Tag Archives: testosterone


Natural testosterone promotes moral behavior, supplements promote utilitarian choices

Testosterone’s influence on behavior is more nuanced than we previously assumed, a new paper reports.


Image credits Fathromi Ramdlon.

Although previous research has linked high levels of testosterone to immoral behavior, a new study reports that testosterone supplements can actually make people more sensitive to moral norms. The results suggest that the hormone’s influence on behavior is more complicated than previously thought.

Testing Testosterone

“There’s been an increasing interest in how hormones influence moral judgments in a fundamental way by regulating brain activity,” said Bertram Gawronski, a psychology professor at The University of Texas at Austin (UT Austin).

“To the extent that moral reasoning is at least partly rooted in deep-seated biological factors, some moral conflicts might be difficult to resolve with arguments.”

The team used a system similar to the trolley problem in philosophy — a runaway trolley will kill five people unless someone chooses to pull a lever, redirecting the trolley to another track, where it will kill one person instead — and adapted it to test how far testosterone can influence our moral judgments.

The researchers created 24 dilemmas associated with real-life events to simulate situations that put utilitarian decisions, those that focus on the greater good, such as saving the largest number of people, against deontological decisions which focus on moral norms, such as avoiding an action that would harm someone. Prior research suggested that higher levels of testosterone are associated with stronger utilitarian preferences.

To put that to the test, the team ran a double-blind study in which 100 participants received a placebo and 100 participants received testosterone supplements.

“The study was designed to test whether testosterone directly influences moral judgments and how,” said Skylar Brannon, a psychology graduate student at UT Austin.

“Our design also allowed us to examine three independent aspects of moral judgment, including sensitivity to consequences, sensitivity to moral norms and general preference for action or inaction.”

The researchers created 24 dilemmas associated with real-life events to simulate situations that put utilitarian decisions, those that focus on the greater good, such as saving the largest number of people, against deontological decisions which focus on moral norms, such as avoiding an action that would harm someone. Prior research suggested that higher levels of testosterone are associated with stronger utilitarian preferences.

The team says this likely comes down to people with particular personality traits tending to have different levels of naturally-occurring testosterone. For example, people with high levels of psychopathy tend to have high levels of testosterone and exhibit lower sensitivity to moral norms. This doesn’t mean that testosterone is the cause of psychopaths’ insensitivity to moral norms, however. If anything, the findings suggest that testosterone  has the opposite effect, increasing people’s sensitivity to moral norms.

“The current work challenges some dominant hypotheses about the effects of testosterone on moral judgments,” Gawronski said.

“Our findings echo the importance of distinguishing between causation and correlation in research on neuroendocrine determinants of human behavior, showing that the effects of testosterone supplements on moral judgments can be opposite to association between naturally occurring testosterone and moral judgments.”

The study helps flesh-out our understanding of the link between testosterone and behavior, but it definitely raises more questions than it answers. For now, it’s safe to say that the dynamic between the two is more complicated than we assumed — but more research is needed to shed light on the details.

The paper “Exogenous testosterone increases sensitivity to moral norms in moral dilemma judgements” has been published in the journal Nature Human Behaviour.

Testosterone protects against inflammation

Testosterone might protect against inflammation, a study on mice suggests. Researchers found that administering a simple anti-inflammatory drug like ibuprofen to pregnant mice can increase survival rates in embryos.

During pregnancy, the body changes in a number of ways to protect the embryo, and as the pregnancy progresses, the fetus. For instance, inflammation in the mother’s body is oftentimes suppressed, so that the side effects don’t do any damage. However, not much is known about the consequences of maternal and fetal inflammation during pregnancy.

Inflammation is the natural process through which the body responds to injury and infection. Inflammation gets a lot of bad rep, but it’s actually an essential process associated with healing. Without inflammation as a physiological response, wounds would fester, and infections could become deadly. But inflammation can also be triggered by a perceived internal threat, even when there isn’t a disease to fight or an injury to heal and can cause problems in and of itself.

DNA damage is a well-known cause of inflammation. John Schimenti and colleagues from Cornell University wanted to investigate how DNA mutations (that caused defective DNA replication and repair during embryo development) affect the survival rates of mice embryos. They found that on average, male embryos were much more likely to survive than female embryos. The cause for this, researchers suspect, is testosterone, which can act as a common anti-inflammatory.

To confirm this theory, researchers administered pregnant mice ibuprofen, a non-steroidal anti-inflammatory drug (NSAID). After this treatment, survival rates for both males and females were equal, confirming the theory.

