South Of Heaven

How did humans conquer the world?

Partly, because they were friendly to strangers.

Research findings published in the March 11 edition of the journal Science by an international team of noted anthropologists, including several from Arizona State University, who study hunter-gatherer societies, are informing the issue by suggesting that human ancestral social structure may be the root of cumulative culture and cooperation and, ultimately, human uniqueness.

Because humans lived as hunter-gatherers for 95 percent of their species' history, current foraging societies provide the best window for viewing human social evolution, according to the authors. Given that, the researchers focused on co-residence patterns among more than 5,000 individuals from 32 present-day foraging societies around the globe, including the Gunwinggu, Labrador Inuit, Mbuti, Apache, Aka, Ache, Agta and Vedda. Their findings identify human hunter-gatherer group structure as unique among primates.

Professor Kim Hill of ASU's School of Human Evolution and Social Change in the College of Liberal Arts and Sciences, is the lead author, along with Robert Walker of the University of Missouri. The collaborative effort involved ASU professors James Eder and Ana Magdalena Hurtado; ASU anthropology graduate student Miran Božičević; and anthropologists from SIL International, Dallas; Southern Methodist University, Dallas; Hawassa University, Ethiopia; Washington State University; Durham University, UK; University of Utah; and Stanford University.

Their finding showed that across all groups, adult brothers and sisters frequently live together, making it common for male in-laws to co-reside. They also found that it was equally common for males or females to move from or remain with family units. This is in contrast to other primate species, where either males or females move to another group at puberty.

A major point in the study is that foraging bands contain several individuals completely unconnected by kinship or marriage ties, yet include males with a vested interest in the offspring of daughters, sisters and wives. This organization mitigates the group hostility frequently seen in other apes and also promotes interaction among residential groups, thereby leading to the development of a large social network.

"The increase in human network size over other primates may explain why humans evolved an emphasis on social learning that results in cultural transmission," said Hill. "Likewise, the unique composition of human ancestral groups promotes cooperation among large groups of non-kin, something extremely rare in nature."

I guess I'm highly evolved

A most modern human is me.

As if the recent prediction that half of all Americans will have diabetes or pre-diabetes by the year 2020 isn't alarming enough, a new genetic discovery published online in the FASEB Journal provides a disturbing explanation as to why: we took an evolutionary "wrong turn." In the research report, scientists show that human evolution leading to the loss of function in a gene called "CMAH" may make humans more prone to obesity and diabetes than other mammals.

"Diabetes is estimated to affect over 25 million individuals in the U.S., and 285 million people worldwide," said Jane J. Kim, M.D., a researcher involved in the work from the Department of Pediatrics at the University of California, San Diego in La Jolla, CA. "Our study for the first time links human-specific sialic acid changes to insulin and glucose metabolism and therefore opens up a new perspective in understanding the causes of diabetes."

In this study, which is the first to examine the effect of a human-specific CMAH genetic mutation in obesity-related metabolism and diabetes, Kim and colleagues show that the loss of CMAH's function contributes to the failure of the insulin-producing pancreatic beta cells in overweight humans, which is known to be a key factor in the development of type 2 diabetes. This gene encodes for an enzyme present in all mammalian species except for humans and adds a single oxygen atom to sialic acids, which are sugars that coat the cell surface.

To make their discovery, the researchers used two groups of mice. The first group had the same mutant CMAH gene found in humans. These mice demonstrated that the CMAH enzyme was inactive and could not produce a sialic acid type called NeuSGc at the cell surface. The second group had a normal CMAH gene. When exposed to a high fat diet, both sets of mice developed insulin resistance as a result of their obesity. Pancreatic beta cell failure, however, occurred only in the CMAH mutant mice that lacked NeuSGc, resulting in a decreased insulin production, which then further impaired blood glucose level control. This discovery may enhance scientific understanding of why humans may be particularly prone to develop type 2 diabetes. Results may also suggest that conventional animal models may not accurately mirror the human situation.

"The diabetes discovery is an important advance in its own right. It tells us a lot about what goes wrong in diabetes, and where to aim with new treatments," said Gerald Weissmann, M.D., Editor-in-Chief of the FASEB Journal, "but its implications for human evolution are even greater. If this enzyme is unique to humans, it must also have given us a survival advantage over earlier species. Now the challenge is to find the function of CMAH in defending us against microbes or environmental stress or both. This evolutionary science explains how we can win some and lose some, to keep our species ahead of the extinction curve."

