When it comes to having sex, first-born girls tend to lose their virginity at a later age than their younger sisters, according to new Australian research.

The study, which was presented to an Australian Society for Human Biology conference recently, was carried out by researcher Fritha Milne, from the University of Western Australia, who examined the sexual appetites and behaviours of siblings.

Previous studies have shown that firstborns are more likely to be confident and family oriented, whilst middle-born children have the toughest time. Now, it seems there are also differences when it comes to reproductive strategies, including the age at first sexual intercourse, first pregnancy and first birth, with the middle-born children standing out in the survey results.

Middle-born males have sex for the first time at a younger age than their brothers, and last-born females are younger when they have sex for the first time. But middle-born children of both sexes tend to have fewer children of their own, the report suggested, with females 2.6 times more likely to fall pregnant at any given age.

Milne said that her work confirmed the first five years of a child’s life are important:

During this time the young must elicit support and resources from the parents,

If there are any siblings, then the siblings have to compete for the limited resources of the parents.

In order to maximise the resources that the children get they have to find themselves a different niche within the family to get those resources from the parents.

She went on to explain that the oldest children tend to align themselves with the “parental status quo,” which partly explains why they’re more conservative in their sexual choices.

Posted by Jonathan as Biology, Sociology at 9:09 PM BST

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A large body of research has shown that women are more responsive to masculine voices, faces, and odours at times when they’re most likely to become pregnant, but according to Professor Nicolas Guéguen, a psychologist at the University of South Brittany in France, no studies have probed the obvious outcome of such inclinations.

So, Professor Guéguen and his team recruited several young men to experimentally hit on women at a street corner, in order to determine whether fertility affects receptivity to male advances or not. And, it seems that women are most likely to give their phone number to a male stranger during the fertile phase of their menstrual cycle.

Professor Guéguen said:

[previous] studies did not focus on women’s behaviour. [This is] the first study to test the role of the menstrual cycle on courtship request, in a real social context and not in laboratory.

In conducting their study, which was published in the journal Biological Psychology, the scientists recruited five handsome 20-year-old men (selected from a larger group and judged for attractiveness by 28 women), in order to experimentally express interest in women passing a street corner, by asking the unsuspecting females for a date.

On nice summer days, the young men approached the first young woman they saw passing the street corner and delivered a standardized pick-up line:

Hello. My name’s Antoine. I just wanted to say that I think you’re really pretty. I have to go to work this afternoon, and I was wondering if you would give me your phone number. I’ll phone you later and we can have a drink together someplace.

If the woman gave her number, “Antoine” responded: “See you soon,” and left. If she refused, a similarly cheery response of: “Too bad. It’s not my day. Have a nice afternoon!” was given.

Almost immediately after the encounter, and regardless of how the subject responded, a female researcher approached the woman and informed her of the experimental nature of the encounter, asking the woman to complete a short questionnaire. The survey asked questions about age, contraception use and days since her last period (or pregnancy status). Although none of the questions gauged her likely disappointment at the deception.

Of 506 women that were approached, just 51 declined to take part in the survey. And, from analysing the responses of the 455 active participants, Guéguen noted that in total, 8.6% of the women provided their phone number to the men. However, women not taking oral contraception were more than twice as likely to accept the men’s offer as women taking the pill (12% versus 5.8%). Although this could just reflect the likelihood that women on the pill may be more likely to already have a man in their life than women not taking birth control.

However, when Guéguen analyzed the data according to the women’s fertility, a more interesting trend emerged – Amongst naturally cycling women, those in their fertile phase accepted 21.7% of advances, whilst women in the midst of their periods responded to just 7.8% of men, a significant statistical difference that did not exist for women on the pill.

Professor Guéguen cautiously suggests his interpretations may offer real-world behavioural support for research showing that women are most receptive to advances when they are likely to get pregnant.

Hormones could play a role in the study’s results, since estradiol (a form of oestrogen) and progesterone levels rise and fall during a woman’s cycle, and most birth control pills contain progesterone. But Guéguen cautions that a woman’s relationship status could mask such associations, because single women could be less likely to be on birth control.

