Tag Archives: Evolution

What does it mean to be human?

Analysing the genetics of ancient humans means changing ideas about our evolution.

The Gibraltar 2 skull, discovered in 1926 in Devil's Tower Cave, was the second Neanderthal skull to be found in Gibraltar. Photo credit: Muséum d'Anthropologie, campus universitaire d'Irchel, Université de Zurich (Suisse) : Homo neanderthalensis (Gibraltar), via Wikipedia

The Gibraltar 2 skull, discovered in 1926 in Devil’s Tower Cave, was the second Neanderthal skull to be found in Gibraltar. Photo credit: Muséum d’Anthropologie, campus universitaire d’Irchel, Université de Zurich (Suisse) : Homo neanderthalensis (Gibraltar), via Wikipedia

GAIA VINCE 
March, 2017

The Rock of Gibraltar appears out of the plane window as an immense limestone monolith sharply rearing up from the base of Spain into the Mediterranean. One of the ancient Pillars of Hercules, it marked the end of the Earth in classical times. Greek sailors didn’t go past it. Atlantis, the unknown, lay beyond.

In summer 2016, Gibraltar is in the throes of a 21st-century identity crisis: geographically a part of Spain, politically a part of Britain; now torn, post Brexit, between its colonial and European Union ties. For such a small area – less than seven square kilometres – Gibraltar is home to an extraordinarily diverse human population. It has been home to people of all types over the millennia, including early Europeans at the edge of their world, Phoenicians seeking spiritual support before venturing into the Atlantic, and Carthaginians arriving in a new world from Africa.

But I’ve come to see who was living here even further back, between 30,000 and 40,000 years ago, when sea levels were much lower and the climate was swinging in and out of ice ages. It was a tough time to be alive and the period saw the species that could, such as birds, migrate south to warmer climes, amid plenty of local extinctions. Among the large mammal species struggling to survive were lions, wolves and at least two types of human: our own ‘modern human’ ancestors, and the last remaining populations of our cousins, the Neanderthals.

By understanding more about these prehistoric people, we can learn about who we are as a species today. Our ancestors’ experiences shaped us, and they may still hold answers to some of our current health problems, from diabetes to depression.

View of Gorham's Cave, a sea cave in the east face of the Rock of Gibraltar, Gibraltar. Photo credit: Gibmetal77/Wikipedia

Everyone of European descent has some Neanderthal DNA in their genetic makeup. Above, view of Gorham’s Cave, a sea cave in the east face of the Rock of Gibraltar, Gibraltar. Photo credit: Gibmetal77/Wikipedia

I’m picked up outside my hotel by archaeologists Clive and Geraldine Finlayson, in a car that itself looks fairly ancient. Typical for this crowded little peninsula, they are of diverse origins – he, pale-skinned and sandy-haired, can trace his ancestry back to Scotland; she, olive-skinned and dark-haired, from the Genoese refugees escaping Napoleon’s purges. How different we humans can look from each other. And yet the people whose home I am about to visit truly were of a different race.

We don’t know how many species of humans there have been, how many different races of people, but the evidence suggests that around 600,000 years ago one species emerged in Africa that used fire, made simple tools from stones and animal bones, and hunted big animals in large cooperative groups. And 500,000 years ago, these humans, known as Homo heidelbergensis, began to take advantage of fluctuating climate changes that regularly greened the African continent, and spread into Europe and beyond.

By 300,000 years ago, though, migration into Europe had stopped, perhaps because a severe ice age had created an impenetrable desert across the Sahara, sealing off the Africans from the other tribes. This geographic separation enabled genetic differences to evolve, eventually resulting in different races, although they were still the same species and would prove able to have fertile offspring together. The race left behind in Africa would become Homo sapiens sapiens, or ‘modern humans’; those who evolved adaptations to the cooler European north would become Neanderthals, Denisovans and others whom we can now only glimpse with genetics.

Neanderthals were thriving from Siberia to southern Spain by the time a few families of modern humans made it out of Africa around 60,000 years ago. These Africans encountered Neanderthals and, on several occasions, had children with them. We know this because human DNA has been found in the genomes of Neanderthals, and because everyone alive today of European descent – including me – has some Neanderthal DNA in their genetic makeup. Could it be that their genes, adapted to the northerly environment, provided a selective advantage to our ancestors as well?

It was like Neanderthal City

Neanderthal engraving in Gorham's Cave, Gibraltar Date2 September 2014, 21:05:41 Source	Own work Author	AquilaGib (Stewart Finlayson, Gibraltar Museum) via Wikipedia

Neanderthal engraving in Gorham’s Cave, Gibraltar Photo:  AquilaGib (Stewart Finlayson, Gibraltar Museum) via Wikipedia

After driving through narrow tunnels on a road that skirts the cliff face, we pull up at a military checkpoint. Clive shows the guard our accreditation and we’re waved through to park inside. Safety helmets on to protect from rockslides, we leave the car and continue on foot under a low rock arch. A series of metal steps leads steeply down the cliff to a narrow shingle beach, 60 metres below. The tide is lapping the pebbles and our feet must negotiate the unstable larger rocks to find a dry path.

I’ve been concentrating so hard on keeping my footing that it is something of a shock to look up and suddenly face a gaping absence in the rock wall. We have reached Gorham’s Cave, a great teardrop-shaped cavern that disappears into the white cliff face and, upon entering, seems to grow in height and space. This vast, cathedral-like structure, with a roof that soars high into the interior, was used by Neanderthals for tens of thousands of years. Scientists believe it was their last refuge. When Neanderthals disappeared from here, some 32,000 years ago, we became the sole inheritors of our continent.

