evolution

(A firm heelclacking is heard on the stairs.)

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The ratio between the body circumference at the waist and the hips (or WHR) is a secondary sexual trait that is unique to humans and is well known to influence men’s mate preferences. Because a woman’s WHR also provides information about her age, health and fertility, men’s preference concerning this physical feature may possibly be a cognitive adaptation selected in the human lineage. […]

We analyzed the WHR of women considered as ideally beautiful who were depicted in western artworks from 500 BCE to the present. These vestiges of the past feminine ideal were then compared to more recent symbols of beauty: Playboy models and winners of several Miss pageants from 1920 to 2014. We found that the ideal WHR has changed over time in western societies: it was constant during almost a millennium in antiquity (from 500 BCE to 400 CE) and has decreased from the 15th century to the present. Then, based on Playboy models and Miss pageants winners, this decrease appears to slow down or even reverse during the second half of the 20th century.

The universality of an ideal WHR is thus challenged, and historical changes in western societies could have caused these variations in men’s preferences.

{ PLOS | Continue reading }

You live and you learn

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The “hygiene hypothesis” […] suggests that people in developed countries are growing up way too clean because of a variety of trends, including the use of hand sanitizers and detergents, and spending too little time around animals.

As a result, children don’t tend to be exposed to as many bacteria and other microorganisms, and maybe that deprives their immune system of the chance to be trained to recognize microbial friend from foe.

That may make the immune system more likely to misfire and overreact in a way that leads to allergies, eczema and asthma, Hesselmar says. […]

In their latest research, the researchers took a look at how people wash their dishes. […] In families who said they mostly wash dishes by hand, significantly fewer children had eczema, and somewhat fewer had either asthma or hay fever, compared to kids from families who let machines wash their dishes.

{ NPR | Continue reading }

photo { Daria Zhemkova photographed by Mario Kroes }

Brass and reeds, brace and ready!

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A study has shown that in contemporary hunter-gatherer tribes, men and women tend to have equal influence on where their groups lives and who they live with. The findings challenge the idea that sexual equality is a recent invention, suggesting that it has been the norm for humans for most of our evolutionary history.

Mark Dyble, an anthropologist who led the study at University College London, said: “There is still this wider perception that hunter-gatherers are more macho or male-dominated. We’d argue it was only with the emergence of agriculture, when people could start to accumulate resources, that inequality emerged.” […]

Dyble said that egalitarianism may even have been one of the important factors that distinguished our ancestors from our primate cousins. “Chimpanzees live in quite aggressive, male-dominated societies with clear hierarchies,” he said. “As a result, they just don’t see enough adults in their lifetime for technologies to be sustained.”

{ Raw Story | Continue reading }

Now baby we can do it take the time, do it right, we can do it baby

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The sexual selection concept arises from the observation that many animals had evolved features whose function is not to help individuals survive, but help them to maximize their reproductive success. This can be realized in two different ways:

• by making themselves attractive to the opposite sex (intersexual selection, between the sexes), or
• by intimidating, deterring or defeating same-sex rivals (intrasexual selection, within a given sex).

Thus, sexual selection takes two major forms: intersexual selection (also known as ‘mate choice’ or ‘female choice’) in which males compete with each other to be chosen by females; and intrasexual selection (also known as ‘male–male competition’) in which members of the less limited sex (typically males) compete aggressively among themselves for access to the limiting sex. The limiting sex is the sex which has the higher parental investment, which therefore faces the most pressure to make a good mate decision.

For intersexual selection to work, one sex must evolve a feature alluring to the opposite sex, sometimes resulting in a “fashion fad” of intense selection in an arbitrary direction. Or, in the second case, while natural selection can help animals develop ways of killing or escaping from other species, intrasexual selection drives the selection of attributes that allow alpha males to dominate their own breeding partners and rivals.

{ Wikipedia | Continue reading }

Canine teeth, horns, claws, and the sheer size and strength of certain male animals provide strong examples of physical weapons, and aggression is a behavioral weapon among humans and other animals. A peacock’s tail, which is useless and costly to sustain, is the most famous example of an ornament. Showing off and creativity may be the human equivalents of this ornamentation. Certain polygynous species, such as the elephant seal, become weapon specialists, relying primarily on intrasexual combat to achieve reproductive success. Other species, such as the peacock and numerous birds of paradise, specialize in intersexual selection to produce extravagant male ornaments. Humans are versatile animals who rely on a large brain to facilitate amassing and facultatively employing a large repertoire of survival and reproductive strategies, including weapons and ornaments.

