Going, Going, Gone? Human Sperm Counts Are Plunging

Accumulated evidence confirms that human sperm counts have fallen markedly in industrialized countries since the 1930s. Male fertility and reproductive health are threatened.

The Benefits of Breastfeeding...for Mothers

Breast-feeding benefits mothers, not just babies. It speeds recovery of the womb after birth. Later in life, risks of heart disease and breast and ovarian cancer are reduced.

St. Valentine’s Day and the Biology of Romantic Kissing

For Westerners, kisses and Valentine’s Day are inseparable. But new cross-cultural evidence challenges evolutionary inferences regarding possible biological functions of kissing.

Dining on Leftovers: Do Women Lose by Not Eating Afterbirth?

Unlike all other primates and most other mammals, human mothers do not usually devour the placenta after birth. Are they missing out on important benefits because of this?

Bonking Without Bones: An Evolutionary Enigma

New studies clarify the evolution of a "penis bone" in most primates—except humans.

Pandora’s Pillbox: The Age-Old Quest for Longer Lives

Prolonging human lifespan is a long-cherished goal. Medical science has boosted average life expectancy, but can it increase the maximum? Not according to evolutionary biology.

Coping With Hormonal Ups and Downs

Major hormonal changes across the menstrual cycle may influence a woman’s mood, well-being and performance. But apart from PMS side-effects are milder than often thought.
Original cartoon by Alexandra Martin, inspired by an interview retort from Sharon Stone

Intimately Connected

Research sheds new light on biological origins of women’s sexuality.

A Downside for Trophy Wives: Sexually Diminished Husbands

Increasing reproductive problems with age are by no means confined to women. Clear evidence of similar drawbacks for men has been widely ignored. Trophy wives pay a high price!

Unmanned: An Unnatural History of Human Castration

Deliberate castration, long used to punish criminals and prisoners of war, has also yielded harem guards and has been inflicted on young boys to stop their voices from breaking.

Honey, I Squished the Kids’ Heads!

Around the world, people have tightly bound their babies’ heads to produce distinctive shapes. Extreme cases in South America have spawned wild stories of intervention by aliens.

Summertime Sex and Springtime Babies

Human populations have regular year-round birth patterns. Births typically peak in spring in the north but 6 months later in the south, hinting at control by an internal clock.

Beating the Biological Clock with Eggs in the Freezer

A widespread tendency to delay pregnancy clashes with reduced fertility and increased risks later in life. Will deep-freezing eggs of young women for later use solve the problems?

What Dogs Can Tell Us About Sex and Conception

Sperm survival in the womb for 10 days or more rules out the standard model of human conception.

A Biological Function for Oral Sex?

High blood pressure affects 10% of pregnancies in which a mother’s immune system over-reacts to the fetus. Long-term sexual priming by a specific male partner reduces the risk.

The Ripley Effect: Alien Intruders in the Womb

A fetus in its mother’s womb must somehow evade detection by her immune system. In an "Alien"-like scenario, genes that permit this have been captured from once harmful viruses.

Sleeping With Baby: Good or Bad?

A crucial decision parents must make after birth is whether to sleep with the infant. Some claim that sudden infant death is more likely. But bed-sharing promotes breast-feeding.

Why Must Childbirth Be So Challenging?

Childbirth is excruciatingly painful because a baby’s relatively large head passes through a woman's narrow pelvis. A tight limit on head size explains why more brain growth occurs after birth and why babies are relative helpless for the first year. But a new view is that birth timing is constrained not by the pelvis but by an upper limit on the mother’s energy turnover.

Sexually Transmitted Diseases: An Evolutionary View

Sexually transmitted diseases are unlikely to arise with monogamous mating. Yet several human venereal diseases, notably syphilis, have sometimes spread epidemically. Promiscuous mating in nonhuman primates is correlated with higher levels of white blood cells and faster evolution of immunity genes connected with defences against pathogens. So where do humans fit in?

When Is the Best Time to Give Birth?

Medical intervention in human birth is now so widespread in industrialized countries that deliveries are seldom spontaneous. Yet with no intervention there is clear persistence of a general mammalian 24-hour biorhythm in birth hour. Is this just a carryover from ancestors that gave birth during their inactive period, or is that basic rhythm still biologically important?

The Loveliness of Luscious Loins

Studies of attractive features of women’s body shape have rarely considered the side view. This is needed to assess the importance of curvature of the loins and protrusion of the buttocks. Apparently, special adaptation of the lower spine in women to permit maintenance of the centre of gravity over the hips during pregnancy feeds into men’s assessment of attractiveness.

Waists, Hips and the Sexy Hourglass Shape

Various studies have recorded men’s attractiveness ratings of alternative representations of women’s body shape. Tests often involve simple features such as the ratio between waist and hip widths. The aim has been to identify features that evolved as signals of mate breeding potential. But could such simple indicators influence the complex process of human partner choice?

Miscarriages: Conception Without Birth

Miscarriage is a rarely discussed, almost taboo topic. Couples hit by pregnancy loss are usually unprepared and left alone to cope with grief and imagined guilt. Popular belief has it that miscarriage affects only 5% of pregnancies, but 15-20% are reported. Far greater losses occur before pregnancy is clinically recognizable, and only 25% of conceptions lead to birth.

Oxytocin — The Multitasking Love Hormone

Oxytocin is widely known because hospitals routinely use it to trigger and support birth. The hormone also triggers milk ejection during breastfeeding. But it is also involved elsewhere, including bonding. Oxytocin has significant effects on brain function as well as on the reproductive organs. But it has very ancient origins, so what was its initial function?

Does Size Matter for Women?

Penis size has figured prominently in discussions of the evolution of human reproductive biology and mate choice. But, despite the lock-and-key relationship, relatively little attention has been given to female counterparts of the penis — the clitoris and vagina. So reliable information is scarce. Investigation of what is available yields some intriguing conclusions.

Womb for One

The single-chambered womb of women is rare among mammals, which mostly have two separate womb chambers. Through developmental accident, a double womb occasionally recurs in women, but surprisingly does not stand in the way of successful pregnancy. Reduction from two chambers to one in evolutionary has some connection with single births, but there are twists in the story.

Expanding on Penis Size

Correlation between erect and flaccid penis lengths is a statistical artifact. On average, extension through erection is the same in all men. The “plunger hypothesis”, that human penis shape is adapted to remove semen from rival males, is shown to be far-fetched. But stretched length of the penis may have a connection with the size ratio between index and ring fingers.

Penis Size Matters

Myths regarding human penis size have acquired a life of their own but are easily debunked by analyses of reliable data from available quantitative studies. Men do not have the longest penis found among primates. There are no conspicuous differences in average penis size between human populations. And shoe size is not a reliable guide to male endowment.
Of Penis Bones and Shamans

Of Penis Bones and Shamans

It has been suggested that Adam's “rib” used to create Eve was in fact his penis bone. But hoofed mammals lack one, so how was it known that men had lost it? Carnivores have a penis bone, so dogs are a possible but unlikely source of knowledge. It turns out that bears (now extinct in much of the Middle East) were around, and their long penis bones figure in shamanic rites.
Original cartoon by Alex Martin

Sick of Being Pregnant?

Nausea, often the first sign of pregnancy, afflicts three-quarters of mothers-to-be. For two-thirds of those women nausea will lead to actual vomiting. So why does it happen? Pregnancy sickness has often been explained away as a side-effect of hormonal changes during pregnancy. But there is evidence that nausea and vomiting evolved to protect both mother and fetus.