Tweets from around the world, plotted by location as part of a new study. Click to enlarge. Image via First Monday/Leetaru et. al.

It’s hard to appreciate just how quickly and thoroughly Twitter has taken over the world. Just seven years ago, in 2006, it was an idea sketched out on a pad of paper. Now, the service is used by an estimated 554 million users—a number that amounts to nearly 8 percent of the all humans on the planet—and an estimated 170 billion tweets have been sent, with that number climbing by roughly 58 million every single day.

All these tweets provide an invaluable source of news, entertainment, conversation and connection between people. But for scientists, they’re also valuable as something rather different: raw data.

Because Twitter features an open API (which allows for tweets to be downloaded as raw, analyzable data) and many tweets are geotagged, researchers can use billions of these tweets and analyze them by location to learn more about the geography of humans across the planet. Last fall, as part of the Global Twitter Heartbeat, a University of Illinois team analyzed the language and location of over a billion tweets from across the U.S. to create sophisticated maps of things like positive and negative emotions expressed during Hurricane Sandy, or support for Barack Obama or Mitt Romney during the Presidential election.

As Joshua Keating noted on Foreign Policy‘s War of Ideas blog, members of the same group, led by Kalev Leetaru, have recently gone one step further. As published in a new study earlier this week in the online journal First Monday, they analyzed the locations and languages of 46,672,798 tweets posted between October 23 and November 30 of last year to create a stunning portrait of human activity around the planet, shown at the top of the post. They made use of the Twitter decahose, a data stream that  captures a random 10 percent of all tweets worldwide at any given time (which totaled 1,535,929,521 for the time period), and simply focused on the tweets with associated geographic data.

As the researchers note, the geographic density of tweets in many regions—especially in the Western world, where computers, mobile devices, and Twitter are all used at peak levels—closely matches rates of electrification and lighting use. As a result, the maps of tweets (such as the detail view of the continental U.S., below) end up looking a lot like satellite images of artificial light at night.

Click to enlarge. Image via First Monday/Leetaru et. al.

As a test to see how well tweets matched artificial light use, they created the composite map below, in which tweets are shown as red dots and nighttime lighting is shown as blue. Areas where they correspond in frequency (and effectively cancel each other out) are shown as white, and areas where one outweighs the other remain red or blue. Many areas end up looking pretty white, with some key exceptions: Iran and China, where Twitter is banned, are noticeably blue, while many countries with relatively low electrification rates (but where Twitter is still popular) appear as red.

Click to enlarge. Image via First Monday/Leetaru et. al.

The project got even more interesting when the researchers used an automated system to break down tweets by language. The most common language in Twitter is English, which is represented in 38.25 percent of all Tweets. After that came Japanese (11.84 percent), Spanish (11.37 percent), Indonesian (8.84 percent), Norwegian (7.74 percent) and Portugese (5.58 percent).

The team constructed a map of all tweets written in the 26 most popular languages, with each represented by a different color, below:

Click to enlarge. Image via First Monday/Leetaru et. al.

While most countries’ tweets are dominated by their official languages, many are revealed to include tweets in a variety of other languages. Look closely enough, and you’ll see a rainbow of colors subtly popping out from the grey dots (English tweets) that blanket the U.S.:

Click to enlarge. Image via First Monday/Leetaru et. al.

Among other analyses, the research team even looked at the geography of retweeting and referencing—the average distance between a user and someone he or she retweets, as well as the average distance between that user and someone he or she simply references in a tweet. On average, the distance for a retweet was 1,115 miles and 1,118 for a reference. But, counterintuitively, there was a positive relationship between the number of times a given user retweeted or referenced another user and their distance: Pairs of users with just a handful of interactions, on the whole, were more likely to be closer together (500-600 miles apart) than those with dozens of retweets and references between them.

This indicates that users who live far apart are more likely to use Twitter to interact on a regular basis. One explanation might be that the entities with the most followers—and thus the most references and retweets—are often celebrities, organizations or corporations, users that people are familiar with but don’t actually have a personal relationship with. A global map of retweets between users is below:

Click to enlarge. Image via First Monday/Leetaru et. al.

The paper went into even more detail on other data associated with tweets: the ratio between mainstream news coverage and number of tweets in a country (Europe and the U.S. get disproportionate media coverage, while Latin America and Indonesia are overlooked), the places Twitter has added the most users recently (the Middle East and Spain) and the places where users have, on average, the most followers (South America and the West Coast).

There are a few caveats to all this data. For one, though the tweets analyzed number in the tens of millions, they are still just 0.3 percent of all tweets sent, so they might not adequately represent all Twitter patterns, especially if users who enable geotagging behave differently than others. Additionally, in the fast-changing world of Twitter, some trends might have already changed significantly since last fall. But as Twitter continues to grow and as more data become available, it stands to reason that this sort of analysis will only become more popular for demographers, computer scientists and other researchers.

We find different pitches attractive because of the body size they signal—and a touch of breathiness is crucial to take the edge off a man’s deep voice. Image via Flickr user linda

Who you’re physically attracted to might seem like a frivolous, random preference. In recent years, though, science has told us that our seemingly arbitrary tastes often reflect unconscious choices that are based upon very relevant biological traits.

In general, we find symmetric faces more attractive, likely because they reflect a healthy underlying genome. Women typically prefer men with more distinctively masculine facial features because they indicate high testosterone levels and physical strength, while men prefer women with exaggerated youthful features, possibly because of the evolutionary advantages a male gets when coupling with a younger mate.

Despite all this research into our visual appearances, though, scientists have done relatively little digging into our auditory preferences when it comes to sexual attraction. Why do we find certain peoples’ voices attractive–and why do we sometimes find other types of voices such a turn-off? Specifically, why do women generally prefer men with deep voices, and men prefer women with higher ones?

At least according to a paper published today in PLOS ONE, the explanation is relatively simple: It’s all about body size. Researchers from University College London found that, at least among a sample of 32 participants, high-pitched female voices females were found to be attractive because they indicated the speaker had a small body. Deep male voices, on the other hand, were judged as more attractive because they conveyed that the speaker had a large frame—but were found to be most attractive when tempered by a touch of “breathiness,” suggesting the speaker had a low level of aggression despite his large size.

The group, led by Yi Xu, figured this out by playing recordings of digitally manipulated voices to the participants. The males in the study heard a computer-generated female voice saying phrases such as “I owe you a yo-yo” in which the voice was manipulated with a number of digital alterations in terms of pitch, formant (the particular peaks and valleys in a sound’s frequency spectrum) and other qualities.