We're pretty much the same and have been

Here's the news. There probably isn't much difference between us folks today and the earliest Homo Sapiens folk who wandered around 200,000 years ago.

That human evolution follows a progressive trajectory is one of the most deeply-entrenched assumptions about our species. This assumption is often expressed in popular media by showing cavemen speaking in grunts and monosyllables (the Geico Cavemen being a notable exception). But is this assumption correct? Were the earliest humans significantly different from us?

In a paper published in the latest issue of Current Anthropology, archaeologist John Shea (Stony Brook University) shows they were not.

The problem, Shea argues, is that archaeologists have been focusing on the wrong measurement of early human behavior. Archaeologists have been searching for evidence of "behavioral modernity," a quality supposedly unique to Homo sapiens, when they ought to have been investigating "behavioral variability," a quantitative dimension to the behavior of all living things.

Human origins research began in Europe, and the European Upper Paleolithic archaeological record has long been the standard against which the behavior of earlier and non-European humans is compared. During the Upper Paleolithic (45,000-12,000 years ago), Homo sapiens fossils first appear in Europe together with complex stone tool technology, carved bone tools, complex projectile weapons, advanced techniques for using fire, cave art, beads and other personal adornments. Similar behaviors are either universal or very nearly so among recent humans, and thus, archaeologists cite evidence for these behaviors as proof of human behavioral modernity.

Yet, the oldest Homo sapiens fossils occur between 100,000-200,000 years ago in Africa and southern Asia and in contexts lacking clear and consistent evidence for such behavioral modernity. For decades anthropologists contrasted these earlier "archaic" African and Asian humans with their "behaviorally-modern" Upper Paleolithic counterparts, explaining the differences between them in terms of a single "Human Revolution" that fundamentally changed human biology and behavior. Archaeologists disagree about the causes, timing, pace, and characteristics of this revolution, but there is a consensus that the behavior of the earliest Homo sapiens was significantly that that of more-recent "modern" humans.

Shea tested the hypothesis that there were differences in behavioral variability between earlier and later Homo sapiens using stone tool evidence dating to between 250,000- 6000 years ago in eastern Africa. This region features the longest continuous archaeological record of Homo sapiens behavior. A systematic comparison of variability in stone tool making strategies over the last quarter-million years shows no single behavioral revolution in our species' evolutionary history. Instead, the evidence shows wide variability in Homo sapiens toolmaking strategies from the earliest times onwards. Particular changes in stone tool technology can be explained in terms of the varying costs and benefits of different toolmaking strategies, such as greater needs for cutting edge or more efficiently-transportable and functionally-versatile tools. One does not need to invoke a "human revolution" to account for these changes, they are explicable in terms of well-understood principles of behavioral ecology.

This study has important implications for archaeological research on human origins. Shea argues that comparing the behavior of our most ancient ancestors to Upper Paleolithic Europeans holistically and ranking them in terms of their "behavioral modernity" is a waste of time. There are no such things as modern humans, Shea argues, just Homo sapiens populations with a wide range of behavioral variability. Whether this range is significantly different from that of earlier and other hominin species remains to be discovered. However, the best way to advance our understanding of human behavior is by researching the sources of behavioral variability in particular adaptive strategies.

I suspect that Neanderthals probably pretty much behaved like us too. A few differences here and there, but the main difference between us and earlier versions of us is the shared technologies we have accrued. Physically, mentally, we're all pretty much the same and have been for a long, long time.

Human brains are getting smaller

Last year I had a blog on an article in Discover Magazine on the curious fact that humans' brains have been getting smaller over the last 20,000 years. Discover has finally put the article up on its website. Here.

If you could hop into your time machine and visit some Cro-Magnons' cave you'd find that your new friends had bigger craniums. In fact, people all over the world had bigger brains back then. And now people all over the world have smaller brains. What gives?

The author goes through several theories, from better, more efficient wiring (like radios going from tubes to transistors) to maybe we are just evolving into idiots. (Friday I crossed paths with three idiot drivers in less than a mile, but that wouldn't be a real scientific survey.)

One particularly interesting theory is that we are becoming more domesticated. If you look at animals in the wild their brains are larger than their domesticated cousins. Being out on your own in the wild requires quick thinking. When you live in a society there is a division of labor, and a division of thinking. And how are we domesticating ourselves? We in societies weed out the violent troublemakers. If you belonged to a hunter-gatherer tribe and you got out of line you would be killed or simply kicked out, which would be tantamount to being killed.