Testosterone is the primary male sex hormone. It’s also often seen as the underlying cause for male aggression, but the hormone actually interacts with the male body in numerous complex ways. This isn’t the first time testosterone has been highlighted as a potential way to treat inflammation — previous studies from 2013 all the way to 2019 have come up with consistent findings.

Journal Reference: The study “Female-biased embryonic death from inflammation induced by genomic instability” has been published in Nature. 10.1038/s41586-019-0936-6

Credit: Mad Men.

Testosterone boost makes men more likely to buy luxury brands

Animal research has established a link between hierarchical social interactions and testosterone, with high-testosterone individuals generally conveying elevated status in their social group. In modern western society, males often signal their status by purchasing and flaunting consumer goods that are typically difficult to access by individuals with fewer resources. A new study published in Nature Communications was able to further provide evidence of this relationship: a single dose of testosterone was enough to enhance men’s preferences for luxury brands.

Credit: Mad Men.

Credit: Mad Men.

Social hierarchies are ubiquitous across the animal kingdom. At the group level, hierarchies lessen friction between leaders and followers, enabling better group coordination and reducing conflict for resources. At the individual level, social rank can have a significant impact on mating opportunities, access to resources, stress levels, and social influence, depending on how high or low the status is. It’s no wonder that from fish to humans, individuals will exert effort and energy to climb the social ladder and increase their status.

In early hunter-gatherer societies, men would seek to elevate their status, or prestige, within the group by displaying superior hunting skills or by exerting dominance through physical aggression. In modern times, men don’t need to bash heads or hunt wild boar in order to gain a better position within the social hierarchy. Psychologists have identified various strategies by which individuals can gain status in today’s age, such as attaining a culturally-relevant skill (earning a degree) or displaying wealth through positional consumption.

The idea is that seemingly wasteful behavior, such as paying thousands of dollars on designer clothing or a flashy watch, signals to others an apparent abundance of resources. In a new study, Gideon Nave and colleagues at the Wharton School of the University of Pennsylvania investigated whether elevated testosterone levels might influence consumer spending in men.

In many animals species, testosterone levels jump during the breeding season, causing males to engage in conspicuous displays of status — examples include courtship singing in birds or growth of antlers in stags.

The team recruited 243 male volunteers ranging from ages 18 to 55 and separated them in two groups: half were given a dose of testosterone, in gel form, while the other half received an inert placebo gel.

a) Preference task showing the setup and main dependent variable. b) Mean social rank and quality association ratings of brands pre-classified based on a pretest as high vs. low rank. c) Mean preference toward the high (versus low) social rank brands for the two treatment groups. Credit: Nature Communications.

a) Preference task showing the setup and main dependent variable. b) Mean social rank and quality association ratings of brands pre-classified based on a pretest as high vs. low rank. c) Mean preference toward the high (versus low) social rank brands for the two treatment groups. Credit: Nature Communications.

Each participant was asked to choose their favorite from a pair of brand-name products, such as jeans. For each pair, the products were of similar quality but of different status significance.

The results suggest that even that single dose of testosterone drove men to prefer higher-status brands over their lower-status alternatives, albeit of equal quality. The effect was especially pronounced when the products had a label advertising their status-enhancing properties. In a related note, another study published last week found that men who are of high status in their social group are rewarded by a boost of testosterone. With today’s study, one might assert that testosterone and status seem to be in an interdependent relationship.

Salve and oil.

Compounds in essential oil may impact hormones, promote male breast development

Essential oils do more than make your skin smell good — they also interfere with your hormonal balance, new research has found.

Salve and oil.

Image credits Kathy Zinn.

Pre-puberty male gynecomastia (breast tissue growth) is a relatively rare condition. There are numerous underlying conditions that can lead to gynecomastia, however, and in certain cases, doctors can’t pinpoint any immediately apparent cause.

A new study could shed light on the root of such cases: the team found that eight chemical compounds contained in lavender and tea tree oils interfere with hormone levels by promoting estrogen and inhabiting testosterone secretion.

Essential oils are used in the manufacturing of many products such as soaps, lotions, shampoos, or hair-styling products. They’re sometimes mixed in cleaning products, even seeing some use in medicinal treatments, but despite being widely seen as benign, even health-promoting compounds, lead researcher Tyler Ramsey from the National Institute of Environmental Health Sciences says caution is the better part of valor when using such oils.

“Our society deems essential oils as safe. However, they possess a diverse amount of chemicals and should be used with caution because some of these chemicals are potential endocrine disruptors,” he says.