The specific manipulations either conveyed a smaller body size or a larger one, based upon previous research that matched various voice qualities with different body sizes in humans. When asked to rate the voice’s attractiveness on a 1 to 5 scale, the men preferred the voices that suggested a smaller female. Past a certain point, though, higher voices were judged as no more attractive that slightly deeper ones. Listen to the most and least attractive (both, admittedly creepy) voices below:

The female participants’ voice preferences were similar, but slightly more nuanced. On the whole, they preferred deeper voices, which signaled a large body size, but another trait was also crucial: “breathiness.” The researchers hypothesized that this breathiness effectively takes the edge off a voice, making a man with a presumed large frame seem less aggressive and angry. They also polled the participants on whether they thought the simulated voices sounded angry or happy, and the breathy deep males voices were generally perceived as much happier and less angry than the less breathy (i.e. “pressed”) deep ones. Listen to the most and least attractive male voices below:

Beyond explaining the popularity of Barry White, the researchers say these findings correspond to much of what we know about voice preferences in the rest of the animal kingdom. Birds and other mammals, it turns out, have long been known to advertise their physical characteristics via the sound qualities in their mating calls.

All this points to an obvious question, though: Why would males prefer smaller females, and females prefer larger males in the first place? The researchers don’t attempt to address this question, but this duality reflects the sexual dimorphism present in most animal species. These differences generally result from sexual selection giving incentive to different mating strategies—so in this case, our voice preferences suggest that women benefit, in evolutionary terms, by mating with larger, but less aggressive men, while males benefit from mating with smaller females.

As the same time, what we commonly consider attractive varies dramatically over time and location—for example, dozens of prehistoric “Venus figurines,” discovered all over the world, portray extremely voluptuous female figures. So, if we tested the preferences of all humans throughout history, we might find a less obvious trend. This preference for small-voiced females and big-voiced males, then, might simply be an artifact of our contemporary cultural concepts of “attractiveness,” rather than a deep-seated evolutionary choice after all.

A new study shows that fathers and mothers are equally skilled at picking out their infant’s unique cry—if they spend the same amount of their time parenting. Image via Wikimedia Commons/Voiceboks

After a baby orangutan is born, it’ll spend the first two years of its life completely dependent on its mother—maintaining direct physical contact with her for at least the first four months—and breastfeeding for up to five years in total. During that time, it will likely never meet its father. Polar bears are also born helpless, surviving on their mothers’ milk through the harsh Arctic winter, but polar bear fathers provide no parenting, and have even been known to eat their cubs on occasion if they get the chance.

Both of these facts reflect a pattern common across the animal kingdom: In most species, mothers are inherently much more involved in parenting than fathers, and evolution has driven them to develop parenting instincts that are absent in their male counterparts.

A new experiment, though, suggests that contrary to conventional wisdom, one animal species remains a pretty significant exception to this rule: humans. It’s often believed that nobody can recognize a baby’s cry as accurately as his or her mother, but a study published today in Nature Communications by a team of French scientists led by Erik Gustafsson of the University de Saint-Etienne found that fathers can do it equally well—if they spend as much time with their offspring as mothers do.

The study involved 29 babies from France and the Democratic Republic of Congo, all less than half a year old, along with each of their mothers and 27 of their fathers (2 could not be located for the study). The researchers recorded the cries these infants made while being bathed, and then played them back to their parents (along with the cries of other babies) later on. To this non-parenting bystander, the cries (published along with the paper) generally seem pretty similar—like the one below, they all sound, well, like a quintessential baby’s cry:

In one of those astounding feats of parenthood, though, the parents did way better than chance in identifying which of the seemingly-identical cries belonged to their child from the sound alone. Each parent heard a random sequence of 30 different cries (24 from 8 other babies, and 6 from their own), and on average, they correctly identified 5.4 of their baby’s cries, while making 4.1 false-positives (incorrectly identifying another infant’s cry as their child’s). Although having this skill doesn’t necessarily indicate that a parent provides expert care, it does reflect a remarkably well-attuned connection between parent and infant.

When the researchers split the data along gender lines, they found something interesting. The factor that best predicted which parents were best at identifying their child’s cries was the amount of time the parent spent with their babies, regardless of if they were the mother or father.

Of the 14 fathers who spent an average of 4 or more hours a day with their babies, 13 correctly identified 98% of their total cries (and the outlier still got 90% right). The 29 mothers who spent a comparable amount of time with their children (that is, all the mothers in the study) got the same 98% correct. The remaining 13 fathers who spent less than 4 hours a day with their kids, though, were only able to identify 75% of the cries correctly.

The finding might not seem particularly surprising—of course whichever parents spend the most time with their children will be best at identifying the nuances of his or her pitch—but it cuts against the grain of previous research on this topic, which found that mothers seemed to be naturally better than fathers at identifying their own infants’ cries. (People often make the same assumption, the researchers say—in an informal survey they took of 531 students at the University de Saint-Etienne, 43% felt mothers were better, and the rest thought fathers and mothers were equally good at identifying their baby’s cries, while none felt fathers were.) But previous studies didn’t take into account the amount of time parents typically spent with their children on a daily basis.

The results suggest that experience and learning may be more critical to good parenting than innate skills. Far from being inherently disadvantaged in recognizing their babies’ cries, males who spent lots of time parenting turned out to be just as good as females at the task—so in terms of this particular skill, at least, parenting is less an inherent talent than a one to be practiced and developed. This also implies that whoever is the primary caregivers for a baby—whether grandparents, aunts, uncles or people unrelated to the child—may develop the same ability to distinguish the cries of the child in their care from other children.

Of course, while the findings don’t depict any innate asymmetry in parenting skills between the sexes, they do reveal an enormous asymmetry in the behavior of parents regardless of their continent, predicated on traditional gender roles. Every mother participating in the study spent enough time with their kids to develop the skill tested, while just about half of the fathers did—and two fathers couldn’t even be located to participate in the study in the first place.

Fathers might have the same innate parenting skills as mothers, but only if they make the enormous time investment necessary. This study indicates that it’s usually not the case, and though its sample size was extremely limited, broader data sets show the same. According to the most recent Pew Research data on parenting, the average American mother spends 14 hours per week in child care duties, compared to just 7 hours for the average father—so while men can develop the ability to know their babies just as well as women, most fathers out there probably haven’t so far.

Natalie Portman was among the most often-mentioned names of the 2000s, according to a new study, reflecting the fact that true celebrity lasts longer than 15 minutes. Image via Wikimedia Commons/Real TV Films

In 1968, Andy Warhol—already famous in his own right—further added to his celebrity by creating a lasting cliché: “In the future, everyone will be world-famous for 15 minutes.”

Prescient as Warhol might have been, it seems we haven’t reached that future quite yet, at least according to science. A new study, published today in the American Sociological Review, finds that true fame lasts a good deal longer than 15 minutes. In an analysis of the celebrity journalism nationwide, researchers found that the most famous (and most often-mentioned) celebrities stick around for decades.

