Later On

A blog written for those whose interests more or less match mine.

Archive for the ‘Evolution’ Category

Living among humans favours fearless problem-solvers interested in new things. That’s how city birds get smarter

leave a comment »

Menno Schilthuizen, an ecologist and evolutionary biologist at Naturalis Biodiversity Center in Leiden in the Netherlands, holds a chair in evolution at Leiden University. His latest book is Darwin Comes to Town: How the Urban Jungle Drives Evolution (2018). He writes in Aeon:

A crumbling concrete wall, a ramp and a vast expanse of asphalt on which identical silvery-grey sedans are slowly circling and zigzagging between traffic cones. It does not seem like much but, to urban biologists, the Kadan driving school in the Japanese city of Sendai is hallowed ground. The four of us (the biology students Minoru Chiba and Yawara Takeda, the biologist Iva Njunjić, and I) have been sitting on that crumbling wall for several hours now, hoping to observe what this place is famous for.

It was here that, in 1975, the local carrion crows (Corvus corone) discovered how to use cars as nutcrackers. The crows have a predilection for the Japanese walnut (Juglans ailantifolia) that grows abundantly in the city. The pretty nuts (a bit smaller than commercial walnuts, and with a handsome heart-shaped interior) are too tough for the crows to crack with their beaks, so for time immemorial they have been dropping them from the air onto rocks to open them. Everywhere in the city, you find parking lots strewn with the empty nutshells: the crows either drop them in flight or carry them to the tops of adjoining buildings and then throw them over the edge onto the asphalt below.

But all this flying up and down is tiring, and sometimes the nuts need to be dropped repeatedly before they split. So, at some point, these crows came up with a better idea. They would drop nuts among the wheels of slow-driving cars, and pick up the flesh after the car had passed. The behaviour started at the Kadan driving school, where there are plenty of slow-moving cars, was copied by other crows, and so spread to other places in the city where slow-moving giant nutcrackers were common, such as near sharp bends in the road, and at intersections. At such places, rather than dropping the nuts from above, the crows would station themselves by the roadside and place them more accurately on the road. Since then, the fad has also turned up in other cities in Japan.

In 1995, the zoologist Yoshiaki Nihei then at Tohoku University in Sendai made a detailed study of the behaviour. He observed how the crows would wait near a traffic light, wait for it to turn red, then step in front of the cars, place their nuts, and hop back to the curb to wait for the light to change. When the traffic had passed, they would return to the road to retrieve their quarry. His work revealed the crows’ finesse in handling their ‘tool’. For example, the birds would sometimes move a walnut a few centimetres if it took too long for it to be hit by a wheel. In one case, he even saw how a crow would walk into the path of an oncoming car, forcing it to brake, and then quickly toss a nut in front of its wheels.

These fascinating observations languished in relatively obscure Japanese scientific papers until 1997. That year, the BBC came to Sendai to film the crows for David Attenborough’s series The Life of Birds. His voice-over made them an instant hit: ‘They station themselves at pedestrian crossings … Wait for the lights to stop the traffic. Then, collect your cracked nut in safety!’

So, finding ourselves in this city with its famous urban crows, our merry band devote the day to viewing them for ourselves. Minoru and Yawara tell us that the crows’ trick is well-known in town. In fact, it is a favourite pastime to throw the crows nuts and watch them perform. So, with a bag of walnuts brought all the way from the Netherlands, we try our luck. But the crows are not cooperating. We have already spent the whole morning at traffic lights at intersections, stupidly waiting on canvas folding chairs at the mercy of the surprised stares of endless motorists but, so far, in vain. And we have now ended up at the reputed epicentre, the Kadan driving school. It is getting hot, and we’re hungry and tired. With glazed-over eyes, we stare at the heaps of nuts we have laid out at various positions on the school’s test range. The school’s students carefully avoid them, and the crows fly over without even looking down. This is what urban fieldwork is like.

