If you watch chimpanzees from different parts of Africa, you’ll see them doing very different things. Some use sticks to extract honey from beehives, while others prefer leaves. Some use sticks as hunting spears and others use them to fish for ants. Some drum on branches to get attention and others rip leaves between their teeth.
These behaviours have been described as cultural traditions; they’re the chimp equivalent of the musical styles, fashion trends and social rules of humans. They stem from the readiness of great apes to ape one another and pick up behaviours from their peers. But a new study complicates our understanding of chimp cultures. Kevin Langergraber at the Max Planck Institute for Evolutionary Anthropology has found that much of this variation in behaviour could have a genetic influence.
Not Exactly Pocket Science is a set of shorter write-ups on new stories. It is meant to complement the usual fare of detailed pieces that are typical for this blog.
Chimp see, chimp do – back-scratching technique passes among disabled chimps
Tinka’s hands are paralysed. His fingers are permanently flexed, he can’t bend his wrists and to top it all off, he has a chronic skin condition. His body itches frequently and without dextrous hands, he can’t scratch himself properly. Fortunately, Tinka is an ingenious fellow. He uses his motionless hands to grab a liana (a thick, woody vine) and, stretching it taut, he rubs his itching body against it. Tinka’s a chimpanzee and he has found a way of getting to those hard-to-reach places, like a human towelling their back.
Tinka’s a member of the Sonso chimp community in Uganda, which has high rates of disability, inflicted by man-made snares. The snares were intended for duiker and bush pig, but with hundreds in the area, some chimps inevitably got caught. The snares have been removed but not before they inflicted permanent handicaps on a third of the Sonso chimps. But from this tragedy came an opportunity to study the spread of cultural traditions in wild chimps – an opportunity that’s been seized by Catherine Hobaiter and Richard Byrne form the University of St Andrews.
It’s clear that chimps can pick up new traditions from one another in captivity but their ability to do so in the wild is unclear. In natural conditions, it’s very hard to spot the birth of a new behaviour and to identify the individual who started it. It’s also difficult to work out if others are copying the innovator or just performing acts that were already within their repertoire. But Tinka bucks the trend. His liana-scratch technique is his invention. No other chimp in Sonso, or anywhere else in Africa, does the same thing. And Hobaiter and Byrne have found that at least 6 other chimps have taken up the technique, all of whom lived in the same area as Tinka.
There’s no element of active teaching here. After merely watching Tinka perform his special move, the apeing apes could do it themselves sometime later. Chimp see, chimp do. What’s more, many of these imitators aren’t handicapped and the technique doesn’t seem to offer them any benefits – they could just scratch or groom themselves if they wanted. Hobaiter and Byrne think that this is just a “behavioural fad”, reflective of the chimpanzee’s natural predilection for copying its peers.
Reference: PLoS ONE: http://dx.doi.org/10.1371/journal.pone.0011959
Aphids drop and roll when they detect mammal breath
For a colony of aphids, there can be few fates as humiliating as being suddenly eaten by a passing goat. Plant-eating mammals pose a great threat to plant-eating insects. One chomp can unwittingly take out an entire colony. But as hungry mammals get closer, they give off a warning –hot, wet breath. Pea aphids take this as a cue to stop, drop and roll – they let go of their plant en masse and fall away from the jaws of death.
Moshe Gish discovered this unusual strategy by allowing a goat to feed on alfalfa plants infested with pea aphids. He found that, at the last minute, two-thirds of the colonies dropped to the ground. When he flicked the leaves, only a quarter of the colonies dropped off and when he cast a shadow overhead, they did nothing. It was the animal’s breath that did it.
The aphids also drop when they sense predators like ladybirds, but they do so more quickly and consistently when they sense mammal breath. Gish could even make individual aphids abandon leaf by directing a puff of goat or human breath at them using a tube. By playing around with these artificial puffs, he found that it wasn’t the presence of any particular chemical that did the trick, but the combination of heat and humidity.
This is the first time that anyone has found an animal that defends itself against being accidentally eaten by plant-eaters. The ability to detect mammal breath isn’t unique to aphids though – mosquitoes use the same skill to find a blood meal, while other insects and arthropods respond to the hot and humid vapours by releasing toxic chemicals. But for the generally defenceless pea aphid, mammal breath means only one thing: drop or die.
Reference: Current Biology, citation to be confirmed
Men who think that size really matters should probably not think too hard about the Y chromosome. This bundle of genes is the ultimate determinant of manliness, and it happens to be a degenerate runt. Over a few hundred million years, it has shrunk considerably, jettisoning around 97% of its original genes. Where it was once a large library of genes, now it’s more a struggling independent bookstore. This loss of information defined the youth of the Y chromosome but nowadays, things are different. Renovation is the order of the day.