I pause, perched on a rock inside the entrance, in order to consider this – people not so different from myself once sat here, facing the Mediterranean and Africa beyond. Before I arrived in Gibraltar, I used a commercial genome-testing service to analyse my ancestry. From the vial of saliva I sent them, they determined that 1 per cent of my DNA is Neanderthal. I don’t know what health advantages or risks these genes have given me – testing companies are no longer allowed to provide this level of detail – but it is an extraordinary experience to be so close to the intelligent, resourceful people who bequeathed me some of their genes. Sitting in this ancient home, knowing none of them survived to today, is a poignant reminder of how vulnerable we are – it could so easily have been a Neanderthal woman sitting here wondering about her extinct human cousins.

Gorham’s Cave seems an oddly inaccessible place for a home. But Clive, who has been meticulously exploring the cave for 25 years, explains that the view was very different back then. With the sea levels so much lower, vast hunting plains stretched far out to sea, letting people higher on the rock spot prey and signal to each other. In front of me would have been fields of grassy dunes and lakes – wetlands that were home to birds, grazing deer and other animals. Further around the peninsula to my right, where the dunes gave way to shoreline, would have been clam colonies and mounds of flint. It was idyllic, Clive says. The line of neighbouring caves here probably had the highest concentration of Neanderthals living anywhere on Earth. “It was like Neanderthal City,” he adds.

Deep inside the cave, Clive’s team of archaeologists have found the remains of fires. Further back are chambers where the inhabitants could have slept protected from hyenas, lions, leopards and other predators. “They ate shellfish, pine seeds, plants and olives. They hunted big game and also birds. There was plenty of fresh water from the springs that still exist under what is now seabed,” Clive says. “They had spare time to sit and think – they weren’t just surviving.”

He and Geraldine have uncovered remarkable evidence of Neanderthal culture in the cave, including the first example of Neanderthal artwork. The ‘hashtag’, a deliberately carved rock engraving, is possibly evidence of the first steps towards writing. Other signs of symbolic or ritualistic behaviour, such as the indication that Neanderthals were making and wearing black feather capes or headdresses as well as warm clothes, all point to a social life not so different to the one our African ancestors were experiencing.

Clive shows me a variety of worked stones, bone and antler. I pick up a flint blade and hold it in my hand, marvelling at how the same technology is being passed between people biologically and culturally linked but separated by tens of thousands of years. Other sites in Europe have uncovered Neanderthal-made necklaces of strung eagle talons dating back 130,000 years, little ochre clamshell compacts presumably for adornment, and burial sites for their dead.

These people evolved outside of Africa but clearly had advanced culture and the capability to survive in a hostile environment. “Consider modern humans were in the Middle East perhaps 70,000 years ago, and reached Australia more than 50,000 years ago,” says Clive. “Why did it take them so much longer to reach Europe? I think it was because Neanderthals were doing very well and keeping modern humans out.”

But by 39,000 years ago, Neanderthals were struggling. Genetically they had low diversity because of inbreeding and they were reduced to very low numbers, partly because an extreme and rapid change of climate was pushing them out of many of their former habitats. A lot of the forested areas they depended on were disappearing and, while they were intelligent enough to adapt their tools and technology, their bodies were unable to adapt to the hunting techniques required for the new climate and landscapes.

“In parts of Europe, the landscape changed in a generation from thick forest to a plain without a single tree,” Clive says. “Our ancestors, who were used to hunting in bigger groups on the plains, could adapt easily: instead of wildebeest they had reindeer, but effectively the way of capturing them was the same. But Neanderthals were forest people.

“It could’ve gone the other way – if instead the climate had got wetter and warmer, we might be Neanderthals today discussing the demise of modern humans.”

This is why ancient genetics and ancient genomics are so powerful – you can look at an individual and say, ‘Did they have this gene or not?’

Although the Neanderthals, like the Denisovans and other races we are yet to identify, died out, their genetic legacy lives on in people of European and Asian descent. Between 1 and 4 per cent of our DNA is of Neanderthal origins, but we don’t all carry the same genes, so across the population around 20 per cent of the Neanderthal genome is still being passed on. That’s an extraordinary amount, leading researchers to suspect that Neanderthal genes must be advantageous for survival in Europe.

Interbreeding across different races of human would have helped accelerate the accumulation of useful genes for the environment, a process that would have taken much longer to occur through evolution by natural selection. Neanderthal tweaks to our immune system, for example, may have boosted our survival in new lands, just as we prime our immune system with travel vaccines today. Many of the genes are associated with keratin, the protein in skin and hair, including some that are linked to corns and others that play a role in pigmentation – Neanderthals were redheads, apparently. Perhaps these visible variants were considered appealing by our ancestors and sexually selected for, or perhaps a tougher skin offered some advantage in the colder, darker European environment.

Some Neanderthal genes, however, appear to be a disadvantage, for instance making us more prone to diseases like Crohn’s, urinary tract disorders and type 2 diabetes, and to depression. Others change the way we metabolise fats, risking obesity, or even make us more likely to become addicted to smoking. None of these genes are a direct cause of these complicated conditions, but they are contributory risk factors, so how did they survive selection for a thousand generations?

It’s likely that for much of the time since our sexual encounters with Neanderthals, these genes were useful. When we lived as hunter-gatherers, for example, or early farmers, we would have faced times of near starvation interspersed with periods of gorging. Genes that now pose a risk of diabetes may have helped us to cope with starvation, but our new lifestyles of continual gorging on plentiful, high-calorie food now reveal harmful side-effects. Perhaps it is because of such latent disadvantages that Neanderthal DNA is very slowly now being deselected from the human genome.