Perhaps, Minoru and Yawara finally admit, it is too early in the year. The nuts are not ripe yet, the young birds have just fledged, and groups of crows are marauding the city to feast on other things, such as the ripe mulberries that are in abundance everywhere. I sigh and stare a bit more. Then, I hear a cracking noise behind me. I turn around to see that Iva has begun eating our stock of walnuts. She looks at me defiantly: ‘What? They’re not going to come anyway!’

Carrion crows do not occur only in Japan. They also exist in western Europe, where you can similarly find plenty of cars, pedestrian crossings and walnuts. And yet carrion crows in Europe somehow never learnt to exploit human automobile traffic in the Rube-Goldbergian way that they do in Japan.

That is not to say that humans in Europe are safe from having their behaviour manipulated by birds, as demonstrated to us for nearly a century by the famous (and annoying) milk bottletop-opening skills of tits – lively songbirds with a handsome pattern of yellow, black and blue (the blue tit, Cyanistes caeruleus), and olive-green (the great tit, Parus major).

Tits – in fact, all birds – cannot digest milk. Unlike mammals, they lack the enzymes needed to break down the lactose. But the layer of cream that collects at the top of old-fashioned, unhomogenised milk contains very little lactose, and a hungry bird in winter could do worse than supplement its fat intake with a bit of rich cream snatched from the neck of a milk bottle. And that is exactly what tits had been doing for a while in the late-19th and early 20th century in England and elsewhere in Europe, when milkmen were still in the habit of leaving open bottles of milk on people’s doorsteps in the morning. Before the resident mammal would have time to open the door and bring the bottles into safety, a tit would swoop in, land on the neck of a bottle, and dip its beak in the cream inside, consuming up to an inch of the coveted food.

Unfortunately, the very first stages of the ensuing game of attrition between human and bird are lost in the mists of time. Presumably, it was a matter of racing to the front door as soon as the milkman’s cart was spotted, not to give the tits a chance to steal any cream. Tits, not to be outdone, would be hanging out near people’s doorsteps at milk-delivery time to try to get there first. In any case,  . . .

Continue reading.

Written by LeisureGuy

20 April 2018 at 3:04 pm

Primeval Salt Shakes Up Ideas on How the Atmosphere Got Its Oxygen

leave a comment »

Nola Taylor Redd writes in Scientific American:

Ancient sea salt drilled from a geologic basin in Russia is providing dramatic new clues as to how Earth’s early atmosphere became oxygen-rich—allowing life as we know it to evolve. Buried deep beneath the surface for billions of years, the salt reveals surprising clues about the chemistry of the ocean and atmosphere from long ago.

The salt, excavated by an international team led by Russian scientists, is about a billion years older than other, similar geologic samples. Its age puts it smack in the middle of Earth’s Great Oxygenation Event, the ancient period in which oxygen began to dominate atmospheric chemistry. “This is a truly unique, one-of-a-kind deposit,” says Clara Blättler, a geochemist at Princeton University. Blättler is the lead author of a study appearing in the March 23 Science on the salty new samples. They are made up of minerals left behind when water evaporates. “Because these evaporite minerals are our most direct way of sampling ancient sea waters, this deposit gives us a snapshot of seawater in the interval time when we don’t really have any other direct constraints.”

Within the three-kilometer-long, cylindrical core excavated from the Russian basin, Blättler and her colleagues identified a 600-meter-thick deposit of sulfate-rich materials, including halite (aka sodium chloride)—the crystalline progenitor of common table salt. The deposit’s immense size and various trace geochemical markers, Blättler says, both suggest it formed in ocean water rather than in any freshwater source.

Over a billion years ago, the team speculates, ocean water covered the Lake Onega river basin in the Russian Republic of Karelia on the country’s western border with Finland. Brine washing into a shallow part of the basin was trapped and eventually evaporated, leaving behind the salts it carried. The thickness of the deposit reveals the process recurred many times, gradually building up the reservoir the Russian researchers later excavated. “There’s no way you can form that much from just evaporating one batch,” says Mark Claire, a researcher at the University of Saint Andrews in Scotland and a co-author of the research.

