How the zebra got its stripes?

A very interesting paper has been published by Brenda Larison and her colleagues in the Royal Society Open Science Journal to answer common and frequent questions:
Why Zebras has got stripes? Why are their role?

Many explanations have been suggested, including social cohesion, thermoregulation, predation evasion and avoidance of biting flies. Identifying the associations between phenotypic and environmental factors is essential for testing these hypotheses and substantiating existing experimental evidence.

In contrast to recent findings, we found no evidence that striping may have evolved to escape predators or avoid biting flies. Instead, we found that temperature successfully predicts a substantial amount of the stripe pattern variation observed in plains zebra.

Figure 2. Predicted levels of hind leg stripe thickness (left) and torso stripe definition (right), from a random forest model based on 16 populations. Hind legstripethickness is best predicted by BIO3 and BIO11. Torsostripe definition is best predicted by BIO3, BIO11 and BIO13.

The full article is available to download HERE.

Why Is Canada’s Wolf Population Splitting Into Two Groups?

Why Is Canada's Wolf Population Splitting Into Two Groups?

Chester Starr of the Heiltsuk First Nation knows that the wolves of British Columbia come in two varieties: timber wolves on the mainland and coastal wolves on the islands. Genetic research has finally confirmed what Starr’s tribe has always known.

It was Starr’s “traditional ecological knowledge” that initially inspired Polish Academy of Sciences researcher Astrid V. Stronen and University of Calgary scientist Erin Navid to take a closer look at British Columbia’s wolves. They wanted to see whether the Heiltsuk Nation’s folk knowledge was reflected in the wolves’ genes. Continue reading

Humans have always been the nemesis of the planet’s wildlife

By George Monbiot, published in the Guardian 25th March 2014

Zimbabwe elephant poaching

A dead elephant in the Hwange National Park, Zimbabwe, thought to have died after poachers poisoned a salt lick with cyanide. Photograph: Aaron Ufumeli/EPA

You want to know who we are? Really? You think you do, but you will regret it. This article, if you have any love for the world, will inject you with a venom – a soul-scraping sadness – without an obvious antidote.

The Anthropocene, now a popular term among scientists, is the epoch in which we live: one dominated by human impacts on the living world. Most date it from the beginning of the industrial revolution. But it might have begun much earlier, with a killing spree that commenced two million years ago. What rose onto its hindlegs on the African savannahs was, from the outset, death: the destroyer of worlds.

Before Homo erectus, perhaps our first recognisably-human ancestor, emerged in Africa, the continent abounded with monsters. There were several species of elephants. There were sabretooths and false sabretooths, giant hyaenas and creatures like those released in The Hunger Games: amphicyonids, or bear dogs, vast predators with an enormous bite.

Amphicyonid ("bear dog") skeleton

Professor Blaire van Valkenburgh has developed a means by which we could roughly determine how many of these animals there were(1). When there are few predators and plenty of prey, the predators eat only the best parts of the carcass. When competition is intense, they eat everything, including the bones. The more bones a carnivore eats, the more likely its teeth are to be worn or broken. The breakages in carnivores’ teeth were massively greater in the pre-human era(2).

Blaire van Valkenburgh's tooth breakage graph

Not only were there more species of predators, including species much larger than any found on earth today, but they appear to have been much more abundant – and desperate. We evolved in a terrible, wonderful world – that was no match for us.

Homo erectus possessed several traits that appear to have made it invincible: intelligence, cooperation; an ability to switch to almost any food when times were tough; and a throwing arm that allowed it to do something no other species has ever managed – to fight from a distance. (The increasing distance from which we fight is both a benchmark and a determinant of human history). It could have driven giant predators off their prey and harried monstrous herbivores to exhaustion and death.

Illustration of a prehistoric mastodon

Artist’s rendition of a prehistoric mastodon. Photograph: Bettmann/Corbis

As the paleontologists Lars Werdelin and Margaret Lewis show, the disappearance of much of the African megafauna appears to have coincided with the switch towards meat eating by human ancestors(3). The great extent and strange pattern of extinction (concentrated among huge, specialist animals at the top of the food chain) is not easy to explain by other means.