To come to the finding, a number of sociologists each spent a multi-year sabbatical meticulously combing the “Stars: They’re Just Like Us” feature of UsMagazine. Several reportedly declined to return to the field of academia, apparently taking their talents to the analytical departments of the glossy magazine industry full-time.

Just kidding! In all seriousness, the sociologists, led by Eran Shor of McGill University and Arnout van de Rijt of Stony Brook University, used an automated search took a random sample of roughly 100,000 names that appeared in the entertainment sections of 2,200 daily American newspapers published between 2004 and 2009. Their sample didn’t include every single name published, but rather a random selection of names published at all different frequencies—so it wouldn’t be useful for telling you who was the most often-mentioned celebrity overall, but would be illustrative of the sorts of trends that famous (and not-so-famous) names go through over time.

The ten most frequently-mentioned names in their sample: Jamie Foxx, Bill Murray, Natalie Portman, Tommy Lee Jones, Naomi Watts, Howard Hughes, Phil Spector, John Malkovich, Adrien Brody and Steve Buscemi. All celebrities, they note, were relatively famous before the year 2000, in some cases decades earlier (Howard Hughes rose to fame in the 1920s). All ten names, additionally, are still fairly well-known today.

Overall, 96 percent of the most famous names in the sample (those mentioned more than 100 times over the course of a given year) had already been frequently featured in the news three years earlier, further dispelling the 15 minutes cliché. Furthermore, if a name was mentioned extremely often in its first year of appearing, it stood a greater chance of sticking around for an extended period of time.

There is, however, some truth to 15-minutes idea: Names of lesser fame (those less frequently mentioned to start) exhibit significantly higher amounts of turnover from year to year. The researchers say these names mostly fall into the category of people involved in newsworthy events—such as natural disasters and crimes—rather than people who readers find newsworthy in their own right. As an example, Van de Rijt mentions Chelsey Sullenberger, the US Airways pilot who briefly achieved celebrity after successfully executing an emergency landing on the Hudson River in 2011, but is now scarcely frequently mentioned in the press.

The list of the most famous names, though, stays relatively similar every year. “The vast majority of coverage goes to names that have already been in the news for several years, and new names rarely penetrate the higher strata of fame,” the researchers write in the study. The bottom of the fame hierarchy is filled with new names annually, but at the top, they write, is “a reshuffling of already familiar names and not rapid replacement of an outgoing cohort by an incoming cohort.”

Apart from the newspaper data, the team also looked at a much smaller sample of celebrity mentions on blogs and TV, and found a similar trend. New media, it seems, follow roughly the same pattern as old outlets—which is why you don’t see much about figures like the “balloon boy” across the web nowadays either.

Frivolous as the work may seem, the researchers say it bears important conclusions about our society. Upward mobility in the celebrity world is extremely scarce. Becoming famous requires some combination of talent and luck that allows a person to break into the elite class of being mentioned over and over by the press. But what is that combination–what makes a person famous? Or is it that the press has created a cycle that allows a person to remain famous, in some cases after his or her career has peaked, or even after his or her death?”

No word yet on whether scientists will someday be able to create a multivariable model to quantify celebrity “fierceness” over time as well.

Being socially isolated increases your chance of death, but not simply because you’re feeling lonely. Image via Flickr user eflon

One of the most unprecedented trends of modern society is the number of people who choose to live alone. As sociologist Eric Klinenberg observed in his 2012 book Going Solo, living alone was virtually unheard of in most world cultures throughout history prior to the 20th century, but an estimated 32.7 million people now live alone in the United States, accounting for about 28 percent of the country’s households today, compared with 17 percent in 1970.

The medical and mental effects of this shift are complex. As Klinenberg notes, many people who live alone still remain highly social and connected with friends and family, so living alone doesn’t necessarily mean that a person is isolated.

But what of those who live alone and are socially isolated? In a study published today in the Proceedings of the National Academy of Sciences, a group of researchers from University College London attempted to explore the health consequences of those who are isolated from others, and found that limited contact with others increases a person’s overall risk of death over time.

The group, led by Andrew Steptoe, examined data on the 6,500 older adults (aged 52 and up) who took part in the English Longitudinal Study of Ageing in 2004, and monitored which participants survived up until last March. The researchers specifically looked at the association between mortality (overall risk of death) and a pair of conditions: social isolation (as indicated by a lack of contact with others) and loneliness (as reflected by participants’ answers on a survey).

In total, 14.1 percent of the people who’d participated in the survey had died in the 8 years after the study was administered, but those who were classified as socially isolated had died at considerably higher rates. Of the most socially isolated respondents, 21.9 percent did not survive to March 2012, as compared with 12.3 percent of the least isolated. Even after the participants’ baseline health and demographic factors were taken into account, being socially isolated still correlated to an increase in their mortality.

Interestingly, though, defining oneself as lonely—via the answers about one’s emotions and psychological state on the survey—did not have the same effect. Those who were lonely did have overall higher mortality, but this was because on average, they were older and had poorer baseline health conditions at the start. When the researchers controlled for baseline health and age, the mortality gap between the lonely and the non-lonely largely vanished.

This indicates that the real danger of living alone is not feeling lonely per se, but having reduced contact with others. One possibility is that an older person who seldom sees friends and family is less likely to get the help they need in managing various ailments, and is probably also less likely to be encouraged to go see a doctor when new health problems pop up. The researchers speculate that living alone might even cause people to have poorer health habits, such as smoking, eating an unhealthy diet and getting less physical activity.

This jibes with previous work by other researchers, such as the fact that living alone with a serious cardiovascular problem makes you more likely to die, and a 2011 Finnish finding that living on your own increases your risk of mortality from an alcohol-related death. Being around others, it seems, helps us ensure that we take better care of ourselves—so if you’re planning on joining the many who have opted to live solo, you’re best off making sure you maintain frequent contact with friends and family.

Sign up for our free email newsletter and receive the best stories from Smithsonian.com each week.

The hole in the top of this 100,000-year-old skull from China, researchers say, reflects genetic mutations that result from inbreeding. Image via PLOS ONE/Wu et. al.

In 2010, the surprising discovery that Neanderthals likely crossbred with our ancestors tens of thousands of years ago generated headlines around the world.

Now, we have a new finding about the sex lives of early Homo sapiens: It looks like they engaged in some inbreeding as well.

That is the conclusion of anthropologist Erik Trinkhaus of Washington University in St. Louis and Xiu-Jie Wu and Song Xing of the Chinese Academy of Sciences’ Institute of Vertebrate Paleontology and Paleoanthropology, based on a fractured 100,000-year-old skull excavated from China’s Nihewan Basin. Their finding, published yesterday in PLOS ONE, is that the skull shows evidence of an unusual genetic mutation that is likely the result of high levels of inbreeding.