While I can (sort of) blame my Neanderthal ancestry for everything from mood disorders to being greedy, another archaic human race passed on genes that help modern Melanesians, such as people in Papua New Guinea, survive different conditions. Around the time that the ancestors of modern Europeans and Asians were getting friendly with Neanderthals, the ancestors of Melanesians were having sex with Denisovans, about whom we know very little. Their surviving genes, however, may help modern-day Melanesians to live at altitude by changing the way their bodies react to low levels of oxygen. Some geneticists suspect that other, yet-to-be-discovered archaic races may have influenced the genes of other human populations across the world.

Interbreeding with Neanderthals and other archaic humans certainly changed our genes, but the story doesn’t end there.

I am a Londoner, but I’m a little darker than many Englishwomen because my father is originally from Eastern Europe. We are attuned to such slight differences in skin colour, face shape, hair and a host of other less obvious features encountered across different parts of the world. However, there has been no interbreeding with other human races for at least 32,000 years. Even though I look very different from a Han Chinese or Bantu person, we are actually remarkably similar genetically. There is far less genetic difference between any two humans than there is between two chimpanzees, for example.

The reason for our similarity is the population bottlenecks we faced as a species, during which our numbers dropped as low as a few hundred families and we came close to extinction. As a result, we are too homogeneous to have separated into different races. Nevertheless, variety has emerged through populations being separated geographically – and culturally, in some cases – over thousands of years. The greatest distinctions occur in isolated populations where small genetic and cultural changes become exaggerated, and there have been many of them over the 50,000 years since my ancestors made the journey out of Africa towards Europe.

According to the analysis of my genome, my haplogroup is H4a. Haplogroups describe the mutations on our mitochondrial DNA, passed down through the maternal line, and can theoretically be used to trace a migratory path all the way back to Africa. H4a is a group shared by people in Europe, unsurprisingly, and western Asia. It is, the genome-testing company assures me, the same as Warren Buffet’s. So what journey did my ancestors take that would result in these mutations and give me typically European features?

 Interior of Krapina Neanderthal Museum in Krapina, Croatia. Photo credit: Tromber, Wikipedia

Interior of Krapina Neanderthal Museum in Krapina, Croatia. Photo credit: Tromber, Wikipedia

There exists an uneasy relationship between biology and culture

“I was dumped by helicopter in the wilderness with two other people, a Russian and an indigenous Yukaghir man, with our dogs, our guns, our traps, a little food and a little tea. There we had to survive and get food and furs in the coldest place on Earth where humans live naturally – minus 60 degrees.”

Eske Willerslev lived for six months as a trapper in Siberia in his 20s. Separately, his identical twin brother Rane did the same. When they were teenagers, their father had regularly left them in Lapland to survive alone in the wilderness for a couple of weeks, fostering a passion for the remote tundra and the people who live there, and they went on increasingly lengthy expeditions. But surviving practically alone was very different. “It was a childhood dream, but it was the toughest thing I have ever done,” Eske admits.

These experiences affected the twins deeply, and both have been driven towards a deeper understanding of how the challenge of survival has forged us as humans over the past 50,000 years. It led Eske into the science of genetics, and to pioneering the new field of ancient DNA sequencing. Now director of the Centre for GeoGenetics at the Natural History Museum of Denmark, Eske has sequenced the world’s oldest genome (a 700,000-year-old horse) and was the first to sequence the genome of an ancient human, a 4,000-year-old Saqqaq man from Greenland. Since then, he has gone on to sequence yet more ancient humans and, in doing so, has fundamentally changed our understanding of early human migration through Europe and beyond. If anyone can unpick my origins, it is surely Eske.

First, though, I go to meet his twin Rane, who studied humanities, went into cultural anthropology and is now a professor at Aarhus University. He’s not convinced that his brother’s genetic approach can reveal all the answers to my questions: “There exists an uneasy relationship between biology and culture,” he tells me. “Natural scientists claim they can reveal what sort of people moved around, and they are not interested in having their models challenged. But this cannot tell you anything about what people thought or what their culture was.”

To put this point to Eske, I visit him in his delightful museum office, opposite a petite moated castle and in the grounds of the botanic gardens – there could scarcely be a more idyllic place for a scientist to work. Greeting him for the first time, just hours after meeting Rane, is disconcerting. Identical twins are genetically and physically almost exactly the same – looking back, many years from now, at DNA left by the brothers, it would be all but impossible to tell them apart or even to realise that there were two of them.

Eske tells me that he is increasingly working with archaeologists to gain additional cultural perspective, but that genetic analysis can answer questions that nothing else can. “You find cultural objects in certain places and the fundamental question is: Does that mean people who made it were actually there or that it was traded? And, if you find very similar cultural objects, does that mean there was parallel or convergent cultural evolution in the two places, or does that mean there was contact?” he explains.

“For example, one theory says the very first people crossing into the Americas were not Native Americans but Europeans crossing the Atlantic, because the stone tools thousands of years ago in America are similar to stone tools in Europe at the same time. Only when we did the genetic testing could we see it was convergent evolution, because the guys carrying and using those tools have nothing to do with Europeans. They were Native Americans. So the genetics, in terms of migrations, is by far the most powerful tool we have available now to determine: was it people moving around or was it culture moving around? And this is really fundamental.”