At the Oxford megafauna conference last week, I listened as many of the world’s leading scientists in this field mapped out a new understanding of the human impact on the planet(4). Almost everywhere we went, humankind erased a world of wonders, changing the way the biosphere functions. For example, modern humans arrived in Europe and Australia at about the same time – between 40 and 50,000 years ago – with similar consequences. In Europe, where animals had learnt to fear previous versions of the bipedal ape, the extinctions happened slowly. Within some 10 or 15,000 years, the continent had lost its straight-tusked elephants, forest rhinos, hippos, hyaenas and monstrous scimitar cats.

In Australia, where no hominim had set foot before modern humans arrived, the collapse was  almost instant. The rhinoceros-sized wombat(5), the ten-foot kangaroo, the marsupial lion, the monitor lizard larger than a Nile crocodile(6), the giant marsupial tapir, the horned tortoise as big as a car(7) – all went, in ecological terms, overnight.

A few months ago, a well-publicised paper claimed that the great beasts of the Americas – mammoths and mastodons, giant ground sloths, lions and sabretooths, eight-foot beavers(8), a bird with a 26-foot wingspan(9) – could not have been exterminated by humans, because the fossil evidence for their extinction marginally pre-dates the evidence for human arrival(10).

A pack of dire wolves and two mammoths

Artist’s rendition of a pack of dire wolves and two mammoths. Photograph: Stocktrek Images/Alamy

I have never seen a paper demolished as elegantly and decisively as this was at last week’s conference. The archaeologist Todd Surovell demonstrated that the mismatch is just what you would expect if humans were responsible(11). Mass destruction is easy to detect in the fossil record: in one layer bones are everywhere, in the next they are nowhere. But people living at low densities with basic technologies leave almost no traces. With the human growth rates and kill rates you’d expect in the first pulse of settlement (about 14,000 years ago), the great beasts would have lasted only 1,000 years. His work suggests that the most reliable indicator of human arrival in the fossil record is a wave of large mammal extinctions.

These species were not just ornaments of the natural world. The new work presented at the conference suggests that they shaped the rest of the ecosystem. In Britain during the last interglacial period, elephants, rhinos and other great beasts maintained a mosaic of habitats: a mixture of closed canopy forest, open forest, glade and sward(12). In Australia, the sudden flush of vegetation that followed the loss of large herbivores caused stacks of leaf litter to build up, which became the rainforests’ pyre: fires (natural or manmade) soon transformed these lush places into dry forest and scrub(13).

In the Amazon and other regions, large herbivores moved nutrients from rich soils to poor ones, radically altering plant growth(14,15). One controversial paper suggests that the eradication of the monsters of the Americas caused such a sharp loss of atmospheric methane (generated in their guts) that it could have triggered the short ice age which began 12,800 years ago, called the Younger Dryas(16).

And still we have not stopped. Poaching has reduced the population of African forest elephants by 65% since 2002(17). The range of the Asian elephant – which once lived from Turkey to the coast of China – has contracted by 97%; the ranges of the Asian rhinos by over 99%(18). Elephants distribute the seeds of hundreds of rainforest tree species; without them these trees are functionally extinct(19,20).

Is this all we are? A diminutive monster that can leave no door closed, no hiding place intact, that is now doing to the great beasts of the sea what we did so long ago to the great beasts of the land? Or can we stop? Can we use our ingenuity, which for two million years has turned so inventively to destruction, to defy our evolutionary history?


1. eg Wendy J. Binder and Blaire Van Valkenburgh, 2010. A comparison of tooth wear and breakage in Rancho La Brea sabertooth cats and dire wolves across time. Journal of Vertebrate Paleontology.


