Dawkins remarks that it is possible for mutual altruism to incur, and thereby solve the Prisoner’s Dilemma, if conditions such as iterated encounters, threat of retaliation, and “forgiveness” are met. He uses the example of the live-let-live strategy employed by British and German troops on WW1 and the strict alternation of sexes by hermaphrodite fishes. Such dynamics is also echoed in a special kind of mutual altruism among vampire bats.
The work of G.S. Wilkinson explains how non-kin individuals engage in altruistic behaviors. Albeit a significant amount of blood-sharing cases involve close relatives, he found that vampire bats sometimes donate blood to their unrelated counterparts to save them from starving. Such behavior is within the tenets of a Prisoner’s Dilemma. A Donate-Donate strategy is a win-win strategy because the cost of donating trumps the huge benefit of saving a comrade's life; in addition, when the unfortunate time comes of an unlucky forage, a vampire bat would greatly benefit from the prospect of a reciprocal donation. Interestingly, this is evidenced by repeating experiments from Wilkinson wherein a bat was removed and starved for a night and returned to the roost. In thirteen cases, twelve involved donation from a previous benefactor/friend, proving the condition for reciprocation.
Tuesday, October 27, 2009
Friday, October 23, 2009
Mothers and Daughters
The conflict boils down to whose preference of sex ratio will be maintained--- the Queen’s 1:1 or the female workers’ 3:1 female to male ratio.
Why does the Queen invest in a 1:1 sex ratio?
Her genes can benefit best if she invests equally in both sexes. This is supported by Fischer calculations on optimal sex ratios done by Trivers and Hare.
Why do female workers favor a 3:1 ratio, or more sisters?
Since sisters share the same father, they share his genes 100% of the time. On the other hand, males, which are unfertilized eggs and do not require a father, only carry the queen’s genes. Thus, sisters are more related to one another than to their brothers, whose genes they share only 25% of the time. It is best for a female worker to refrain from rearing and let the queen be a sister-making machine.
Who wins?
Using 20 species of ants, Triver and Hare estimated sex ratios in terms of investment in reproductives and found a 3:1 female to male ratio. “Workers are running the show for their own benefit.”
What are the exceptions?
Some species of ants use slaves (workers from other colonies) to perform the chores. Long story short, the power now lies on the slaves, which are unrelated to the rest of the brood, rather than on the true-born workers. The queen can thus get away with the slaves countermeasures because their countermeasures won’t work on her, being totally unrelated to them.
In some species, a queen mates with several males, which makes the average relatedness of sisters to be as low as 25%.
My head is spinning.....
Why does the Queen invest in a 1:1 sex ratio?
Her genes can benefit best if she invests equally in both sexes. This is supported by Fischer calculations on optimal sex ratios done by Trivers and Hare.
Why do female workers favor a 3:1 ratio, or more sisters?
Since sisters share the same father, they share his genes 100% of the time. On the other hand, males, which are unfertilized eggs and do not require a father, only carry the queen’s genes. Thus, sisters are more related to one another than to their brothers, whose genes they share only 25% of the time. It is best for a female worker to refrain from rearing and let the queen be a sister-making machine.
Who wins?
Using 20 species of ants, Triver and Hare estimated sex ratios in terms of investment in reproductives and found a 3:1 female to male ratio. “Workers are running the show for their own benefit.”
What are the exceptions?
Some species of ants use slaves (workers from other colonies) to perform the chores. Long story short, the power now lies on the slaves, which are unrelated to the rest of the brood, rather than on the true-born workers. The queen can thus get away with the slaves countermeasures because their countermeasures won’t work on her, being totally unrelated to them.
In some species, a queen mates with several males, which makes the average relatedness of sisters to be as low as 25%.
My head is spinning.....
Monday, October 12, 2009
Natural Selection and Sexual Selection
Darwin personifies nature as “an active power” that affords better chances of occurrences for profitable variations. Changes in the conditions of life yield individuals with a wide array of variability. In this connection, the slightest differences in structure can turn the scale for the struggle of existence; individuals carrying desirable traits will survive and reproduce more. Thus, natural selection is a tool for “scrutinizing the traits”, rejecting the bad ones and preserving the good ones for subsequent generations. As one example, he states how natural selection “gives” grouse their particular color for preserving them from prey hawks, who are guided by eyesight. On a different note, he distinguishes this from sexual selection, which he calls something that depends not on the struggle for existence but on the struggle between individuals of one sex for the possession of the other sex. E.g., the male Guiana birds display their plumage to females whose primary criteria for the fittest mate is attractiveness.
Dawkins, on the other hand, is saying the same thing but blurs the line between the two. He asserts that natural selection operates in conjunction with sexual selection so as to enable “selfish machines” have as many surviving offspring as possible. The challenge comes when the asymmetry arises between the sexes as to who will invest more in producing the offspring, and that’s when sexual selection comes in handy. Females start off with the disadvantage of investing more in the form of a large egg and stands to lose more if the offspring dies than the male who can at anytime abandon without any cost; hence there must be some sort of evolutionary counter pressure against males. An example is the domestic-bliss strategy wherein females choose their males carefully, looking for fidelity and domesticity traits.
Dawkins, on the other hand, is saying the same thing but blurs the line between the two. He asserts that natural selection operates in conjunction with sexual selection so as to enable “selfish machines” have as many surviving offspring as possible. The challenge comes when the asymmetry arises between the sexes as to who will invest more in producing the offspring, and that’s when sexual selection comes in handy. Females start off with the disadvantage of investing more in the form of a large egg and stands to lose more if the offspring dies than the male who can at anytime abandon without any cost; hence there must be some sort of evolutionary counter pressure against males. An example is the domestic-bliss strategy wherein females choose their males carefully, looking for fidelity and domesticity traits.
Subscribe to:
Comments (Atom)