Reconstruction of a Homo neanderthalensis man and woman, in the Neanderthal Museum, Mettmann, Germany. Photo credit: UNiesert - Sariling gawa/Wikipedia

Reconstruction of a Homo neanderthalensis man and woman, in the Neanderthal Museum, Mettmann, Germany. Photo credit: UNiesert – Sariling gawa/Wikipedia

What Eske went on to discover about Native American origins rewrote our understanding completely. It had been thought that they were simply descendants of East Asians who had crossed the Bering Strait. In 2013, however, Eske sequenced the genome of a 24,000-year-old boy discovered in central Siberia, and found a missing link between ancient Europeans and East Asians, the descendants of whom would go on to populate America. Native Americans can thus trace their roots back to Europe as well as East Asia.

And what about my ancestors? I show Eske the H4a haplotype analysed by the sequencing company and tell him it means I’m European. He laughs derisively. “You could be and you could be from somewhere else,” he says. “The problem with the gene-sequencing tests is that you can’t look at a population and work back to see when mutation arose with much accuracy – the error bars are huge and it involves lots of assumptions about mutation rates.

“This is why ancient genetics and ancient genomics are so powerful – you can look at an individual and say, ‘Now we know we are 5,000 years ago, how did it look? Did they have this gene or not?’”

While ancient genomics can help satisfy curiosity about our origins, its real value may be in trying to unpick different health risks

The things that we thought we understood about Europeans are coming unstuck as we examine the genes of more ancient people. For example, it was generally accepted that pale skin evolved so we could get more vitamin D after moving north to where there was little sun and people had to cover up against the cold. But it turns out that it was the Yamnaya people from much further south, tall and brown-eyed, who brought pale skins to Europe. Northern Europeans before then were dark-skinned and got plenty of vitamin D from eating fish.

It is the same with lactose tolerance. Around 90 per cent of Europeans have a genetic mutation that allows them to digest milk into adulthood, and scientists had assumed that this gene evolved in farmers in northern Europe, giving them an additional food supply to help survive the long winters. But Eske’s research using the genomes of hundreds of Bronze Age people, who lived after the advent of farming, has cast doubt on this theory too: “We found that the genetic trait was almost non-existent in the European population. This trait only became abundant in the northern European population within the last 2,000 years,” he says.

It turns out that lactose tolerance genes were also introduced by the Yamnaya. “They had a slightly higher tolerance to milk than the European farmers and must have introduced it to the European gene pool. Maybe there was a disaster around 2,000 years ago that caused a population bottleneck and allowed the gene to take off. The Viking sagas talk about the sun becoming black – a major volcanic eruption – that could have caused a massive drop in population size, which could have been where some of that stock takes off with lactose.”

While ancient genomics can help satisfy curiosity about our origins, its real value may be in trying to unpick some of the different health risks in different populations. Even when lifestyle and social factors are taken into account, some groups are at significantly higher risk of diseases such as diabetes or HIV, while other groups seem more resistant. Understanding why could help us prevent and treat these diseases more effectively.

It had been thought that resistance to infections like measles, influenza and so on arrived once we changed our culture and started farming, living in close proximity with other people and with animals. Farming started earlier in Europe, which was thought to be why we have disease resistance but Native Americans don’t, and also why the genetic risks of diabetes and obesity are higher in native Australian and Chinese people than in Europeans.

“Then,” says Eske, “we sequenced a hunter-gatherer from Spain, and he showed clear genetic resistance to a number of pathogens that he shouldn’t have been exposed to.” Clearly, Europeans and other groups have a resistance that other groups don’t have, but is this really a result of the early agricultural revolution in Europe, or is something else going on?

Eske’s analysis of people living 5,000 years ago has also revealed massive epidemics of plague in Europe and Central Asia, 3,000 years earlier than previously thought. Around 10 per cent of all skeletons the team analysed had evidence of plague. “Scandinavians and some northern Europeans have higher resistance to HIV than anywhere else in the world,” Eske notes. “Our theory is that their HIV resistance is partly resistance towards plague.”

It could be that the cultural changes we have made, such as farming and herding, have had less influence on our genes than we thought. Perhaps it is simply the randomness of genetic mutation that has instead changed our culture. There’s no doubt that where mutations have occurred and spread through our population, they have influenced the way we look, our health risks and what we can eat. My ancestors clearly didn’t stop evolving once they’d left Africa – we’re still evolving now – and they have left an intriguing trail in our genes.

At the Gibraltar Museum, a pair of Dutch archaeology artists have created life-size replicas of a Neanderthal woman and her grandson, based on finds from nearby. They are naked but for a woven amulet and decorative feathers in their wild hair. The boy, aged about four, is embracing his grandmother, who stands confidently and at ease, smiling at the viewer. It’s an unnerving, extraordinarily powerful connection with someone whose genes I may well share, and I recall Clive’s words from when I asked him if modern humans had simply replaced Neanderthals because of our superior culture.

“That replacement theory is a kind of racism. It’s a very colonialist mentality,” he said. “You’re talking almost as if they were another species.”

Creative Commons

Gaia Vince is a writer and broadcaster specialising in science and the environment. She has been the front editor of the journal Nature Climate Change, the news editor of Nature and online editor of New Scientist. Her work has appeared in newspapers and magazines in the UK, USA and Australia, including the GuardianScienceScientific American and Australian Geographic. She writes for BBC Online and devises and presents science programmes for BBC radio. Her first book, Adventures in the Anthropocene: A journey to the heart of the planet we made, is out now. She blogs at WanderingGaia.com and tweets at @WanderingGaia. She lives in London.

This story by Gaia Vince was edited by Michael Regnier, fact-checked by Francine Almash, copy-edited by Rob Reddick.

Note: Professor Eske Willerslev is a research associate at the Wellcome Trust Sanger Institute, which is funded by a core grant from the Wellcome Trust, which publishes Mosaic.