3. Lars Werdelin, 2013. King of Beasts. Scientific American.


5. Diprotodon.

6. Megalania.


8. Castoroides ohioensis

9. The Argentine roc (Argentavis magnificens).

10. Matthew T. Boulanger and R. Lee Lyman, 2014. Northeastern North American Pleistocene megafauna chronologically overlapped minimally with Paleoindians. Quaternary Science Reviews 85, pp35-46.


12. Christopher J. Sandom et al, 2014. High herbivore density associated with vegetation diversity in interglacial ecosystems. Proceedings of the National Academy of Sciences, vol. 111, no. 11, pp4162–4167.

13. Susan Rule et al, 23rd March 2012. The Aftermath of Megafaunal Extinction: Ecosystem Transformation in Pleistocene Australia. Science Vol. 335, pp 1483-1486. doi: 10.1126/science.1214261.

14. Christopher E. Doughty, AdamWolf and Yadvinder Malhi, 11 August 2013. The legacy of the Pleistocene megafauna extinctions on nutrient availability in Amazonia. Nature Geoscience vol. 6, pp761–764. doi: 10.1038/ngeo1895.

15. Adam Wolf, Christopher E. Doughty, Yadvinder Malhi, Lateral Diffusion of Nutrients by Mammalian Herbivores in Terrestrial Ecosystems. PLOS One, doi: 10.1371/journal.pone.0071352.

16. Felisa A. Smith, 2010. Methane emissions from extinct megafauna. Nature Geoscience 3, 374 – 375. doi:10.1038/ngeo877.

17. Fiona Maisels, pers comm. This is an update of the figures published here:





Is the Dingo Special Enough to Save?


A startling discovery: Commonly believed to be a breed of wild dog, scientists now consider the dingo to be a species in its own right. Photo: Neil Newitt

When you look at the picture above, what do you see? A wild dog? A strangely colored wolf? Or something entirely different: a dingo? For centuries, scientists have debated whether Australia’s native canine is its own species or merely a type of wolf or dog. Now, based on physical and genetic evidence, a team of scientists is making the case that the dingo is a unique species that deserves protection under Australia’s federal conservation laws. If they can’t convince governments and landholders, the dingo may be doomed.

Wild dingoes live across Australia, in grasslands, deserts, and even wetlands and forests. Archaeological evidence suggests that the animal arrived on the continent at least 3500 years ago as people sailed back and forth from Asia, where it first appeared, then continued to evolve in isolation until the arrival of Europeans and their dogs in the late 18th century. The European naturalists who first heard descriptions of the dingo believed it represented a new species of canine and gave it a species name to match: Canis dingo. Domesticated dogs, on the other hand, are known as Canis lupus familiaris, indicating that they are a subspecies of wolf (Canis lupus).

But over the next 300 years, scientists began to argue about what to call the dingo, given the lack of early physical specimens and the fact that the original classifications were based on nothing more than a painting and description given by Australia’s first governor, Arthur Phillip. Dingoes have continued to change as they bred with settler dogs. Today, Australia’s native canine is most often referred to by scientists as C. lupus dingo, relegating it to a subspecies of wolf based on a notion that dingoes evolved from wolves in Asia. Recent studies suggest that dingoes, dogs, and wolves are cousins, all descended from a distant ancestor.

That classification left University of Sydney wildlife biologist Mathew Crowther unsatisfied, given his experience studying wild dingoes. He believed that conservation and management decisions were not being based on firm evidence. “A dingo is a distinctive thing in Australia,” identifiable by its erect ears, bushy tail, and neck that can arc backward into prime howling position, he says. Still, it’s difficult to tell a dingo from a dingo-dog hybrid, or even a feral dog, because natural variation within dingoes is poorly understood and mating with wild dogs may have altered the genome of living dingoes, Crowther explains.

