Just over one hundred and thirty years ago Charles Darwin, in The Descent of Man and Selection in Relation to Sex (1871), developed remarkably accurate conclusions about man's ancestry, based on a review of general comparative anatomy and psychology in which he regarded sexual selection as a necessary part of the evolutionary process. But the attention of biologists turned to the more general concept of natural selection, in which sexual selection plays a complex role that has been little understood. This volume significantly broadens the scope of modern evolutionary biology by looking at this important and long neglected concept of great importance. In this book, which is the first full discussion of sexual selection since 1871, leading biologists bring modern genetic theory and behavior observation to bear on the subject. The distinguished authors consider many aspects of sexual selection in many species, including man, within the context of contemporary evolutionary theory and research. The result is a remarkably original and well-rounded view of the whole concept that will be invaluable especially to students of evolution and human sexual behavior. The lucid authority of the contributors and the importance of the topic will interest all who share in man's perennial fascination with his own history. The book will be of central importance to a wide variety of professionals, including biologists, anthropologists, and geneticists. It will be an invaluable supplementary text for courses in vertebrate biology, theory of evolution, genetics, and physical anthropology. It is especially important with the emergence of alternative explanations of human development, under the rubric of creationism and doctrines of intelligent design.

/pdf/sexual-selection-and-the-descent-of-man-1871-1971-446kq7o7lj.pdf

Sexual selection and the descent of man, 1871-1971

Theory and data suggest that a male in good condition at the end of the period of parental investment is expected to outreproduce a sister in similar condition, while she is expected to outreproduce him if both are in poor condition. Accordingly, natural selection should favor parental ability to adjust the sex ratio of offspring produced according to parental ability to invest. Data from mammals support the model: As maternal condition declines, the adult female tends to produce a lower ratio of males to females.

https://science.sciencemag.org/content/sci/179/4068/90.full.pdf

Natural selection of parental ability to vary the sex ratio of offspring.

A method was developed for the semiquantitative assessment of body hair growth, and suitable for use in the study of clinical problems associated with hirsuties in women. Five gradings based on densities and areas involved, were determined for each of 11 sites. Findings from application of the method to a control group of 430 women (ages, 15–74 years) are reported. Hair tended to increase on the face and disappear from all other sites with advancing years. In younger age groups a significant amount of hair was found on the forearm and leg in most subjects, but a zero grading was much the commonest finding at all other sites. It is suggested that 2 factors may be involved: one of protective nature with main expression on the forearm and leg, and the other related to hormone levels or sensitivity, with clearest expression elsewhere. An “hormonal” score obtained by adding the gradings obtained from 9 of the 11 sites (excluding the forearm and leg) is being employed in clinical studies.

Clinical assessment of body hair growth in women

Joseph Pickrell and colleagues analyze genome-wide association data for 42 human phenotypes or diseases and identify several hundred loci influencing multiple traits. They also find several traits with overlapping genetic architectures as well as pairs of traits showing evidence of a causal relationship.

/pdf/detection-and-interpretation-of-shared-genetic-influences-on-48uvfdagn9.pdf

Detection and interpretation of shared genetic influences on 42 human traits

Immune reactivity is greater in females than in males. In both experimental animals and in man there is a greater preponderance of autoimmune diseases in females, compared with males. Studies in many experimental models have established that the underlying basis for this sex-related susceptibility is the marked effects of sex hormones. Sex hormones influence the onset and severity of immune-mediated pathologic conditions by modulating lymphocytes at all stages of life, prenatal, prepubertal, and postpubertal. However, despite extensive studies, the mechanisms of sex hormone action are not precisely understood. Earlier evidence suggested that the sex hormones acted via the thymus gland. In recent years it has become apparent that sex hormones can also influence the immune system by acting on several nonclassic target sites such as the immune system itself (nonthymic lymphoid organs), the central nervous system, the macrophage-macrocyte system, and the skeletal system. Immunoregulatory T cells appear to be most sensitive to sex hormone action among lymphoid cells. Several mechanisms of action of sex hormones are discussed in this review. The possibility of using sex hormone modulation of immune responses for the treatment of autoimmune disorders is a promising area for future investigation.

Sex hormones, immune responses, and autoimmune diseases. Mechanisms of sex hormone action

This account summarizes certain aspects of a study which is to be published in detail eisewhere and has the following aims: (1) To establish types or categories of scalp hairiness which can be used as standards for classitication and grading of the extent of common ba1dness.t (2) To survey the incidence of these scalp types in members of each sex throughout life, beginning with the first appearance of hair in the fetus. (3) To gain information regarding the relationship of scdp types to factors which influence the development of baldness, in particular to genetic, age, and endocrine factors. (4) To ascertain if bald men, as compared with men who did not become bald, have higher titers of urinary ketosteroids or a greater development of a secondary sex character, axillary hair, which can be measured quantitatively and used as an index of certain aspects of the endocrine status. This part af the study stems from the fact that common baldness is induced by androgenic stimulation (Hamilton, 1942). ( 5 ) To test if the tendency to acquire baldness of the scalp is associated with a disposition to baldness on another part of the body where alopecia is common, i e . , on the lateral surfaces of the legs.

Patterned loss of hair in man; types and incidence.

The position of orifices of hair follicles was charted with reference to one to four small, permanent tattoos which were made in the skin with India ink. The tattoos were judged to be permanent if the ink could still be seen 48 hours after tattooing. At this time, the position of the tattoos and the orifices of follicles containing terminal hairs was drawn to scale as illustrated in FIGURE 1. Areas chosen for tattooing contained 6 to 12 hairs. The separately identified hairs were then plucked and preserved for microscopical study. A few hairs were observed to break upon plucking. If the stub could not be pulled immediately, it was removed after an interval of 7 days. Plucked areas were observed a t weekly intervals until the regeneration of hairs had been completed. A hair was considered to have regenerated when its tip projected above the skin. The time required for regeneration of a hair was calculated upon the number of days between plucking of an old hair and the appearance of a new hair above the skin, as observed a t intervals of 7 days. If a new

James B. Hamilton

Papers

Patterned loss of hair in man; types and incidence.

Regeneration and rate of growth of hairs in man

CHAPTER 16 – Age, Sex, and Genetic Factors in the Regulation of Hair Growth in Man: A Comparison of Caucasian and Japanese Populations1

Studies of growth throughout the lifespan in Japanese: growth and size of nails and their relationship to age, sex, heredity, and other factors.

Duration of Life and Causes of Death in Domestic Cats: Influence of Sex, Gonadectomy, and Inbreeding