The team’s analysis shows this ancient ocean water carried roughly 20 percent as many sulfates as are found in modern seawater. Sulfate concentration in ocean water is a key tracer of how much oxygen is the atmosphere—and how it gets there in the first place.

This is the first direct quantitative measurement of the otherwise-murky chemistry of the ocean more than two billion years ago, according to Timothy Lyons, a geochemist at the University of California, Riverside, who was not involved in the research. “What they are doing is as reliable as these things can ever be in rocks this old,” he says. The results are consistent with other, more circumstantial records left by carbon and trace minerals, he adds.

Other sulfate evaporite samples are rare. The characteristic that allows the sulfates to dissolve into water can also make them hard to find; when water washes over a previous deposit it can redissolve the evaporites, erasing the records and laying down newer ones. That means similar deposits are few and far between. Blättler says her samples clearly did not interact with much water—or they would have disappeared. “For some unknown geological reason these were preserved, and they were a little bit unexpected,” she says.


Three billion years ago Earth’s atmosphere lacked the abundant molecular oxygen (O2) that makes air breathable for complex life today. It was not until the Great Oxygenation Event, a mysterious transition that occurred from 2.7 to 2.4 billion years ago, that this gas—crucial to life as we know it—began to substantially accumulate in the atmosphere. . .

Continue reading.

Written by LeisureGuy

22 March 2018 at 1:19 pm

Posted in Evolution, Science

Evolve or die: Why our human ancestors learned to be social more than 320,000 years ago

leave a comment »

Deborah Netburn reports in the LA Times:

New discoveries in eastern Africa suggest that human behaviors like symbolic thought and the creation of extended social networks were established at least 320,000 years ago — tens of thousands of years earlier than previously thought.
The work, published as a trio of papers Thursday in Science, sheds new light on the often murky story of when our ancestors first started acting like humans, and why, experts said.

“What we are seeing is a complex set of developments that may represent new ways of surviving in an unpredictable environment,” said Rick Potts, a paleoanthropologist and director of the Smithsonian’s Human Origins program. “It is a package we didn’t know occurred so early, and right at the root of our species.”

For more than 30 years, Potts has led excavations in southern Kenya at a site known as the Olorgesailie Basin, which was occupied by hominids for more than 1 million years.

The 50-square-mile area has yielded a sequence of stone tools that date back as far as 1.2 million years, allowing researchers to see how human technology and behavior has changed over time.

The authors found that for roughly 700,000 years, from 1.2 million to 499,000 years ago, the hominids who populated this basin relied almost entirely on one simple, all-purpose stone tool known as a hand ax. It was generally between 4 and 10 inches long, shaped like a teardrop and chipped all the way around.

Anthropologists believe this basic hand ax was used for a variety of purposes, including cutting through joints of large animals, chopping down trees and digging in the ground for roots, tubers or water.

“It was very successful for a long period of time when fluctuations in the environment were somewhat modest,” Potts said. “Then all hell broke loose.”

Geological evidence from the site indicates that around 499,000 years ago, the region experienced tremendous upheaval. Volcanic activity increased, and new faults developed in Earth’s crust. This led to earthquakes that destroyed the ancient lake basin and pushed it up out of the ground. Because of this, there is a gap in the archaeological record of about 180,000 years when no new sediments were laid down at the site.

Over time, however, wind and rain caused river channels to form in what once was the lake basin, and eventually new sediment layers began to form. These processes led to a more recent set of archaeological data that starts about 320,000 years ago and continues until 3,000 years ago.

When Potts and his colleagues began excavating the newer material from the river channels, they found that hominid behavior at the Olorgesailie Basin had changed completely between the time the lake sedimentation ended and the river sedimentation began.

For example, the hand axes had been replaced by smaller, more sophisticated tools that could be attached to sticks and hurled through the air. In addition, the team found that some of the obsidian rock used to make the new tools came from 25 to 30 miles away. In the older sediments, nearly all the material used to create tools originated within 5 miles of the site.