The researchers used CT scanning and 3D modeling to join together for the first time the 5 pieces of the fractured skull—known as Xujiayao 11, named for the site where it was found back in 1977—and realized that it exhibited an unusual deformity. When the pieces are combined, they leave a hole on the crown of the skull, but there is no evidence that the fracture was caused by a traumatic injury or disease. As a result, they consider it most likely that the hole is a defect known as an enlarged parietal foramen.

The researchers use CT scans and 3D modeling to piece together the fractured skull for the first time. Image via PLOS ONE/Wu et. al.

Nowadays, this hole is mostly found in people with a particular pair of genetic mutations on chromosomes 5 and 11—most often a consequence of inbreeding—and occurs in about 1 of 25,000 live births. The mutation interferes with bone formation in the skull over the first five months of an infant’s life, when the pieces of the skull are supposed to fuse together to cover up the “soft spot.”

Given the tiny sample size of human skulls this old and the fact that similar kinds of genetic abnormalities have been seen so often in other prehistoric skulls—the researchers count 22 individuals with skull deformities discovered from this era—Trinkhaus thinks the simplest explanation is that small and unstable human populations forced our ancestors to inbreed.

If no inbreeding occurred, “the probability of finding one of these abnormalities in the small available sample of human fossils is very low, and the cumulative probability of finding so many is exceedingly small,” he said in a press statement. “The presence of the Xujiayao and other Pleistocene [2.6 million to 12,000 years ago] human abnormalities therefore suggests unusual population dynamics, most likely from high levels of inbreeding and local population instability.”

Such inbreeding was likely inevitable, given that most of humanity likely lived in small, isolated populations for most of our species’ evolution. For example, some scientists believe that an earlier population bottleneck that predated this skull may have driven the worldwide human population to as low as 2,000 individuals, at times making inbreeding a necessity. Our ancestors certainly didn’t understand the importance of genetic diversity and the dangerous consequences of inbreeding. But with such a scant population, the survival of our species might actually have depended on our ancient grandmothers procreating with their male relatives.

The good news? The researchers say that the genetic deformity preserved in this skull as a result of inbreeding may not have been too detrimental for this individual. Normally, it’s linked with major cognitive problems, but that’s doubtful in this case, given the demanding conditions of surviving in the Pleistocene. This prehistoric human appears to have survived to a ripe old age—which, in those days, probably means the individual lived into his or her thirties.

An intriguing new study suggests that infants dislike those who are different from themselves. Image via Flickr user paparutzi

In one of the fastest-growing areas in psychology, researchers are gaining insight into the mental processes of subjects that are barely able to communicate: babies. In recent years, innovative and playful experimental setups have suggested that infants as young as six months old have a sense of morality and fairness, and that 18-month-olds are capable of altruistically helping others.

Some of this research, though, has also shed light on babies’ dark side. A new study published in Psychological Science suggests that 9- to 14-month-olds exhibit a particularly unwelcome trait—in watching a puppet show, at least, they seem to prefer their own kind, and support puppets that pick on those who are different from them.

Because babies can’t communicate verbally, J. Kiley Hamlin of the University of British Columbia has pioneered the use of puppet shows to probe their psychology and better understand how they see the world. In this study, her research team put on an show in which 52 infant participants were led to identify themselves as similar to one of the characters in the show and different from the other.

To accomplish this, the researchers started off by asking the infants to pick a food, either graham crackers or green beans (a little surprisingly, a full 42 percent chose the vegetables). Then, the infants were shown a pair of rabbit puppets, one who liked graham crackers and one who liked green beans:

Once they’d solidly demonstrated each rabbit’s choice, one of them—either the one with the same preference as the infant observer, or the one with an opposite preference—would be randomly chosen to encounter a pair of new characters: one dog, termed a “helper,” and another, called a “harmer.” As the rabbit played with a ball and dropped it, the nice “helper” dog threw it back, but the mean “harmer” dog (below) held onto the ball:

After both of the scenes were over, both dogs were presented to the infant, and the particular dog that the baby first reached for was interpreted as the character it preferred.

The results were a bit startling: When the infants had watched a play involving a rabbit with a food choice that matched theirs, 83 percent preferred the “helper” dog. When they’d watched a play with a rabbit who liked a different food, 88 percent chose the “harmer” dog. This held true regardless of the babies’ original food choices—the only thing that mattered was whether the rabbit’s identity, it terms of food choice, matched their own.

To further parse the motivations underlying the infants’ choices, the researchers conducted a similar experiment that involved a neutral dog that neither help nor harmed the rabbit. In this part of the study, the older infants’ preferences revealed that when watching rabbits who had different favorite foods than them, they not only liked “harmer” dogs more than neutral dogs, but strongly preferred even neutral dogs when compared to “helpers” (this was true among the 14-month-olds, but not the 9-month-olds). In other words, it seemed that they not only wanted to see the rabbit treated poorly, but also would rather see it treated neutrally than get some help.

Of course, when designing experiments for subjects that can’t use words to communicate, the simplest of variables could potentially throw off the results. It’s unclear, for example, if the researchers alternated which side the “helper” and “harmer” puppets appeared on, so the babies could have been influenced by their emerging sense of handedness. In the past, critics of such puppet show experiments have also charged that a baby merely reaching for one puppet or another might be an impulsive reflex, rather than reflecting an underlying moral judgement.

What’s clear, though, is that this experiment demonstrated a consistent reflex across the babies tested. While extrapolating this to mean that the babies are racist or bigoted is probably a step too far—for one, they were merely considering individual puppets, not groups of puppets with similar characteristics—it does raise interesting questions about the origins of xenophobia in an individual’s lifetime.

A Neanderthal’s skull (right) was larger than a human’s (left) and had a similar inner volume for mental capacity, but new research indicates less of it was devoted to higher-order thinking. Image via Wikimedia Commons/DrMikeBaxter

Neanderthals never invented written language, developed agriculture or progressed past the Stone Age. At the same time, they had brains just as big in volume as modern humans’. The question of why we Homo sapiens are significantly more intelligent than the similarly big-brained Neanderthals—and why we survived and proliferated while they went extinct—has puzzled scientists for some time.

Now, a new study by Oxford researchers provides evidence for a novel explanation. As they detail in a paper published today in the Proceedings of the Royal Society B, a greater percentage of the Neanderthal brain seems to have been devoted to vision and control of their larger bodies, leaving less mental real estate for higher thinking and social interactions.