Jennifer Hughes from MIT revealed the recent history of the Y chromosome by comparing the human and chimp versions. They are incredibly different. They have rapidly evolved since the two species last shared a common ancestor 6 million years ago. In this relatively short span of time, the two Ys have accumulated differences that other chromosomes would take 310 million years to build up. It’s the sort of genetic disparity you’d expect to see between humans and chickens, not between us and our closest relatives!
This drastic remodelling contradicts the current view of Y evolution, which suggests that the chromosome has stagnated. It has lost so many of its genes that some scientists thought it might waste away altogether within another 10 million years. But rumours of its impending demise had been greatly exaggerated. In 2005, Hughes showed that Y isn’t shrinking at the breakneck pace of old.
That result was based on a comparison of individual genes on the two chromosomes. Since then, Hughes has managed to fully sequence the chimp Y, the first time this has been accomplished for a non-human animal. Considering how small the chromosome is, sequencing it is remarkably tricky. It has lots of long, repetitive sequences that are subtly different and hard to tell apart through conventional means.
Nonetheless, Hughes managed it. By comparing the two sequences, she found that the Y chromosome is an island of difference in a sea of resemblance. The chimp and human genomes are famous for their similarity; they’re a 98.8% match for each other. And indeed, where the chimp and human Y sequences align, they are a 98% match, just like the rest of the genome. But they don’t align very well. Around 30% of the chimp Y chromosome has no human counterpart and vice versa.
If you tickle a young chimp, gorilla or orang-utan, it will hoot, holler and pant in a way that would strongly remind you of human laughter. The sounds are very different. Chimp laughter, for example, is breathier than ours, faster and bereft of vowel sounds (“ha” or “hee”). Listen to a recording and you wouldn’t identify it as laughter – it’s more like a handsaw cutting wood. But in context, the resemblance to human laughter is uncanny.
Apes make these noises during play or when tickled, and they’re accompanied by distinctive open-mouthed “play faces”. Darwin himself noted the laugh-like noises of tickled chimps way back in 1872. Now, over a century later, Marina Davila Ross of the University of Portsmouth has used these noises to explore the evolutionary origins of our own laughter.
Davila Ross tickled youngsters of all of the great apes and recorded the calls they make (listen to MP3s of a tickled chimp, gorilla, bonobo and orang-utan). She used these recordings to build an acoustic family tree, showing the relationships between the calls. Scientists regularly construct such trees to illustrate the relationships between species based on the features of their bodies or the sequences of their genes. But this is the first time that anyone has applied the same technique to an emotional expression.
The tree linked the great apes in exactly the way you would expect based on genes and bodies. To Ross, this clearly shows that even though human laughter sounds uniquely different, it shares a common origin with the vocals of great apes. It didn’t arise out of nowhere, but gradually developed over 10-16 million years of evolution by exaggerating the acoustics of our ancestors. At the very least, we should now be happy to describe the noises made by tickled apes as laughter without accusations of anthropomorphism, and to consider “laughter” as a trait that applies to primates and other animals
Chimps are known to make a variety of tools to aid their quest for food, including fishing sticks to probe for termites, hammers to crack nuts and even spears to impale bushbabies. But a taste for honey has driven one group of chimps in Gabon’s Loango National Park to take tool-making to a new level.
To fulfil their sweet tooth, the chimps need to infiltrate and steal from bee nests, either in trees or underground. To do that, they use a toolkit of up to five different implements: thin perforators to probe for the nests; blunt, heavy pounders to break inside; lever-like enlargers to widen the holes and access the different chambers; collectors with frayed ends to dip into the honey; and swabbers (elongated strips of bark) to scoop it out.
Some of the tools are even fit for the Swiss army, combining multiple functions into the same stick. For example, some were obviously modified at both ends, but one was blunt while the other was frayed, suggesting that they doubled as enlargers and collectors.
These observations were made by Christophe Boesch from the Max Planck Institute for Evolutionary Anthropology and they emphasise yet again the extraordinary brainpower of chimpanzees. It takes an uncommon intellect to be able to design and manufacture a suite of tools and use them in sequence to extract a foodstuff that’s hidden from sight.
Many men think of little else besides sex and meat, but male chimpanzees will sometimes exchange one for the other. Chimps are mostly vegetarian but they will occasionally supplement their diet by hunting other animals, especially monkeys. Males do most of the hunting, but they don’t eat their spoils alone – often, they will share the fresh meat with females, even those who are unrelated to them. Some scientists have suggested that this apparently selfless act is a trade – the males are giving up their nutritious catch in exchange for sex.