The research was prompted by a growing number of reported cases of gynecomastia associated with an usage or exposure to essential oils. More damning, the symptoms subsided once the patients stopped using the oils, associated products, or otherwise limited exposure to the oils. It was also spurred on by previous findings of co-author Dr. Kenneth Korach, who reported back in 2007 that lavender and tea tree oil would interfere with the activity of male-specific hormones, which could affect the development of boys hitting puberty.

The new study took an in-depth look at eight key chemicals contained in the oils. Four of these were shared in both lavender and tea tree oil, while the other four were found in either oil. To determine the effect of each compound, the team isolated samples of each, and then applied these to human cancer cells in the lab, recording any changes they observed.

All eight compounds showed varying degrees of estrogen promotion, testosterone inhibition, or both. More worryingly, most of these eight compounds are found in some 65 other types of essential oils, Ramsey explains.

“Lavender oil and tea tree oil pose potential environmental health concerns and should be investigated further,” he said.

This hormonal effect could explain why people using essential containing such chemicals run a higher risk of developing breast tissue. Naturally, some individuals will be more sensitive to the effects than others, and the level of use/exposure is also an important factor — so individual mileage may vary. So far, the results do suggest that better regulation or a higher level of consumer awareness are required to limit the negative health impacts of essential oils and products that contain them.

But before you assault an essential oil stand crying bloody vengeance, keep in mind that this study has some significant limitations. Chief among them stand the use of cancer cells and the dosages used. Cancer cells, which is what the team used as a subject, may or may not accurately represent the response of other tissues — say, of healthy breast tissue. The dosages (concentrations) the team used could also not accurately recreate the dosage a living, in-vivo cell might experience.

Living organisms also maintain a complex set of checks and balances on hormonal levels, which a culture of cancer cells in a lab couldn’t replicate.

All these limitations should be addressed by future studies before a definite link between gynecomastia in children and tea tree or lavender oil can be established. Until then, here is a list of safety guidelines on the use of essential oils from the Aromatherapy Trade Council:

  • Precautions should be observed when using essential oils since they are highly concentrated.
  • Do not apply undiluted essential oils directly to the skin.
  • Never use undiluted oils on children under the age of three.
  • If you are pregnant you must seek the advice of your doctor, midwife or aromatherapist before using any essential oils.
  • When used appropriately, essential oils and aromatherapy products are safe for all the entire family.

The study results will be presented today, 19 March, at the Endocrine Society’s annual meeting in Chicago.

Recents studies show how coffee is good for your health

Steaming hot, iced, blended, black, creamy. Coffee! It comes in many forms, and it’s part of my daily routine. It’s part of many others’ too. Last week several established publications’ websites were running coffee-related articles, touting this beverage’s health benefits. Scientists have remarked on this drink’s healthful qualities in the past. The idea that coffee is good for you is not a new one.

The Relationship with Diabetes

The delightful drink seems to help in warding off type 2 diabetes. The sex hormone-binding globulin, or SHBG for short, is a protein which controls the sex hormones in the human body: testosterone and estrogen. It has also been considered to have a key role in the evolution of this specific type of diabetes.

It has been observed that drinking coffee will increase the amount of plasma of SHBG. A few years ago, a study showed that women who ingested a minimum of four cups each day were slightly less likely to develop diabetes as opposed to those who didn’t drink it at all.

Help in Other Areas

The Best Way to Start the Day Right. Source: Pixabay.

Coffee, primarily the caffeinated kind, has been known to prevent as well as alleviate Parkinson’s disease. The consumption of caffeine has been found to significantly decrease the number of Parkinson’s cases. In fact, it may even aid in simple movement in individuals afflicted with the disease.

It provides some benefits for those who are concerned about their heart. Small daily doses can assist in preventing heart failure. In one study, it was shown that the risk of heart failure in people drinking four European cups of coffee per day was reduced by 11%.

Newer studies show that the regular intake of a relatively small amount of coffee can bring down the chances of premature death by 10%. Additional benefits could possibly include preventing cirrhosis, decrease the likelihood of multiple sclerosis (MS), and prevent the onslaught of colon cancer. However, to be certain whether these benefits are actually present in coffee more tests are needed. It is also one of the very best sources of antioxidants which protect the human body against destructive molecules called free radicals. This is good since free radicals are believed by many scientists to bring about cancer, blood vessel disease, and other serious ailments.

The Biggie: Coffee and Liver Health

From Pot to Cup. Source: Pixabay.

