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Psychiatrist Randolph M. Nesse has argued that Fisher's principle illustrates the dominance of individual-level selection over group selection because, regardless of the hypothetical sex imbalance of a group, the genes of a parental organism produce offspring of the less frequent sex in order to maximize their transmission to subsequent ...
The Trivers–Willard hypothesis has been applied to resource differences among individuals in a society as well as to resource differences among societies.Investigations in humans pose a number of practical and methodological difficulties, [6] but while a 2007 review of previous research found that empirical evidence for the hypothesis was mixed, the author noted that it received greater ...
As of 2024, the global sex ratio at birth is estimated at 107 boys to 100 girls (1,000 boys per 934 girls). [8] By old age, the sex ratio reverses, with 81 older men for every 100 older women; across all ages, the global population is nearly balanced, with 101 males for every 100 females. [8]
Temperature-dependent sex determination (TSD) is a type of environmental sex determination in which the temperatures experienced during embryonic/larval development determine the sex of the offspring. [1] It is observed in reptiles and teleost fish, with some reports of it occurring in species of shrimp.
The XO sex-determination system (sometimes referred to as X0 sex-determination system) is a system that some species of insects, arachnids, and mammals use to determine the sex of offspring. In this system, there is only one sex chromosome, referred to as X. Males only have one X chromosome (XO), while females have two
Here, sex change is age-dependent. For example, the California sheephead stays a female for four to six years before changing sex [35] since all California sheephead are born female. [38] A terminal-phase male bluehead wrasse. Bluehead wrasses begin life as males or females, but females can change sex and function as males. Young females and ...
In eusocial species, the parent-offspring conflict takes on a unique role because of haplodiploidy and the prevalence of sterile workers. Sisters are more related to each other (0.75) than to their mothers (0.5) or brothers (0.25). In most cases, this drives female workers to try and obtain a sex ratio of 3:1 (females to males) in the colony.
Some chromosomal sex determination systems in animals. A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. [1] Most organisms that create their offspring using sexual reproduction have two common sexes and a few less common intersex variations.