In this lesson we explore altruism; its meaning, evolution, and helpful terms. Reflection questions are explored at the end of the lesson involving hymenoptera, eusocial speccies, and factors that led to the evolution of eusocial’s extreme form of altruism.
Ground Squirrels: The squirells were making a high pitch noise when predators were present.
Why would the squirrels make this noise that would alert predators to their location?
Weaver Ants: The ants were holding leaves together to form a bridge for the worker ants to move across.
Why would the ants express this behavior?
In the eusocial Hymenoptera, a order of insects including bees, ants, and thousands of other insect species, consist of individuals unable to pass on their genes due to various reasons. In the case of the weaver ants, most of the ants are sterile. So, How can these individuals pass on genes if they are unable to reproduce?
To investigate this questions we must understand altruism and the altruistic behaviors these species manifest. Altruism can be defined as the helpful behavior that lowers the helper’s reproductive success while increaing the reproductive success of the individual being helped. The ultimate puzzle og the evolution of altruism was questions by Darwin. If the self-sacraficing altruists were unable to reproduce it would be a logical assumption that this behavior would be naturally selected against and should disappear over time.
So, Why have altruism evolved and not been selected against?
A number of rationale have been theorized to answer this questions including; intelligent disign theory, group selection, indirect selection, and kin selection. Animal Behavioralists tend to employ kin selection theory. This theory have been proven time after time to be useful for scientific investigations. “Kin selection theory has been used to show altruism can spread through a population if the cost to the altruist in terms of a reduction in the number offspring produced [multiplied by the coefficient of relatedness between the altruist and those offspring] is less than the increase in the number of related individuals helped by the altruist [multiplied by the average coefficient of relatedness between the altruist and the helped relatives].(Animal Behavior, John Alcock)”
Exploring this theory further we must know specific terms including:
Direct Selection: Acts on traits that promote success in personal reproduction
Direct Fitness: A measure of personal reproduction (your own offspring that survive and reproduce.)
Indirect Selection (Kin Selection): Acts on traits that promote success in the reproduction of nondescendant relatives.
Indirect Fitness: A measure of the number of relatives that the altruist helps to survive and reproduce.
Inclusive Fitness: Direct Ftiness + Indirect Fitness (A total measure of the genetic success of an individual)
An altruist can promote transmittion of their genes indirectly by their behaviors helping a relative. Kin or Indirect Selection results in a increase of genes transmitted indirectly by an individual to the next generation in the bodies of relatives that exist because of the altruist’s help. The Kin selection theory underlies modern “gene-centered thinking.”
Individuals should behave in a way that boost their inclusive fitness (defined above), this is achieved by self-sacrafice or self- serving conflict with others.
Who would an individual be more inclined to be altruistc towards?
This question can be easily answered in a quantitative sense.
Imagine a woman is left to raise 2 nephews and 1 neice. Would it be more benefitial in terms of fitness to raise 1 child of her own or these 3 nephews/neice?
Upon review of the picture above we can see that from one child the woman would have .5 direct fitness and from 3 nephews/neices she would only have .375 indirect fitness. Since .5>.375 it would be more benefitial for the woman to raise her own child.
What are Hymenoptera?
Hymenoptera are “membrane winged” insects which include; bees, ants, and wasps. There are over 150,00 species of Hymenoptera
What are some main characteristics of Eusocial Species?
A Eusocial Species is the highest level of organization of animal sociality. The characteristics they possess include; cooperative brood care, overlapping generations within a colony of adults, and division of labor.
What factors led to the evolution of this extreme form of altruism?
In a paper written by M.A. Nowack, ‘The evoltuion of Eusociality.’, the evolution of eusocial species are lead by five factors. The first is a formation of groups this leads to the next factor that the occurance of preadaptive traits caused the groups to form tightly giving the colony a valuable and defensible nest. Appearances of mutations also caused the persistance of the group, silencing dispersal behavior. Natural selection by environmental factors shaped the emergent traits caused by interactions of the group members, and multilevel selection drove changes in the colony life cycle and social structure.
Nowak, M.A., Tamita, C.E., & WIlson, E.O. (2010). THE EVOLUTION OF EUSOCIALITY. Nature, 466(7310), 1057-1062. http://doi.org/10.1038/nature09205
BONUS: check out this video on Altruism