Perhaps the biggest health factor it basks in being associated with is liver health. Marc Gunter, head of a recent large-scale European study noted by National Geographic, has stated coffee drinking is linked to good health in the liver and circulatory systems. He also says it can account for lower inflammation levels in those who drink it as opposed to those who don’t.

The discoveries this study has led to supply the strongest defense to date for the healthful qualities of coffee. Gunter informed the scientific community and the public that he plans to examine the beverage’s chemical compounds in an attempt to know what makes it healthful.

We have actually seen how it can aid in liver conditions for several years. For instance, it was found that consuming three cups of coffee on a daily basis reduced the chances of getting liver cancer by 50%! Decaf also decreases the number of enzymes located in the liver. Thus, it is seen that caffeine is not always the prime healthy aspect provided in coffee. Drinking the beverage frequently has been associated with decreasing the risk of primary sclerosing cholangitis (PSC) which is a rare disease infecting the liver’s bile ducts.

As we’ve seen, coffee has quite a few benefits when drunk regularly and moderately. The important thing to recognize now is that many specific studies need to done on coffee itself and how it relates to treating various illnesses.

Ibuprofen long-term use linked to infertility in men

Scientists discovered that long-term use of ibuprofen — the most common painkiller worldwide — reduces testosterone tissue levels in young healthy men, affecting fertility, erections, muscle mass, libido, and mood. The painkiller’s extensive use over a period of more than two weeks is associated with a state of compensated hypogonadism.

Via Pixabay/Vnukko

What is Ibuprofen?

Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) used to treat fever, pain, and inflammation. Even though the US National Institutes of Health warns buyers that this substance is linked to increased risks of heart attacks, strokes, gastric and intestinal ulcers and perforations, Ibuprofen is still available over the counter (OTC) worldwide.

Of course, it wouldn’t be such a tragedy if people would take ibuprofen only on doctor’s orders. But the availability of the drug and the innocent reputation it still has are alarming.

Bernard Jégou, co-author, and director of the Institute of Research in Environmental and Occupational Health in France first studied the interactions of common analgesics such as aspirin, paracetamol (Tylenol), and ibuprofen with pregnancy. He discovered that all three drugs affected the development of the fetus’s testes.

However, the effects of such medication on adult males were still unknown. So, to truly understand the matter, Jégou’s team thought of an extensive study.

Source: Max Pixel

In vivo, ex vivo and in vitro

The “In vivo” (inside the living body) experiment involved 31 healthy men between the ages of 18 and 35 who had their blood testosterone levels measured by the researchers. The volunteers were separated into two groups, 14 subjects receiving a 44-day ibuprofen treatment (600 mg, twice a day) and the other 17 participants being offered a placebo. When researchers measured testosterone blood levels, they found them unchanged.

What did change was the testosterone to LH (luteinizing hormone) and FSH (follicle-stimulating hormone) ratio. These two hormones are testosterone regulators. When the production of testosterone is low, the pituitary gland synthesizes more LH and FSH, thus signaling the Sertoli and Leydig cells in the testicle to produce more testosterone. This condition is known as compensatory hypogonadism and it usually affects older men and smokers.

Next was the “ex vivo” (outside the living body) component of the study. Doctors studied the effect of ibuprofen on testicular tissue samples received from donors. After exposing Leydig cells to ibuprofen for two days, researchers found that the drug disrupted male hormone synthesis. The “in vitro” (in the test tube) phase findings were consistent with the testicular tissue experiment.

“It is sure that these effects are reversible,” Jégou told CNN. “However, it’s unknown whether the health effects of long-term ibuprofen use are reversible” he added.,

At this moment, Ibuprofen is considered to be the broadest male endocrine-disturbing drug from all chemical classes. Physicians advise taking this medicine with caution, no longer than 10 days in a row.

Findings appeared in the journal Proceedings of the National Academy of Sciences. 

Male contraceptive rub-on gel trial starts in 2018

A new method of male contraception will be tested starting April 2018. The product is a rub-on gel that contains two hormones: progestin and synthetic testosterone. The progestin decreases the sperm count by preventing the testes from producing enough testosterone, hence reducing the regular production of sperm. The artificial testosterone will keep the hormonal balance intact, without allowing the body to conduct spermatogenesis.

This study on male hormonal contraception will be the largest one ever conducted. Researchers will monitor 400 couples from the United States, UK, Kenya, Italy, Chile, and Sweden during a four-year clinical trial. First, the couples will use both female and male contraceptive methods, until the sperm count will drop to less than 1 million per millimeter. Next, the couples will resort only to applying the gel which is effective for approximately 72 hours.

