Earliest bat shows flight developed before echolocation

Blogging on Peer-Reviewed ResearchTheir heads and bodies of bats have amassed an extraordinary array of adaptations that have make them lords of the night sky. Today, the thousand-plus types of bats make up a fifth of living mammal species. Richard Dawkins once described the evolution of bats as “one of the most enthralling stories in all natural history” and as of this week, the story has a clearer beginning.

OnychonycterisThe success of bats hinges on two key abilities: their mastery of flight, a feat matched only by birds and insects; and echolocation, the ability to navigate their way through pitch-blackness by timing the reflections of high-pitched squeaks. For evolutionary scientists, the big question has always been: which came first?

The ‘clawed bat’

Until now, fossil bats haven’t provided any clues for all of them show signs of both echolocation and flight. But a stunning new fossil, discovered by Nancy Simmons from the American Museum of Natural History is an exception and it provides a categorical answer to the long-running debate – the earliest bats could fly but could not echolocate.

The new creature hails from the Green River in Wyoming and is known as Onychonycteris, meaning “clawed bat”. Its fossils date back to about 52.5 million years ago and by comparing it to other prehistoric bats, Simmons found that it is the most ancient member of this lineage so far discovered. It acts as a ‘missing link’ in bat evolution, much like the famous Archaeopteryx hinted that birds may have evolved from dinosaurs.

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Whales evolved from small aquatic hoofed ancestors

Blogging on Peer-Reviewed ResearchTravel back in time to about 50 million years ago and you might catch a glimpse of a small, unassuming animal walking on slender legs tipped with hooves, by the rivers of southern Asia. It feeds on land but when it picks up signs of danger, it readily takes to the water and wades to safety.

Indohyus

The animal is called Indohyus (literally “India’s pig”) and though it may not look like it, it is the earliest known relative of today’s whales and dolphins. Known mostly through a few fossil teeth, a more complete skeleton was described for the first time last week by Hans Thewissen and colleagues from the Northeastern Ohio Universities. It shows what the missing link between whales and their deer-like ancestors might have looked like and how it probably behaved.Whales look so unlike other mammals that it’s hard to imagine the type of creature that they evolved from. Once they took to the water, their evolutionary journey is fairly clear. A series of incredible fossils have documented their transformation into the masterful swimmers of today’s oceans from early four-legged forms like Pakicetus and Ambulocetus (also discovered by Thewissen). But what did their ancestors look like when they still lived on land?

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Chimps trump university students at memory task

Blogging on Peer-Reviewed ResearchWe humans aren’t used to having our intelligence challenged. Among the animal kingdom, we hold no records for speed, strength or size but our vaunted mental abilities are unparalleled. That is, until now. New research from Kyoto University shows that some chimps have a photographic memory that puts humans to shame.

Chimps trump university students at memory taskSana Inoue and Tetsuro Matsuzawa have found that young chimps have an ability to memorise details of complex images that is literally super-human. Boffin chimp Ayumu, outperformed university students in memory tasks where they had to rapidly memorise numbers scattered on a touchscreen and press them in numerical order.

This is the first time that an animal has outmatched humans in a mental skill. Recently, I’ve previously blogged about animals that show abilities once considered to be uniquely human, including jays that can plan for the future, rats that know how much they know, cultured chimps, tool-combining crows, and discriminating elephants.

But in all these cases, the animals merely showed that they could do similar types of mental feats to us. They never challenging our abilities in terms of complexity or scale. Simply put, a crow may be able to combine tools together, but it’s never going to be able to engineer a computer.

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The social life of our extinct relatives

Blogging on Peer-Reviewed ResearchOne of our extinct evolutionary cousins, Paranthropus robustus, may have walked like a man but it socialised like a gorilla. Using only fossils, UCL scientists have found that P.robustus males were much larger than females, competed fiercely for mates and led risky lives under heavy threat from predators.

I wrote an article about the cool new finding for Nature Network. Here’s the opening and you can read the full article here.

A single fossil can tell you about the shape, diet and movements of an extinct animal but with enough specimens, you can reconstruct their social lives too.

Charles Lockwood of University College London used an unusually large collection of fossils to peer back in time at the social structures of one of our closest extinct relatives, Paranthropus robustus, which inhabited southern Africa between 1.2 million and 2 million years ago.