Even though ancestral men may have used intrasexual combat more than intersexual ornaments in acquiring mates and much human female choice may also have derived from male contests, modern men use both intrasexual and intersexual mating strategies as evidenced by much research showing a clear association between mating motivation and various behaviors that constitute weapons and ornaments in men. Specific weapon-like behaviors under mating investigation include physical or direct aggression in response to provocation, social dominance and status, endorsing warring attitudes, and producing a low voice pitch. The studied ornament-like behaviors include conspicuous material consumption, risk taking, humor, being unique and non-conforming, becoming loss averse, making generous financial donations, and exhibiting heroic altruism, all of which are preferred by women.

These studies suggest that, similar to other male animals, men can exhibit weapon-like and ornament-like behaviors, but, unlike many male animals that specialize in either weapons or ornaments nearly to the exclusion of the other, men seem to have developed the versatility to acquire and apply both strategies to facultatively respond to intrasexual and intersexual competition. Men may use weapons and ornaments facultatively as situational responses to intersexual and intrasexual conditions and, over time, may also develop behavioral tendencies in using one strategy more frequently over the other, adding to the vast individual differences along a weapon-ornament dimension.

{ Evolutionary Psychology | PDF }

photo { Jerry Schatzberg }

‘Why are there beings at all, and why not rather nothing?’ –Heidegger

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Imagine a virus wipes out everyone on the planet except [a man]. […] He finds the last woman on Earth. […] Can they repopulate the Earth? To do so, their children would have to mate with one another, or mom and dad, in order to rebuild the human race. All the incestuous taboos aside, is this even genetically possible?

Inbreeding has unfortunate genetic consequences due to the increased inheritance of recessive genes, which can result in neonatal death. Inbred children that survive are at increased risk of congenital birth defects, reduced fertility, smaller size, immune deficiencies, cystic fibrosis, and more. These defects are also likely to be passed on to their children as well. […]

Some real-life examples of the consequences of inbreeding can be found in places where there are restricted breeding opportunities — for example, within monarchies, islanders, or closed societies. Hemophilia was notoriously prevalent in European royal families. Some Amish societies have a larger number of children born with extra digits on their hands or feet. Jews of Eastern European descent tend to have higher rates of a number of genetic diseases, including cystic fibrosis. […]

The net result of inbreeding is that the resulting population loses a diverse genetic portfolio, which means they are less resistant to rare diseases and deformities. The smaller the gene pool, the faster it gets dirty. Such individuals would also have less diverse immune systems, making it much easier for a single germ to wipe them all out. […]

In addition to the genetic landmines, the family would likely have a very difficult time overcoming the innate resistance most species have against inbreeding. Evolution knows that inbreeding is not good for the species, so it engineered a built-in “incest taboo” that creates a strong aversion to such behavior. A devil’s advocate, however, could argue that the biological barrier to familial sex could be overcome through artificial insemination.

What about using a sperm bank? Sperm is stored in liquid nitrogen, so it would stay frozen for a short time after the power goes out. However, you’d have to act fast because no one is around to monitor the storage tanks and top off the liquid nitrogen as it evaporates.

There are practical concerns to consider as well. The last man and woman, as well as their kids, would need to have large numbers of children and, unless one of the founders happens to be a doctor, it is hard to imagine many of these babies surviving in such a world. Even if they (and mom) survive childbirth, there are countless opportunities for them to perish in this type of environment before reaching childrearing age.

{ The Scope | Continue reading }

art { Hilo Chen, Beach 166, 2010 }

‘It is no more in our power to love always than it was not to love at all.’ –La Bruyère

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Darwin made a famous distinction between men’s and women’s mating strategies, between choosy, coy females and ardent, promiscuous males. […]

Yet, as also anticipated by both Darwin and Trivers, empirical studies of both non-humans and humans reveal extraordinary flexibility in mating and investment behavior, both within and between the sexes. Reproductive strategies are clearly not an invariant, species-specific characteristic, but rather facultative responses to individual- and population-level social and ecological circumstances, rendering conditional mating strategies optimal. […]

For example, across the ethnographic record, human societies can range from polyandrous to polygynous mating patterns, same-sex marriage can be institutionalized as with woman-to-woman unions in East Africa and men can spend considerable amounts of time and effort in beautifying themselves as in West Africa. […]

Until recently, the study of sex-differentiated reproductive behaviour has relied on the long-standing model of sexual selection developed by Trivers. This model links sex roles directly to the differential investment in young by males and females. In its simplest form, this model posits that because males invest less initially (in sperm), they have a higher potential reproductive rate (PRR) and benefit more from mating multiply than do females. As a consequence, selection typically would favour mate-seeking and competitive behaviour in males, and heavy investment in parental care in females. […]

Using data from eight Makushi communities of southern Guyana, characterized by varying adult sex ratios contingent on migration, we show that even within a single ethnic group, male mating effort varies in predictable ways with the ASR. At male-biased sex ratios, men’s and women’s investment in mating effort are indistinguishable; only when men are in the minority are they more inclined towards short-term, low investment relationships than women.