This article first appeared on Mosaic and is republished here under a Creative Commons licence.

Links:

Gibralter Museum: http://www.gibmuseum.gi/Welcome.html

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An Ancient Fossil’s Lessons About Cancer

Volume rendered image of the external morphology of the foot bone shows the extent of expansion of the primary bone cancer beyond the surface of the bone. Patrick Randolph-Quinney (UCLAN)

Volume rendered image of the external morphology of the foot bone shows the extent of expansion of the primary bone cancer beyond the surface of the bone. Patrick Randolph-Quinney (UCLAN)

By Richard Gunderman 
August, 2016

In late July, an international team of researchers announced that they had identified evidence of cancer in the fossilized remains of a biological relative of human beings who lived about 1.7 million years ago.

It is rare to find fossils from the hominid family tree. Finding one with such well-preserved evidence of a tumor is rarer still.

It seems that cancer has been with us for quite some time, and this finding highlights one of the most fascinating questions about it: why cancer exists in the first place.

Cancer is a deadly disease and would have been particularly lethal before the recent development of effective treatments. So why didn’t it – or our susceptibility to it – die out long ago?

To put the question somewhat differently, why should organisms, including human beings, carry within our DNA the instruments of our own destruction – tumor suppressor genes and oncogenes just waiting for environmental insults before they kill their carriers? Shouldn’t organisms with such genes be selected against in the evolutionary competition to survive and reproduce?

An ancient osteosarcoma

Before addressing that question, let’s go back to the 1.7-million-year-old tumor.

The researchers found the cancer in a metatarsal, one of the long bones of the foot found just behind the toes. The researchers examined the specimen with high-resolution x-rays, revealing the lesion in greater detail and producing a three-dimensional image, which revealed an “irregular spongy woven bone texture with a cauliflower-like external appearance.” In other words, the cells of the tumor had grown in a disorganized fashion and were ballooning out from the shaft of the bone – features of a malignancy. They concluded that it was a bone cancer, probably an osteosarcoma.

A different view of the tumor in the metatarsal bone. Edward Odes/University of the Witwatersrand

As a radiologist working in a children’s hospital, I regularly see x-ray, CT and MRI scans of patients with osteosarcomas. They account for a fraction of all primary bone cancers, and are most often diagnosed in adolescence and young adulthood. One unusual feature of the South African report is the location of the tumor – the leg and arm are much more common sites than the foot.

Osteosarcomas arise from abnormal bone-producing cells. In fact, the name osteosarcoma comes from Greek roots meaning “bone” and “fleshy growth.”

Osteosarcomas aren’t just found in humans. They represent the most common bone malignancy found in dogs and cats. In fact, osteosarcomas are more common in dogs than people, especially in large species such as greyhounds and great danes.

Cancer has been around for much longer than 1.7 million years. In Indianapolis, our Children’s Museum features the fossilized skull of a Gorgosaurus, a relative of Tyrannosaurus rex which lived during the Cretaceous period about 70 million years ago. It shows clear evidence of a golf-ball-sized mass inside the skull cavity.

Cancer isn’t a single disease

One challenge in attempting to understand the causes of cancer is the fact that cancer is not a single disease.

There are many different types of cancer, which can be categorized according to the organ in which they originate – lung cancer, colon cancer, breast cancer and so on. Better yet, they can be categorized by the type of tissue they represent. For example, carcinomas arise from epithelial or lining cells, sarcomas from connective cells, and leukemias from blood-forming cells.

What we call cancer really represents a family of disorders, all of which can be lumped together because of a common feature – disrupted regulation of cell growth.

For example, genes that normally suppress cell growth may be damaged, leading to uncontrolled proliferation. An indication that all cancers are not the same is the fact that they have very different prognoses and treatments.

Today evidence suggests that many cancers can be traced to environmental exposures, such as tobacco, dietary carcinogens, infections, and air and water pollution. It seems unlikely that tobacco or air pollution could have caused cancer millions of years ago, but it’s possible that some dietary and infectious agents may have been more common in the remote past.

Chromosomes and oxygen

One of the first explanations for how cancer could result from chromosomal damage was provided by a medical school professor of mine at the University of Chicago, Janet Rowley, M.D. In the 1970s, Dr. Rowley showed that in many patients with a type of leukemia, CML, portions of chromosomes 9 and 22 had been exchanged, proving that changes in DNA could lead to cancer.

Part of the blame for cancer may be placed on a rather unexpected culprit, a molecule without which human life would be utterly impossible – oxygen. Oxygen is necessary for our cells to convert food to energy. This is one of the reasons that the human body is equipped with over 60,000 miles of blood vessels, which enable red blood cells to carry oxygen to each of our 75 trillion cells.

But oxygen is not an entirely benign molecule. In fact, it is highly reactive and even toxic in high concentrations. And early in Earth’s history, oxygen levels began to rise dramatically, as plants capable of photosynthesis – a process that produces oxygen – proliferated. More oxygen permitted the development of multicellular organisms capable of transporting oxygen to all of their cells.

Oxygen becomes problematic when superreactive forms of it are formed. For example, when ionizing radiation strikes a cell, it can form superoxides that react avidly with nearby molecules. When one of the nearby molecules is DNA, damage to genes occurs, producing mutations that can be carried from one generation of cells to another. In some cases, a transformation to cancer may result.

Human malignant osteosarcoma (bone cancer) cells from a leg mass. National Cancer Institute via Wikimedia Commons

Will cancer always be with us?