Envious capuchin monkeys react badly to raw deals

Blogging on Peer-Reviewed ResearchIn my last post, I wrote about two studies which showed that even bacteria cooperate towards a common goal and can be infiltrated by cheating slackers. In one of the studies, cheaters were eventually weeded out through natural selection because their rise to prominence created such havoc for the group that each individual bacterium suffered.

Envious capuchin monkeys react badly to raw dealsIn this scenario, slacking wasn’t punished but merely reduced over time. But more complex creatures, like humans, have the capacity to actually recognise unfairness and punish it directly. It turns out that we’re very keen on doing that; so strong is our innate sense of justice that we’ll often punish cheaters at our own expense.

Two years ago, Sarah Brosnan and Frans de Waal at the Yerkes National Primate Research Center found that brown capuchin monkeys also react badly to receiving raw deals. Forget bananas – capuchins love the taste of grapes and far prefer them over cucumber. If monkeys were rewarded for completing a task with cucumber while their peers were given succulent grapes, they were more likely to shun both task and reward.

That suggested that the ability to compare own efforts and rewards with those of our peers evolved much earlier in our history than we previously thought. Of course, animal behaviour researchers always need to be careful that they’re not reading too much into the actions of the animals they study.

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Elephants smell the difference between human ethnic groups

It’s tempting to think that elephants have their own PR agency. Just last week, their mighty reputation was damaged by the revelation that they are scared away by bees but they have bounced back with a new study that cements their standing among the most intelligent of animals.

A wary elephant catches the scent of MassaiLucy Bates and colleagues from the University of St Andrews have found that African elephants (Loxodonta africana) can tell the difference between different human ethnic groups by smell alone. They also react appropriately to the level of threat they pose.

The Massai, for example, are a group of cattle-herders, whose young men sometimes prove themselves by spearing elephants. Clearly, it would pay to be able to sort out these humans from those who post little threat, like the Kamba.

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Buzzing bees scare elephants away

It’s a myth that elephants are afraid of mice, but new research shows that they’re not too keen on bees. Even though they fearlessly stand up to lions, the mere buzzing of bees is enough to send a herd of elephants running off. Armed with this knowledge, African farmers may soon be able to use strategically placed hives or recordings to minimise conflicts with elephants.

Elephants turn tail at the sound of beesIain Douglas-Hamilton and Fritz Vollrath from Kenyan conservation charity Save the Elephants first suspected this elephantine phobia in 2002, when they noticed that elephants were less likely to damage acacia trees that contained beehives.

Animals as powerful as the African elephant can go largely untroubled by predators. Their bulk alone protects them from all but the most ambitious of lion prides.

But these defences do nothing against the African bees, which can sting them in their eyes, behind their ears and inside their trunks. Against these aggressive insects, the elephants are well justified in their caution and local people have reported swarms of bees chasing elephants for long distances.

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Sabre-toothed cats had weak bites

The sabre-toothed cat is one of the most famous prehistoric animals and there is no question that it was a formidable predator, capable of bringing down large prey like giant bison, horses, and possibly even mammoths. The two massive canines – the largest teeth of any mammal – are a powerful visual. But while they were clearly powerful weapons, scientists have debated their use for over 150 years.

Now, a new study shows that Smilodon, the most iconic of the sabre-tooths, had a surprisingly weak bite. They were a precision weapon that were used to deliver a single, final wound to an already subdued victim – the equivalent of an assasin’s stiletto rather than a swordsman’s blade.

Earlier suggestions pictured Smilodon using its teeth to hang onto the back of large prey, to slash their abdomens open, or to impale them at the end of a flying pouce. One of the most popular theories said that the cat would have used its teeth to sever arteries and airways with a decisive bite to the throat – a quicker technique than the suffocating neck bites used by modern lions.

Working out how strongly Smilodon could bite would go a long way towards deciding on one of these theories and to do that, palaeontologists have studied the animal’s fossilised skull. Even then, opinions have gone either way depending on which bit of the skull they looked at. The muscle attachment points suggest it has small jaw muscles, but the bite could have been powered from the neck. The lower jaw is smaller, but strongly built, lending weight to the idea of a powerful bite.

To get some clearer answes, Colin McHenry and colleagues from the University of Newcastle, Australia decided to put Smilodon‘s skull through a digital crash-test. They used a technique called ‘finite element analysis‘ or FEA, which is typically used in mechanical engineering and crash-testing for cars.