The research team, led by Eiluned Pearce, came to the finding by comparing the skulls of 13 Neanderthals who lived 27,000 to 75,000 years ago to 32 human skulls from the same era. In contrast to previous studies, which merely measured the interior of Neanderthal skulls to arrive at a brain volume, the researchers attempted to come to a “corrected” volume, which would account for the fact that the Neanderthals’ brains were in control of rather differently-proportioned bodies than ours ancestors’ brains were.

A replica of the La Ferrassie 1 Neanderthal skull, the largest and most complete Neanderthal skull ever found. Image via the Natural History Museum London

One of the easiest differences to quantify, they found, was the size of the visual cortex—the part of the brain responsible for interpreting visual information. In primates, the volume of this area is roughly proportional to the size of the animal’s eyes, so by measuring the Neanderthals’ eye sockets, they could get a decent approximation of their the visual cortex as well. The Neanderthals, it turns out, had much larger eyes than ancient humans. The researchers speculate that this could be because they evolved exclusively in Europe, which is of higher latitude (and thus has poorer light conditions) than Africa, where H. sapiens evolved.

Along with eyes, Neanderthals had significantly larger bodies than humans, with wider shoulders, thicker bones and a more robust build overall. To account for this difference, the researchers drew upon previous research into the estimated body masses of the skeletons found with these skulls and of other Neanderthals. In primates, the amount of brain capacity devoted to body control is also proportionate to body size, so the scientists were able to calculate roughly how much of the Neanderthals’ brains were assigned to this task.

After correcting for these differences, the research team found that the amount of brain volume left over for other tasks—in other words, the mental capacity not devoted to seeing the world or moving the body—was significantly smaller for Neanderthals than for ancient H. sapiens. Although the average raw brain volumes of the two groups studied were practically identical (1473.84 cubic centimeters for humans versus 1473.46 for Neanderthals), the average “corrected” Neanderthal brain volume was just 1133.98 cubic centimeters, compared to 1332.41 for the humans.

This divergence in mental capacity for higher cognition and social networking, the researcher argue, could have led to the wildly different fates of H. sapiens and Neanderthals. “Having less brain available to manage the social world has profound implications for the Neanderthals’ ability to maintain extended trading networks,” Robin Dunbar, one of the co-authors, said in a press statement. “[They] are likely also to have resulted in less well developed material culture—which, between them, may have left them more exposed than modern humans when facing the ecological challenges of the Ice Ages.”

Previous studies have also suggested that the internal organization of Neanderthal brains differed significantly from ours. For example, a 2010 project used computerized 3D modeling and Neanderthal skulls of varying ages to find that their brains developed at different rates over the course of an individual’s adolescence as compared to human brains despite comparable brain volumes.

The overall explanation for why Neanderthals went extinct while we survived, of course, is more complicated. Emerging evidence points to the idea that Neaderthals were smarter than previously thought, though perhaps not smart enough to outmaneuver humans for resources. But not all of them had to—in another major 2010 discovery,a team of researchers compared human and Neanderthal genomes and found evidence that our ancestors in Eurasia may have interbred with Neanderthals, preserving a few of their genes amidst our present-day DNA.

Apart from the offspring of a small number of rare interbreeding events, though, the Neanderthals did die out. Their brains might have been just as big as ours, but ours might have been better at a few key tasks–those involved in building social bonds in particular—allowing us to survive the most recent glacial period while the Neanderthals expired.

Though submerged in a shipwreck for millennia, the ancient Roman medicinal tablets were kept sealed in tin containers (left), ensuring the pills inside remained dry (right). Image via PNAS/Giachi et. al.

Around 120 B.C.E., the Relitto del Pozzino, a Roman shipping vessel, sank off the coast of Tuscany. More than two millennia later, in the 1980s and 90s, a team sent by the Archeological Superintendency of Tuscany began to excavate the ruins, hauling up planks of rotting wood.

“It wasn’t an easy task. The wreck is covered by marine plants and their roots. This makes it hard to excavate it,” underwater archaeologist Enrico Ciabatti told Discovery News in 2010. “But our efforts paid off, since we discovered a unique, heterogeneous cargo.”

The Relitto del Pozzino shipwreck contained a variety of cargo, including lamps that originated in Asia minor (above). Image courtesy of Enrico Ciabatti

That cargo, it turned out, included ceramic vessels made to carry wine, glass cups from the Palestine area and lamps from Asia minor. But in 2004, the archaeologists discovered it also included something even more interesting: the remains of 2,000-year-old medicine chest.

Although the chest itself—which had presumably belonged to a Roman doctor—was apparently destroyed, researchers found a surgery hook, a mortar, 136 wooden drug vials and several cylindrical tin vessels (called pyxides) all clustered together on the ocean floor. When they x-rayed the pyxides, they saw that one of them had a number of layered objects inside: five circular, relatively flat grey medicinal tablets. Because the vessels had been sealed, the pills had been kept completely dry over the years, providing a tantalizing opportunity for us to find out what exactly the ancient Romans used as medicine.

Now, as revealed today in a paper in the Proceedings of the National Academy of Sciences, a team of Italian chemists has conducted a thorough chemical analysis of the tablets for the first time. Their conclusion? The pills contain a number of zinc compounds, as well as iron oxide, starch, beeswax, pine resin and other plant-derived materials. One of the pills seems to have the impression of a piece of fabric on one side, indicating it may have once been wrapped in fabric in order to prevent crumbling.

Based on their shape and composition, the researchers venture that the tablets may have served as some sort of eye medicine or eyewash. The Latin name for eyewash (collyrium), in fact, comes from the Greek word κoλλυρα, which means “small round loaves.”

Although it remains to be seen just how effective this sort of compound would have been as an actual eye treatment, the rare glimpse into Roman-era medicinal practices is fascinating nonetheless. The vast majority of our knowledge of ancient medicine comes from writings—which may vary in accuracy and lack crucial details—so the presence of actual physical evidence is especially exciting.

A front, profile, and rear view of one of the medicinal tablets. Image via PNAS/Giachi et. al.

Baby bonobos share papayas. Photo from Jingzhi Tan

In 1719, Daniel Defoe wrote in Robinson Crusoe, ”He declar’d he had reserv’d nothing from the Men, and went Share and Share alike with them in every Bit they eat.” Defoe’s famous sharing phrase has persisted throughout the years, passing from parent to child as a lesson on the virtues of sharing with family, peers and even strangers.

But in the context of evolution and survival of the fittest, sharing makes no sense. Until now, scientists assumed that humans alone subscribed to this behavior, especially when it comes to sharing with strangers, and wrote the trait off as a quirk stemming from our unique cognitive and social development.

Sure, primatologists know that great apes help and voluntarily share food with other group mates (acts that indirectly benefits themselves). But strangers? Such a behavior is unheard of amidst species that often compete aggressively with other groups and even murder foreign individuals.

