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 fitnessor 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 "Asexual reproduction cuttings definition of empathy" is not identical to the everyday concept. 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.
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. Asexual reproduction cuttings definition of empathy 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.
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 termitessterile 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: 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.
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 Asexual reproduction cuttings definition of empathy 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?
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 it seems that 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 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, 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 ManDarwin discussed the origin of altruistic and self-sacrificial behaviour among humans. Such behaviour is obviously disadvantageous at the individual level, as Darwin realized: Darwin's suggestion is that the altruistic behaviour in question may have evolved by a process of Asexual reproduction cuttings definition of empathy selection.
The concept of group selection has a chequered and controversial history in evolutionary biology. The founders of modern neo-Darwinism—R.
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.
Williams and J. 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; see Sober and WilsonSegestraleOkashaLeigh and Asexual reproduction cuttings definition of empathy for details of the history of this debate. These free-riders will have an obvious fitness advantage: So even if a group Asexual reproduction cuttings definition of empathy 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. If group selection is not the correct explanation for how the altruistic behaviours found in nature evolved, then what is? In the s and s a rival theory emerged: This theory, discussed in detail below, apparently showed how altruistic behaviour could evolve without the need for group-level selection, and quickly gained prominence among biologists interested in the evolution of social behaviour; the empirical success of kin selection theory contributed to the demise of the group selection concept.
However, the precise relation between kin and group selection is a source of ongoing controversy see for example the recent exchange in Nature between Nowak, Tarnita and Wilson and Abbot et. Sober and Wilson The basic idea of kin selection is simple. Imagine a gene which causes its bearer to behave altruistically towards other organisms, e. 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 Asexual reproduction cuttings definition of empathy closely related they are.