The doctors have instructed the male participants to rub half a teaspoon of gel on their upper arms and shoulders daily. The most significant risk to the birth control’s inefficiency is forgetfulness. In fact, forgetting to take birth control at the same time every day is the primary factor in female contraception failure.

Via TBIT/Pixabay

 Luckily, the scientists designed the product to have a safety net: a half-life of over 24 hours.

“I am very confident that if men put the gel on every day and apply it correctly, it will be effective,” said Stephanie Page, a professor of medicine at the University of Washington and one of the investigative leaders of the trial, reported MIT Technology Review.

Researchers didn’t choose this pharmaceutical form — the gel — by chance. Usually, the artificial testosterone is rapidly metabolized by the body. By delivering testosterone in gel form, the blood levels of the hormone will be adequate for a longer time, thanks to the slow transdermal absorption.

This trial is based on a paper published in July 2012, involving two gels that had to be applied to different body parts. The study involved 99 men and lasted six months. The outcomes were still not enough for the product to be approved for commercial distribution, so Diana Blithe’s team from the US National Institutes of Health started working on another, more extensive, study.

Source: Gadini/Pixabay

One question still lingers in our heads: Will men use hormonal contraception? Even though the method seems simple, there is no assurance the public will embrace the product quickly.  Researcher R. Sitruk-Ware thinks that younger men will especially be interested in using the drug.

The scientist told MIT Technology Review that “This is about gender equity. Men would also like to be able to regulate their own fertility and not be forced into fatherhood.”

Her view, indeed, makes a strong point. The implications of this study are humongous. This easy to use male birth control might reduce unwanted pregnancies worldwide, thus diminishing child abandonment, or even solving Earth’s overpopulation.


Testosterone makes men more confident in their instincts, less likely to question their impulses

Hotheaded, driven, impulsive — that’s Holywood’s archetypical main action movie dude. But there might be a kernel of truth to this over-the-top silver screen persona, as a new paper reports on the effects of testosterone on behavior.


Image credits Chris & Karen Highland / Flickr.

Now, I don’t often partake into the habit of generalizing behavior by gender — men like to keep an open mind, after all. But I think we can all agree that (to some extent) if something seems fun, bragworthy, or will impress someone but isn’t exactly sensible, there’s one guy close at hand ready to take up the challenge. We’re also the half of the table more likely to jump into a pub melee and/or send you a lot of texts with the word “duck” autocorrected in afterward. In short, men are on often regarded as the less restrained, more aggressive, more impulsive of the sexes.

A team of researchers from Caltech, the Wharton School, Western University, and ZRT Laboratory set out to see if men’s higher levels of sex-hormone testosterone can explain this tendency to rely on intuitive judgements at the expense of cognitive reflection — the self-scrutinizing process by which someone stops to consider if these gut reactions actually make sense. They report that men given doses of the hormone performed worse on a test designed to measure levels of cognitive reflection compared to their counterparts who received a placebo.


The study included 243 male testees and was the largest ever conducted of its type. Participants were randomly assigned to receive a dose of either testosterone or placebo gels before the test began. They were also evaluated on their motivation levels, engagement with the test, and basic math skills before the tasks through a simple test.

The questions generally involved or required math to solve. They weren’t particularly hard, but they were designed in such a way as to seem really simple and elicit a ‘gut’ solution. For example, take the following task: If a bat and a ball cost $1.10 in total, and the bat costs $1 more than the ball, how much does the ball cost?

Not exactly rocket science™, is it? The trick is that for most people, our brains blurt out “10 cents” before we get a chance to think about it. This answer is incorrect because then the bat would only be 90 cents more expensive than the ball. If you go through the mental process of evaluating your result, you’ll conclude that the ball, in fact, costs 5 cents and the bat $1.05. But a person who relies on their gut instinct is more likely to answer “10 cents” without going through cognitive reflection, giving the team a good indication of how often someone just goes with their instincts vs how often they check the validity of their intuition.

The participants could take as much time as they wanted on the test and were offered $1 for each correct answer and an additional $2 if they answered all the questions correctly as an incentive.

“What we found was the testosterone group was quicker to make snap judgments on brain teasers where your initial guess is usually wrong,” says Colin Camerer, Caltech’s Robert Kirby Professor of Behavioral Economics and Chair of the T&C Chen Center for Social and Decision Neuroscience Leadership. “The testosterone is either inhibiting the process of mentally checking your work or increasing the intuitive feeling that ‘I’m definitely right.'”

