Genemanship Chapter 6

The Selfish Gene All copies of a gene, not just that present in one organism! A gene may be able to assist replicas of itself NOT individual altruism! Remember our unit of heredity is the gene, therefore it is brought about by gene selfishness

Recognizing Genes The odds of a gene that both produces a trait and the association to treat those with that trait well is unlikely Dawkins calls this the Green Beard Altruism Effect There are different ways that this may appear Dawkins argues that the act of altruism can lead one to deduce that the recipient also likely carries that gene or it would go extinct--also unlikely as an actual effect

Recognizing Genes Kin have a greater than average chance of sharing genes Explains why parent-child altruism is so common W.D. Hamilton took this idea and expressed it in mathematics Discussing rare genes in order to assume not everyone has it (i.e. discussing selection based on having two eyes is rather pointless)

Kinship Exactly ½ of your genes comes from your father and ½ from your mother Your siblings also have the same condition, therefore you share approximately ½ of your genes with your siblings (depends on odds) The index of relatedness shows how related two individuals are Siblings are ½ (assuming no incest and ignoring certain insects)

Calculating Index of Relatedness Find the most recent common ancestor of both individuals Climb "up" the family tree and "down" to the other individual Multiply ½ by itself for the number of steps of generation distance (g) The portion of relatedness due to that ancestor is (½)g

Calculating Index of Relatedness Needs to work out the relatedness of each lowest common ancestor (a) Most of the time, this will be 2 (one of each parent) If the lowest common ancestor is the individual in question, it would be 1 Multiply by this number, therefore a x (½)g = IR

Interpreting the Index of Relatedness Odds are that in a relationship such as third cousin (1/128), the gene is almost as likely to appear in a random individual The closer to 1, the greater the support the gene should offer Identical twins would be at 1 (exact same genes)

Interpreting the Index of Relatedness The minimum requirement of a suicidal gene would be that it has to save more than the inverse of its index of relatedness (i.e. ½ has to save more than 2, ¼ has to save more than 4, etc.) so that the gene benefits If one can determine that the other is an identical twin (clone?), the concern should be exact for the other as the self

Kin Altruism Parental care falls under kin altruism Genetically, the relationship between parent and child is the same as that between siblings, so the same level of care should be present for each Why isn't it?

Kin Altruism The fact that parents pass genes to offspring but siblings cannot is irrelevant because we are talking about copies of genes, not individuals E. O. Wilson proposes the idea that kin selection is a mechanism for group selection. How does Dawkins refute this?

Kin Selection E. O. Wilson claims that kin selection is a variant of group selection, and Dawkins concedes that a family is a type of group However, Dawkins uses Hamilton's argument that the distinction between family and non-family is not clear-cut, but based on mathematical probability

Kin Selection Because no line can be drawn between family or non-family (do you include third cousins? Fourth cousins?), Hamilton argues that we should see altruism simply based off of the index of relatedness Therefore, Dawkins concludes that it is not group selection, but a special case of gene selection

Kin Selection in the Real World Organisms can't know exactly how related they are to other individuals Statistical risks also need to be calculated (the odds of actually dying) Grandparents and grandchildren have the same relatedness, but grandchildren have a greater expectation of life

Rapid Calculations The behavioral genes behave as if it had performed these calculations Bizarre? Maybe not. We do this all the time! (Apparently squirrels are less capable of certain calculations, judging by the roadsides)

Simulating Survival Methods Ignoring factors such as age, we can simulate how a gene would act in order to benefit itself in ALL copies of a gene Benefits would be positive, risks would be negative Net benefit = Benefit to self - risk to self + ½ benefit to brother - ½ risk to brother + ½ benefit to child - ½ risk to child + ¼ benefit to niece - ¼ risk to niece, etc...

Simulating Survival Methods Results of the sum = net benefit score The action with the largest net benefit score is most likely to become an ESS Used to determine kin altruism actions

Simulating Survival Methods A practical example would be food calls One could hoard all of the food to itself, but sharing may benefit the copies of the gene that appears in other organisms The "calculation" is run subconsciously, and the organism determines whether it is worth it

Back to Gene Language Genes that survive are those that on average manage to characterize the environment of species in the past Therefore "estimates" of costs and benefits are based on past "experience" "Experience" = genes that survived

Determining Relatedness Organisms don't know for sure whether they are related or not Behavior would be based on how much they do know For example, an organism knows that she and her brother came from the same mother but do not know who the father was. The genes would average the relatedness of brother to half brother and come up with 3/8.

Determining Relatedness Organisms that look similar are more likely to share genes If organisms are not very mobile, recognizing any individual as kin is likely true (this would explain apparent altruism in favor of group selection)

Determining Relatedness This can be hijacked! In nature, some organisms typically only sit on their own eggs, therefore they would not notice if they were given other eggs (farm-raised chickens, gulls) One species has developed an adaptation to take advantage of this: the cuckoo

Offspring In situations where eggs do not move, there is no need to recognize them, but chicks can wander, so they need to be recognized (gulls) If they can roll, they need to be recognizable (guillemots) Why bother?

Offspring If birds took turns sitting on each other's nest, one guillemont could "decide" not to sit on eggs, allowing its own egg to be sat on but not investing in others

Offspring Adoption should not be a stable strategy Hasn't been prominent enough to be selected against, so motherly instincts win Babies can take advantage of this by looking cute (yes, this is a legitimate evolutionary strategy!) and hijacking genes

Determining Relatedness So back to our question: why is parent-child altruism more common than siblings? Animals can only estimate relatedness More likely to know your offspring (particularly females) You know yourself, so even twins would not be 100% altruistic towards each other Selfishness has the certainty of knowing 100% of genes