Evolutionary Anthropology Computer Simulations
Descriptions of the three different programs have been handed out to you together with this exercise. Please read those carefully before you start the computer exercises.
You find the program in the folder for this class in the MCL.
1) The Evolution of Infanticidal Mechanisms in Male Langurs:
Explanations:
"months between dominant males" is the amount of time that the dominant male is in control of a harem of females"
"INFANTICIDE TYPE" allows you to pick the sort of design feature you want to compare against each other (kill newborn, kill lactating, and none)
"yellow square" is the most common, wild type, against which the mutant has to compete
"red diamond" is the mutant design feature, which has to prove itself to be successful to outcompete the wild type.
"fixated" means it has taken over the wild type altogether, that means the wild genes are no longer in the population.
"harem size" is the number of females in a harem.
"red diamond form frequency" allows you to control the initial distribution of the mutant form in the population.
Questions:
1) Is the mutation (red diamond form) "kill newborns" a more successful strategy than the wild type (yellow square type) "none"?
If so, about how many generations does it take to "fixation"?
How about "kill lactating"? Which of the two is a more successful adaptation, measured in terms of the generations that it takes to fixation?
What happens if you set the wild type (yellow diamond) to "kill newborns and compare it with the mutant" "kill lactating"?
2) How do you think will harem size affect the success of the mutant "kill newborn" or "kill lactating"?
Now change "harem size", keeping the parameters for infanticide type as wild type versus "kill lactating"?
How does a larger harem change the speed of fixation (number of generations?) in comparison to a smaller harem?
3) Now change the residence time of the resident male’s tenure. Keeping the parameters as in 1), how does a prolonged residence affect the rate of the mutant’s fixation?
How does a shortened tenure of the resident male affect the rate of the mutant’s fixation?
2) The Evolution of Incest Avoidance Mechanisms
Explanations:
"probability that a potential mate is related" just means the likelihood that the mate you choose is actually related to you. Setting the probability to .5 means that every second person you consider to mate with is related to you to some degree, such as cousins, half-sibs, etc.
"mating threshold" specifies at which degree of relatedness you will no longer mate with someone. If you set it to anyone, you will mate with anyone, including your relatives.
"avg. lethals/indiv." specifies how many recessive lethal alleles each person has on average. For every gene locus (place on the chromosome) a person can have two different alleles (gene variants). Some of these alleles will express their phenotypic effects when the person has only a single copy (dominant alleles) whereas other alleles need to be present in a double dose to express their phenotypic effect (recessive alleles). Using this parameter you can specify how many of these recessive lethals a person has on average.
"yellow square form" is the most common, wild type, against which you want to compare the success of your mutant form, which is the "red diamond form".
"Red diamond form frequency" lets you specify the frequency of the mutant design feature in the population.
Questions:
1) Under which conditions do you think people are likely to encounter mates that are relatives?
What happens if you set the yellow diamond form (the most common) as "anyone" and the "red diamond form" (the mutant) as "first cousin"? It means you would mate with anyone except for those that are first cousins or closer related to you. Does this mutant become fixated? If so after how many generations?
How does the result change when you increase the threshold, i.e. exclude even 2nd cousins from your choice of mates. Does it take longer or shorter to fixation?
2) Now increase the "avg. lethals/indiv". How does this affect the rate of fixation with the previous parameters (as in 1) ?
3) Now increase your diamond form frequency to 0.5. That means, the mutant is already in every other person. Describe a situation our ancestors might have encountered where a "mutant" started out with a frequency of 0.5?
3) Reciprocation in Vampire Bats
Explanations:
As you notice, this program looks different than the other two.
Bats go out hunting for blood every night. They have a prespecified degree of hunting success. the "Individual Food Levels" display indicates how successful a particular bat (numbered 1 through 12) has been that night. At the bottom end is "Starvation", that happens when a bat’s food level has dropped too low. But remember, an unsuccessful hunter can ask her girlfriend for blood. A green light means, she got it, a red light means she didn’t, which could be either because the other one did not want to give her any, or, just didn’t have any hunting success herself that night.
This simulation lets you see which of the three strategies, defecting, cooperating, or tit for tat would be the most successful and eventually fixated over the other wild forms.
A "defector" is always defecting, never giving up food.
A "cooperator" is always sharing upon request, no matter whether girlfriend gave her something the last time she needed it.
A "tit for tat" is a bat strategy that makes sharing dependent on whether the requester shared with her the last time she asked her.
When you check "slow" in the upper left hand corner, the program will ask you want to proceed with the next generation. You can stop here for a moment and see how the food levels are, before you continue. The "fast" version does it automatically for you, replacing died bat strategist with those strategists which brought in most of the food (i.e. the most successful strategists in terms of food supply will replace the dead one).
Questions:
1) Go to the strategies menu and select a population of all defectors (those who refuse to share). Then run the simulation and see how well the individuals in this population fare. How many die?
2) Now go to the strategies menu and select a population of all cooperators. Do you notice any difference in the survival of individuals in the two populations?
3) Next, compare who does better by using 6 cooperators with 6 defectors. After how many generations do you see a sizable change from the initial distribution?
4) Now compare 6 cooperators with 6 tit for tats. Who does better?
5) What happens if you 6 tit for tats and 6 defectors. Who does better on the long run?
6) And finally, using a 4, 4, 4 setting, who will be the winner in the long run?
7) Finally, change the number of hunting nights between each mating. In the 4, 4, 4, setting, what changes do you see in comparison 6) ?
8) and if you shorten it, what do you get?