Being able to define what a dingo is—and isn’t—is increasingly important in Australia. While some scientists argue that dingoes with no dog DNA fill the important niche of apex predator in Australia’s ecosystem by eating feral cats and foxes, ranchers lump dingoes, feral dogs, and dingo-dog hybrids into the category of pests that attack and kill valuable livestock. Current policies in some jurisdictions of Australia aim to exterminate dingo-dog hybrids while conserving dingoes. But without a clear definition of what distinguishes a dingo, it’s hard to manage wild dingoes, dingo-dog hybrids, and free-roaming domestic dogs, says Damian Morrant, an ecologist with James Cook University, Cairns, who was not involved in the new study. He says the work is a “baseline” for developing clear guidelines for identifying dingoes in the wild.

To begin sorting dingo from nondingo, Crowther and his colleagues at the universities of Sydney, New South Wales, and Western Sydney reviewed genetic work conducted by other researchers and began tracking down pre-1900 dingo specimens, which would allow them to study the species before it encountered—and mated with—domestic dogs brought by European settlers. “One of our colleagues went to all the European [natural history] museums: London, Paris, Germany, Oslo,” Crowther explains. The team discovered a range of coat colors on dingoes preserved in the museums: yellow, brown, ginger/red, black, and white. That indicated that these colors are not the product of recent mating with dogs, and that animals boasting them today can be considered pure dingoes.

The researchers also compared the skulls of the dingo specimens with those of wolves and similar-looking domestic dogs such as Australian cattle dogs and collies. While there were overlaps, the dingoes had wider and shorter skulls and no hind leg dewclaws, vestigial toes that don’t touch the ground, which are common among dogs and wolves, the team reported online this week in the Journal of Zoology. Based on these physical and genetic differences, the researchers propose changing the dingo’s scientific name back to Canis dingo, once again classifying it as its own species.

Given the contentious attitudes about dingoes as either top predators or pests, as well as the uncertainty among scientists about their evolutionary past, the paper will “inflame passions across the board,” says Christopher Dickman, a conservation ecologist at the University of Sydney who is not part of the team. And so it has. Although J. William Ballard, an evolutionary geneticist at the University of New South Wales in Sydney, says the study provides a “road map for the debate,” he believes the methodology is weak and the data unconvincing. Still, dingo specialists such as Christopher Johnson, a conservation biologist and ecologist at the University of Tasmania, Sandy Bay Campus, welcome the work. “It places the dingo on firmer biological ground as a distinct [group],” he says.

Crowther and his colleagues acknowledge that they’ve not yet identified “consistent and clear diagnostic features” that characterize all members of C. dingo, but they claim they’ve set limits on physical traits of the species. And for conservation and land managers that’s a start, says Euan Ritchie, an ecologist at Deakin University, Melbourne Burwood. “If it looks like a dingo, smells like a dingo, and acts like a dingo, is that enough” to count it as a dingo?


Access to the paper:

How do polar bears stay warm? Research finds an answer in their genes

polar bear looking straight at camera

New study is part of a broader genomic research program aimed at understanding what makes a polar bear a polar bear

A polar bear looking straight at the camera
A male polar bear. Credit: U.S. Geological Survey, Steven C. Amstrup
polar bear walking on an icy terrain
A male polar bear walks on pack ice. Credit: U.S. Fish and Wildlife Service, Eric Regehr
polar bear walking by water
A polar bear in Alaska. Credit: U.S. Fish and Wildlife Service, Steve Hillebrand
a polar bear lying down and facing camera
A polar bear at rest. Credit: U.S. Fish and Wildlife Service, Susanne Miller
Charlotte Lindqvist in front of a background showing a polar bear walking in a cold climate
Charlotte Lindqvist, assistant professor of biological sciences University at Buffalo led the study, which is part of a larger research program devoted to understanding how the polar bear has adapted to the harsh Arctic environment.
 In the winter, brown and black bears go into hibernation to conserve energy and keep warm.

But things are different for their Arctic relative, the polar bear. Within this high-latitude species, only pregnant females den up for the colder months.

So how do the rest survive the extreme Arctic winters?

New research points to one potential answer: genetic adaptations related to the production of nitric oxide, a compound that cells use to help convert nutrients from food into energy or heat.

In a new study, a team led by the University at Buffalo reports that genes controlling nitric oxide production in the polar bear genome contain genetic differences from comparable genes in brown and black bears.