Here's an interesting comparison between chimpanzees and bonobos:

The two scientists point to the results of studies comparing the cognitive abilities of wolves and dogs. Wolves, with their larger brains, are more prone to flashes of insight, allowing them to solve problems on their own; dogs, with smaller brains, excel at using humans to help them. “Wolves seem to be a little bit more persistent than dogs in solving simple problems like how to open a box or navigate a detour,” Hare says. “Wolves persevere when dogs readily give up.” On the flip side, dogs leave wolves in the dust when it comes to tracking the gaze and gestures of their masters—or as Hare puts it, “They are very good at using humans as tools to solve problems for them.” And while dogs may appear lazy and pampered, some can survive for multiple generations in areas far removed from humans—an indication, Hare says, that they have retained an ability to adapt to the wild.

For more insight, Hare is now studying other primates, notably bonobos. He tells me he suspects that these great apes are domesticated chimps. As if on cue, bursts of exotic, birdlike trills suddenly drown out his voice over the phone. “Sorry about that,” he shouts over the line. “Those are the bonobos.” It turns out that as I am speaking to him, Hare is not at his desk at Duke but in a Congo forest where the bonobos live. “Bonobos look and behave like juvenile chimps,” he continues. “They are gracile. They never show lethal aggression and do not kill each other. They also have brains that are 20 percent smaller than those of chimps.”

Hare thinks bonobos became domesticated by occupying an ecological niche that favored selection for less aggressive tendencies. That niche, he says, offered more abundant sources of nutrition, so a habit of fighting over meals became less important to survival. From that lineage came the bonobos, highly cooperative primates known for their peaceful ways.

Both Wrangham and Hare see parallels between bonobo development and our own. Our self-domestication, they think, may hold the key to our species’s extraordinary motivation to cooperate and communicate —arguably the twin pillars supporting the whole of our civilization.

So if you've still got enough brain cells in your noggin, read the whole article. Utterly fascinating.

Neanderthals lived as long as modern humans

Here is a report that says that Neanderthals had pretty much the same lifespan as modern humans when they coexisted. Not that anyone lived all that long back in those days.

Erik Trinkaus, PhD, Professor of Anthropology in Arts & Sciences, examined the fossil record to assess adult mortality for both groups, which co-existed in different regions for roughly 150,000 years. Trinkaus found that the proportions of 20 to 40-year-old adults versus adults older than 40, were about the same for early modern humans and Neandertals.

This similar age distribution, says Trinkaus, reflects similar patterns of adult mortality and treatment of the elderly in the context of highly mobile hunting-and-gathering human populations.

The study, "Late Pleistocene Adult Mortality Patterns and Modern Human Establishment, was published the week of Jan. 10, 2011 in the Proceedings of the National Academy of Sciences.

Older individuals are rarely found among the remains of late archaic humans, which has prompted some researchers to propose that Neandertals had an inherently shorter life expectancy, contributing to their demise.

However, if early modern humans did have a demographic advantage, Trinkaus argues, it was more likely due to high fertility rates and lower infant mortality.

"If indeed there was a demographic advantage for early modern humans, at least during transitional phases of Late Pleistocene human evolution, it must have been the result of increased fertility and/or reduced immature mortality," writes Trinkaus in the paper's conclusion. "Neither adult longevity nor proposed modest shifts in developmental rates are likely to have played a role in this demographic transition.

I'd linked to an article a few months ago which suggested that Neanderthals aged faster than humans. Maybe not, or maybe not enough to make a difference. That came out before it turned out that lots of humans are carrying around bits of Neanderthal DNA. There was also an article going back a year or two which suggested that Neanderthal birth canals weren't as big as modern human birth canals, which may have caused more birth complications.

More to chew on.

Chickens that kicked butt

 
Well, actually they are extinct members of the ibis family. But they had club-like "hands" on their wings and punched their enemies. And they lived on Jamaica.

Paleontologists at Yale University and the Smithsonian Institution have discovered that Xenicibis, a member of the ibis family that lived about ten thousand years ago and was found only in Jamaica, most likely used its specialized wings like a flail, swinging its upper arm and striking its enemies with its thick hand bones.

"No animal has ever evolved anything quite like this," said Nicholas Longrich of Yale, who led the research. "We don't know of any other species that uses its body like a flail. It's the most specialized weaponry of any bird I've ever seen."