Another reason that cancer has persisted is the fact that it tends to be a disease of older organisms. Only 1 percent of the cancers diagnosed each year in the U.S. occur in children. So for most of our biological history, when life expectancy was shorter, hominids reproduced and died of other causes long before cancer had a chance to develop.

In advanced countries today, mortality rates due to other diseases, such as infections, heart disease and stroke, have fallen so far that many more people are living to advanced ages, by which point the series of mutations necessary to induce cancer have had sufficient time to occur. In effect, rising cancer rates are in part a sign of general good health and longevity.

Can we make cancer disappear? The fundamental problem with cancer cells is that they do not know when to stop growing and die, and as a result, they keep proliferating in an uncontrolled fashion. While this is highly injurious to the organism, the existence of genes that promote cell growth is obviously crucial for organisms to grow and survive in the first place.

Consider an automobile. Just two weeks ago, the brakes on my car failed, a dangerous situation. We might wish that cars were built so that the brakes could never fail, but the only way to eliminate the possibility of brake failure would be to do away with the brake system altogether, a far more hazardous proposition.

The same thing can be said about cancer. We might wish that we were built without genes that can contribute to the development of cancer, but normal growth and development – and yes, even death – might not be possible without them. When it comes to life, we must take the bad as well as the good, though this is not to say that we cannot make strides in preventing and curing cancer.

The finding of cancer in the bone of a 1.7-million-year-old human relative isn’t just a biological oddity – it is a reminder of what it means to be both alive and human. Life is fraught with hazards. Thriving biologically (and biographically) does not mean eliminating all risks but managing the ones we can, both to reduce harm and promote a full life.

Creative CommonsThe Conversation

Richard Gunderman is Chancellor’s Professor of Medicine, Liberal Arts, and Philanthropy at Indiana University. This article was originally published on The Conversation. Read the original article.

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Why cats are fussy, and dogs will eat most anything

By Hannah Rowland, University of Cambridge
November, 2015

"Feed me." © Deborah Jones 2015

“Feed me.” © Deborah Jones 2015

Anyone who’s watched a cat throwing up after munching on grass knows that our feline friends aren’t natural plant eaters. So you might be surprised to discover that these carnivorous animals share some important genes that are more typically associated with herbivores. And this might help explain why cats aren’t always easy to please when it comes to food.

New research suggests that cats possess the genes that protect vegetarian animals from ingesting poisonous plants by giving them the ability to taste bitter. Animals use their sense of taste to detect whether a potential food is nutritious or harmful. A sweet taste signals the presence of sugars, an important source of energy. A bitter taste, on the other hand, evolved as a defence mechanism against harmful toxins commonly found in plants and unripe fruits.

Evolution has repeatedly tweaked animals’ taste buds to suit various dietary needs. Changes in an animal’s diet can eliminate the need to sense certain chemicals in food, and so receptor genes mutate, destroying their ability to make a working protein.

One example of this comes from strictly meat-eating cats, who can no longer taste sweetness. But if bitter detection evolved to warn of plant toxins, then it stands to reason that cats, which (usually) eschew plants, shouldn’t be able to taste bitter either. Humans and other vegetable-munching animals can taste bitter because we possess bitter taste receptor genes. If cats have lost the ability to taste bitterness, we should find that their receptor genes are riddled with mutations.

Geneticists at the Monell Chemical Senses Center in Philadelphia scoured the genome of cats and other carnivorous mammals like dogs, ferrets, and polar bears to see if our carnivorous cousins have bitter genes. They were surprised to find that cats have 12 different genes for bitter taste. Dogs, ferrets, and polar bears are equally well endowed. So, if meat eating animals are unlikely to encounter any bitter morsels, why do they boast genes for tasting bitterness?

Taste test

To find out, Peihua Jiang, a molecular biologist at Monell, put cat taste buds to the test. He inserted the cat taste receptor gene into human tissue cells in the lab. When combined, the cell and the gene act as a taste receptor that responds to chemicals dropped onto it.

Jiang discovered that the cat’s taste receptors responded to bitter chemicals found in toxic plants and to compounds that also activate human bitter receptors. The cat bitter taste receptor, known as Tas2r2, responded to the chemical denatonium benzoate, a bitter substance commonly smeared on the fingernails of nail-biting children.

So why have cats retained the ability to detect bitter tastes? Domestic cats owners know how unpredictable cats’ dietary choices can be. Some of the “presents” cats bring to their owners include frogs, toads, and other animals that can contain bitter and toxic compounds in their skin and bodies. Jiang’s results show that bitter receptors empower cats to detect these potential toxins, giving them the ability to reject noxious foods and avoid poisoning.

But how often do meat-loving cats actually get exposed to bitter and toxic compounds in their diet, compared with the plethora of plant toxins that their vegetarian counterparts have to contend with? Jiang suggests this is not enough to explain why cats have retained such an arsenal of receptors.

Instead, cat taste receptors may have evolved for reasons other than taste. In humans, bitter taste receptors are found not only in the mouth, but also in the heart and in the lungs, where they are thought to detect infections. It remains to be seen if feline bitter receptor genes also double-up as disease detectors.

The discovery of feline bitter receptors might explain why cats have got a reputation as picky eaters. But their unfussy canine counterparts have a similar number of bitter taste receptors – so why are cats so finicky? One answer might lie in how the cat receptors detect bitter-tasting compounds. Research published earlier this year by another team of researchers showed that some of the cat taste receptors are especially sensitive to bitter compounds, and even more sensitive to denatonium than the same receptor in humans.

Perhaps cats are also more sensitive to bitter chemicals than dogs, or they may detect a greater number of bitter compounds in their everyday diet. Food that tastes bland to us or to a dog could be an unpleasant gastronomic experience for cats. So rather than branding cats as picky, perhaps we should think of them as discerning feline foodies.