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Genetic study puts damper on gray whales’ comeback

The eastern Pacific gray whale has bounced back from the brink of extinction to a healthy population of 22,000 individuals. But by measuring the genetic diversity of these whales, scientists have estimated that the original population was up to five times larger. The whales aren’t out of the danger zone yet, and climate change may explain why.

Twenty-two thousand sounds like a huge number. It’s happens to be number of eastern Pacific gray whales currently swimming off the coast of North America. It’s certainly much larger than 140, the number of whales that aboriginal people of this area are allowed to hunt. And it’s far, far bigger than zero, the population size that the whales were rapidly approaching in the mid 20th century.

The gray whale hasn’t fully recovered from a century or more of huntingObviously, it’s all relative. Twenty-two thousand is still much less than ninety-six thousand. That’s the size of the original gray whale population and it’s three to five times the current count. Not exactly cause for conservational complacency, then.

Previously, conservationists and whalers alike could only speculate on the number of whales that lived before their flirtation with extinction. But now, Elizabeth Alter and Stephen Palumbi from Stanford University have managed to pin down a figure by looking at the genetic diversity of living whales. And their results suggest that despite a rebound that Hollywood would envy, the grays are still a pale shadow of their former strength.

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Ground squirrels use infrared signals to fool heat-seeking rattlesnakes

Rattlesnakes can track their prey using the infrared light given off by the warm bodies. But ground squirrels can use this super sense against the snakes. By pumping blood into their tails, they give off infrared signals that fool the snakes’ heat-seekers.

Ground squirrels use infrared signals to fool rattlesnakesIt seems like an uneven match. In one corner, the unassuming California ground squirrel (Spermophilus beechyi), 30cm in length. In the other, the northern Pacific rattlesnake (Crotalus oreganos), more than twice the length of the squirrel, and armed with hinged fangs that pack a lethal venom. But thanks to a cunning adaptation, the squirrel often gets an unexpected upper hand in this bout.

Squirrels vs snakes

Ground squirrels live in a series of burrows that keep them out of reach of most predators. Snakes, however, have exactly the right body plan for infiltrating long sinuous tunnels, and it’s not surprising that they are the squirrels’ major predators. It’s equally unsurprising that the squirrels have developed ways of defending themselves against snakes.

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Altruistic chimpanzees clearly help each other out

Many scientists have argued that only humans show true altruistic behaviour. But a group of Ugandan chimps is set to change all that by showing clear signs of true selflessness, helping other unrelated chimps with no desire for reward.

Why do we help each other, instead of constantly looking out for ourselves? This is one of the most compelling questions in modern biology. Evolutionary and game theory alike predict that selfish behaviour should be the rule with altruism the exception, and animal experiments have largely supported this idea.

Nature, ‘red in tooth and claw’, is painted as a fierce competition between selfish individuals and their even more selfish genes. In this stark landscape, true altruism is a rare quality and some scientists believe that it’s one that only we humans possess.

Even our closest relatives, chimpanzees, are not exempt from this dividing line. Certainly, there is a large amount of anecdotal evidence of chimps helping each other or even saving each others’ lives. But some thinkers believe that this behaviour, along with other seemingly selfless animal acts, is actually self-serving in one of two ways.

The chimps could be helping their relatives in order to advanced the spread of its own genes, which family members are likely to share. Or they could be doing a favour for another individual, in the knowledge that it will be repaid later on. Either way, it’s the do-gooder that eventually benefits.

Humans, on the other hand, seem to flaunt this rule. We often help others who are not relatives and who are unlikely to repay the favour. We go out of our way to be helpful, and sometimes even risk personal harm to do so.

Two tests for altruism

Now, Felix Warneken and colleagues form the Max Planck Institute for Evolutionary Anthropology have found compelling evidence that we are not alone. Contrary to previous studies, they have found that chimps also behave altruistically in a very human way. They help out unrelated strangers without expectation of reward, and even go to great lengths to do so.

Warneken studied 36 chimps at Ngamba Island Chimpanzee Sanctuary, Uganda and looked at their willingness to help a human handler. To minimise the effect of any human-chimp bond, he only looked at chimps that were born in the wild, and used experimenters who the chimps had never seen before.