“With all the changes in the global climate, it becomes more relevant to look into what sorts of adaptations exist in organisms that live in these high-latitude environments,” said lead researcher Charlotte Lindqvist, PhD, UB assistant professor of biological sciences.

“This study provides one little window into some of these adaptations,” she said. “Gene functions that had to do with nitric oxide production seemed to be more enriched in the polar bear than in the brown bears and black bears. There were more unique variants in polar bear genes than in those of the other species.”

The paper, titled “Polar Bears Exhibit Genome-Wide Signatures of Bioenergetic Adaptation to Life in the Arctic Environment,” appeared Feb. 6 in the journal Genome Biology and Evolution.

Co-authors include scientists from UB, Penn State University, the U.S. Geological Survey Alaska Science Center, Durham University and the University of California, Santa Cruz.

The genetic adaptations the research team saw are important because of the crucial role that nitric oxide plays in energy metabolism.

Typically, cells transform nutrients into energy. However, there is a phenomenon called adaptive or non-shivering thermogenesis, where the cells will produce heat instead of energy in response to a particular diet or environmental conditions.

Levels of nitric oxide production may be a key switch triggering how much heat or energy is produced as cells metabolize nutrients, or how much of the nutrients is stored as fat, Lindqvist said.

“At high levels, nitric oxide may inhibit energy production,” said Durham University’s Andreanna Welch, PhD, first author and a former postdoctoral researcher at UB with Lindqvist. “At more moderate levels, however, it may be more of a tinkering, where nitric oxide is involved in determining whether — and when — energy or heat is produced.”

The research is part of a larger research program devoted to understanding how the polar bear has adapted to the harsh Arctic environment, Lindqvist said.

In 2012, she and colleagues reported sequencing the genomes of multiple brown bears, black bears and polar bears.

In a paper in the Proceedings of the National Academy of Sciences, the team said comparative studies between the DNA of the three species uncovered some distinctive polar bear traits, such as genetic differences that may affect the function of proteins involved in the metabolism of fat — a process that’s very important for insulation.

In the new study, the scientists looked at the mitochondrial and nuclear genomes of 23 polar bears, three brown bears and a black bear.

The research was funded by the University at Buffalo and the National Fish and Wildlife Foundation.

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Dogs likely originated in Europe more than 18,000 years ago, UCLA biologists report

By Stuart Wolpert November 14, 2013
Wolves likely were domesticated by European hunter–gatherers more than 18,000 years ago and gradually evolved into dogs that became household pets, UCLA life scientists report.

“We found that instead of recent wolves being closest to domestic dogs, ancient European wolves were directly related to them,” said Robert Wayne, a professor of ecology and evolutionary biology in UCLA’s College of Letters and Science and senior author of the research. “This brings the genetic record into agreement with the archaeological record. Europe is where the oldest dogs are found.”
Ancient dog fossil A fossil of a dog that lived approximately 8,500 years ago, from the Koster archaeological site in Illinois. (Credit: Del Baston)
The UCLA researchers’ genetic analysis is published Nov. 15 in the journal Science and featured on the journal’s cover.

In related research last May, Wayne and his colleagues reported at the Biology of Genomes meeting in New York the results of their comparison of the complete nuclear genomes of three recent wolf breeds (from the Middle East, East Asia and Europe), two ancient dog breeds and the boxer dog breed.

“We analyzed those six genomes with cutting-edge approaches and found that none of those wolf populations seemed to be closest to domestic dogs,” Wayne said. “We thought one of them would be, because they represent wolves from the three possible centers of dog domestication, but none was. All the wolves formed their own group, and all the dogs formed another group.”

The UCLA biologists also hypothesized at that conference that a now-extinct population of wolves was more directly related to dogs.

For the current study in Science, the researchers studied 10 ancient “wolf-like” animals and eight “dog-like” animals, mostly from Europe. These animals were all more than 1,000 years old, most were thousands of years old, and two were more than 30,000 years old.