To firm up the results, Guéguen is also repeating the study in scenarios where men may be more likely to get a woman’s cellphone number, describing a follow up study where:

Twenty-year-old women were approached by 20-year-old males in nightclubs and solicited to dance with them during the period when slow songs were played

And noting:

Until this study comes out, guys may want to focus their attention on less personal cues to a women’s interest.

Posted by Jonathan as Biology, Psychology at 11:34 PM BST

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The usefulness of sex, according to an intriguing new theory of evolutionary biology, may be its ability to promote genes that play well with many other partners, rather than just those that shine with one specific set of genes.

This idea of genetic mixability, described in the journal Proceedings of the National Academy of Sciences hits on the difficulties that Evolutionary biologists have had in understanding the role of sex in population genetics and Darwin’s survival-of-the-fittest mantra.

Lead author Adi Livnat, a Miller Institute post-doctoral fellow based at UC Berkeley’s Department of Electrical Engineering and Computer Sciences said:

During the past century, it has often been assumed that sexual reproduction should somehow facilitate the increase in fitness under natural selection, leading to the ‘best’ combinations of genes. But no agreement has been reached on whether and how this could really work. One might think, for example, that by bringing together genes from different individuals, sexual reproduction could create a very successful combination of genes. But just as sexual reproduction will create that very successful combination of genes, it could also break it down in the next generation.

That sex can actually impede the increase in the fitness of the population raises the question of how it could remain the dominant form of reproduction across all manner of species, when the fact remains that sexual reproduction (the merging of genes from different individuals to create genetically unique offspring) is the reproductive method of choice from humans to plants to many fungi. So, this form of reproduction must be doing something right in terms of evolution.

Thinking laterally, instead of making the standard assumption that sexual reproduction increases the average fitness of a population, the researchers came up with a new measure they call “mixability” to represent a gene’s ability to perform well across many different combinations.

They tested the mixability measure in a number of scenarios, within a well-established population-genetic framework and found that if the goal is to maximize fitness by finding a particularly good combination of genes, asexual reproduction – which increases a population’s numbers at a much faster rate than sexual reproduction – works very well.

In contrast, sexual reproduction, through the process of recombination and segregation of chromosomes, strongly favours genes that work well in many different variations rather than any one good combination. In that view, the authors wrote, alleles of the same gene compete with each other based upon how well they perform on average rather than how well they perform in any one specific combination.

Co-author Marcus Feldman, Professor of Biology at Stanford University, and a world-renowned theorist in evolutionary biology said:

It’s important to note that during the process of evolution, the mixability value increases, though it doesn’t increase all the time. The approach we take is different from usual because we’re interested in Evolutionary transience, and in the long run, our mixability value may actually decrease because too much variability is lost from the population.

Even so, sexual reproduction has a great advantage for mixability compared with asexual reproduction, according to the models used in the paper.

Livnat started thinking about this problem in discussions with co-author Christos Papadimitriou, Professor of computer sciences at the University of California, Berkeley, and a leading computer theorist whose research includes optimization algorithms. Such programming is widely used to find best outcomes in applications such as computer networks, transportation planning and financial models.

The researchers explained that of the two main techniques for optimization programming, the first, known as simulated annealing, solves problems using a process analogous to asexual reproduction, whilst the second, known as genetic algorithms, is inspired by sexual reproduction. Genetic algorithms should theoretically be the more efficient of the two techniques for finding the best solutions to a problem because they mimic an approach that is so dominant in nature. However, it turns out that genetic algorithms often perform no better than simulated annealing.

Professor Papadimitriou said:

We were trying to figure out why an algorithm that mimics a good idea in nature was not coming up with better results. It dawned on us that what sexual reproduction is doing is not maximizing fitness, but doing something more subtle. It is bringing about genetic variants that perform well across many possibilities in connection with a great variety of genetic partners. If a particular gene variant can do well with many other alleles, not just a highly specialized variant, evolution is advanced.

The researchers noted that when the human genome was sequenced in 2003, there was surprise that humans didn’t possess far more genes than other species. It turns out that how those genes are combined may be a critical factor in distinguishing humans from other species, supporting the importance of flexibility over fitness.

Feldman, who has studied the evolution of sex and recombination for more than three decades, said he expects this new theory to trigger much debate among his peers, adding:

This problem of understanding sex will go on being one of the central issues in evolution.