The testosterone group scored significantly lower than their placebo counterparts, answering 20% fewer questions correctly, on average. They were also quicker to give incorrect answers and gave “correct answers more slowly than the placebo group,” the authors note. This effect wasn’t seen in the results of the initial math test, showing a “clear and robust causal effect of [testosterone] on human cognition and decision-making,” the team concludes.

They believe this cognitive shift stems from testosterone’s documented effect of increasing confidence levels. The hormone is also believed to enhance the male drive for higher social status, and higher levels of confidence enhance status, the authors write.

“We think it works through confidence enhancement. If you’re more confident, you’ll feel like you’re right and will not have enough self-doubt to correct mistakes,” Camerer says.

The results should raise questions about the negative effects testosterone-replacement therapy might incur, he adds. The practice is aimed at reversing the decline in sex drive experienced by many middle-aged men, but in light of the new findings, it’s likely that their behavior and decision-making processes also change following the procedure.

The paper “Single dose testosterone administration impairs cognitive reflection in men” has been published in the journal Psychological Science.

These lionesses have grown a mane and are acting like males

Five lionesses in Botswana have grown male-like manes and one is even roaring and humping other females.

Photo by Simon Dures.

The lion king you see above is actually a queen – and she’s not the only one looking like this. Geoffrey D. Gilfillan at the University of Sussex in Falmer, UK and colleagues have reported five lionesses sporting a mane at the Moremi Game Reserve in Botswana’s Okavango delta.

As we learn when we’re kids, male lions have a big mane, they roar, and they’re the kings of the savannah. Females are a bit smaller and don’t have the rich hair, but they do most of the hunting. However, there’s a small group which doesn’t fit that description, as Gilfillan learned. He started studying these lionesses back in March 2014 and especially focused on a female he called SaF05.

“While SaF05 is mostly female in her behaviour – staying with the pride, mating males – she also has some male behaviours, such as increased scent-marking and roaring, as well as mounting other females,” says Gilfillan.

“Although females do roar and scent-mark like males, they usually do so less frequently,” he says. “SaF05, however, was much more male-like in her behaviour, regularly scent-marking and roaring.”

She’s not alone in exhibiting these masculine features. Four other females have been spotted doing similar things and also growing manes. It’s not clear why this happens, but it’s most likely linked to an increased testosterone production. In lions, testosterone directly affects the mane. Castrated lions, for example, will lose their ability to produce testosterone and their mane will fall off as a result. Something like this, but in reverse, could be what’s happening here. It wouldn’t be the first time either. In 2014 13-year-old lioness named Emma at the National Zoological Gardens of South Africa started to grow an incredible mane.

This is how female lions generally look like. Photo by Mr. TinDC

Biologists working at the zoo removed her ovaries and found something surprising.

“Surprisingly, the ‘ovaries’ that were removed only contained cells normally seen in the testicles of males. This was obviously where the testosterone was being produced,” said the zoo’s clinical veterinarian, Adrian Tordiffe, at the time.

“After her ovaries were removed, Emma gradually lost her mane hair and returned to her normal female good looks.”

The changes might offer a bonus when the pride is competing with other prides, but it might also signal something much more worrying. The females might be carrying a very rare genetic mutation which also makes them infertile. This means that the anomaly will not spread to the offspring, but it also means that the pride will have a hard time creating offspring in the first place.

Luke Hunter, president and chief conservation officer at the global wild cat conservation organisation Panthera, believes there’s no reason to worry.

“I don’t think this is anything to be concerned about,” says Hunter. “Although the females are apparently infertile, they otherwise appear to live long, healthy lives. And from a conservation perspective, there is nothing to suggest the pattern is increasing or will ever be anything more than a rare, local phenomenon.”

From a scientific point of view, it’s extremely interesting. A notable episode took place when SaF05 hunted a zebra. A neighboring pride then stole the zebra from her and in response, she went and killed two cubs from the other pride. This is extremely uncommon for females but quite common in males.

Journal Reference: Rare observation of the existence and masculine behaviour of maned lionesses in the Okavango Delta, Botswana.

Good fathers’ testosterone level drops when expecting a baby

A news study found that men show shifts in behavior from mating-oriented to parent-oriented while their partners’ pregnancy develops. These changes are determined by changes in testosterone levels across pregnancy and hormonal linkage with their partner.