The biologists studied the mitochondrial DNA of the animals, which is abundant in ancient remains. (Mitochondria are tiny sub-cellular structures with their own small genome.) By comparing this ancient mitochondrial DNA with the modern mitochondrial genomes of 77 domestic dogs, 49 wolves and four coyotes, the researchers determined that the domestic dogs were genetically grouped with ancient wolves or dogs from Europe — not with wolves found anywhere else in the world or even with modern European wolves. Dogs, they concluded, derived from ancient wolves that inhabited Europe and are now extinct.

Wayne said that that the domestication of predatory wolves likely occurred among ancient hunter–gatherer groups rather than as part of humans’ development of sedentary, agricultural-based communities.

“The wolf is the first domesticated species and the only large carnivore humans ever domesticated,” Wayne said. “This always seemed odd to me. Other wild species were domesticated in association with the development of agriculture and then needed to exist in close proximity to humans. This would be a difficult position for a large, aggressive predator. But if domestication occurred in association with hunter–gatherers, one can imagine wolves first taking advantage of the carcasses that humans left behind — a natural role for any large carnivore — and then over time moving more closely into the human niche through a co-evolutionary process.”

The idea of wolves following hunter–gatherers also helps to explain the eventual genetic divergence that led to the appearance of dogs, he said. Wolves following the migratory patterns of these early human groups would have given up their territoriality and would have been less likely to reproduce with resident territorial wolves. Wayne noted that a group of modern wolves illustrates this process.
“We have an analog of this process today, in the only migratory population of wolves known existing in the tundra and boreal forest of North America,” he said. “This population follows the barren-ground caribou during their thousand-kilometer migration. When these wolves return from the tundra to the boreal forest during the winter, they do not reproduce with resident wolves there that never migrate. We feel this is a model for domestication and the reproductive divergence of the earliest dogs from wild wolves.

“We know also that there were distinct wolf populations existing ten of thousands of years ago,” Wayne added. “One such wolf, which we call the megafaunal wolf, preyed on large game such as horses, bison and perhaps very young mammoths. Isotope data show that they ate these species, and the dog may have been derived from a wolf similar to these ancient wolves in the late Pleistocene of Europe.”

In research published in the journal nature in 2010, Wayne and colleagues reported that dogs seem to share more genetic similarity with living Middle Eastern gray wolves than with any other wolf population, which suggested a Middle East origin for modern dogs. The new genetic data have convinced him otherwise.

“When we previously found some similarity between Middle Eastern wolves and domestic dogs, that similarity, we are now able to show, likely was the result of interbreeding between dog and wolves during dog history. It does not necessarily suggest an origin in the Middle East,” Wayne said. “This alternative hypothesis, in retrospect, is one that we should have considered more closely. As hunter–gatherers moved around the globe, their dogs trailing behind probably interbred with wolves.”

Wayne considers the new genetic data “persuasive” but said they need to be confirmed with an analysis of genetic sequences from the nucleus of the cell (roughly 2 billion base pairs) — a significantly larger sample than that found in mitochondrial DNA (approximately 20,000 base pairs). This is challenging because the nuclear DNA of ancient remains tends to become degraded.

While Wayne plans to pursue this follow-up research, he said he does not expect a nuclear genome analysis to change the central finding. However, he said, it will fill in more of the details.

“This is not the end-story in the debate about dog domestication, but I think it is a powerful argument opposing other hypotheses of origin,” he said.

There is a scientific debate over when dogs were domesticated and whether it was linked with the development of agriculture fewer than 10,000 years ago, or whether it occurred much earlier. In the new Science research, Wayne and his colleagues estimate that dogs were domesticated between 18,000 and 32,000 years ago.

The research was federally funded by the National Science Foundation.