As part of the new study, the researchers analyzed a number of recently discovered partial skeletons of Xenicibis and found that the wings were drastically different from anything they'd seen before. "When I first saw it, I assumed it was some sort of deformity," Longrich said. "No one could believe it was actually that bizarre."

The bird, which was the size of a large chicken, is anatomically similar to other members of the ibis family except for its wings, which include thick, curved hand bones unlike those of any other known bird. Xenicibis also had a much larger breastbone and longer wings than most flightless birds. "That was our first clue that the wings were still being used for something," Longrich said.

While other birds are known to punch or hammer one another with their wings, Xenicibis is the only known animal to have used its hands, hinged at the wrist joint, like two baseball bats to swing at and strike its opponents. Although modern day ibises do not strike one another in this fashion, they are very territorial, with mates often fighting other pairs over nesting and feeding rights.

It's also possible that the birds used their club-like wings to defend themselves against other species that might have preyed on the birds' eggs or young. Xenicibis is unusual in that it became flightless even in the midst of a number of predators, including the Jamaican yellow boa, a small extinct monkey and over a dozen birds of prey.

The team found that two of the wing bones in the collection showed evidence of combat, including a fractured hand bone and a centimeter-thick upper arm bone that was broken in half. The damage is proof of the extreme force the birds were able to wield with their specialized wings, Longrich said.

But they didn't have tootbrushes

This news story does some analysis regarding plant material found on Neanderthal teeth. The long story short, Neanderthals were omnivorous like modern humans. They weren't restricted to just eating meat, as used to be believed.

Researchers from George Washington University and the Smithsonian Institution have discovered evidence to debunk the theory that Neandertals' disappearance was caused in part by a deficient diet -- one that lacked variety and was overly reliant on meat. After discovering starch granules from plant food trapped in the dental calculus on 40-thousand-year-old Neandertal teeth, the scientists believe that Neandertals ate a wide variety of plants and included cooked grains as part of a more sophisticated, diverse diet similar to early modern humans.

"Neandertals are often portrayed as very backwards or primitive," said Amanda Henry, lead researcher and a post-doctoral researcher at GW. "Now we are beginning to understand that they had some quite advanced technologies and behaviors."

Dr. Henry made this discovery together with Alison Brooks, professor of anthropology and international affairs at GW, and Dolores Piperno, a GW research professor and senior scientist and curator of archaeobotany and South American archaeology at the Smithsonian National Museum of Natural History, Washington D.C., and Smithsonian Tropical Research Institute, Panama.

The discovery of starch granules in the calculus on Neandertal teeth provides direct evidence that they made sophisticated, thoughtful food choices and ate more nutrient-rich plants, for example date palms, legumes and grains such as barley. Until now, anthropologists have hypothesized that Neandertals were outlived by early modern humans due in part to the former's primitive, deficient diet, with some scientists arguing Neandertals' diets were specialized for meat-eating. As such, during major climate swings Neandertals could be outcompeted by early humans who incorporated diverse plant foods available in the local environment into their diets.

Drs. Henry, Brooks and Piperno's discovery suggests otherwise. The researchers discovered starch granules in dental calculus, which forms when plaque buildup hardens, on the fossilized teeth of Neandertal skeletons excavated from Shanidar Cave in Iraq and Spy Cave in Belgium. Starch granules are abundant in most human plant foods, but were not known to survive on fossil teeth this old until this study. The researchers' findings indicate that Neandertals' diets were more similar to those of early humans than originally thought. The researchers also determined from alterations they observed in the starch granules that Neandertals prepared and cooked starch-rich foods to make them taste better and easier to digest.

"Neandertals and early humans did not visit the dentist," said Dr. Brooks. "Therefore, the calculus or tartar remained on their teeth, preserving tiny clues to the previously unknown plant portion of their diets."

Dr. Henry is currently a post-doctoral researcher in the Columbian College of Arts and Sciences Hominid Paleobiology program at the George Washington University, where she also received her Ph.D. in Jan. 2010. Her research focuses on the uses of plant foods by human ancestors. In Jan. 2011, Dr. Henry will begin leading an independent research group focusing on the evolution of human diet at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. Dr Brooks' research focuses on the evolution of modern human behavior. Dr. Piperno is a pioneer in the detection and study of plant microfossils and the evolution of human diets.

"This significant finding provides new insight on the plight of the Neandertals," said Peg Barratt, dean of GW's Columbian College of Arts and Sciences. "It's also an excellent example of our dynamic partnership with the Smithsonian to further advance learning and discovery."

