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

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.

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.

Testicles Are Cool

An odd feature of most mammals is descent of the testes. Testes migrate from a protected position by the kidneys to end up in pouches outside the body cavity. Many attempts have been made to explain this strange development, ranging from the pull of gravity through sexual display to avoiding concussion. In fact, the lower temperature in the scrotum provides the key.

The Second Curse on Women: Menopause

Women rapidly lose fertility when about 50. Maximum lifespan is about 125 years, so infertility lasts decades. Menopause has unpleasant side-effects and may be seen as the second curse of womankind, although it does at least mark the end of the first curse, menstruation. But did menopause evolve, or is it just a byproduct of recently extended lifespans?

The First Curse on Women: Menstruation

During menstruation a woman typically sheds almost a fluid ounce of blood. Substantial iron loss results, so strong selection must have led to its evolution. But a convincing explanation remains elusive. Any hypothesis must explain why menstruation is limited to higher primates and a few other mammals, and also why menstruation is so strikingly heavy in women.

Sniffing Around for Mr. Right

Does some genetic agenda underlie our choice of mating partners? Evidence from other mammals indicates that male status influences mate choice by females, but there are also pointers to a more subtle mechanism in which a female aims for an optimal match between a male's genes and her own. Instead of seeking good genes in a mate, females may look for complementary genes.

Female Orgasms: Getting Off or Getting On?

Male orgasms are clearly linked to ejaculation, but the function of female orgasms is debated. Women's orgasms are variable and have no obvious function. Explanations range from a role in pair-bonding to the proposal that they are a functionless byproduct of development, like men's nipples. But is it true, as often claimed, that female orgasms are unique to humans?

Why Midwives Are Needed

“I will greatly multiply your pain in childbirth. In pain you will bring forth children.” This is the divine punishment of Eve and all her female descendants proclaimed in the Christian Bible (Genesis 3:16). Childbirth continues to challenge women everywhere, but through biological necessity.

Got Milk, Got Unwanted Hormones?

The cow’s milk we drink today is quite unlike milk that our predecessors drank without apparent harm for two millennia. Over the past century, farm procedures have changed radically to increase milk yields. Most importantly, milking has been extended into middle and late pregnancy, markedly increasing levels of steroid hormones, especially oestrogens, in the milk.

Deliver Unto Caesar: A Surgical Epidemic

Caesarian births are escalating everwhere, in industrialized and developing countries alike. WHO recommended that rates should not exceed 10-15%, but in the USA one in three births involve C-section and rates are even higher in some other countries. Yet the procedure has substantial risks for mothers and infants. Are we moving toward a world of mandatory C-sections?

Breast is Best for Growing Brains

Substantial evidence reveals a significant difference in brain development between breast-fed babies and bottle-fed babies. Breast-fed infants score higher in mental performance tests. Reported differences have generally been small — just a few points — but breast-feeding benefits increase with duration, resulting in a greater difference over time.

Keeping Expectant Mothers Guessing

Remarkably, due dates for human births are still commonly estimated using a rule of thumb advocated in 1812. But normal births can occur up to a month on either side of the predicted date. Such uncertainty is not only inconvenient for expectant mothers; it also increases the risks in timing medical interventions.

How Do Owl Monkeys Do It?

It is well known that owl monkeys are exceptional among higher primates in being active at night rather than by day. But it is far less widely known that their reproductive biology is even more unusual. Extremely low levels of sperm production, when first reported, were interpreted as a pathological condition attributable to irreversible effects of vitamin E deficiency.

Kamikaze Sperms or Flawed Products?

Fertility experts have long known that human semen contains many defective sperms. It has been suggested that our deviant sperms evolved in response to direct competition, but the alternative interpretation is that they are simply the outcome of slack quality control.

An Acute Sense of Loss?

Many mammals have a penis bone, but humans count among numerous exceptions. New experiments with mice have linked the size of a male's penis bone to reproductive success.

Sperm Wars: Dispatch From a Conscientious Objector

If two or more males copulate with the same female close enough in time for viable sperms to co-occur, direct competition can arise. Sperm competition has long been a hot topic in evolutionary biology, and convincing findings have ben reported for several animal species. But how good is the evidence for the notion that humans are biologically adapted for sperm competition?

The Stork-and-Baby Trap

Equating correlation with causation is a cherished, age-old tradition that is not going to stop any time soon.

Spectators on Steroids

We greet with righteous indignation any report of top athletes being caught red-handed using banned steroids to enhance performance. By contrast, far less is said about the involuntary exposure to steroid-like chemicals suffered by all, athletes and spectators alike.

Sperm Counts Updated

In 1992, a key review reported evidence for a widespread decline in human sperm counts over a 50-year period. This wake-up call encountered strident opposition, including a claim that reduced sperm counts were an artifact of changing counting methods. This claim is baseless and reports of declining sperm counts continue to mount. But is male fertility affected?

Out for the Sperm Count

In "The Children of Men", mystery author P.D. James imagines a future world in which the entire human population has become infertile. Sperm counts have fictionally crashed to zero, threatening humankind with extinction. Of course, such doomsday scenarios involving plunging sperm counts reside in the world of fiction. Or do they?

From Origins of Breastfeeding to Lactose Intolerance

To say that humans are mammals is not simply an arcane statement about classifying us in the biological scheme of things. The message is far more profound: We have all of the key biological features that set mammals apart from other animals. Two of them, hair and suckling, are plainly evident. What is not so obvious is that hair and suckling are linked.