Researchers from Duke University decided to challenge the great ape’s bad sharing rep, seeking to discover whether or not our furry relatives may also have a propensity for partitioning goods with animals they do not know. The scientists chose bonobos–a type of great ape sometimes referred to as a pygmy chimpanzee–for their study. Compared to chimpanzees, bonobos possess a relatively high tolerance for strangers, so they seemed like a logical candidate for investigations into the nature of sharing.

At a bonobo sanctuary in the Democratic Republic of the Congo, they enrolled 15 wild-born bonobos orphaned and rescued from the illegal wildlife trade in four experiments. In the first experiment, the researchers led a bonobo into a room piled high with delicious banana slices. Behind two sliding doors, they placed either a friend of the main bonobo or a stranger (a bonobo unrelated and unknown to their main research subject). The bonobo with the bananas could chose to eat the food all on its own, or open the sliding door and invite both or either the friend or stranger to join in. In the second experiment, they placed only one bonobo–either the friend or stranger–behind a door and left the second room empty.

The results, which they describe this week in the journal PLoS One, confounded the researchers. In more than 70 percent of the trials, the bonobos shared their food at least once. They preferred to release the stranger over their group mate, and the stranger in turn often released the other bonobo, even though that meant splitting the food three ways and being outnumbered by two bonobos that already knew each other. They ignored the door leading to the empty room, showing that the novelty of opening the door was not motivating their behavior.

So, were the bonobos willing to share their food with strangers because of an overwhelming desire to interact with the unknown apes, or were they motivated by a sense of altruism? The researchers set up two more experiments to find out. They arranged a rope which, when pulled, released either a bonobo stranger or friend into a room which held more bananas. A mesh divider separated the main bonobo from that room, however, meaning it could neither reach the food or interact directly with the released ape. Even when there was no immediate social or culinary reward on offer, the researchers found, 9 out of 10 bonobos still chose to release their friend or the stranger at least once, allowing the other ape to reach the banana reward.

Bonobos drew the line, however, in the final experiment. This setup allowed both bonobos to access the food, but did not let them interact physically with the stranger or friend. In other words, the main bonobo would have to forfeit some of its food but receive no reward of sniffing, petting or playing with another ape. None of the bonobos chose to open the door, suggesting that the seemingly altruistic sharing of the first two experiments was just a ploy to gain gratifying access to intriguing strangers and, to a lesser extent, friends. The third experiment, however, shows that the bonobos’ motivations are not completely selfish. When the food was so far out of reach that they themselves could not benefit, they allowed a friend or stranger to enjoy it instead.

Bonobos, in other words, break the rules when it comes to sharing, showing that kindness towards strangers is not unique to humans. Oddly enough, unlike their bipedal counterparts, bonobos even seem to prefer strangers to group mates. This behavior, the study authors think, might have evolved to help groups of bonobos expand their social networks. Further investigations may lend clues about evolution of sharing in humans.

“Like chimpanzees, our species would kill strangers; like bonobos, we could also be very nice to strangers,” said Jingzhi Tan, an evolutionary anthropologist at Duke University and lead author of the paper, in a statement. “Our results highlight the importance of studying bonobos to fully understand the origins of such human behaviors.”

New evidence indicates cheese was invented as far back as 5000 BCE, although ancient cheeses wouldn’t have been as varied or refined as the cheeses we have today. Image via Flickr user Skansa Matupplevelser

Archaeologists have long known that cheese is an ancient human invention. Wall murals in Egyptian tombs from 2000 BCE depict cheesemaking, and Sumerian tablets written in cuneiform text seem to describe cheese as well. Our distant ancestors, it seems clear, knew about the wonder that is cheese.

Today, though, cheese lovers have cause to celebrate: New evidence indicates that the invention of the utterly delicious and at times stinky product actually came thousands of years earlier. As described in a paper published today in Nature, chemical analysis of prehistoric pottery unearthed from sites in Poland shows that cheesemaking was invented way farther back than originally believed—roughly 7000 years ago.

A team of researchers from the University of Bristol, Princeton and a group of Polish universities came to the finding by examining an unusual group of artifacts from the Polish sites: clay shards that were pierced with a series of small holes. Struck by their resemblance to in modern-day cheese strainers, they chemically tested the material around the holes, and were vindicated to find ancient traces of the kinds of lipids and fatty acids found in dairy products. These ceramics are attributed to what archaeologists call the Linear Pottery culture, and are dated to 5200 to 4900 BCE.

Researchers tested these perforated ceramic fragments and found ancient dairy residues, indicating they were used as cheese strainers. Image via Salque et. al.

“The presence of milk residues in sieves, which look like modern cheese-strainers, constitutes the earliest direct evidence for cheesemaking,” said lead author Mélanie Salque of the University of Bristol in a statement. “So far, early evidence for cheesemaking were mostly iconographic, that is to say murals showing milk processing, which dates to several millennia later than the cheese strainers.”

Although different cheeses are made by a variety of processes, nearly all start with the separation of milk into liquid whey and solid curds. This is typically accomplished by adding bacteria to the milk, along with rennet (a mix of enzymes produced in animal stomachs), then straining out the liquid from the newly-coagulated curds. These perforated pots, then, seem like they were used to strain out the solids.

The researchers also analyzed other pottery fragments from the site. Several unperforated bowls also had traces of dairy residues, indicating they might have been used to store the curds or whey after separation. They also found remnants of fats from cow carcasses in some of the ceramics, along with beeswax in others, suggesting they were used to cook meat and sealed to store water, respectively. Apart from being capable of making a complex food product like cheese, it seems that these ancient people also created different types of specialized ceramics for different purposes.

The authors of the paper believe this ancient cheesemaking goes a long way in explaining a mystery: why humans bothered to domesticate cows, goats and sheep thousands of years ago, rather than eating their wild ancestors, even though genetic evidence indicates that we hadn’t yet evolved the ability to digest lactose, and thus couldn’t drink milk. Since cheese is so much lower in lactose than milk, they say, figuring out how to make it would have provided a means for unlocking milk’s nutritional content, and gave prehistoric humans incentive to raise these animals over a long period of time, instead of slaughtering them for their meat immediately. Making cheese also gave these people the ability to preserve the nutritional content, since milk spoils much more quickly.

That leaves one more pressing question—what did this ancient cheese actually taste like? Without abundant access to salt or knowledge of the refined heating and ripening processes that are necessary for the variety of cheese we have today, it’s likely that the first cheeses were pretty bland and liquidy. Like ancient Egyptian cheeses, these were probably comparable in texture and taste to cottage cheese, Salque and colleagues noted.