Image credits Chris Price / Flickr

It’s almost hard to imagine that every caring dad was once a skirt-chasing ball of hormones — but it’s true. Somewhere along their transition to parenthood, biology puts a stop to men’s carefree days of sowing wild oats and turns their attention towards nurturing children. This is a very solid strategy from an evolutionary point of view, but we didn’t know exactly how it happened.

A new study found that the answer may be testosterone. While high levels of this androgenic steroid hormone have been associated with aggression and competitive behavior, lower levels promote nurturing behaviors, particularly those related to caring for offspring.

Previous studies show that fathers who are in a relationship and are more involved with children’s care show lower testosterone levels that men who don’t have children. Lower levels of salivary testosterone have also been tied to higher self-reported levels of relationship satisfaction and commitment, a lower interest in sex outside of marriage and a lower chance of divorce. So it would seem that a father’s decrease in testosterone levels during the transition to parenthood leads him from exploring new mating opportunities towards investment into the current relationship and caring for offspring.

Led by Darby Saxbe of the University of Southern California, the study followed 27 couples expecting their first child during pregnancy and first few months after birth. The parents’ testosterone levels were measured during this pregnancy, and participants rated their investment, commitment, and satisfaction with their partner a few months after their child’s birth.

The team found that fathers showed significant declines in testosterone while the pregnancy progressed, and a significant positive correlation with the mother’s testosterone levels. A better correlation between the mother’s and father’s testosterone levels during pregnancy was associated with higher levels of father involvement after the child’s birth —  the degree of synchrony between the parents predicted the fathers’ investment, commitment, and satisfaction in the couple relationship.

Interestingly, they also found that testosterone levels before the birth of the child predicted the relationship outcomes after the birth, even after adjusting for fathers’ scores of investment early on in the pregnancy.

“The direction of our effects suggests that hormonal change and synchrony predict relationship investment, not the other way around; that is, relationship investment at the first prenatal assessment was not significantly associated with testosterone change or coordination with mothers,” concluded the authors.

The full paper, “Fathers’ Decline In Testosterone And Synchrony With Partner Testosterone During Pregnancy Predicts Greater Postpartum Relationship Investment” has been published in the journal Hormones and Behavior.

How maternal testosterone levels can cause anxiety in offspring

Women suffering from polycystic ovary syndrome (PCOS) show elevated levels of testosterone and testosterone derivatives in their systems, as well as an increased risk of anxiety and depression. As the offspring of these women (both sons and daughters) show similar symptoms, it’s been believed that PCOS can be transmitted through genetic code. However, a new idea comes to question this — specifically, the fact that the fetuses of mothers with PCOS are gestating in high levels of testosterone is what causes these symptoms.

Image via theodysseyonline

High levels of maternal testosterone during gestation are known to affect brain morphology and function in offspring and research has been able to link it to feelings of anxiety in both mice and humans. An international team of researchers studied the levels of androgen receptors in different brain regions associated with anxiety and depression to find out exactly how maternal testosterone and anxiety are linked.

The offspring of rats that showed elevated levels of testosterone were anxious, with behavior indicative of this much more pronounced in female baby rats than male babies. The team found that the excess testosterone during gestation diminished the ability of the child to respond to the hormone — much like how you stop registering smell or taste if it persists for too long.

Messenger RNA levels (that encode testosterone receptors information and other similar molecules) were lower in the amygdalae and hippocampuses of the offspring, with a stronger effect on the females. The amygdala in particular has an important role to play in processing emotions, and dysfunctionalities here have been linked with several anxiety disorders.

To confirm that testosterone can have these effects, the researchers recapitulated both the anxiety and the diminished receptor levels in adult female mice by injecting them with testosterone.

“The maternal testosterone dose used may masculinize the brain of female offspring,” the authors conclude about their rat model.

But it’s not just a masculinization — levels of a serotonin receptors were similar in the amygdalae and hippocampuses of testosterone treated mice of both sexes, but less than those of the control group.

This suggests that high testosterone levels in women suffering from PCOS during gestation cause anxiety in two generations. It makes the females themselves anxious, and it can alter the brain morphology of offspring, leading to anxiety disorders. And while the children do not inherit the higher level of testosterone in their system, they show less receptors for the hormone in their brain, influencing their behavious.

This is a level of transmission that is not genetic, but it’s clearly inheritable.


Transition to civilization led to drop in testosterone

A composite image shows the facial differences between an ancient modern human with heavy brows and a large upper face and the more recent modern human who has rounder features and a much less prominent brow. The prominence of these features can be directly traced to the influence of the hormone testosterone. Photo Credit: Robert Cieri, University of Utah

According to a new study published in Current Anthropology, our transition into modern civilization has probably coincided with a drop in testosterone. It’s very likely (though not entirely proven) that it was the transition to civilization that precipitated the drop.