{ Royal Society Open Science | Continue reading }

Using new data from the United Kingdom’s Annual Population Survey, we find that […] marriage may help ease the causes of the mid-life dip in life satisfaction and that the benefits of marriage are unlikely to be short-lived. We explore friendship as a mechanism which could help explain a causal relationship between marriage and life satisfaction, and find that well-being effects of marriage are about twice as large for those whose spouse is also their best friend.

{ National Bureau of Economic Research | Continue reading }

‘I have no knowledge of myself as I am, but merely as I appear to myself.’ –Kant

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[P]eople who are depressed display some surprising advantages in their thinking skills. Depressed people:

1. process information more deeply.
2. are more accurate at complex tasks.
3. make better judgements on detail-oriented information.
4. make more accurate cost-benefit analyses.

The researchers developed a new questionnaire which measures ‘analytical rumination’, a mental process which is thought to be an ancient defence mechanism and the root of depression.

Analytical rumination is where people turn problems over in their heads to the exclusion of all else, trying to look for a solution.

They first examine the problem’s cause, then the things that need solving, any possible solutions plus the costs and benefits of each solution.

The symptoms of depression, which often include lethargy, difficulty sleeping, poor concentration and disinterest in other people or the external world, may actually be ways of saving energy while a person is focusing on the problem.

{ PsyBlog | Continue reading }

‘Then they plunged a great needle into my butt and BAM! out I went for two whole days. When I woke up, wow! Rats all over the floor, wailing and screaming. We ate potatoes with spoons.’ –Edie Sedgwick

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Why do we dream? It’s still a scientific mystery. The “Threat Simulation Theory” proposes that we dream as a way to simulate real-life threats and prepare ourselves for dealing with them. “This simulation in an almost-real experiential world would train the brain to perceive dangers and rapidly face them within the safe condition of sleeping,” write the authors of a new paper that’s put the theory to the test. […]

The researchers contacted thousands of first-year students at the end of the day that they sat a very important exam. […] over 700 of the students agreed to participate and they completed a questionnaire about their dreams and sleep quality the previous evening, and any dreams they’d had about the exam over the course of the university term. […] The more exam dreams a student reported having during the term, the higher their grade tended to be.

{ BPS | Continue reading }

collage { Eugenia Loli }

‘Retenez ceci : il n’y a de bon, de vrai, de gai, de triste, d’aimable, de variable, de désirable, de potable, de chantable, de célébrable, d’idolâtrable, que le delta qui existe depuis la ceinture d’une femme jusqu’à ses jarretières.’ –George Sand & Alfred de Musset

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Pham and Schackelford (2013) argued that men with more attractive partners are at a greater recurrent risk of sperm competition because other men are more likely to woo them into having affairs. Therefore, men with more attractive partners have more reason to be concerned about and more likely to engage in behaviour aimed to detect infidelity. The idea that cunnilingus, oral sex performed on a woman, could function to detect infidelity was proposed in a 2006 book, but this study is the first to test this empirically. The idea is that oral sex may allow a man to detect the presence of another man’s semen through smell or taste. […]

As side-note I’d like to point out that there is a common misconception often advanced by its critics that evolutionary psychology assumes that everything that people do is somehow an evolutionary adaptation and that evolutionary psychologists cannot or will not acknowledge that some behaviours are simply by-products of other adaptations with no special function of their own. This is a gross misrepresentation of what evolutionary psychology is about and in fairness to the authors of the study they were attempting to actually test whether or not their hypothesis about the adaptive function of oral sex is valid, rather than just assuming it is. It is quite possible that oral sex has no evolutionary function in itself. Humans are a highly sexed species compared to most mammals and engage in many non-procreative sexual acts, perhaps for pleasure alone. Oral sex might simply be a by-product of this interest in sex that humans have. However, if it can be shown that this particular behaviour appears to serve a definite purpose that has an evolutionary history, a reasonable case can be made that it has an adaptive function. […]

They found that “recurrent risk of sperm competition” (attractiveness) predicted interest in performing oral sex independently of relationship length, relationship satisfaction, and duration of intercourse.

{ Psychology Today | Continue reading }

‘love these endocrine supplements i got at the natural foods store. they give you extra endocrine’ –@Mobute

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In response to a threat, the brain triggers the release of epinephrine and cortisol from your adrenal glands into the blood. As a result, your heart beats faster and stronger, your blood vessels dilate to move more blood, and your lung vessels dilate to exchange more oxygen for carbon dioxide. Equally as important, your liver breaks down glycogen (a sugar storage molecule) to glucose and dumps it into your bloodstream.