Posted by Jonathan as Biology, Sociobiology at 12:53 AM BST

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Researchers, based at the Institute of Psychiatry, King’s College London have been analysing archived data from former US soldiers who underwent intensive testing for intelligence, detailed medical examinations and provided semen samples.

The results, published in the journal Intelligence showed that in the men who performed better on intelligence tests, total sperm count was higher, as well as sperm concentration and motility. This suggests that in our ancestors, intelligence and sperm quality were linked, so intelligent men were more likely to reproduce.

It might be argued that brighter people would be less likely to smoke, and more likely to take exercise, both of which are known to impact on mental performance. But, even when lifestyle factors such as body mass index, use of alcohol, tobacco, marijuana, and hard drugs were taken into account, there was still a statistically significant correlation between intelligence and sperm quality.

Lead researcher Dr Rosalind Arden said:

We are not trying to say that under modern conditions intelligent men are going to have more children.

We wanted to test the idea that intelligence is favoured by natural selection.

We look forward to seeing if the results can be replicated in other data sets, with other measures of intelligence and other measures of physical health that are also strongly related to evolutionary fitness.

Dr Allan Pacey, Senior Lecturer in Andrology at the University of Sheffield commented:

The fact that it’s possible to detect a statistical relationship between intelligence and semen quality in adult men probably says more about the co-development of brain and testicles when the man was in his mother’s womb, and therefore how well they both function in adult life, rather than suggesting that playing Sudoku can somehow stimulate more sperm to be produced.

Posted by Jonathan as Biology, Sociobiology at 11:07 PM BST

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In 1956, Denham Harman proposed the theory of ‘oxidative stress‘; in which he claimed that ageing is caused by a build-up of molecular damage to cells, from the actions of reactive forms of oxygen such as superoxide.

These free radicals (oxygen molecules with an imbalance of protons to electrons) are created as by-products of cells metabolising sugars to release energy – So, the Diet and Beauty industry claims that Antioxidants such as vitamins C and E supposedly work to mop these up, thus minimising potential cell damage.

The oxidative stress theory has dominated the field of ageing research ever since it was proposed, but now, a recent study published in the journal Genes and Development, suggests that the idea is probably incorrect and that superoxide is not a major cause of ageing.

David Gems, of University College London, and colleagues at the Institute of Healthy Ageing studied the action of key genes involved in removing superoxide from the bodies of the nematode worm Caenorhabditis elegans, a commonly used organism in research into ageing. By manipulating the worm’s genes, they were able to control the nematode’s ability to ‘mop up’ surplus superoxide and limit potential damage caused by free radicals. This modification should have given the GM nematodes an advantage over normal nematodes, in terms of ageing and lifespan.

However, contrary to the results predicted by the free radical theory of ageing, the researchers found that the lifespan of the worms was relatively unaffected by their ability to tackle the surplus superoxide. So, these findings, combined with similar recent findings from the University of Texas, using mice, suggest that the oxidative stress theory is incorrect.

Dr Gems, who led the study, noted that molecular damage was probably caused by numerous different chemicals within the cell, and went on to say:

Our results spectacularly failed to support the view of the free radical theory.

The fact is that we don’t understand much about the fundamental mechanisms of ageing – the free radical theory has filled a knowledge vacuum for over 50 years now, but it doesn’t stand up to the evidence.

A healthy, balanced diet is very important for reducing the risk of developing many diseases associated with old age, such as cancer, diabetes and osteoporosis, but there is no clear evidence that dietary antioxidants can slow or prevent ageing. There is even less evidence to support the claims of most anti-ageing products.

Dr Alan Schafer, Head of Molecular and Physiological Sciences at the Wellcome Trust, who funded the research, said:

With increasing lifespan comes greater exposure and vulnerability to the ageing process. Research such as this points to how much we have to learn about ageing and the importance of understanding the mechanisms behind this process.

This new study will encourage researchers to explore new avenues in ageing research.

Posted by Jonathan as Biochemistry, Biology at 11:00 PM BST

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Amongst people in their 30s and 40s, and in partnerships where there is an age difference of five or more years, condom use is particularly low.

