CONSCICE EXAMPLES OF COALITIONAL KILLING AND KIN SELECTION
�Coalitional killing� and �kin selection� are explained by Hamilton�s 1975 theory of “inclusive fitness” and Dawkins’ “selfish genes.”
The “coalitional killing” of members of neighboring groups occurs regularly in humans, wolves and chimpanzees. Selection favors components of inter group aggression important to human warfare, including lethal raiding.
“Kin Selection” is the evolutionary strategy that favors the reproductive success of an organism's relatives, even at a cost to the organism's own survival and reproduction. Scientists have found strong empirical support for kin selection.
Here is the basic outline: Genes cooperate to build cells, which cooperate to build bodies, which cooperate to form groups, which kill other groups and disperse themselves into the environment.
Here is a hypothetical example: A cooperating group of men called “A” outgrows its natural resources and attacks a smaller group of people called “B”for its natural resources and women.
The men from group A attack and kill the group B men, rape the group B women and take them for slaves. Several men in group A were killed in the battle but their kin live to reproduce (Kin Selection).
Groups survive because they are able to cooperate for coalitional klling, which can be seen as an aspect of selfish gene behavior.
Jay & Ethan
MORE CHILDREN = MORE GENES
Assume that two groups of five mating pairs exist in a tribe of primitive people. Further assume that the abstract thinking ability is controlled by genes, and that this tribe loses 30% of its population every 20 years due to crop failure and famine.
GROUP #1. Each of the five pairs of this group can see the famine coming and decide to limit themselves to two children. After 20 years, this group has the 10 original adults plus ten children = 20 members.
GROUP #2. Each of the five pairs of this group can't imagine the coming famine and has ten children. After 20 years, this group has the 10 original adults plus fifty children = 60 members.
A famine kills 30% of the tribe which leaves group #1 with 14 members and group #2 with 42 members. This process crop of failure and famine repeats itself every 20 years until group #1 goes extinct.
An alternative scenario would have group #2 (the larger family) killing group #1, taking their share of the food, and possibly eating them too.
The ancestors of everyone alive today -- including you and me -- were selected by a process something like the one described above.
BEST STRATEGY = GROW FAST
The best way to survive in such a milieu is not to live in ecological balance with slow growth, but to grow rapidly and be able to fend off competitors as well as take resources from others.
CONSTANT BATTLES: Why we Fight, Steven A. LeBlanc,St.Martin, 2004;
[pp. 73-75] Not only are human societies never alone, but regardless of how well they control their own population or act ecologically, they cannot control their neighbors' behavior. Each society must confront the real possibility that its neighbors will not live in ecological balance but will grow its numbers and attempt to take the resources from nearby groups. Not only have societies always lived in a changing environment, but they always have neighbors. The best way to survive in such a milieu is not to live in ecological balance with slow growth, but to grow rapidly and be able to fend off competitors as well as take resources from others.
To see how this most human dynamic works, imagine an extremely simple world with only two societies and no unoccupied land. Under normal conditions, neither group would have much motivation to take resources from the other. People may be somewhat hungry, but not hungry enough to risk getting killed in order to eat a little better. A few members of either group may die indirectly from food shortages---via disease or infant mortality, for example---but from an individual's perspective, he or she is much more likely to be killed trying to take food from the neighbors than from the usual provisioning shortfalls. Such a constant world would never last for long. Populations would grow and human activity would degrade the land or resources, reducing their abundance. Even if, by sheer luck, all things remained equal, it must be remembered that the climate would never be constant: Times of food stress occur because of changes in the weather, especially over the course of several generations. When a very bad year or series of years occurs, the willingness to risk a fight increases because the likelihood of starving goes up.
If one group is much bigger, better organized, or has better fighters among its members and the group faces starvation, the motivation to take over the territory of its neighbor is high, because it is very likely to succeed. Since human groups are never identical, there will always be some groups for whom warfare as a solution is a rational choice in any food crisis, because they are likely to succeed in getting more resources by warring on their neighbors.
Now comes the most important part of this overly simplified story: The group with the larger population always has an advantage in any competition over resources, whatever those resources may be. Over the course of human history, one side rarely has better weapons or tactics for any length of time, and most such warfare between smaller societies is attritional. With equal skills and weapons, each side would be expected to kill an equal number of its opponents. Over time, the larger group will finally overwhelm the smaller one. This advantage of size is well recognized by humans all over the world, and they go to great lengths to keep their numbers comparable to their potential enemies. This is observed anthropologically by the universal desire to have many allies, and the common tactic of smaller groups inviting other societies to join them, even in times of food stress.
Assume for a moment that by some miracle one of our two groups is full of farsighted, ecological geniuses. They are able to keep their population in check and, moreover, keep it far enough below the carrying capacity that minor changes in the weather, or even longer-term changes in the climate, do not result in food stress. If they need to consume only half of what is available each year, even if there is a terrible year, this group will probably come through the hardship just fine. More important, when a few good years come along, these masterfully ecological people will/not/grow rapidly, because to do so would mean that they would have trouble when the good times end. Think of them as the ecological equivalent of the industrious ants.