Cristina Gomes and Christophe Boesch from the Max Planck Institute for Evolutionary Anthropology have found new evidence to support this idea. They spent four years in the Tai National Park in Cote d’Ivoire watching a group of 49 chimps, including 5 adult males and 14 females. They recorded a huge amount of data on the group’s behaviour, and across 3,000 hours of observation, they were privy to 262 bouts of chimp sex.
These years of voyeurism told them that meat was a big factor in separating the Casanovas from the sexually frustrated males. Females mated more frequently with males who gave them meat at least once, and meat-sharing was much more important than other shows of support such as grooming, sharing other types of food or taking their sides in fights. None of these other actions had much bearing on the male’s sexual success.
Gomes and Boesch wonder if human hunter-gatherers rely on similar trades. That’s certainly been suggested before, especially since better hunters tend to have more wives (or at least, more affairs). These results do nothing to confirm or deny that idea, but they certainly provide strong evidence that chimps, at least, are indeed exchanging meat for sex.
For humans, our culture is a massive part of our identity, from the way we dress, speak and cook, to the social norms that govern how we interact with our peers. Our culture stems from our ability to pick up new behaviours through imitation, and we are so innately good at this that we often take it for granted.
We now know that chimpanzees have a similar ability, and like us, different groups have their own distinct cultures and traditions.
Now, Andrew Whiten from the University of St Andrews has published the first evidence that groups of chimpanzees can pick up new traditions from each other. In an experimental game of Chinese whispers, he seeded new behaviours in one group and saw that they readily spread to others.
Be it in sports or comedy, they say that timing is everything. In evolution, it’s no different. Many of the innovations that have separated us from other apes may have arisen not through creating new genetic material, but by subtly shifting how the existing lot is used.
Take our brains, for example. In the brains of humans, chimps and many other mammals, the genes that are switched on in the brain change dramatically in the first few years of life. But Mehmet Somel from the Max Planck Institute for Evolutionary Anthropology has found that a small but select squad of genes, involved in the development of nerve cells, are activated much later in our brains than in those of other primates.
This genetic delay mirrors other physical shifts in timing that separate humans from other apes. Chimpanzees, for example, become sexually mature by the age of 8 or 9; we take five more years to reach the same point of development.
These delays are signs of an evolutionary process called “neoteny“, where a species’ growth slows down to the point where adults retain many of the features previously seen juveniles. You can see neoteny at work in some domestic dog breeds, which are remarkably similar to baby wolves, or the axolotl salamander, which keeps the gills of a larva even as it becomes a sexually mature adult. And some scientists, like the late Stephen Jay Gould, have suggested that neoteny has played a major role in human evolution too.
As adults, we share many of the physical features of immature chimps. Our bone structures, including flat faces and small jaws, are similar to those of juvenile chimps, as is our patchy distribution of hair. A slower rate of development may even have shaped our vaunted intelligence, by stretching out the time when we are most receptive to new skills and knowledge. Somel’s research supports this idea by showing that since our evolutionary split from chimpanzees, the activation of some important brain genes has been delayed to the very start of adolescence.
In 1997, Swedish inspectors found several stockpiles of missiles hidden in a local zoo. Apparently, the arsenal had been gathered together for the express purpose of being used against civilians. And who was the mastermind behind this collection? A 19-year-old chimpanzee called Santino.
Santino was born in a German zoo in 1978 and transferred to Furuvik Zoo at the age of 5. To this day, he lives in the zoo’s chimpanzee island – a large outdoor enclosure surrounded by a moat. Throughout his residence, he was mostly docile towards the eager visitors, but all of that changed in 1997 when he started chucking disc-shaped stones at them.
Now many of us may have secretly wanted to take part in a spot of tourist-stoning, but Santino’s antics became so common that visitors were actually in real danger. The zoo staff had to take action. One morning, they swept the chimpanzee island and (unlike some other weapons inspectors) they actually found Santino’s arsenal – five separate caches of stones dotted along the shoreline facing the public area. Each one contained 3-8 missiles including concrete slabs, and algae-covered stones that had clearly been taken from the moat.
Mathias Osvath from Lund University, who describes the behaviour in a new paper, believes that it’s clearly premeditated. Until now, it’s been very difficult to work out if natural chimp behaviour involves true forward-planning or represents a reaction to present circumstances. Is a chimp that gathers twigs for termite-fishing planning for the future, or just responding to a more immediate hunger?
There’s no easy answer to that, but Santino’s case is much clearer. One of his caretakers, Ing-Marie Persson has collected plenty of evidence to show that he was deliberately stockpiling weapons of individual destruction for future acts of tourist-stoning.