Alison Brooks, a paleoanthropologist and Paleolithic archaeologist at George Washington University who contributed to the new work, said it is unlikely that hunter and gatherer societies of that time period would have been able to travel such great distances to procure materials for their weapons.

Instead, the discovery of the transported obsidian suggests that as early as 320,000 years ago, hominids had established social networks that allowed them to exchange gifts with groups from more distant lands, she said. In addition, these relationships could have been strong enough for individuals to turn to their neighbors in times of need.

“Social networks are an extremely important part of early human societies,” Brooks said. “Pastoralists can store food or add cattle to their herds, but for hunter-gatherers, the only way to save for a rainy day is to have friends in distant places.”

The researchers also found evidence that these socially connected hominids were making pigments from rocks, which implies they were sophisticated enough to be capable of symbolic thought. This might have made communication between disparate groups easier.

The authors suggest these new behaviors were not the inevitable result of evolution, but rather a response to massive geological and climate changes that began about 500,000 years ago. Indeed, the fossil record from the site indicates that between 499,000 and 320,000 years ago, 85% of the region’s animals became extinct and were replaced by new lineages and entirely new species.

“That may seem peripheral, but to us, it was pretty central,” Potts said. “It meant that it wasn’t just the humans changing — there was a very big evolutionary picture going on.”

Potts believes that the new suite of human behaviors observed after the 320,000-year mark emerged as a way to cope in an environment that had become less predictable.

Perhaps the only way to make a successful living in this more challenging landscape was for our ancestors to learn to make better tools, create extended networks of friends and learn to communicate with them, he said.

In other words: Evolve or die.

“There are those who rose to the challenge, but there were likely many more who didn’t,” Potts said. “Our family tree is littered with dead branches and ways of life that no longer exist.” . . .

Continue reading.

Evolution is uncaring because it has no mind and no foresight: it is simply a process.

Written by LeisureGuy

21 March 2018 at 10:12 am

Posted in Evolution, Science

Rapid evolution of salmon size

leave a comment »

Take a look at this photo:

The caption: “A photo taken in Astoria, Ore., circa 1910. It was stated that the chinook on the left weighed 116 pounds and the one on the right weighed 121 pounds.”

Why did Chinook salmon so rapidly evolve to a smaller size? The usual reason: strong selection against large Chinook, and not just from people. John Ryan reports at NPR:

While the orcas of Puget Sound are sliding toward extinction, orcas farther north have been expanding their numbers. Their burgeoning hunger for big fish may be causing the killer whales’ main prey, chinook salmon, to shrink up and down the West Coast.

Chinook salmon are also known as kings: the biggest of all salmon. They used to grow so enormous that it’s hard now to believe the old photos in which fishermen stand next to chinooks almost as tall as they are, sometimes weighing 100 pounds or more.

“This has been a season of unusually large fish, and many weighing from 60 to 70 pounds have been taken,” The Oregonian reported in 1895.

Now, more than a century later, “it’s not impossible that we see individuals of that size today, but it’s much, much rarer,” University of Washington research scientist Jan Ohlberger says.

Ohlberger has been tracking the downsizing of salmon in recent decades, but salmon have been shrinking in numbers and in size for a long time. A century’s worth of dam-building, overfishing, habitat loss and replacement by hatchery fish cut the size of the average chinook in half, studies in the 1980s and 1990s found.

Dam-building and fishing have tailed off, but chinooks have been shrinking even faster in the past 15 years, according to a new paper by Ohlberger and colleagues in the journal Fish and Fisheries. Older and bigger fish are mostly gone.

Few fish are making it to old age, which for a chinook salmon means spending five or six years in the ocean after a year or two in fresh water.

“The older fish, which normally come back after five years in the ocean, they come back earlier and earlier,” Ohlberger said.

The trend is clear; the reasons, less so.

Two species eat more chinook salmon than any others: orcas and humans.

The 2,300 or more resident killer whales in the Northeast Pacific Ocean eat about 20 million pounds of chinook salmon per year — roughly equal to the annual commercial catch of chinook in recent years, according to the new study.