The ConversationCreative Commons

Hannah Rowland is a Lecturer in Ecology and Evolution & Research Fellow at Zoological Society of London, University of Cambridge.  This article was originally published on The Conversation. Read the original article.

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Early humans had to feminize to dominate the planet

By Mark Maslin, University College London 
June, 2015

I have always wondered why our species Homo sapiens, that evolved in Africa about 200,000 years ago, seemed to do nothing special for the first 150,000 years. Because it is not until about 50,000 years ago that the first sign of creative thinking emerged with beautiful cave paintings found in Spain, France and Indonesia.

Around the same time a new sub-species referred to as anatomically modern humans or Homo sapiens sapiens appears. Anatomically modern humans were more slender than their earlier ancestors; they had less hair, smaller skulls. They looked basically like us.

But these changes weren’t just cosmetic. Two recent papers throw some light on how the revolutionary development of smaller and more fine-boned humans influenced the growth of cooperative culture, the birth of agriculture and human dominance of the planet.

The first is an analysis of the fossilised skulls of our ancestors during this transitional period, carried out by a team led by Robert Cieri at the University of Utah and published in the journal Current Anthropology.

Cieri and colleagues found the brow ridge (the bony bit above the eye sockets) became significantly less prominent and male facial shape became more similar to that of females. They referred to this as craniofacial feminisation, meaning that as Homo sapiens slimmed down their skulls became flatter and more “feminine” in shape.

They think this must have been due to lower levels of testosterone, as there is a strong relationship between levels of this hormone and long faces with extended brow ridges, which we may perceive today as very “masculine” features.

People with lower levels of testosterone are less likely to be reactively or spontaneously violent, and therefore this enhanced social tolerance. This has a huge knock-on effect. As seen among humans today, we live in populations with extremely high densities with an incredible amount of social tolerance. So a reduction in reactive violence must have been an essential prerequisite for us to be able to live in larger groups and develop cooperative culture.

The idea that humans became more feminine, less aggressive and thus could cooperate in large groups is certainly very intriguing as it would have allowed individuals with different skills to be valued and be reproductively successful due to the reduction of particularly male-male violence. In most primates the physically strongest male tends to dominate, but in early humans the smartest or the most creative males may have come to the forefront.

Human skulls showing feminization in the late Stone Age. Cieri et al

Human skulls showing feminization in the late Stone Age. Cieri et al

The question remains, how did we become more feminine, less violent and more creative? A second paper in the journal Animal Behaviour led by Brian Hare at Duke University may throw some light on to this. He and colleagues compared chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) in West Africa, two closely related species living in very similar environmental conditions either side of the Congo River.

One key distinction between the two species is the size difference between males and females, their “dimorphism”. Male chimps are significant larger than females, whereas the difference in bonobos is much smaller. This difference is driven by different levels of testosterone. The size is just one manifestation of deeper differences that also show up in how the animals interact with one another. Chimpanzees, particularly males are very aggressive, but violence within or between groups is almost non-existent among bonobos. As both these species have a common ancestor there must have been strong selection going on to feminise the bonobos.

Hare and colleagues suggest a process of self-domestication whereby violent individuals are punished and prevented from reproducing. The traits exhibited by bonobos are very similar to the changes observed in species that humans have domesticated such as dogs, cows, guinea pigs and foxes. They postulate the reason why bonobos were able to feminise and chimpanzees did not, is because on the Eastern side of the Congo where the chimps live they are in direct competition with gorillas, whereas the bonobos on the western side have no competition.

Harvard professor Richard Wrangham, a co-author of the Hare paper, suggested in a recent talk that the same process may have happened to early humans.

This feminisation through self-domestication may not only have made humans more peaceful and evenly sized, but may have also produced a more sexually equal society.

A recent study in the journal Science by colleagues of mine at UCL showed that in hunter-gatherer groups in the Congo and the Philippines decisions about where to live and with whom were made equally by both genders. Despite living in small communities, this resulted in hunter-gatherers living with a large number of individuals with whom they had no kinship ties. The authors argue this may have proved an evolutionary advantage for early human societies, as it would have fostered wider-ranging social networks, closer cooperation between unrelated individuals, a wider choice of mates, and reduced chances of inbreeding.

The frequent movement and interaction between groups also fostered the sharing of innovations, which may have helped the spread of culture. As Andrea Migliano, the leader of the study points out, “sex equality suggests a scenario where unique human traits, such as cooperation with unrelated individuals, could have emerged in our evolutionary past.”

It may have only been with the rise of agriculture that an imbalance between the sexes reemerged, as individual men were suddenly able to concentrate enough resources to maintain several wives and many children. Indeed the Robert Cieri led study does show slightly more masculine facial shapes emerging in recent agriculturalists relative to early humans and recent human foragers.

So at the moment we have some tentative hints of what may have happened between 50,000 and 10,000 years ago. Humans may have undergone self-domestication and over many generations weeded out those individuals that were unable to control their reactive violence.

This is not as far-fetched as it sounds – studies of the Gebusi tribe in Papua New Guinea by Bruce Knauft showed significant levels of male mortality due to the tribe deciding that an individual’s behaviour is so intolerable that for the good of the tribe they must be killed.

So human proactive violence – that is, thought out, discussed and planned violence – is used to curb, control and cull reactively violent individuals. This process combined with female mating choices over thousands of years could have selected for males with lower testosterone and more feminine features, which leads to a much more gender-equal society and the start of our cumulative culture.