Co-authors on the Science paper include Olaf Thalmann, a former postdoctoral scholar in Wayne’s laboratory who is currently the Marie Curie Postdoctoral Fellow at Finland’s University of Turku; Daniel Greenfield, a former technician in Wayne’s laboratory; Francesc López-Giráldez, a former graduate student in Wayne’s laboratory who is currently a postdoctoral scholar at Yale University; Adam Freedman, a former postdoctoral scholar in Wayne’s laboratory; Rena Schweizer, a current UCLA graduate student in Wayne’s laboratory; Klaus Koepfli, a former postdoctoral scholar in Wayne’s laboratory; and Jennifer Leonard, who earned her doctorate from UCLA.

Approximately 80 percent of dog breeds are modern breeds that evolved in the last few hundred years, Wayne said. But some dog breeds have ancient histories that go back thousands of years.

Wolves have been in the Old World for hundreds of thousands of years. The oldest dogs from the archaeological record come from Europe and Western Russia. A dog from Belgium dates back approximately 36,000 years, and a group of dogs from Western Russia is approximately 15,000 years old, Wayne said.

UCLA is California’s largest university, with an enrollment of more than 40,000 undergraduate and graduate students. The UCLA College of Letters and Science and the university’s 11 professional schools feature renowned faculty and offer 337 degree programs and majors. UCLA is a national and international leader in the breadth and quality of its academic, research, health care, cultural, continuing education and athletic programs. Seven alumni and six faculty have been awarded the Nobel Prize.

How City Living Is Reshaping the Brains and Behavior of Urban Animals

When next you meet a rat or raccoon on the streets of your city, or see a starling or sparrow on a suburban lawn, take a moment to ask: Where did they come from, so to speak? And where are they going?

In evolutionary terms, the urban environments we take for granted represent radical ecological upheavals, the sort of massive changes that for most of Earth’s history have played out over geological time, not a few hundred years.

Houses, roads, landscaping, and the vast, dense populations of hairless bipedal apes responsible for it: All this is new. A growing body of scientific evidence suggests that the brains and behaviors of urban animals are changing rapidly in response.

“A lot of biologists are really interested in how animals are going to deal with changes in their environments,” said biologist Emilie Snell-Rood of the University of Minnesota. “Humans are creating all these totally new environments compared to what they’ve seen in evolutionary history.”

Snell-Rood is one of many researchers who have updated the conventional narrative of urban animals, in which city life favors a few tough, adaptable jack-of-all-trades — hello, crows! — and those species fortunate enough to have found a built environment similar to their native niches, such as the formerly cliff-dwelling rock doves we now call pigeons and find perched on building ledges everywhere.

The long view, though, is rather more multidimensional. Cities are just one more setting for evolution, a new set of selection pressures. Those adaptable early immigrants, and other species that once avoided cities but are slowly moving in, are changing fast.

As Snell-Rood and colleagues describe in an August 21 Proceedings of the Royal Society B article, museum specimens gathered across the 20th century show that Minnesota’s urbanized small mammals — shrews and voles, bats and squirrels, mice and gophers — experienced a jump in brain size compared to rural mammals.

‘Humans are creating all these totally new environments compared to what animals have seen in evolutionary history.’

Snell-Rood thinks this might reflect the cognitive demands of adjusting to changing food sources, threats, and landscapes. “Being highly cognitive might give some animals a push, so they can deal with these new environments,” she said.

Brain size is, to be sure, a very rough metric, one that’s been discredited as a measure of raw intelligence in humans. For it to fluctuate across a whole suite of species, though, especially when other parts of their anatomy didn’t change, at least hints that something cognitive was going on.

Many other studies have looked at behavior rather than raw cranial capacity. In these, a common theme of emerges: Urban animals tend to be bold, not backing down from threats that would send their country counterparts into retreat. Yet even as they’re bold in certain situations, urban animals are often quite wary in others, especially when confronted with something they haven’t seen before.

“Maybe avoiding danger is an useful trait for some animals living in urban environments,” said biologist Catarina Miranda of Germany’s Max Planck Institute, who in a September Global Change Biology paperdescribed her experiments with rural and urban blackbirds.