“There is a large number of resident killer whales out there that really target chinook, and they target the large chinook,” Ohlberger says. [Selection pressure. – LG]

Continue reading.

Later in the article:

Balcomb points to overfishing, habitat loss and salmon hatcheries that have diluted the gene pool of wild chinooks.

Written by LeisureGuy

18 March 2018 at 12:13 pm

Posted in Evolution, Food, Science

New Evidence Fuels Debate over the Origin of Modern Languages

leave a comment »

One of the books I find myself repeatedly recommending is David Anthony’s The Horse, the Wheel, and Language: How Bronze-Age Riders from the Eurasian Steppes Shaped the Modern World. It’s as enthralling as a great detective novel, and in the course of the history you witness (among other things) the invention of the wheel, which was long after the days of cave men (despite all those cartoons of enormous wheels carved from stone), for reasons the author describes: creating a wheel and axle system requires specialized knowledge based on extensive experience. For that reason, the invention had to await the development of agriculture, of the domestication of horses, and of urban centers before such specialization could be supported. Fascinating book.

In the course of the book, the author looks for the origins of the speakers of the Proto-Indo-European language. And that brings us to a Scientific American article by Roni Jameson, which begins:

Five thousand years ago nomadic horseback riders from the Ukrainian steppe charged through Europe and parts of Asia. They brought with them a language that is the root of many of those spoken today—including English, Spanish, Hindi, Russian and Persian. That is the most widely accepted explanation for the origin of this ancient tongue, termed Proto-Indo-European (PIE). Recent genetic findings confirm this hypothesis but also raise questions about how the prehistoric language evolved and spread.

No written record of PIE exists, but linguists believe they have largely reconstructed it. Some words, including “water” (wód), “father” (pH2-ter) and “mother” (meH2-ter), are still used today. Archaeologist Marija Gimbutas first proposed the Ukrainian origin, known as the kurgan hypothesis, in the 1950s. Gimbutas traced the language back to the Yamnaya people, herders from the southern grasslands of modern-day Ukraine who domesticated the horse.

In 2015 a series of studies sequenced the DNA of human bones and other remains from many parts of Europe and Asia. The data suggest that around 3500 B.C.—roughly the same time that many linguists place the origin of PIE and that archaeologists date horse domestication—Yamnaya genes replaced about 75 percent of the existing human gene pool in Europe. Together with the archaeological and linguistic evidence, the genetic data tipped the scales heavily in favor of the kurgan hypothesis.

Credit: Tiffany Farrant-Gonzalez; Source: “Mapping the Origins and Expansion of the Indo-European Language Family,” by Remco Bouckaert et al., in Science, Vol. 337; August 24, 2012

Newer findings complicate the story, however. In a study published last June in the Journal of Human Genetics, researchers sequenced the mitochondrial DNA of 12 Yamnaya individuals, along with their immediate predecessors and descendants. The remains were found in burial mounds, or kurgans (from which the theory takes its name), in modern-day Ukraine. They had been buried in layers atop one another from the end of the Stone Age through the Bronze Age, between about 4500 and 1500 B.C.—the same time as the genetic replacement event in Europe. The earliest and midrange specimens’ mitochondrial DNA (which is inherited from the mother) was almost entirely local. But the mitochondrial DNA of the most recent specimens included DNA from central Europe, including present-day Poland, Germany and Sweden. This discovery indicates that “there were pendulum migrations back and forth,” says lead author Alexey Nikitin, a professor of archaeology and genetics at Grand Valley State University. In other words, he adds, “it wasn’t a one-way trip.”

These findings give the kurgan hypothesis “a lot more credit,” Nikitin says. But he contends that his new results also show the migration was on a smaller scale than previously speculated; the more recent specimens apparently only made it as far as central Europe before returning, even though the language eventually spread as far as the British Isles. Nikitin also believes the dissemination was not as violent as it is often made out to be. “A military campaign would explain the genetic replacement. But that’s [unlikely to have been] the case,” he says.