In case you haven't noticed, ever since traces of Neanderthal DNA have been found in the human genome our cousins have been getting much better press.

3 billion-year-old genes

This is fascinating, although close to incomprehensible to me. Scientists can figure out what kind of genes were in soft-celled thingies in the primordial soup billions of years ago.

 

About 580 million years ago, life on Earth began a rapid period of change called the Cambrian Explosion, a period defined by the birth of new life forms over many millions of years that ultimately helped bring about the modern diversity of animals. Fossils help palaeontologists chronicle the evolution of life since then, but drawing a picture of life during the 3 billion years that preceded the Cambrian Period is challenging, because the soft-bodied Precambrian cells rarely left fossil imprints. However, those early life forms did leave behind one abundant microscopic fossil: DNA.

Because all living organisms inherit their genomes from ancestral genomes, computational biologists at MIT reasoned that they could use modern-day genomes to reconstruct the evolution of ancient microbes. They combined information from the ever-growing genome library with their own mathematical model that takes into account the ways that genes evolve: new gene families can be born and inherited; genes can be swapped or horizontally transferred between organisms; genes can be duplicated in the same genome; and genes can be lost.

The scientists traced thousands of genes from 100 modern genomes back to those genes' first appearance on Earth to create a genomic fossil telling not only when genes came into being but also which ancient microbes possessed those genes. The work suggests that the collective genome of all life underwent an expansion between 3.3 and 2.8 billion years ago, during which time 27 percent of all presently existing gene families came into being.

Eric Alm, a professor in the Department of Civil and Environmental Engineering and the Department of Biological Engineering, and Lawrence David, who recently received his Ph.D. from MIT and is now a Junior Fellow in the Harvard Society of Fellows, have named this period the Archean Expansion.

Because so many of the new genes they identified are related to oxygen, Alm and David first thought that the emergence of oxygen might be responsible for the Archean Expansion. Oxygen did not exist in the Earth's atmosphere until about 2.5 billion years ago when it began to accumulate, likely killing off vast numbers of anerobic life forms in the Great Oxidation Event.

"The Great Oxidation Event was probably the most catastrophic event in the history of cellular life, but we don't have any biological record of it," says Alm.

Closer inspection, however, showed that oxygen-utilizing genes didn't appear until the tail end of the Archean Expansion 2.8 billion years ago, which is more consistent with the date geochemists assign to the Great Oxidation Event.

Instead, Alm and David believe they've detected the birth of modern electron transport, the biochemical process responsible for shuttling electrons within cellular membranes. Electron transport is used to breathe oxygen and by plants and some microbes during photosynthesis when they harvest energy directly from the sun. A form of photosynthesis called oxygenic photosynthesis is believed to be responsible for generating the oxygen associated with the Great Oxidation Event, and is responsible for the oxygen we breathe today.

The evolution of electron transport during the Archean Expansion would have enabled several key stages in the history of life, including photosynthesis and respiration, both of which could lead to much larger amounts of energy being harvested and stored in the biosphere.

"Our results can't say if the development of electron transport directly caused the Archean Expansion," says David. "Nonetheless, we can speculate that having access to a much larger energy budget enabled the biosphere to host larger and more complex microbial ecosystems."

David and Alm also went on to investigate how microbial genomes evolved after the Archean Expansion by looking at the metals and molecules associated with the genes and how those changed in abundance over time. They found an increasing percentage of genes using oxygen, and enzymes associated with copper and molybdenum, which is consistent with the geological record of evolution.

"What is really remarkable about these findings is that they prove that the histories of very ancient events are recorded in the shared DNA of living organisms," says Alm. "And now that we are beginning to understand how to decode that history, I have hope that we can reconstruct some of the earliest events in the evolution of life in great detail."

Why the farmer and the cowman weren't friends

As Rodgers and Hammerstein opined in "Oklahoma!":

The farmer and the cowman should be friends.
Oh, the farmer and the cowman should be friends.
One man likes to push a plough, the other likes to chase a cow,
But that's no reason why they cain't be friends.

Territory folks should stick together,
Territory folks should all be pals.
Cowboys dance with farmer's daughters,
Farmers dance with the ranchers' gals.

It turns out that this is a theme that has repeated itself over and over in history. As geneticists study the genetic populations around the world time and again populations that farmed replaced hunter-gatherers and herders. Here is a study of how this occurred in Africa.