Prehistoric humans correctly depicted the gait of four-legged animals, such as this bull in the famous cave paintings of Lascaux, France, more frequently than modern artists. Image via Horvath et. al., PLOS ONE

The iconic caveman in popular culture is Fred Flintstone: slow-witted and unskilled. In general, we think of the cave art produced by prehistoric people as crude and imprecise too—a mere glimmer of the artistic mastery that would blossom millenia later, during the Renaissance and beyond.

If this is your impression of prehistoric humans, a new study published today in PLOS ONE by researchers from Eotvos University in Budapest, Hungary, might surprise you. In analyzing dozens of examples of cave art from places such as Lascaux, the group, led by Gabor Horvath, determined that prehistoric artists were actually better at accurately depicting the way four-legged animals walk than artists from the 19th and 20th centuries.

The researchers evaluated the prehistoric artists on the basis of the landmark 1880s finding by British photographer Eadweard Muybridge that horses (and, it was later discovered, most four-legged animals) move their legs in a particular sequence as they walk. The “foot-fall formula,” as it’s called, goes LH-LF-RH-RF, where H means ‘hind,’ F means ‘fore,’ and L and R mean ‘left’ and ‘right,’ respectively. At the time of Muybridge, this was thought to be an entirely novel discovery.

Except, as it turns out, prehistoric people apparently knew it too—and got it right in their drawings the majority of the time. Of the 39 ancient cave paintings depicting the motion of four-legged animals that were considered in the study, 21 nailed the sequence correctly, a success rate of 53.8%. Due to the number of combinations of how a four-legged animal’s gait can be depicted, the researchers state that mere chance would lead to a 26.7% rate of getting it right. Cavemen artists knew what they were doing.

This labelled contour drawing of the Lascaux painting shows that the hoofs are placed on the ground in a realistic manner according to the foot-fall formula. Image via Horvath et. al., PLOS ONE

When the researchers looked at 272 paintings and statues of four-legged animals made during modern times but before Muybridge’s findings in the 1880s, such as a famous horse sketch by Leonardo da Vinci, it turned out that these more recent artists were much worse: They only got the sequence right 16.5% of the time. Remarkably, even the 686 paintings and statues studied that were made more recently than 1887, after scientists knew for sure how four-legged animals walked, still got it right just 42.1% of the time.

In this drawing, even Leonardo da Vinci draws the sequence of a horse’s gait in an unrealistic manner. Image via Horvath et. al., PLOS ONE

Even apart from artists, a sizable number of depictions of four-legged animals made during the 20th century specifically for the sake of accuracy got the sequence wrong too, according to references used in the study. Out of 307 renditions analyzed, just 58.9% of depictions in natural history museums were correct, along with 56.9% of those in taxidermy catalogues, 50% of animal toy models and 36.4% of illustrations in animal anatomy textbooks.

Although the amount of art studied in each group varies greatly, the accuracy rate for animal depictions in prehistoric times is noteworthy. How could prehistoric humans possibly be this skilled at depicting animals such as bulls, antelopes and wild horses? For a potential answer, consider the way these ancient artists probably thought about the animals: as prey.

For prehistoric humans, “the observation of animals was not merely a pastime, but a matter of survival,” the study’s authors write. “Compared to artists of latter eras, when people were not as directly connected to nature, the creators of such cave paintings and carvings observed their subjects better and thus they depicted the walk of the animals in a more life-like manner.”

Many irrelevant factors have been found to sway voters at the polls. Image via Flickr user ragesoss

Most of us believe that our political views are based on the issues, or at the very least, on our views of the candidates’ personal qualities, which might matter when it comes to governing. We imagine that we vote for good policies, or politicians that can serve as steady leaders in times of crisis.

But when it comes to voting, as with many other areas of life, we’re not quite as rational as we like to believe. Sure, with high-profile contests like the race for president, most of us have held views for a long period of time, and these are more likely to be based on logic. But research reveals that, especially for local races or ballot propositions about which we’re less informed, a number of weird, utterly irrelevant factors can easily influence our vote.

1. Timing. Whether a policy question is perceived as a long-term issue or an immediate problem can strongly affect a person’s response to it. In a study published in August by researchers from the University of California, Davis, college students were polled on a local bicycle policy and an affirmative action policy, with the initiatives framed as either something that would be put in place in the next month or in the next year. The researchers found that framing both questions as distant, long-term issues led students to think of them in a more abstract way—and be more likely to change their opinions to conform to the beliefs of the group as a whole. In contrast, when the proposals seemed like immediate possibilities, the students’ views were less flexible.

When polled at schools, voters are more likely to support education funding. Image via Flickr user cliff1066

2. Location. Simply being near a church or school might be enough to change your views on social, religious and educational policies. Last January, psychologists from Baylor University conducted street interviews in the Netherlands and the United Kingdom and discovered that people interviewed near churches tended to describe themselves as more socially conservative than people near government buildings—this trend could be seen even when the researchers controlled for religiousness and ensured that the people polled near churches were simply passing, not entering or exiting them. A 2008 Stanford study came to a similar finding, discovering that people who voted in schools were more likely to support an education funding initiative.

Scientists speculate that these findings might both be the effects of contextual priming, in which environmental cues can unconsciously affect decisions and behavior by activating certain associative areas of the brain. The takeaway from these particular studies? Maybe we shouldn’t put our polling stations in churches or schools.

3. Your Home Team’s Performance. As we reported in September, a study by social scientist Michael K. Miller suggests that one especially irrelevant factor can increase an incumbent’s chances of getting elected: a local sports team’s winning percentage. Looking at mayoral races in 39 cities across the United States from 1948 to 2009, Miller found that an incumbent mayor of a city where all home teams made the playoffs had a nine percent better chance of getting reelected than a mayor of a city where none made the playoffs. A 2004 German study came to a similar conclusion, finding that a win by the national soccer team made the party in power more popular, no matter which party it was. Miller attributes this to the “prosperity model” of voting, in which voters simply vote for the status quo when they feel happy for any reason, related to politics or not.

What does this mean for Obama and Romney? Hard to say. Deep into football season, in Ohio, an important swing state, the Ohio State University team is ranked number five in the country and undefeated—but the team is banned from bowl play due to NCAA sanctions resulting from recruiting and other violations. Both of the state’s pro teams have losing records.

4. Candidate Appearance and Attractiveness. In politics, as in business, we give an unfair advantage to the beautiful. A 2008 Northwestern University study found that people were more likely to vote for candidates, both male and female, that they found attractive. This bias was much stronger, however, when male study participants evaluated female candidates. Female participants also cared about the appearance of “approachability” in males, while male participants found the appearance of “competence” the most important factor in male candidates.

5. A Fear of Death. This might be the strangest one of all. A 2005 study that examined the 2004 Presidential Election found that people in a psychologically neutral state of mind were more likely to vote for Senator John Kerry, but when a similar sample of voters was asked to contemplate death and the afterlife, they became more likely to vote for President George W. Bush. The researchers speculated this may have been related to Bush’s “tough on terror” image in the aftermath of the September 11th attacks—and that a tape by Osama bin Laden that surfaced days before the election might have played a role in tipping it for Bush.

