that evolves by Darwinian natural selection. To say that kin selection

interprets altruistic behaviour as a strategy designed by & #8216;selfish & #8217;

genes to aid their propagation is not wrong; but it is just another

way of saying that a Darwinian explanation for the evolution of

altruism has been found. As Sober and Wilson (1998) note, if one

insists on saying that behaviours which evolve by mechanism such as

kin selection and reciprocal altruism are & #8216;really selfish & #8217;, one ends

up reserving the word & #8216;altruistic & #8217; for behaviours which cannot

evolve

at all.

 

Do the theories of kin selection and reciprocal altruism apply to

human behaviour? This is part of the broader question of whether ideas

about the evolution of animal behaviour can be extrapolated to humans,

a question that fuelled the sociobiology controversy of the 1980s. All

biologists accept that Homo sapiens is an evolved species, and thus

that general evolutionary principles apply to it. However, human

behaviour is obviously influenced by culture to a far greater extent

than that of other animals, and is often the product of conscious

beliefs and desires (though this does not necessarily mean that

genetics has no influence.) Nonetheless, at least some human behaviour

does seem to fit the predictions of the evolutionary theories reviewed

above. In general, humans behave more altruistically (in the

biological sense) towards their close kin that towards non-relatives,

e.g. by helping relatives raise their children, just as kin selection

theory would predict. It is also true that we tend to help those who

have helped us out in the past, just as reciprocal altruism theory

would predict. On the other hand, numerous human behaviours seem

anomalous from the evolutionary point of view. Think for example of

adoption. Parents who adopt children instead of having their own

reduce their biological fitness, obviously, so adoption is an

altruistic behaviour. But it is does not benefit kin -- for parents

are generally unrelated to the infants they adopt -- and nor do the

parents stand to gain much in the form of reciprocal benefits. So

although kin selection and reciprocal altruism may help us understand

some human behaviours, they certainly cannot be applied across the board.

 

Where human behaviour is concerned, the distinction between biological

altruism, defined in terms of fitness consequences, and & #8216;real & #8217;

altruism, defined in terms of the agent's conscious intentions to help

others, does make sense. (Sometimes the label & #8216;psychological

altruism & #8217;

is used instead of & #8216;real & #8217; altruism.) What is the relationship

between

these two concepts? They appear to be independent in both directions,

as Elliott Sober (1994) has argued. An action performed with the

conscious intention of helping another human being may not affect

their biological fitness at all, so would not count as altruistic in

the biological sense. Conversely, an action undertaken for purely

self-interested reasons, i.e. without the conscious intention of

helping another, may boost their biological fitness tremendously.

 

Sober argues that, even if we accept an evolutionary approach to human

behaviour, there is no particular reason to think that evolution would

have made humans into egoists rather than psychological altruists. On

the contrary, it is quite possible that natural selection would have

favoured humans who genuinely do care about helping others, i.e. who

are capable of & #8216;real & #8217; or psychological altruism. Suppose there is an

evolutionary advantage associated with taking good care of one's

children -- a quite plausible idea. Then, parents who really do care

about their childrens' welfare, i.e. who are & #8216;real & #8217; altruists, will

have a higher inclusive fitness, hence spread more of their genes,

than parents who only pretend to care, or who do not care. Therefore,

evolution may well lead & #8216;real & #8217; or psychological altruism to evolve.

Contrary to what is often thought, an evolutionary approach to human

behaviour does not imply that humans are likely to be motivated by

self-interest alone. One strategy by which & #8216;selfish genes & #8217; may

increase their future representation is by causing humans to be

non-selfish, in the psychological sense.

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