All these processes work together to increase your alertness and increase the power of your muscles for a short time — like when mothers who lift cars off their small children. You are now ready to respond to the threat; however, there is an exception — you may do nothing at all.

One of the major control mechanisms of the fight or flight response is the autonomic nervous system. This is part of the peripheral nervous system (PNS, outside the brain and spinal cord) and transmits information from the central nervous system to the rest of the body. The autonomic system controls involuntary movements and some of the functions of organs and organ systems.

Parts of the autonomic system acts like a teeter-totter, it’s their relative balance that controls the outcomes. In the fight or flight response, the sympathetic system predominates and your heart rate increases and your blood vessels dilate.

But what if the parasympathetic system gained an upper hand for a short time? […] The heart slows, the blood vessels constrict in the muscles, blood moves from muscles to the gut, and glycogen is produced from glucose. […] Many people have had the experience of parasympathetic domination coincident to a threat, for some folks it proceeds long enough to have an observable result – they faint. […] when your brain is starved of oxygen and glucose, you pass out. […]

Lower animals will faint as well, but they have additional defenses along these lines. Mammals, amphibians, insects and even fish can be scared enough to fake death. […] There are overlapping mechanisms for feigned death, from tonic immobility (not moving) to thanatosis (thanat = death, and osis = condition of, playing dead). […] One study in crickets showed that those who feigned death the longest were more likely to avoid being attacked, so this is definitely a survival adaptation.

{ biological exceptions | Continue reading }

photo { Steven Brahms }

‘I stick my finger in existence — it smells of nothing.’ –Kierkegaard

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We Westerners have a boring pointing repertoire. Most of the time, we just jut out our arm and index finger. If our hands are occupied — carrying a heavy load, say — then we might resort to a jerk of the head or elbow. But if the pointer finger’s free, we’ll point it.

Not so for the Yupno. Within a few days of their arrival in the valley, Núñez and Cooperrider noticed that the Yupno often point with a sharp, coordinated gesture of the nose and head that precedes them looking toward the point of interest. […]

Pointing, he answered, seems to be a fundamental building block of human communication. Great apes are never seen pointing in the wild. And in human babies, pointing develops even before the first word […]

The Yupno aren’t the only ones who point with their face. Lip pointing — in which protruding lips precede an eye gaze toward the area of interest — has been observed in people from Panama, Laos, and other groups in Australia, Africa, and South America. Head pointing, according to one study, happens frequently among people speaking Arabic, Bulgarian, Korean, and African-American Vernacular English.

{ Phenomena | Continue reading }

Don’t let go of me (Grip my hips and move me)

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Why do fingers get wrinkly in the water? […]

A hypothesis has been proposed which suggests that the wrinkling might be an evolutionary adaptation to make the handling of objects underwater easier. Wrinkling creates a kind of drainage path for water and so enhances the grip on an object (this is called a ‘rain tread’ hypothesis). In order to test if this hypothesis is true Kareklas et al. have recruited volunteers and tested their ability to transfer wet objects when the fingers are wrinkled and not. […]

20 participants had to transfer glass marbles from one container to another in two different conditions (1) take the marble from a container with water pass it through a small hole and put into an empty container and (2) take the marble from a container without water pass it through a small hole and put into an empty container. […]

When the marble ball was dry there was no difference between the transfer time with wrinkly and smooth fingers. However, when the marble was wet then on average it took 12% less time to transfer the object with wrinkly fingers. Therefore, the study concluded that the wrinkling of fingers improves the handling of wet objects (which supports the rain tread hypothesis). Why are our fingers not always wrinkled then? In paper’s discussion Kareklas et al. suggest that there potentially are some fitness trade-offs to the wrinkly fingers. Maybe wrinkled fingers are less sensitive to pain, pressure, heat etc. and are therefore damaged easier, which would explain why it is not good to always have those wrinkles.

{ The Question Gene | Continue reading }

The work done in this room lies at the heart of a department that handles some of the UK’s most cutting-edge research on forensics and anatomy. […]

The hand is Meadows’ area of focus. Variations in scars, skin pigmentation, the smallest nooks and crannies of the fingernail and, most importantly, superficial vein patterns: all of these can build a body of evidence and allow the police to identify an offender in an incriminating photograph. “The back of the hand is part of the anatomy that an offender is quite happy to have in an image, whereas they wouldn’t necessarily want their face captured,” Meadows says. In 2009, Cahid’s work was instrumental in the Neil Strachan case, part of Scotland’s biggest paedophile ring. His unusually distorted lunula (the white half moon at the bottom of a nail) helped identify and convict him.

Meadows and her colleagues have built up the UK’s only database of the hand’s vein patterns, with around 800 samples. Of the 40 or so cases they have worked on, their data have resulted in over 80 per cent of suspects changing their plea.

{ FT | Continue reading }