Nearly 70 percent of those aged between 16 and 19 used a condom with a new partner, compared to 38 percent of men and 29 percent of women aged between 35 and 44, a new study has shown.

This worrying news comes as the number of people diagnosed with sexually transmitted infections (STIs) was shown to have risen by a quarter in just five years, and has sparked calls for an urgent drive to promote condoms to all age groups, and not just young people.

The researchers also found that where there was an age difference between partners of five years or more (regardless of whether the man or woman was older), 44.1% of respondents reported using condoms at first sex, compared to 60.8% in partnerships that were closer in age.

The figures, published in the International Journal of Epidemiology, showed that although the overall number of heterosexual people using condoms for first time sex stood at 55 percent, that figures declined with age.

Author, Dr Catherine Mercer, a lecturer at the Centre for Sexual Health & HIV Research, University College London, said:

Our finding that condom use at first sex declined with increasing age is of concern.

Although a disproportionate amount of partnerships are formed among people in their teens and 20s, the fact is that about 45 percent of marriages are now expected to end in divorce, which means that the ‘population attributable risk’ by those in their 30s and 40s will increase.

Increasing rates of STIs diagnosed among those in their 30s and 40s suggest that interventions that promote consistent condom use with new partners are urgently required.

Not just for young people as has been the focus recently, but for people in their 30s and 40s and older who are increasingly forming new partnerships.

Commenting on her age difference findings, Dr Mercer said:

This may reflect unequal power relations, so that younger people in such partnerships may not have the necessary communication and negotiation skills to ensure safe sex with older partners. This finding may have implications for sex and relationship education and counselling. Improving negotiation skills for women and men may facilitate communication and, in turn, increase the likelihood of condom use in such partnerships.

The researchers analysed the responses of 11,161 people (of whom 6,399 were women), who were interviewed about the last 12 months of their heterosexual relationships, for the second British National Survey of Sexual Attitudes and Lifestyles (Natsal 2).

Participants were asked about their three most recent partnerships and questioned about condom use, age differences in the relationship, where they met and how soon after meeting they had sex.

Of the 11,161 respondents, 9,598 reported a total of 15,488 heterosexual partnerships in the past year. A higher proportion of men’s partnerships were described as “not regular” – 39.1% compared to 20% of women’s partnerships; while a higher proportion of women’s partnerships were marriages or cohabitations – 55.2% versus 38.9% of men’s partnerships.

Men reported having sex sooner after first meeting a partner than women, with one in five men reporting sex within 24 hours of meeting their partner, compared with just one in 10 women.

Posted by Jonathan as Biology, Sociology at 11:09 PM BST

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Teenagers who watch a lot of television featuring flirting, necking, discussion of sex and sex scenes are more likely to be involved with a pregnancy, according to a new study.

The study, published in the November edition of the journal Pediatrics, found that teens who viewed the most sexual content on TV were about twice as likely to get pregnant, or cause a pregnancy, compared to those who saw the least.

Lead author, Anita Chandra, a behavioural scientist at non-profit non-partisan research organization, RAND Corporation said:

Adolescents receive a considerable amount of information about sex through television and that programming typically does not highlight the risks and responsibilities of sex,

Our findings suggest that television may play a significant role in the high rates of teenage pregnancy in the United States.

Researchers from RAND Health claim that exposure to sex on television may influence teen pregnancy by creating the perception that there is little risk to engaging in sex without using contraceptives and accelerating the initiation of sexual intercourse.

There is rising concern about teen pregnancy rates, which after decades of decline may have started creeping up again, fuelling an intense debate about what factors are to blame. And, although TV viewing is unlikely to entirely explain the increase in teen pregnancies, Chandra and others said, the study provides the first direct evidence that it could be playing a significant role.

Chandra and her colleagues surveyed more than 2,000 adolescents three times by telephone from 2001 to 2004; in order to gather information about a variety of behavioural and demographic factors, including television viewing habits. Then, based on a detailed analysis of the sexual content of 23 shows popular among teens in the 2000-2001 TV season, the researchers calculated how often the teens saw characters kissing, touching, having sex, and discussing past or future sexual activity.