University of Utah biology graduate student Robert Cieri analyzed 1,400 ancient and modern human skulls, showing that some 50.000 years ago, when human civilization was starting to be developed, a drop in testosterone also came into place. Skull shape and testosterone levels can be associated, and the decrease in testosterone can be “mapped” by changing skull anatomy.

“Humans are uniquely able to communicate complex thoughts and cooperate even with strangers,” Cieri says. “New research on fossilized Stone Age humans from Europe, Africa and the Near East suggests these traits are linked, developed around 50,000 years ago, and were a driving force behind the development of complex culture.”

It is currently accepted that modern humans, Homo sapiens, appeared about 200.000 years ago, but evidence of civilization, such as symbolic or cultural artifacts and modern tools were only found from 50.000 years ago – about the time when their faces started to become more feminine.

“Human fossils from after modern behavior became common have more feminine faces, and differences between the younger and older fossils are similar to those between faces of people with higher and lower testosterone levels living today,” Cieri says.

It is important to note that lower testosterone is associated with tolerance and cooperation in bonobos and chimpanzees, and with less aggression in humans. It seems very plausible that as humans started to group up in larger and more interconnected settlements, they needed to find less violent ways to sort out their problems – and in the long run, the non-violent path won. This may be the cause, perpetuated by natural selection, or there might be something else involved

“Whatever the cause, reduced testosterone levels enabled increasingly social people to better learn from and cooperate with each other, allowing the acceleration of cultural and technological innovation that is the hallmark of modern human success,” Cieri says.

The caveman theory that says men are better navigators than women because they had to find their back home after hunting is flawed, University of Illinois researchers show.

Why are men better navigators than women? Testosterone, not evolution might be the answer

The caveman theory that says men are better navigators than women because they had to find their back home after hunting is flawed, University of Illinois researchers show.

The caveman theory that says men are better navigators than women because they had to find their back home after hunting is flawed, University of Illinois researchers show.

It’s a rather well-attested fact that men are significantly better than women at spatial navigation, something that holds across a wide variety of species, not just humans. General belief holds that evolution triggered this response since our ancestors needed to return home after traveling vast distances in search of food, while the females stayed home. This theory is flawed according to the University of Illinois, who have proven this not to be the case. Instead, they suggest testosterone as a more reasonable explanation for spatial differences between men and women.

If the evolutionary theory were correct, as in males that were better at navigating had a better chance of survival and thus passed on their genes, then basic genetics tells us that these genes would have been passed to women as well. Still, the discrepancy holds.

The only way a certain gene might be passed to a sex of a species, and not the other, is if that gene would negatively affect one of the sexes and not the other. A good example is nipples. For women, nipples are indispensable and is fairly obvious why (nurture young), however, they serve no purpose in men. So why do men have them? The answer is simple: because it doesn’t hurt them. If nipples would negatively affect men in some sort of way, then they would have disappeared in a matter of a couple of generations.

Still, to test plug holes even further in this evolutionary theory for spatial ability, University of Illinois researchers aggregated data from 35 studies on territorial ranges and spatial abilities in humans and a number of animals, including cuttlefish, deer mice, horses, laboratory mice, meadow voles, pine voles, prairie voles, rats, rhesus macaques and talas tuco-tucos (a type of burrowing rodent).

If the theory was true, then the researchers should have seen a sort of correlation or even a simple link between territorial range and spatial ability. No such thing, however. The scientists found that in the eight out of eleven species where males showed better spatial reasoning than females, this behavior applied regardless of territory size or the extent to which male ranges spanned farther than female ranges. So even though females roamed just as much as males, they still weren’t as good at making their way around as males.

“We find no support for the hypothesis that species differences in home range size dimorphism are positively associated with parallel differences in spatial navigation abilities.”

“The alternative hypothesis that sex differences in spatial cognition result as a hormonal side effect is better supported by the data,” the authors write.

And the key hormone that the researchers believe is actually driving better spatial reasoning is testosterone. Navigational abilities may be a side effect of higher testosterone levels: previous studies have shown that women who take testosterone tend to see an improvement in their spatial navigation abilities.

What’s more important to take away from this, however, is that while a theory might seem intuitive, it might be flawed and showed be considered flawed until solid evidence is brought on the table. An unfounded theory is not a theory, but a story.

The findings of the present study were reported in The Quarterly Review of Biology.