Evolution of Human Sexuality

Quotes

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The Evolution of Human Sexuality (Donald Symons)
- Highlight on Page 5 | Loc. 134-38  | Added on Tuesday, October 23, 2018, 02:31 AM

Learning abilities rarely are general capacities. They are designed to solve the specific problems that have been important in the evolutionary history of a species. Our human bias that the ability to learn necessarily represents evolutionary “advance” or “progress” has distorted our understanding of nonhuman animals and of ourselves. Learning often has disadvantages compared with “innate” development, and even human beings possess “innate” psychic and behavioral predispositions, not because such predispositions are residues of our animal past, but because they regularly resulted in adaptive behavior.
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The Evolution of Human Sexuality (Donald Symons)
- Highlight on Page 6 | Loc. 144-48  | Added on Tuesday, October 23, 2018, 02:33 AM

In the language of evolutionary biology an organism’s “fitness” is a measure of the extent to which it succeeds, compared with other members of the population, in passing on its genes to the next generation. An organism is reproductively successful or unsuccessful only compared with other members of the population, and in this sense reproductive “competition” is inevitable (Williams 1966). If we are told that a given female wolf produced three viable offspring during her lifetime we cannot describe her as successful or unsuccessful, as fit or unfit, until we are told the average number of viable offspring produced by female wolves in the population.
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The Evolution of Human Sexuality (Donald Symons)
- Highlight on Page 6 | Loc. 150-54  | Added on Tuesday, October 23, 2018, 02:33 AM

Nutritional “competition,” for example, is not inevitable in this sense because it is possible to specify the degree to which an organism succeeds in meeting certain absolute nutritional requirements without reference to the nutritional success of other members of the population. That reproductive “competition” is inevitable in the genetic sense does not imply that organisms themselves necessarily will engage in overt reproductive conflict, although it does imply that sexual intercourse normally will not be random. In Darwin’s words (1871:362): “promiscuous intercourse in a state of nature is extremely improbable.”
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The Evolution of Human Sexuality (Donald Symons)
- Highlight on Page 6 | Loc. 158-59  | Added on Tuesday, October 23, 2018, 02:34 AM

selection is for the maximization of “inclusive fitness” (Hamilton 1964), which is the sum of an individual’s own fitness plus its influence on the fitnesses of organisms, other than its direct descendants, with whom it shares genes by common descent.
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The Evolution of Human Sexuality (Donald Symons)
- Highlight on Page 7 | Loc. 164-67  | Added on Sunday, October 28, 2018, 05:57 PM

for example, for the substantial body of evidence that “Human beings, wherever we meet them, display an almost obsessional interest in matters of sex and kinship” (Leach 1966). Inclusive fitness theory may become a powerful predictive tool, but, at present, the implication that it makes specific predictions about what will evolve is likely to foster only misunderstandings,
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The Evolution of Human Sexuality (Donald Symons)
- Highlight on Page 7 | Loc. 171-75  | Added on Sunday, October 28, 2018, 05:58 PM

So-called “altruistic” behaviors can evolve when the positive effects on the fitnesses of kin outweigh the negative effects on personal fitness, but there is no guarantee that such behaviors will evolve. (In the following chapter 1 discuss the semantics of “altruism.”) Lemuel Gulliver wrote in his journal: “Alliance by blood or marriage is a frequent cause of war between Princes, and the nearer the kindred is, the greater is their disposition to quarrel.” Nothing in inclusive fitness theory implies that selection will not sometimes favor maximum violence toward the closest kin.
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The Evolution of Human Sexuality (Donald Symons)
- Highlight on Page 7 | Loc. 178-79  | Added on Sunday, October 28, 2018, 05:59 PM

Proximate, or immediate, causal analyses consider how the behavior came to exist. The answers to questions about proximate causation will be that the animal possesses a particular given complement of genes,
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The Evolution of Human Sexuality (Donald Symons)
- Highlight on Page 8 | Loc. 184-85  | Added on Sunday, October 28, 2018, 06:01 PM

Ultimate, or evolutionary, causal analyses consider why the behavior exists. The answers to questions about ultimate causation will be that the behavior functions in specific ways to maximize the animal’s inclusive fitness.
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The Evolution of Human Sexuality (Donald Symons)
- Highlight on Page 8 | Loc. 196-99  | Added on Sunday, October 28, 2018, 06:03 PM

But just as selection is weak at levels above the individual, so it is weak at levels below the individual; that is, at the levels of the structural, physiological, and neural components that constitute the damp machinery of behavior. It is the organism as a whole that reproduces or fails to reproduce, not any of its components or attributes.
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The Evolution of Human Sexuality (Donald Symons)
- Highlight on Page 9 | Loc. 204-11  | Added on Sunday, October 28, 2018, 06:04 PM

The simple process of evolution, on the other hand, is the central explanatory principle of biology. Alexander (1975) argues that, unlike any known proximate mechanism, differential reproduction is in two senses the most basic unit in the study of life. First, differential reproduction is both common to all life and unique to life. Second, differential reproduction is only one of several evolutionary mechanisms (other mechanisms include, for example, the chance events of mutation and genetic drift), but it is by far the most important determinant of the course of evolution. Natural selection can, for example, alter the rate at which mutations occur (mutability), but the mutations themselves occur randomly with respect to fitness. Mutation thus provides the raw material for the evolutionary process but it is not a guiding force. Differential reproduction occurs continuously in all lineages and at all times; but its effects are cumulative and it can change direction at any time.
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The Evolution of Human Sexuality (Donald Symons)
- Highlight on Page 9 | Loc. 212-16  | Added on Sunday, October 28, 2018, 06:04 PM

In considering the arguments put forward in this book, the distinction between ultimate and proximate causation must be borne in mind. That a given behavior, or behavioral predisposition, has an ultimate explanation does not imply that the behavior has a particular proximate explanation; specifically, it does not imply that the behavior is unlearned or “innate.” Among rhesus monkeys, for example, invariant, species-typical patterns of copulation are the products of natural selection and have obvious adaptive significance, yet deprivation experiments reveal that in both sexes these patterns are partly learned.
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The Evolution of Human Sexuality (Donald Symons)
- Highlight on Page 10 | Loc. 228-31  | Added on Sunday, October 28, 2018, 06:06 PM

The crucial point in Williams’s approach to the study of adaptation is that function must be distinguished from beneficial effect. Williams argues that of all the effects produced by a biological mechanism, at least one may correctly be called its function, or goal, or purpose; but not all beneficial effects may correctly be called functions.