Among the shows the teens watched were “Sex and the City,” “Friends” and “That ’70s Show.” Chandra wouldn’t identify the others, but stressed that they included dramas, comedies, reality shows and even animated programmes on broadcast and cable networks.

Amongst the 718 youths who reported being sexually active during the study, the likelihood of getting pregnant or getting someone else pregnant increased steadily with the amount of sexual content they watched on TV, the researchers found. About 25 percent of those who watched the most were involved in a pregnancy, compared with about 12 percent of those who watched the least. The researchers also took into account other factors such as intelligence, having only one parent, wanting to have a baby and engaging in other risky behaviours.

There were more pregnancies among the oldest teens interviewed, but the rate of pregnancy remained consistent across all age groups among those who watched the racy programs. Fifty eight girls reported getting pregnant and thirty three boys reported being responsible for getting a girl pregnant during the study period. The increased risk emerged regardless of whether teens watched only one or two shows that were explicit or surfed many shows that had occasional sexual content, Chandra noted.

Chandra Continued:

It could be a child wasn’t watching that much TV per week but was watching shows that got a pretty high rating on sexual content, or it could be a kid who was watching a lot of hours but on average was getting just moderate amounts of sexual content from each show.

The researchers recommended that parents spend more time monitoring what their children watch and discussing what they see, including pointing out the possible negative consequences of early sexual activity. Programmers should also include more-realistic portrayals of the risks of sex, such as sexually transmitted diseases and pregnancy.

However, according to Elizabeth Schroeder, Executive Director of Answer, a teen sex education program based at Rutgers University, the study doesn’t adequately address other issues, such as self-esteem, family values and income – saying:

The media does have an impact, but we don’t know the full extent of it because there are so many other factors

Other experts questioned whether the study had established a causal relationship, and Laura Lindberg of the Guttmacher Institute commented:

It may be the kids who have an interest in sex watch shows with sexual content. I’m concerned this makes it seem like if we just shut off the TV we’d dramatically reduce the teen pregnancy rate.

Chandra acknowledged that other factors might play a role but said the findings were compelling because the researchers were able to track the teens over time and found such a striking relationship, saying:

The magnitude of the association we did see was very strong

Posted by Jonathan as Biology, Sociology at 11:14 PM BST

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The “quality” of New Zealand men’s ejaculate has halved over the past two decades – The most dramatic drop of any western country.

This worrying news was presented to a gathering of international fertility researchers in Brisbane, Australia, who were told that the sperm volume carried by the average New Zealand man decreased from about 110 million to 50 million wigglers per millilitre, between 1987 and 2007.

Lead researcher Dr John Peek of Fertility Associates, Auckland, commenting on the relegation of NZ men’s sperm from very good to good quality, said:

It’s rather dramatic indeed, and one of the largest seen in studies in other parts of the world.

So large, in fact, that Dr. Peek suggested that if the downward trend continued towards the 20 million sperm per millilitre “danger mark”, New Zealand would “definitely be running into trouble“. However, the biggest drop was seen in the first decade, with a slower decline in more recent years.

The findings, to be published in the New Zealand Medical Journal, are based on sperm quality data from men volunteering as mystery sperm donors. This contrasts with Australia and the United States, where no decline has been seen; and studies from Scotland and France, which show only marginal declines.

The reasons for the sperm crisis are unclear, but Dr Peek suggested that there were two broad theories on sperm quality decline; one being that semen was affected by environmental toxins, diet and modern changes in lifestyle. The other being a consequence of something that happened when the man was a foetus, i.e. what his mother was exposed to, but both theories are still unclear.

Professor Michael Chapman, from IVF Australia, in Sydney, said the trend was “worrying” for New Zealanders, noting that it was to such a degree that the decline was unlikely to be pure chance. Professor Chapman suggested: “Maybe they have something else going on over the Tasman.”

However, Professor Rob McLachlan, director of Andrology Australia, in Melbourne, said any trend was likely to be global, and the jury was still out as several studies were contradictory. He commented:

Global trends are differing so we don’t have a clear picture on this yet.

And then joking:

New Zealand is unlikely to have a different situation unless you consider all the fertile New Zealand men may be heading over here.

Posted by Jonathan as Biology at 12:09 AM BST

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One of the findings of a study carried out by Biologists and a Psychologist, at The University of Nottingham, is that displays of altruism towards others can be sexually attractive in a partner.