In the first test, the chimps saw a human unsuccessfully trying to reach a stick that they themselves could reach. Warneken found that chimps were all too happy to pass the stick across (video), regardless of whether they were rewarded with a banana or not. In fact, the only thing that affected their readiness to lend a hand was whether the human was struggling for the stick or just passively staring at it.

He found the same thing when he ran a similar set-up with a 36 eighteen-month-old human toddlers, but with toy cubes in lieu of sticks (video). At that age, a baby’s mental abilities are thought to similar to those of chimps, and indeed the only real difference between the two was that the babies were quicker with their assistance.

Passing a stick across is obviously fairly easy but would altruism persist if there was effort involved? Warneken tested this by changing the experiment so that the chimps had to climb over a raceway (video) and the toddlers had to walk past a series of obstacles (video). Those that helped in the first test were happy to do so in the second, again without any rewards.

The third and most important test

A skeptic might argue that this doesn’t show anything. During their stay at the sanctuary, the chimps could have learned that helping any one of their strange two-legged keepers was worth it. The acid test then, was to see if the chimps would help each other.

The first chimp – the subject – could only get into a room with food by lifting the chain attached to its door. But it couldn’t reach the chain – only a second chimp, the observer, could do that. And once again, the chimps proved their selflessness, lifting the chain for their fellow chimps the vast majority of the time (video).

This striking result flies in the face of other studies, which have failed to find altruistic behaviour between chimps. But in a related commentary, Frans de Waal, an international expert of ape behaviour, claimed that these were more tests of generosity than selfishness.

They created specific situations where chimps were motivated to look out for themselves and the species can’t be judged on these scenarios alone. It would be like claiming that all people are selfish after watching the self-interested behaviour of commuters. Failing to show altruism is not the same as proving that it doesn’t happen.

But it does happen – Warneken’s experiments are striking indicators of that. In the third test, the chimps were unrelated, the observer had no chance of getting a share of the food, and their roles were never reversed so there were no opportunities for payback. Clearly, humans are not alone in our desire to help each other. Chimps are now our fellows in altruism and it’s likely that our common ancestor did the same.

What this means for the altruism debate

It’s particularly fascinating that rewards in the first two tests didn’t affect the chimps’ behaviour. This suggests that chimps don’t continually analyse the pros and cons of helping their fellow – if they did, the reward would have motivated them to help even more often.

Instead, de Waal believes that the chimps have evolved psychological systems that steer them towards selflessness. In essence, natural selection has done the analysis for them and decided that altruistic behaviour works to its advantage in the long run. Selfless behaviour then, can evolve for selfish reasons, and that strikes to the very core of the debate on altruism.

Spend enough time reading about this field of research, and you could be forgiven for thinking that some scientists are taking cynical glee at ‘explaining away’ altruism. The extreme reductionist view is that discovering the evolutionary origins of selfless behaviour discredits that behaviour, somehow making it less worthy. As Robert Trivers put it, these models are designed to “take the altruism out of altruism”.

But this viewpoint is blinkered and too focused on the past. Evolutionary explanations can help us understand where an unusual behaviour like selflessness comes from, but they do not alter the value of those behaviours. They can tell us about how a behaviour arose, but not about an animal’s reasons for behaving in that way here and now.

Take sex. Its adaptive benefits are clear – it continues the line and promotes genetic diversity. But animals don’t consider the issue of reproduction every time they have sex and for the most part, humans actively deny it!

According to de Waal, we should now turn our attention to the psychological processes that foster altruism in chimps, and how they are different from those that work in our own minds. Do chimps share our strong sense of empathy, that fuels selflessness by letting us identify with the emotions and needs of others. Do their cultures, like ours, punish and vilify selfish behaviour?

References: Warneken, Hare, Melis, Hanus & Tomasello. 2007. Spontaneous altruism by chimpanzees and young children. PLOS Biology 5: e184.
de Waal. 2007. With a little help from a friend. PLOS Biology 5: e190.

Related posts on chimps:
Chimps show that actions spoke louder than words in language evolution
Not so unique – the chimpanzee Stone Age, and our place among intelligent animals
Cultured chimps pass on new traditions between groups
Chimpanzees make spears to hunt bushbabies

Related posts on altruism:
Army ants plug potholes with their own bodies

Images: from BBC, Nature, Jane Goodall Institute and Ngamba Sanctuary

Resistance to an extinct virus makes us more vulnerable to HIV

Immunity to viral infections sounds like a good thing, but it can come at a price. Millions of years ago, we evolved resistance to a virus that plagued other primates. Today, that virus is extinct, but our resistance to it may be making us more vulnerable to the present threat of HIV.