David Anthony, an anthropologist at Hartwick College, who co-authored several of the earlier genetic studies but was not involved in the latest work, calls the new findings very convincing. “The domestication of the horse created a steppe bridge into India and Iran on the one side and Europe on the other side,” Anthony says. “When [the] Yamnaya people moved into eastern and western Europe, their genetic signature was very different from what was there before,” he explains. “That’s what makes it paint such a clear picture [of how the root language spread] and why you can really see the migrations so easily on a map.”

Yet Anthony disagrees with the interpretation that this was a small and mostly peaceful affair. . .

Continue reading.

Written by LeisureGuy

12 March 2018 at 12:42 pm

Posted in Books, Evolution, Memes, Science

Did Homo erectus speak?

leave a comment »

Daniel Everett, dean of arts and sciences and professor of global studies and professor of sociology at Bentley University in Massachusetts, has an interesting article in Aeon, which I imagine is an extract from his latest book, How Language Began. The article begins:

What is the greatest human technological innovation? Fire? The wheel? Penicillin? Clothes? Google? None of these come close. As you read this, you are using the winning technology. The greatest tool in the world is language. Without it there would be no culture, no literature, no science, no history, no commercial enterprise or industry. The genus Homo rules the Earth because it possesses language. But how and when did we build this kingdom of speech? And who is ‘we’? After all, Homo sapiens is just one of several species of humans that have walked the Earth. Does ‘we’ refer to our genus, Homo, or to our species, sapiens?

To discover the answers to these questions, we need to travel back in time at least 1.9 million years ago to the birth of Homo erectus, as they emerged from the ancient process of primate evolution. Erectus had nearly double the brain size of any previous hominin, walked habitually upright, were superb hunters, travelled the world, and sailed to ocean islands. And somewhere along the way they got language. Yes, erectus. Not Neanderthals. Not sapiens. And if erectus invented language, this means that Neanderthals, born more than a million years later, entered a world already linguistic.

Likewise, our species would have emerged into a world that already had language. In spite of the fact that many paleoanthropologists view erectus as little more than a skinny gorilla, of few accomplishments, far too stupid to have language, and lacking a vocal apparatus capable of intelligible speech, the evidence seems overwhelming that they had language. Erectus needed language. They were capable of language. And, though often denied in evolutionary studies, the ‘leap’ to language was little more than a long series of baby steps, requiring no mutations, nor any complex grammar. In fact, the language of erectus would have been every bit as much a ‘real language’ as any modern language.

Erectus was an imposing creature. Males stood between 173 cm (5′ 8″) and 180 cm (5′ 11″). Their immediate ancestors, the Australopithecine males, were only about 137 cm (4′ 6″) tall (their immediate ancestors might have been Homo habilis, but only if we accept that habilis were not Australopithecines, or that they were a separate species from Homo erectus, neither of which is clear). The brains of these early humans averaged around 950 cubic centimetres in volume, double the size of the Australopithecines, though smaller than those of male Neanderthals (1,450 ccs) and sapiens (1,250-1,300 ccs), but still within the range of modern sapiens females. The vocal apparatus of erectus might not have been much more advanced than that of a modern gorilla or it might have been more similar to ours. But whether their speech sounded different than ours or not, it was nevertheless adequate for language.

Evidence that erectus had language comes from their settlements, their art, their symbols, their sailing ability and their tools. Erectus settlements are found throughout most of the old world. And, most importantly for the idea that erectus had language, open oceans were not barriers to their travel.

Erectus settlements show evidence of culture – values, knowledge structures and social structure. This evidence is important because all these elements enhance each other. Evidence from the erectus settlement studied at Gesher Benot Ya’aqov in Israel, for example, suggests not only that erectus controlled fire but that their settlements were planned. One area was used for plant-food processing, another for animal-material processing, and yet another for communal life. Erectus, incredibly, also made sea craft. Sea travel is the only way to explain the island settlements of Wallacea (Indonesia), Crete and, in the Arabian Sea, Socotra. None of these were accessible to erectus except by crossing open ocean, then and now. These island cultural sites demonstrate that erectus was capable of constructing seaworthy crafts capable of carrying 20 people or more. According to most archaeologists, 20 individuals would have been the minimum required to found the settlements discovered.