The second group, on the other hand, is just the opposite---it consists of ecological dimwits. They have no wonderful processes available to control their population. They are forever on the edge of the carrying capacity, they reproduce with abandon, and they frequently suffer food shortages and the inevitable consequences. Think of this bunch as the ecological equivalent of the carefree grasshoppers. When the good years come, they have more children and grow their population rapidly. Twenty years later, they have doubled their numbers and quickly run out of food at the first minor change in the weather. Of course, had this been a group of "noble savages" who eschewed warfare, they would have starved to death and only a much smaller and more sustainable group survived. This is not a bunch of noble savages; these are ecological dimwits and they attack their good neighbors in order to save their own skins. Since they now outnumber their good neighbors two to one, the dimwits prevail after heavy attrition on both sides. The "good" ants turn out to be dead ants, and the "bad" grasshoppers inherit the earth. The moral of this table is that if any group can get itself into ecological balance and stabilize its population even in the face of environmental change, it will be tremendously disadvantaged against societies that do not behave that way. The long-term successful society, in a world with many different societies, will be the one that grows when it can and fights when it runs out of resources. It is useless to live an ecologically sustainable existence in the "Garden of Eden" unless the neighbors do so as well. Only one nonconservationist society in an entire region can begin a process of conflict and expansion by the "grasshoppers" at the expense of the Eden-dwelling "ants." This smacks of a Darwinian competition---survival of the fittest---between societies. Note that the "fittest" of our two groups was not the more ecological, it was the one that grew faster. The idea of such Darwinian competition is unpalatable to many, especially when the "bad" folks appear to be the winners...
Using modern genetic approaches, a team of researchers has provided strong support for the long-standing, but hotly debated, evolutionary theory of kin selection, which suggests that altruistic behavior occurs as a way to pass genes to the next generation.
The researchers—who include Christina Grozinger, distinguished professor of entomology, and David Galbraith, postdoctoral scholar in entomology, both at Penn State; David Queller, Spencer T. Olin Professor, Washington University in St. Louis; and others—investigated kin selection by examining the social behavior of worker honey bees, which are all female.
They found that the genes the workers inherit from their queen—matrigenes —direct worker bees' altruistic behavior—forgoing production of their own offspring to help rear their siblings. When the queen dies, the workers can begin to selfishly compete with one another to lay eggs. The genes they inherit from their different fathers—patrigenes—direct this behavior.
"We usually think of honey bees as ideal cooperators, with all the members of the colony working together harmoniously," said Grozinger. "Our studies demonstrate that there is actually conflict—called intragenomic conflict—among the genes inherited from the father and those inherited from the mother."
According to Grozinger, in a normal colony, the queen lays all the eggs and the workers remain sterile and help raise the queen's offspring. When the queen dies, the workers either behave altruistically by remaining sterile and helping rear the remaining offspring and the new offspring of their sisters or they behave selfishly by activating their own ovaries and laying their own unfertilized eggs, which develop into males.
"In 2003, David Queller published a key model using kin selection theory that predicted that under queenless conditions in a honey bee colony, the patrigenes would promote selfish behavior in the workers, while the matrigenes would promote altruistic behavior," said Galbraith.
According to Queller, this conflict is the result of unequal distribution of the matrigenes and patrigenes among the workers. All the workers in the colony share the same set of matrigenes. In contrast, because the queen mated with 10 or more males, the workers have different patrigenes. If a worker behaves altruistically and helps rear her sisters' offspring, she ensures that her matrigenes are passed on. However, more of her patrigenes pass to the next generation if she behaves selfishly and lays her own eggs.
"It is very strange to think that your genes might be fighting with each other based on whether they came from your mother or your father," said Queller. "Yet, this is just what we found. It turns out that when a queen dies, worker bees behave the way their fathers want them to, producing sons when possible." The results appear today (Jan. 11) the Proceedings of the National Academy of Sciences.
According to Queller, this intragenomic conflict supports the theory of kin selection first proposed by William Hamilton in 1964. Altruism is defined as reducing one's own reproductive output to help others reproduce. So kin selection theory predicts that altruism will only evolve to help related individuals. Using kin selection theory, David Haig, professor, Harvard University, developed models predicting intragenomic conflict, which Queller then extended to social insect societies.
In 2010, however, biologist E.O. Wilson and colleagues published a paper that argued kin selection is not needed for altruistic behavior to evolve.
"While Queller's model made very specific predictions about the behavior of matrigenes and patrigenes in social insects, it was not possible to test this prediction until modern genomic tools were developed that allowed us to specifically track both matrigenes and patrigenes in the same individual," said Grozinger.
The researchers created 18 different male-female crosses of two different genetic stocks of honey bees—Africanized bees, which produce larger ovaries, and European bees, which produce smaller ovaries. The crosses enabled the workers to determine which of the genes—those from fathers versus those from mothers—were active in the offspring. The team housed the worker bee offspring without a queen, stimulating some to start producing eggs.
The researchers first demonstrated that worker bees with Africanized fathers and European mothers had larger ovaries and were more likely to become reproductively active than bees with European fathers and Africanized mothers. According to Grozinger, this demonstrated that the reproductive traits of the workers were more strongly influenced by their patrigenes than matrigenes.
"We identified more than 100,000 sections of DNA, called single nucleotide polymorphisms, that were present in the genomes of either the mother or the father, but not both," said Galbraith. "This exercise enabled us to determine which pieces of RNA in their worker offspring were produced by the matrigenes versus patrigenes."
Next, the researchers harvested workers bees' ovaries and sequenced the entire set of RNA molecules to see which of their inherited genes were expressed to a greater extent.
"We found that expression of the patrigenes, but not matrigenes, was strongly associated with worker egg-laying behavior," Galbraith said.
According to researchers, they next plan to explore intergenomic conflict in other systems.
"What is amazing about Queller's model is that it provides very detailed predictions for how matrigenes and patrigenes behave in different social insect species and different contexts—in some cases, matrigenes are the selfish ones," Grozinger said.
Explore further: Study spells out why some insects kill their mothers
More information: Testing the kinship theory of intragenomic conflict in honey bees (Apis mellifera)www.pnas.org/cgi/doi/10.1073/pnas.1516636113
Journal reference: Proceedings of the National Academy of Sciences
Provided by: Pennsylvania State University