Previous research has shown that many factors top the list of desirable mate characteristics, including intelligence, physical attractiveness and wealth. The new study, which will be published in the November issue of the British Journal of Psychology, suggests another trait could be a person’s unselfish tendencies.

In three studies of more than 1,000 people Dr Tim Phillips and his fellow researchers discovered that women placed significantly greater importance on altruistic traits, in all three studies.

Dr Phillips stated:

Evolutionary theory predicts competition between individuals and yet we see many examples in nature of individuals disadvantaging themselves to help others.

In humans, particularly, we see individuals prepared to put themselves at considerable risk to help individuals they do not know for no obvious reward.

Participants in the studies answered questions about a range of qualities they look for in a mate, including examples of altruistic behaviour such as ‘donates blood regularly’ and ‘volunteered to help out in a local hospital’. Women placed significantly greater importance on altruistic traits in all three studies.

Furthermore, both sexes may consider altruistic traits when choosing a partner. One hundred and seventy couples (340 individuals), with an average age of 58, who reported being married or in a long-term relationship, were asked to rate how much they preferred altruistic traits in a mate and report their own level of altruistic behaviour.

The strength of preference in one partner was found to correlate with the level of altruistic behaviour typically displayed in the other partner, suggesting that altruistic traits may well be a factor both men and women take into account when choosing a mate.

Dr Phillips said:

For many years the standard explanation for altruistic behaviour towards non-relatives has been based on reciprocity and reputation - a version of “you scratch my back and I’ll scratch yours”. I believe we need to look elsewhere to understand the roots of human altruism.

The expansion of the human brain would have greatly increased the cost of raising children so it would have been important for our ancestors to choose mates both willing and able to be good, long-term parents. Displays of altruism could well have provided accurate clues to this and genes linked to altruism would have been favoured as a result.

Sexual selection could well come to be seen as exerting a major influence on what made humans human.

Dr Tom Reader, in the School of Biology, said:

Sexual preferences have enormous potential to shape the evolution of animal behaviour. Humans are clearly not an exception: sex may have a crucial role in explaining what are our most biologically interesting and unusual habits.

Posted by Jonathan as Biology, Psychology at 11:18 PM BST

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According to new research from Utrecht University, the rapidity of ejaculation in men is genetically determined.

Neuropsychiatrist, Dr Marcel Waldinger and Pharmacological Researcher Paddy Janssen studied 89 Dutch men who suffer from the primary form of premature ejaculation, in other words, men who always had this problem.

In their experiment, the female partners of the participants in the study used a stopwatch at home to measure the time until ejaculation, each time they had intercourse, over the course of a month. A control group of 92 men was also studied, and the results will be published in the Journal of Sexual Medicine.

Dr Waldinger emphasises:

This study applies to men who have always ejaculated prematurely from their first sexual contact onwards and not for men who started suffering from this later on in life.

Serotonin deficiency.

In men who suffer from premature ejaculation, the substance serotonin appears to be less active between the nerves in the section of the brain that controls the ejaculation. Amongst other things, this substance is linked to sexual activity and appetite. It’s a substance that transfers a signal from one neuron to another. Due to the low activity of serotonin, this signal transfer does not occur properly in men with the primary form of premature ejaculation.

Gene responsible.

A gene which had already been discovered, namely 5-HTTLPR, appears to be responsible for the amount and activity of serotonin, which means that it controls the rapidity of ejaculation. Three types of the gene exist: LL, SL and SS. The study showed that the LL type causes a more rapid ejaculation. On average, men with LL ejaculate twice as quickly as men with SS, and also almost twice as quickly as men with SL. The researchers are currently also looking for other genes that are involved in ejaculation.

Not psychological.

As far back as 1998, researcher Marcel Waldinger predicted that both the rapidity with which men ejaculate and the primary form of premature ejaculation were genetically determined, explaining:

This theory contradicts the idea, which has been common for years, that the primary form of premature ejaculation is a psychological disorder. The results of our research confirm the genetic theory and may contribute to possible gene therapy against premature ejaculation.

Posted by Jonathan as Biochemistry, Biology at 3:36 AM BST

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