Many extinct viruses are not completely gone. Some members of a group called retroviruses insinuated themselves into our DNA and became a part of our genetic code.

Our resistance to the ancient PtERV1 may explain our vulnerability to HIV.Indeed, a large proportion of the genomes of all primates consists of the embedded remnants of ancient viruses. Looking at these remnants is like genetic archaeology, and it can tell us about infections both past and present.

Viral hitchhikers

When retroviruses (such as HIV, right) infect a cell, they insert their own DNA into their host’s genome, using it as a base of operations. From there, the virus can pop out again and make new copies of itself, re-infect its host or move on to new cells.

If it manages to infect an egg or sperm cell, the virus could pass onto the next generation. Hidden inside the embryo’s DNA, it becomes replicated trillions of times over and ends up in every single one of the new individual’s cells.

These hitchhikers are called ‘endogenous retroviruses’. While they could pop out at any time, they quickly gain mutations in their DNA that knocks out their ability to infect. Unable to move on, they become as much a part of the host’s DNA as its own genes.

In 2005, a group of scientists led by Evan Eichler compared endogenous retroviruses in different primates and found startling differences. In particular, chimps and gorillas have over a hundred copies of the virus PtERV1 (or Pan troglodytes endogenous retrovirus in full). Our DNA has none at all, and this is one of the largest differences between our genome and that of chimps.

Our ancestors shared a similar geographical range to the ancestors of these apes, and would have encountered the same viruses, including PtERV1. And yet, we were spared from infection, while the apes were not. Why?

Protecting against an ancient virus

HIV daughter particles - retroviruses like HIV can integrate into a host’s DNAShari Kaiser and colleagues from the University of Washington and the Fred Hutchinson Cancer Research Center believed that the answer lies in a protein called TRIM5α that defends us from retroviruses. It latches onto the outer coat of incoming viruses, and tells other proteins to dismantle or destroy them.

Other primates have their own versions of TRIM5α that protect against a different range of viruses, and the protein has evolved dramatically in different primate lineages. Kaiser believed that our version of TRIM5α protected us from PtERV1, while that of other apes did not. To test her idea, all she had to do was to resurrect a dead virus.

Obviously, PtERV1 is long extinct, but its remnants exist inside the genomes of chimps. Kaiser compared dozens of these remnants and by identifying common elements, she worked out the ancestral sequence of the virus.

She created a small part of PtERV1 and fused it with bits of a modern virus, MLV, to create a fully-functioning hybrid. To nullify any potential for spread beyond the lab, she crippled the virus so that it could infect once and only once.

The reconstructed virus successfully infected mammal cells in a lab, but not when human TRIM5α was around. The guardian protein demolished the virus’s infectivity, reducing it by more than 100 times. As Kaiser predicted, our genomes are free of PtERV1 because TRIM5α killed it before it could reach our DNA.

Resist one virus, succumb to another

TRIM5a provides antiviral protection that seesaws between different virus species.But this protection carries a price – it makes us vulnerable to HIV. Over the course of primate evolution, humans made an important change in the amino acid sequence of TRIM5α that allowed the protein to fight off PtERV1. When Kaiser changed the protein back to its original form, she found that it gained the ability to fight off HIV, but lost its resistance to PtERV1.

In fact, Kaiser found that no primate species has a version of TRIM5α capable of fighting off both viruses at the same time. We are resistant to ptERV1 and vulnerable to HIV, but chimps, gorillas, baboons and rhesus macaques show the reverse strengths and weaknesses.

When it comes to retrovirus immunity, there is no win-win situation. Having defeated one enemy, we have unwittingly made ourselves more vulnerable to another.

Reference: Kaiser, Malik & Emerman. 2007. Restriction of an extinct retrovirus by the human TRIM5a antiviral protein. Science 316:1756 – 1758.

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Related posts on viruses and virus evolution:
The upside of herpes – when one infection protects against another
Viruses evolve to be more infectious in a well-connected population
Round peg, square hole – why our bird flu drugs are a fluke

Related posts on new medical discoveries:
Drugs that work against each other could fight resistant germs
The secret of drug-resistant bubonic plague
Neutralising anthrax – moving closer to a cure

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