How We Do It

The evolution and future of human reproduction

Robert D. Martin Ph.D.

Just How Important Is Breast Size in Attraction?

Across cultures, men do not consistently prefer large breasts.

Bountiful Breasts: Mixed Signals in Sex and Motherhood

Uniquely among mammals, women’s breasts start to swell at puberty. But the evolution of breast size and men’s responses remain enigmatic.

Trading Semen: The Tale of Artificial Insemination

Artificial insemination, the simplest way to assist reproduction, is still widely used and even abused. Refinements include freezing semen and injection of semen into the womb.

Antibiotic Apocalypse: Going, Going, Gonorrhoea

Antibiotic resistance dramatically illustrates evolutionary change under selection. Gonorrhoea and other bacteria have become superbugs, resistant to several antibiotics.

Intersex: Life in the Overlap Zone

Male/female distinctions overlap in an intersex zone. Some intersex people have atypical sets of sex chromosomes, but most have gene variants on other chromosomes.

No Substitute for Sex

Increasing use of “gender” as an alternative to “sex,” notably in the humanities, is inappropriate. In essence, sex is biological while gender is cultural.

Strange Head Shapes: Revisiting Nefertiti, Akhenaten and Tut

Strange head shapes due to early binding arose sporadically worldwide. New reports add sites in northeast China, document local change and bolster findings for Ancient Egypt.

The Pope Who Advocated Birth Control

Chasteberry trees contain a hormone-like substance that affects reproduction in baboons and humans. Pope John XXI prescribed a conception-blocking European type for birth control.

Orgasms, Oxytocin, Oviducts

Female orgasm is not a functionless byproduct of penis development. Orgasms are closely linked to the clitoris—part of a largely hidden complex—and may boost sperm transport.

Ectopic Embryos: Pregnancy in the Wrong Place

If a fertilized egg fails to reach the womb, pregnancy begins in the wrong place, usually in an oviduct. Birth is impossible, so this life-threatening condition requires surgery.

The Sperm that Fertilizes: Champion Swimmer or Lucky Winner?

Sperm transit through the womb and oviducts is often portrayed as a fierce contest. But contractions in the womb and oviducts also propel sperms towards the fertilization site.

Funky Valentine: Love at First Whiff?

In primates, dominant males usually copulate more often, but this does not guarantee paternity. Subordinate males may sire infants if their immunity genes provide a better match.

It’s All Bawls: Coping with Inconsolable Infants

Colic — excessive crying by babies during the first 3 months — worries parents but is usually benign, mostly vanishing within 10 weeks. Effective treatment is at last in sight.

Sexy Silhouettes: Slim Waists, Broad Hips, and Fertility

Mens’ preferences for images of narrow-waisted women purportedly evolved to maximize health and fertility. But wasp waists actually signal low fat levels and suboptimal condition.

Genital Mutilation of Girls and Women

Ritual mutilation of the external genitals of girls or women, less widespread and far more variable than male circumcision, is generally more extreme and much riskier.

Rites of Circumcision

Circumcision, once performed on teens as a ritual, is now often carried out soon after birth on medical advice.

Sperm Selection: Fertilization Not Random After All?

Attempts to develop a reliable method for pre-selecting a baby’s sex finally succeeded. Sperms with X- or Y-chromosomes can be effectively separated using a cell flow device.

Boy or Girl: Couples Trying to Load the Dice

Evidence indicates that timing of coitus relative to ovulation influences a baby’s sex. But, contrary to Shettles' method, coitus near ovulation is more likely to produce girls.

Testicle Saga: Escape from the Abdomen

Most marsupials and placentals have descended testes, although many exceptions exist. Now new evidence indicates descent in a common ancestor.

Sexy Scents

Pheromones—scent signals that evolved for communication between individuals—have been identified for sexual activity in mice. Do comparable signals exist in humans?

Do Men Have the Balls for Promiscuity?

The myth that humans are biologically adapted for promiscuous mating with sperm competition is widely accepted but conflicts with existing data.

Monogamy Anchored in Our Genes?

Humans are often seen as biologically primed for monogamy. Absence of adaptations for sperm competition indicates single-male mating, but more likely mild polygyny than monogamy.

Sex on a Cycle?

Studies of women’s sexual motivation often assume an influence of hormonal changes across the menstrual cycle. But the expected sexuality peak around ovulation is commonly absent.

Beauty and the Beard

Darwin suggested that men’s beards evolved through sexual selection exerted by female mate choice. But recent studies indicate that beards may primarily signal social dominance.

Breastfeeding No Option? Women Need Remedies, Not Bullying

Courtney Jung’s book "Lactivism" rightly condemns bullying of mothers who do not breastfeed but misrepresents abundant evidence demonstrating substantial benefits of breastfeeding.

Fake Sex Hormones: Chemicals Damage Health and Reproduction

DDT and DES were just the beginning of a series of environmental chemicals that act as fake hormones, seriously disrupting our health and reproduction.

Masturbation: Self-Abuse or Biological Necessity?

Masturbation has slowly lost its evil reputation from previous centuries. Human studies and primate research both indicate that it brings benefits rather than health risks.

Bigfoot Parents Have Small Brains

Birds and mammals mostly show intensive parenting, linked to their “warm-blooded” nature and quite large brains. Incubator birds show no care of their chicks and have tiny brains.

A Sperm’s Obstacle Course to the Egg

If too many sperms surround the egg, catastrophic fertilization by more than one may occur. A woman’s reproductive tract is adapted to tightly constrain sperm numbers near the egg.

Why Too Many Sperms Spoil the Egg

Men can produce too many sperms as well as too few. Excessive sperm numbers around an egg can result in multiple fertilization, abnormal chromosome numbers, and miscarriage.

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