“Most of the birds that never approach new objects or enter new environments in this long period of time are urban,” Miranda said. “There are many new dangers in a town for a bird. Cars can run you over. Cats can eat you. Kids can take you home.”

Somewhat counterintuitively, bold urban animals also tend to be less-than-typically aggressive, a pattern documented in species as disparate as house sparrows and salamanders, the latter of which are a specialty of Jason Munshi-South, an evolutionary biologist at the City University of New York. The city’s salamanders — there aren’t many, but they’re there — “tend to be languid,” said Munshi-South. “If you try to pick them up, they don’t try to escape as vigorously as they do outside the city. I wonder if there’s been natural selection for that.”

If so, it might be driven by high population densities of salamanders in the city. Aggressive neighbors don’t tend to be good neighbors. Through that lens, city animals could be domesticating themselves, a process that can occur without direct human intervention.

Even more fundamentally, muted stress responses have been found in many species of urban animals. When surprised or threatened, their endocrine systems release lower-than-usual amounts of stress hormones. It’s a sensible-seeming adaptation. A rat that gets anxious every time a subway train rolls past won’t be very successful.

“They’re clearly attenuating their physiological response to stress, probably because they’re constantly inundated with noise, traffic, and all kinds of environmental stresses in cities,” said biologist Jonathan Atwell of Indiana University. “If they were ramping that response up all the time, it would be too costly.”

A challenging question is whether traits like these represent inherited biological changes or what researchers call phenotypic plasticity: the ability to make on-the-fly adjustments to circumstance.

Some adaptations, such as the swath of genetic mutations that Munshi-South identified in New York City’s white-footed mice, are clearly heritable. Others are learned. In many cases, both processes are likely involved, said Atwell, who studied the question in his research on songbirds called dark-eyed juncos around San Diego.

The San Diego juncos sing at higher frequencies than those living in rural, traffic-free settings. When Atwell raised some of their chicks in a quiet place, that rise in song frequency dropped by about half, suggesting an even split between heritability and plasticity.

Where things get really interesting, though, is with social learning and animal culture — all those animal habits and abilities that are not inborn, but taught. “I suspect that often it’s not their cognitive abilities evolving, but cultural evolution going on,” said Atwell. “Anytime animals can learn behavior from one another, I think there might be cultural evolution.”

Urban squirrels, for example, seem to have adjusted to vocalization-drowning ambient noise by making tail-waving a routine part of communications. Perhaps this was instinctive in a few animals, then picked up by others. Likewise, squirrels might learn about traffic by seeing others get run over, said Snell-Rood. Rats could see brethren die after eating poisoned bait, then teach pups to avoid the traps.

‘You could imagine some kind of speciation over long periods of time.’

These possibilities are only hypothetical, but hardly implausible. After all, other animals traditionally recognized as clever — such as crows who share information about untrustworthy humans, ortemple-dwelling Asian monkeys who pickpocket tourists — are clearly learning about us, and intelligence has only been studied in a few species.

Not all changes in urban animals will represent adaptations to urban living, however.

Most genetic mutations are neither beneficial nor harmful, at least not right away. They simply happen and, over long periods of time, accumulate in populations through what’s known as genetic drift. In isolated groups, drift’s effects are magnified, as are so-called founder effects, in which entire populations bear the genetic imprint of a few early animals. For these creatures, urban adaptations won’t necessarily represent adjustments to city life, but simple happenstance.

How might this play out in deep time? If humans can keep civilization intact long enough, will urban animal populations eventually become their own distinct species — bold, relaxed, and clever, with a store of learned information about our habits, and perhaps a few other traits that arise by chance?

Nobody knows, said Snell-Rood, but “you could imagine some kind of speciation over long periods of time.” She noted, though, that not all the changes seen in urban animals are necessarily permanent. The big brains of those city-dwelling Minnesota mammals, for instance, seemed to shrink after a few decades of urban adaptation.

“The way I interpret it is that during the initial colonization, it pays to be smart,” Snell-Rood said. Once city life becomes predictable, “you can go back to having a smaller brain.”