The ConversationCreative Commons

Mark Maslin is Professor of Climatology at UCL. This article was originally published on The Conversation. Read the original article.

 

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Facts and Opinions is an online journal of select and first-rate reporting and analysis, in words and images: a boutique for slow journalism, without borders. Independent, non-partisan and employee-owned, F&O performs journalism for citizens, funded entirely by readers. We do not carry advertising or solicit donations from foundations or causes. Subscribe by email to our free FRONTLINES, a blog announcing new works, and the odd small tale. Look for evidence-based reporting in Reports; commentary, analysis and creative non-fiction in OPINION-FEATURES; and image galleries in PHOTO-ESSAYS. Some of our original works are behind a paywall, available with a $1 site day pass, or with a subscription from $2.95/month – $19.95/year. If you value journalism, please help sustain us.

 

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Evolutionary insights underscore need for new natural-world taxonomy

 

Carolus Linnaeus's first, or 1735, edition of Systema Naturae is the "In the Beginning" text of animal and plant classification. Shown is a scam of Table of the Animal Kingdom (Regnum Animale).

Carolus Linnaeus’s first, or 1735, edition of Systema Naturae is the “In the Beginning” text of animal and plant classification. Shown is a scan of Table of the Animal Kingdom (Regnum Animale).

By Ben Holt and Knud Andreas Jønsson, Imperial College London
November 15, 2014

A cat is, of course, a cat. Lions are cats too, as are leopards, lynxes and so on – the “Felidae” family contains 41 species in total. But what about other closely related species such as hyenas or mongooses? These animals are not in the cat family: they are cat-like “Feliformia”, but are in their own separate families.

So why are some species grouped together in the same families and others separated into different families? It might surprise you to learn that there is no general answer to this question, despite the fact that we now know a lot about evolutionary relationships for groups like mammals. Science has moved on and so should the way we classify life on earth.

The science of “taxonomy” categorises species (such as Homo sapiens, in the case of humans) into broader groups such as orders (for example primates) or kingdoms (for example Animalia). Current approaches date back to 18th century Swedish biologist Carl Linnaeus. Linnaeus saw all living things as creations of god and sorted them into hierarchical groups according to how similar or different he perceived them to be.

Evolution hadn’t even been theorised in Linnaeus’s lifetime. These days, we have a huge amount of DNA and fossil data to map out how, and when, one species branched out from another. Modern taxonomists therefore aim to base their decisions on evolutionary relationships, but the process remains subjective and there has been no attempt to standardise practises across all species on earth.

Taxonomic groups such as birds and mammals represent “classes” under current classification systems, which are then subdivided into orders, families and genera. Our research uses the latest evolutionary trees for birds and mammals to demonstrate that current taxonomic classifications are highly inconsistent.

To resolve this issue, we can use evolutionary trees directly in order to consistently create taxonomic ranks. We applied a technique known as “temporal banding” to the bird and mammal trees, producing new classifications that reduce amount of evolutionary divergence within groups to a minimum. Under these new schemes, 70 per cent of bird groups and 61 per cent of mammal groups need to be revised.

Biologists have generally determined the major taxonomic orders fairly consistently – we found that the big groups, such as parrots, hummingbirds and swifts, rabbits and hares, opossums and so on, have been made in a fairly constant manner. But classification can zoom in much further than this – there are 372 species of parrot, for instance, grouped into 86 genera. These more specific groupings are sometimes not much better than if they had been defined at random.

Our study considered relationships within taxonomic groups that scientists use on a daily basis. This isn’t just a debate for scientists though, as these classifications have an important impact on what species we choose to study and how we communicate our observations of the natural world.

The New Zealand rockwren (Xenicus gilviventris) provides an excellent example of this. These are fairly unique species, not closely related to other species of wren, and are of conservation concern. When we classified bird species in a consistent manner, New Zealand rockwrens became their own taxonomic order, highlighting their evolutionary uniqueness to everyone.

In another example, the dog family (Canidae) and the cat family (Felidae) currently have similar numbers of species but, under our standardised system, the cat family is expanded to include civets, hyenas, mongooses, fossas, and other relatives. As a result the new cat family contains four times more species than the dog family, which remained unchanged.

Since these new families are defined on a consistent basis, they tell us something about the evolution of these groups: cats have diversified far more than dogs over a similar time period.

An example from the birds sees the owls, which are currently in the order Strigiformes, split in to two new orders: barn owls and true owls. These two groups are too distantly related to be lumped together.

Such grouping by evolutionary divergence is controversial and many taxonomists will still feel that classifications should be focused on physical characteristics – what we call morphological similarity. However, this focus on what animals look like just adds inconsistency.

A classification system based on morphology makes sense in theory, but in practise it leads to a high level of subjectivity. It is hard to imagine an objective approach based on morphology that could be applied across the entirety of life on earth. How could someone evaluate the physical difference between a bacterium and an animal?

We are currently undergoing a revolution in DNA technology and our understanding of the tree of life is improving quickly. Our study demonstrates an approach that can consistently incorporate this information into the way we classify and view the natural world.

Creative Commons

The Conversation

Ben Holt receives funding from the Grand Challenges in Ecosystems and Environment Initiative, www3.imperial.ac.uk/ecosystemsandenvironment/grandchallenges.

Knud Andreas Jønsson receives funding from the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme (FP7/2007-2013) under REA grant agreement n° PIEF-GA-2011-300924. Knud Andreas Jønsson is affiliated with Department of Life Sciences, Imperial College London, Silwood Park campus, Ascot SL5 7PY, U.K; and Department of Life Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, UK .

This article was originally published on The Conversation. Read the original article.

 

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