The Hazda, Sandawe, Pygmies, and Khoesan (Bushmen, Nama, etc.), are often considered ‘relic’ populations. Remnants of diverse groups which were marginalized or absorbed by the Bantu in their expansion south and east from their urheimat. And it is interesting that the Khoesan are on the same branch as the Mbuti Pygmies of the eastern Congo, who are a particularly distinctive group genetically. The Hadza and Sandawe are non-Bantu populations in Tanzania. They also seem to speak languages with some affinity to that of the Khoesan. The “long branch” of the Hadza suggests genetic drift through a population bottleneck. As the last hunter-gatherers of East Africa it is likely that there has been very little gene flow between themselves and the farming majority, so their effective population has been low.

This seems to be another case where farmers rapidly exploded demographically and totally marginalized hunter-gatherers. The widespread presence of Khoesan and Pygmies is obviously a function of ecology. In the cooler and dry lands of southwest Africa the Bantu crops did not flourish. Additionally, some of the Khoikhoi became herders. Similarly, the deep rainforest was not congenial to agriculture either. In the comments below Randy McDonald asks:

Razib: Might the implications of the outcompetition of the Jomon be more proof that genetic diversity among humans today has shrunk considerably from the period predating the expansion of agricultural civilizations?

We often talk about Africa’s genetic diversity. What if what we see across much of the continent is actually greatly diminished from what it once was? It was famously reported last winter that Bushmen seem to differ genetically amongst themselves more than Europeans and Asians do. These two latter groups have been separate for at least 40,000 years. Granted, Eurasians went through a bottleneck “Out of Africa,” but the great diversity of the Bushmen is possibly a last compressed snapshot of what was before the Bantu expansion.

There is now evidence (but not absolute proof) that the original human population in Europe was mostly replaced by a group of farmers who originated in Turkey.

Why dogs are smarter than cats

They're more sociable.

Over millions of years dogs have developed bigger brains than cats because highly social species of mammals need more brain power than solitary animals, according to a study by Oxford University.

For the first time researchers have attempted to chart the evolutionary history of the brain across different groups of mammals over 60 million years. They have discovered that there are huge variations in how the brains of different groups of mammals have evolved over that time. They also suggest that there is a link between the sociality of mammals and the size of their brains relative to body size, according to a study published in the PNAS journal.

The research team analysed available data on the brain size and body size of more than 500 species of living and fossilised mammals. It found that the brains of monkeys grew the most over time, followed by horses, dolphins, camels and dogs. The study shows that groups of mammals with relatively bigger brains tend to live in stable social groups. The brains of more solitary mammals, such as cats, deer and rhino, grew much more slowly during the same period.

Previous research which has looked at why certain groups of living mammals have bigger brains has relied on studies of distantly-related living mammals. It was widely believed that the growth rate of the brain relative to body size followed a general trend across all groups of mammals. However, this study by Dr Susanne Shultz and Professor Robin Dunbar, from Oxford University's Institute of Cognitive and Evolutionary Anthropology (ICEA), overturns this view. They find that there is wide variation in patterns of brain growth across different groups of mammals and they have discovered that not all mammal groups have larger brains, suggesting that social animals needed to think more.

Lead author Dr Susanne Shultz, a Royal Society Dorothy Hodgkin Fellow at ICEA, said: 'This study overturns the long-held belief that brain size has increased across all mammals. Instead, groups of highly social species have undergone much more rapid increases than more solitary species. This suggests that the cooperation and coordination needed for group living can be challenging and over time some mammals have evolved larger brains to be able to cope with the demands of socialising.'

Co-author and Director of ICEA Professor Robin Dunbar said: 'For the first time, it has been possible to provide a genuine evolutionary time depth to the study of brain evolution. It is interesting to see that even animals that have contact with humans, like cats, have much smaller brains than dogs and horses because of their lack of sociality.'

The research team used available data of the measurements of brain size and body size of each group of living mammals and compared them with similar data for the fossilised remains of mammals of the same lineage. They examined the growth rates of the brain size relative to body size to see if there were any changes in the proportions over time. The growth rates of each mammal group were compared with other mammal groups to see what patterns emerged.

Of course, you wouldn't know it from the recent examples in our household. Kirby our now deceased Akita was big and goofy. He was sociable, but he wasn't all that smart. Arabella, our cat, may not be intelligent but she knows how to get what she wants. It's been really cold the last week so Ari takes advantage of our space heaters. Even if it the space heater is turned off she'll sit in front of it, and I guess it's smart because it encourages us to turn it on.