A new study suggests that readers are much more likely to pay for content if they think the request is a fair one. Image via Flickr user Joe Schlabotnick

In March of 2011, the New York Times introduced a paywall, requiring a $15 to $35 monthly subscription from online readers if they wanted to read more than 20 articles per month (in April 2012, that total was lowered to 10). The jury’s still out on whether this strategy will help the newspaper survive in the digital era, as publishers struggle to determine how exactly to convince readers to pay for something that was previously free.

As of July, it was reported that the paper had about 500,000 digital subscribers, bringing in some $100 million in revenue—but the Web site’s traffic has also dipped significantly, as the paywall drove many readers away to other sites. Additionally, tips on easy ways to circumvent the paywall have spread across the Internet, indicating that many visitors read content without paying.

A study published Wednesday in Cyberpsychology, Behavior, and Social Networking could help shed some light on why most readers have declined to pay. Put simply, the site hasn’t done a great job of explaining why the paywall was initiated. The study’s findings indicate that justifying to potential subscribers why content can’t be free is important in convincing them to pay. Although the site’s “paywall message” has varied over time, at the start, it read in part: “As you may know, we are now charging for unlimited access to our online content. You can come back next month for another 20 free articles or choose unlimited access with a Digital Subscription.”

“When participants were provided with a compelling justification for the paywall—that the NYT was likely to go bankrupt without it—their support and willingness to pay increased,” the researchers, Jonathan Cook of Columbia University and Shahzeen Attari of Indiana University, write in the study. The majority of study participants did not pay either way, simply visiting other sites or circumventing the paywall (younger and more frequent visitors were much more likely to choose the latter), but those surveyed were much more likely to pay when they felt that the request was a fair one.

The findings were based on a pair of web surveys, one conducted with 954 regular online readers of the newspaper just after the paywall was announced, and another conducted ten weeks later among the 400 who responded from the original group. This sample pool was split into two groups at the start—one that, along with information about the paywall, was told that the New York Times had an annual profit of $5 million and would likely make money with or without online subscriptions, and another that learned how advertising revenue was much lower online than in print, and that without digital subscriptions, the newspaper would likely go bankrupt. The majority of both groups declined to buy a subscription, but even so, the latter group was more likely to view the site as valuable and paid for subscriptions in larger numbers.

Although it’s hard to view the findings as particularly positive if you hope for a future for paid online journalism content, one important conclusion is that explaining the justification of paywalls to readers matters much more than the New York Times might have anticipated. If readers feel their payment will simply enrich a prosperous company, they’ll go elsewhere or cheat, but if they think they’re providing necessary support for a service they enjoy, they might just shell out the money.

“Our results imply that many NYT readers resisted the newly implemented paywall,” the researchers write, noting that unique visitors to the site dropped by 3.3 million over the year after the paywall was introduced. “As other content providers follow the lead of the NYT, they may benefit from providing compelling justifications that convince consumers of financial necessity.”

Anthropologists argue that the presence of grandmothers has been crucial in driving human evolution. Image via Flickr user Mrs Logic

For years, anthropologists and evolutionary biologists have struggled to explain the existence of menopause, a life stage that humans do not share with our primate relatives. Why would it be beneficial for females to stop being able to have children with decades still left to live?

According to a study published today in the journal Proceedings of the Royal Society B, the answer is grandmothers. “Grandmothering was the initial step toward making us who we are,” says senior author Kristen Hawkes, an anthropologist at the University of Utah. In 1997 Hawkes proposed the “grandmother hypothesis,” a theory that explains menopause by citing the under-appreciated evolutionary value of grandmothering. Hawkes says that grandmothering helped us to develop “a whole array of social capacities that are then the foundation for the evolution of other distinctly human traits, including pair bonding, bigger brains, learning new skills and our tendency for cooperation.”

The new study, which Hawkes conducted with mathematical biologist Peter Kim of the University of Sydney and Utah anthropologist James Coxworth, uses computer simulations to provide mathematical evidence for the grandmother hypothesis. To test the strength of the idea, the researchers simulated what would happen to the lifespan of a hypothetical primate species if they introduced menopause and grandmothers as part of the social structure.

In the real world, female chimpanzees typically live about 35 to 45 years in the wild and rarely survive past their child-bearing years. In the simulation, the researchers replicated this, but they gave 1 percent of the female population a genetic predisposition for human-like life spans and menopause. Over the course of some 60,000 years, the hypothetical primate species evolved the ability to live decades past their child-bearing years, surviving into their sixties and seventies, and eventually 43 percent of the adult female population were grandmothers.

How would grandmothers help us live longer? According to the hypothesis, grandmothers can help collect food and feed children before they are able to feed themselves, enabling mothers to have more children. Without grandmothers present, if a mother gives birth and already has a two-year-old child, the odds of that child surviving are much lower, because unlike other primates, humans aren’t able to feed and take care of themselves immediately after weaning. The mother must devote her time and attention to the new infant at the expense of the older child. But grandmothers can solve this problem by acting as supplementary caregivers.

In the hypothesis—and in the computer simulation—the few ancestral females who were initially able to live to postmenopausal ages increased the odds of their grandchildren surviving. As a result, these longer-lived females were disproportionately likely to pass on their genes that favored longevity, so over the course of thousands of generations, the species as a whole evolved longer lifespans.

But why would females evolve to only ovulate for 40 or so years into these longer lives? Hawkes and other advocates of the hypothesis note that, without menopause, older women would simply continue to mother children, instead of acting as grandmothers. All children would still be entirely dependent on their mothers for survival, so once older mothers died, many young offspring would likely die too. From an evolutionary perspective, it makes more sense for older females to increase the group’s overall offspring survival rate instead of spending more energy on producing their own.

Hawkes goes one step further, arguing that the social relations that go along with grandmothering could have contributed to the larger brains and other traits that distinguish humans. “If you are a chimpanzee, gorilla or orangutan baby, your mom is thinking about nothing but you,” she says. “But if you are a human baby, your mom has other kids she is worrying about, and that means now there is selection on you—which was not on any other apes—to much more actively engage her: ‘Mom! Pay attention to me!’”

As a result, she says, “Grandmothering gave us the kind of upbringing that made us more dependent on each other socially and prone to engage each other’s attention.” This trend, Hawkes says, drove the increase in brain size, along with longer lifespans and menopause.

The theory is by no means definitive, but the new mathematical evidence serves as another crucial piece of support for it. This could help anthropologists better understand human evolution—and should give you another reason to go thank your grandmother.