Sex and Evolution: Bateman, Trivers-Willard, Coolidge, and Their Effects

All of the following are from secondary sources. It's dangerous; I know. Read them with caution.

Bateman Effect ... (Bateman, AJ, 1948, Intrasexual slsection in Drosophila, Heredity, 2:349-368) nearly all females but only a few males mate. (Ridley M, 1993, The Red Queen, NY: Penguin, p179; also Wright R, 1994, The Moral Animal, NY: Pantheon). Originally based on fruitfly data, the principle has been verified since for many species including humans. To produce more children, males mate with as many females as possible and prevent other males from mating with the same female, leaving some males with no partners. The female strategy is opposite the male's. Mating more often will not give her more children because of her time investment for each child. Because of the high availability of males, the females' optimum strategy is to mate only with the best, even if it means sharing him with other females. Females are generally choosy about mating while the males eagerly race to score, sometimes attempting to mate even with inanimate objects!(1) That competition to impress the women was thought to encourage the development of secondary sexual traits (large antlers on deer, long necks on giraffes, big tail feathers on peacocks) in males. The exceptions to this pattern consist of a relatively few species in which the males sit the eggs and make a larger time commitment to the children than the females do. The sex making the greater parental investment is the more cautious one in mating. George Williams cast this relationship in terms of "sacrifice" by each sex; Trivers substituted the concept of "Parental Investment." These principles are thought to underlie human courtship patterns.

Coolidge Effect ... Ridley cites (p 299) the following: "..President Calvin Coolidge and his wife being shown around a farm. Learning that a cockerel could have sex dozens of times a day, Mrs. Coolidge said, 'Please tell that to the President.' On being told, Mr. Coolidge asked, 'Same hen every time?' "Oh, no, Mr. President. A different one each time.' 'Tell that to Mrs. Coolidge.'" Generally, males temporarily perform more vigorously after a change in female partners.

Trivers-Willard Effect (1973) ... Female optimal reproductive strategy is to produce sons early in life and daughters later. The logic is that a younger, more healthy female will produce sons that are also healthy and more likely to carry her genes to the next generations. As she ages, her sons are less likely to be healthy. Since nearly all females mate whereas unfit males do not, her next best plan then becomes that of producing girls. The Effect is seen in several species and cultures; the mechanism is unknown.(2) The Trivers-Willard Effect has been extended from the physical health of the mother to her economic resources. Wealthy women are more indulgent of sons; poorer women are more indulgent and protective of daughters. See Wright for a discussion of these data. See the posting on "Trivers-Willard and K-Selection vs. r-Selection: Even Our Mothers May Be Allergic to Us Guys"

Baldwin Effect ... (See Schull J, 1996, The Classics in Their Context and in Ours. In Belew R & Mitchell M, Adaptive Individuals in Evolving Populations: Models and Algorithms. Reading, MA, Addison Wesley, pp 33-38; see also the paper by Baldwin, A New Factor in Evolution, in Belew & Mitchell.) James Mark Baldwin attempted to imagine a way around the "Central Dogma" that individual development does not modify the gametes. No matter how much a male grows large muscles, his son will not be more likely born with large muscles. Baldwin assumed that part of an organism's strategies is finding environments where it can function with greater reproductive success. He argued that if the ability to learn a particular set of behaviors produces greater reproductive success for one generation, then we should observe ever more children with the enhanced ability in the next generation. Random variation should produce even more superior organisms who will have a mating advantage even within this already selected group. Eventually a generation will appear where the behavior appears instinctively. Almost no one believes Baldwin now (see paper by G.G. Simpson in Belew & Mitchell); however, there are still many references to the Baldwin Effect, perhaps because of Baldwin's own zeal. People are still trying to get around the principle that learning and practice during ontogeny have no effect on the information in gametes within or across generations. See the papers in Belew & Mitchell.

Waddington Effect ... to physiological systems what Baldwin attempted for behavioral traits. Also called, "canalization." (Also see Schull for a brief discussion and the paper by Waddington in the same volume.) ---------------------------

This next is from E.O. Wilson (1980) Sociobiology (Abridged Edition), Cambridge MA: Harvard University Press.

Bruce Effect ... odors from a new male mouse causes the pregnant female to abort the litter started by her former partner. Sometimes viewed as a summary of the exaggerated competition between fathers and stepchildren in nearly all species. Death is a common ending for children from an absent father, even in some human cultures. Abuse is estimated as between 3-40 times more likely with adopted than with natural children. (Wright, The Moral Animal). Despite similar outcomes, mice and primates likely have different mechanisms. The need for higher parental investment may underlie our reluctance to rear a child who has none of our features. Males don't want to invest their own marginal attention to someone else's child; they also don't want their mate investing her time in them either. The lack of overlap in traits could also make it less likely the child will establish an alliance with the stepfather. Each will antagonize the other.

NOTES:

1) Male turkeys have been seen to attempt mating with a suspended head! Other bipedal males are amorous with inflated dolls. Both phenomena can be attributed to the Bateman Effect and superoptimal stimuli eliciting behavior programs that ordinarily ensure reproduction.

2) Some estimates are that 1.62 males are conceived for every female. Differential mortality within the womb gives us ratios wherein there are roughly equal numbers born of each sex. These data may be attributed to antigen production by male fetuses and production of antibodies by the mother. (Spreen O, Risser A, & Edgell D, 1995, Developmental Neuropsychology, p 103). See posting on Trivers-Willard Effect.

• Trivers-Willard and K-Selection vs r-Selection: Even Our Mothers May be Allergic to Us Guys by James Brody, 6/20/97
• Early Maternal Death & Mating Strategy by James Brody, 7/12/97
• Mate Selection: Telling the Lies We Want to Hear by James Brody, 9/7/97
• GI Jane and Darwin by James Brody, 9/16/97
  • XX most important? - Not to YOU? by John Fentress, 10/5/97
• Maternal Influence and Sex of the Infant by James Brody, 9/27/97
• Eros and Phase Shifts by James Brody, 1/10/98
  • Tidbit on Hebb's Phase Sequence shifts by John Fentress, 1/13/98
    • Hebb and Phase Shifts by James Brody, 1/14/98
  • Recirculating Ideas with New Twists by John Fentress, 1/17/98
• Gender and the DSM by James Brody and Robin Walker, 2/18/98
  • Longer Term Balances by James Brody, 2/18/98
• Gluteated Walker by Robin Walker, 7/3/98