Because the stone tools of erectus were simple and slow to evolve, some have rushed to conclude that they lacked intelligence for language. But stone-cutting implements are simply not the whole story. The evidence for erectusisland settlements means that they built water-transport craft. Erectus seem to have had art as well, as exemplified in the 250,000-year-old Venus of Berekhat Ram.

Further, archaeologists have discovered 400,000-year-old wooden thrusting and throwing spears in lower Saxony (called the ‘Schöningen spears’), which suggest a robust hunting culture. Thrusting spears, for example, require at least one member of a group to get close enough to the prey, such as mastodons, to pierce them with the weapon. Hunting culture entails cooperation and planning with others. . .

Continue reading.

Written by LeisureGuy

28 February 2018 at 11:19 am

Posted in Evolution, Science

Was Cooking a Pivotal Step in Human Evolution?

leave a comment »

Alexandra Rosati writes in the Scientific American:

The shift to a cooked-food diet was a decisive point in human history. The main topic of debate is when, exactly, this change occurred.

All known human societies eat cooked foods, and biologists generally agree cooking could have had major effects on how the human body evolved. For example, cooked foods tend to be softer than raw ones, so humans can eat them with smaller teeth and weaker jaws. Cooking also increases the energy they can get from the food they eat. Starchy potatoes and other tubers, eaten by people across the world, are barely digestible when raw. Moreover, when humans try to eat more like chimpanzees and other primates, we cannot extract enough calories to live healthily. Up to 50 percent of women who exclusively eat raw foods develop amenorrhea, or lack of menstruation, a sign the body does not have enough energy to support a pregnancy—a big problem from an evolutionary perspective.

Such evidence suggests modern humans are biologically dependent on cooking. But at what point in our evolutionary history was this strange new practice adopted? Some researchers think cooking is a relatively recent innovation—at most 500,000 years old. Cooking requires control of fire, and there is not much archaeological evidence for hearths and purposefully built fires before this time.

The archaeological record becomes increasingly fragile farther back in time, however, so others think fire may have been controlled much earlier. Anthropologist Richard Wrangham has proposed cooking arose before 1.8 million years ago, an invention of our evolutionary ancestors. If the custom emerged this early, it could explain a defining feature of our species: the increase in brain size that occurred around this time.

What is the connection between cooking and brains? Understanding how and why our brains got so big has been a major puzzle because such a brain is metabolically expensive. In fact, the brain needs more energy for its size than any other organ. Although it might seem being smarter is always better, having a big brain exerts a high toll. Ancestral humans may have compensated for this energy cost by cooking food.

Like all ideas about human evolution, the cooking hypothesis can only be tested indirectly—without a time machine we cannot know exactly what happened in our evolutionary history. But there are several converging pieces of evidence that support Wrangham’s cooking hypothesis.

Fossils show the teeth and digestive track of Homo erectus decreased in size around the same time brain size increased. This evidence likely means our ancestors started eating softer, higher-quality foods (although not necessarily cooked). New archaeological research has also continued to push back the earliest known date for the control of fire. For example, traces of purposeful fire at Wonderwerk Cave in South Africa have been dated at more than a million years old. Recent studies further suggest humans have genetic adaptions for eating cooked foods—some of which are old, at least predating our split from Neandertals. Finally, some of my own work, with psychologist Felix Warneken, has shown chimpanzees possess many of the foundational cognitive capacities needed to start cooking—such as a preference for cooked food, patience to wait for foods to be cooked and the capacity to plan for and transport foods to a cooking site. These data mean ancestral humans likely shared the same abilities, and could have started cooking rapidly after gaining the ability to control fire.

These converging pieces of evidence point to  . . .

Continue reading.

Written by LeisureGuy

26 February 2018 at 12:42 pm

Posted in Evolution, Food, Science

%d bloggers like this: