How the Zebra Got Its Stripes: Darwinian Stories Told Through Evolutionary Biology by Léo Grasset.
Title: How the Zebra Got Its Stripes: Darwinian Stories Told Through Evolutionary Biology.
Author: Léo Grasset (translated by Barbara Mellor).
Genre: Non-fiction, science, evolutionary biology, animals.
Country: France.
Language: English.
Publication Date: 2017.
Summary: Why do giraffes have such long necks? Why are zebras striped? Why does the clitoris of the female hyena exactly resemble and in most respects function like the male's penis? Why do elephants engage in dictatorship, while buffalo in democracy? Do dung beetles navigate by the stars? And how scientifically accurate was the Lion King, exactly? Deploying the latest scientific research and his own extensive observations in Africa, Léo Grasset offers answers to these questions and many more. Intelligent, well-researched, accessible and humorous, Gasset answers all the most burning questions and dispels some of the most common stereotypes we have when it comes to biology, evolution, and the world around us.
My rating: 8.5/10.
My review:
♥ No, you did not misread that: the female spotted hyena (Crocuta crocuta) has a clitoris shaped like a penis. It is known in scientific jargon as a pseudo-penis. An imitation, basically, but a seriously good one. In fact, the female hyena imitates the male genitalia in their entirety: she also has a faux scrotum and faux keratin spines (a very widespread characteristic in mammals) on her faux penis, and not only can she get an erection with her clitoris but she also urinates through it. She has no separate vaginal entrance: her entire external genitalia take the form of a male penis. With the naked eye, it is hard to tell the difference between the male hyena and the female.
When it comes to giving birth, this organ causes the female serious difficulty, because her offspring enter the world via this narrow pseudo-penis. As a result, 15 per cent of mothers die during their first labour, and no fewer than 60 per cent of hyena cubs die at birth. From the evolutionary point of view, therefore, there has to be a pretty persuasive upside to justify the presence of this organ. One advantage is that it is difficult for the males to mate with the females by force; even when she is willing. It will take several attempts before the couple managed to find the right position, because he has to insert his penis into her pseudo-penis. For hyenas, successful mating is a whole art in itself, demanding a degree of expertise from the male and so allowing the female all the time she needs to choose her preferred partner.
..The female genitalia are faithful copies of the male ones, and some theorise that the organ's mimicry is too perfect to be simply a hormonal accident. Instead, they believe that the sexes' resemblance is the result of natural selection, possibly to cut down on rivalry among females. As yet, there is no consensus over the reason for this bizarre mimicry; our only certainty is that there must have been a very strong process of selection underlying it.
♥ To summarise: men's nipples seem to have no function; their presence is generally explained as the result of a foetal developmental constraint that is too strong and an evolutionary selection process that is too weak to eliminate them.
♥ So perhaps Darwin was right after all: giraffes use their long necks in order to avoid competition. Fossil evidence supplies further backing for his hypothesis: it appears that giraffes developed their long necks between fourteen and twelve million years ago, a period during which Africa underwent a general aridification and its forests gave way to savannah. As the number of trees diminished, competition for each tree must have increased, so favouring the selection of a long neck.
Fortunately, one explanation does not exclude the other: the ability to graze the higher branches is probably an advantage that shaped the evolution of the long neck for both sexes, while its use as a cudgel in competition between males is an evolutionary factor that explains the significant difference in thickness between male and female skulls. In summary, the giraffe's neck has a number of uses, and it can be difficult to say which of them has most strongly influenced its evolution.
♥ The gazelle's flight is completely random: researchers have found that predicting the next swerve of a gazelle in flight is impossible, and that this is a highly effective strategy in ensuring its survival when attacked. This is not an isolated example of an animal exploiting chance to its advantage...
♥ The existence of random forms of behaviour may seem slightly surprising - most views of animal behaviour suggest that it has been optimised by natural selection, and that individuals adopt compromises that tend to the best possible outcomes, for example what is known as "optimal foraging theory", where predators attack at the "right moment", or where herbivores migrate on precise dates, or animals gather in coordinated groups. But the fact that a behaviour may be finely optimised does not mean that it cannot also be random: if a gazelle with an unpredictable trajectory can survive longer and eventually produce more baby gazelles than a gazelle with a predictable trajectory, then evolution will select the "chancy" trajectory. Chance may therefore underlie adaptation, and despite appearances there is no contradiction between "optimisation" and "randomness". To imagine that something that behaves in an uncertain way is less effective than its predictable equivalent is an irrational cognitive bias, if a very widespread one among humans.
♥ Another example, on a much smaller scale, is found in the common vinegar fly (Drosophila melanogaster), often misnamed the fruit fly, which has compound eyes made up of many facets or ommatidia. There are two types of ommatidia, one sensitive to warm colours and the other to cold colours. The combination of these facets endows the fly with colour vision, but how can the ommatidia be mixed up effectively in order to produce an even visual image? A simple and low-energy solution is to rely on chance. Thanks to what statisticians call the law of large numbers, the warm- and cold-sensitive ommatidia stand every chance of being evenly distributed, and this is even more the case if their numbers are very high. Since there are several hundred of them, this is a clever ploy that-thanks to chance-is extremely successful.
♥ Among the least intuitive of phenomena known to humanity is the principle of quantum superposition. In the quantum world, a particle may exist in a state that does not correspond to a unique and well-defined classical valve. For example, an object might be neither red nor blue, but its interaction with other objects will fix it as a specific colour, whether red or blue. The physicist Erwin Schrödinger illustrated the weirdness of quantum superposition with the image of a cat shut in a sealed box, together with a quantum particle in a state of superposition and a monitor that will automatically release a substance poisonous to the cat when the particle becomes fixed in one of its two possible states. As long as the box remains sealed, there is no disturbance or observation that can fix the particle to a given value, and it stays in a state of superposition. According to quantum mechanics, the cat is therefore neither dead nor alive. As soon as an observer opens the box, the particle makes a "choice" between its two potential states and the detection apparatus either does or does not release the poison. As the slightest disturbance can tip this system towards a "choice", in a process known as "decoherence", it is extremely difficult to maintain a particle in a state of superposition, especially at an ambient temperature.
Yet recent experiments show that nature may have found a number of ways of maintaining electrons in a state of quantum superposition. One example may be found in the plant world, at the very heart of photosynthesis. Photosynthesis is beyond all doubt the most important biochemical process in the living world, introducing solar energy into the biosphere and feeding the entire network of food chains that depend upon it: herbivores, predators, parasites - when it comes down to it, all are dependent on the efficiency of photosynthesis. Light is absorbed by chlorophyll-containing molecular "antennae" that harness photons and transmit them to biochemical reaction centres where their energy is released. Recent research has suggested that these antennae may be able to keep photons in a state of quantum superposition, which would enable them to simultaneously explore the different routes leading to the reaction centres, to "select" the shortest one, and to maximise energy efficiency.
In other species, some organs involved in navigation and detection of magnetic fields also seem to make use of particles in quantum superposition. Quantum physics might even play a part in the appearance of mutation in DNA - the process on which the permanent renewal of diversity rests - through "quantum tunnelling", for example. From ecology to quantum effects, biologists are interested in chance for a variety of reasons: because it can be selected through evolution, because it generates philosophical debates about its origins, and also because it is by definition mysterious and intrinsically surprising. Increasingly, researchers are making it central to their work, and are no longer relegating it to the status of mere "statistical noise". Chance enables us to explain and understand. Life is a gamble.
♥ The problem with domesticating zebras is twofold: they are often very aggressive, and they are also much more slender in build than a horse or donkey, and therefore inappropriate as either mounts or beats of burden.
..We need to clear up one thing: zebras' stripes are, in fact, white, on a black background. The zebra embryo starts off completely black, before bands of white begin to appear, caused by an inhibition in the production of melatonin (the protein responsible for the black coloration). These bands eventually produce the stripes that will be unique to that individual throughout its life. You may be surprised to learn that zebras are not absolutely symmetrical: there are important differences between the patterns on their left side and their right side - the same effect can be seen on many tabby cats.
..Zebras' stripes disrupt predator perception
..It can be shown, for example, that a striped animal will appear larger than it actually is, which complicates matters for the predator which must estimate accurately when and where to strike. In addition to this, stripes disrupt the predator's perception of the speed and direction of its prey, in exactly the same way as the dazzle camouflage painted on warships in order to disrupt the aim of enemy gunners before the invention of radar. In 2013 serious research recommended that fast-moving military vehicles should be painted with zebra stripes in order to disrupt the aim of enemy personnel armed with rocket launchers.
Simulations have recently shown that the stripes of a moving zebra can produce two optical illusions, both of which reverse the perceived direction of movement. The first of these has a stroboscopic effect, of the kind generally seen in movies when revolving objects such as the wheels of a car are filmed. In certain natural light conditions too, such objects can give the impression of turning slowly, of standing still, or even of turning in the opposite direction. The second is the barber-pole illusion, in which the diagonal stripes seem to drift upwards as the pole rotates. In an article published in 2014 Martin How and Johannes Zanker suggested the diagonal stripes on zebras' coats produce both these optical illusions and that this disrupts the perceptions of predators who are thus inclined to launch their attacks inaccurately and miss their prey.
Zebras' stripes deter flies
This idea has its origins in the observations that tsetse flies and other flying horrors land less frequently on striped objects than on plain ones, and has been tested on horseflies, the females of which feed on blood.
Horseflies possess an ability to see polarised light that enables them to pinpoint puddles with accuracy: the light reflected from the surface of the water is polarised, as may be seen when they are viewed through polarised sunglasses which cut out horizontal light rays such as reflections from the sea or a wet road surface, so enabling us to see what lies under the waves or view the road without being dazzled. Horseflies use this method to detect the pools where they lay their eggs and find their prey: the herbivores that come there to drink.
In the polarised vision of horseflies, however, zebras' stripes create an effective form of camouflage, as the black-and-white stripes reflect the light in different directions and at different intensities. In an experiment in 2014, biologists observed that horseflies did in fact land less often on models of zebras with stripes than on models without stripes. From this, the authors of the experiment concluded that if stripes fulfilled this function, then they must have been selected - at least in part - for this reason. In 2014 Tim Caro, a professor if wildlife biology, and others at the University of California, David, published the results of research that seems to confirm this hypothesis. They noted the natural distribution of numerous subspecies of Equidae - the taxonomic family of horses and related animals - and point out that regions where horseflies are naturally present coincide closely with regions where members of the family Equidae are striped. Other indicators back this up, including a correlation between the number of stripes on the abdomen of species in a given region and the presence of tsetse flies in that area. So perhaps zebras evolved their stripes as a response to the pesky flies that feed on them.
Zebras' stripes help to dissipate heat
In 2015, in a Royal Society article entitled "How the zebra got its stripes: a problem with too many solutions", Brenda Larison at UCLA and an international group of scientists set out to update a 1990s hypothesis: this proposed that the function of zebras' stripes was not to escape from predatory lions or avoid unwelcome attentions from horseflies, but rather to reduce the negative effects of heat. The authors show that, out of all the environmental variables, temperature best explains the geographical disparity in stripe thickness. In hotter regions the stripes are thicker and in cooler regions they tend to disappear. An extreme example can be found in the quagga, a now-extinct subspecies of the zebra, which lived in the coolest region of South Africa and had no stripes at all over most of its body.
The authors don't, however, explain the mechanism by which stripes confer on their bearer the ability to avoid heat. They propose two hypotheses. First, it may be that the direct determining factor is not the temperature itself, but rather one of its consequences. Tsetse flies and horseflies, for instance, could be carriers of larger numbers of parasites in hotter regions, and the stripes might merely be a defence against these parasites - detectable through the prism of temperature. Second, the black stripes might heat up more than the pale ones, causing slight currents of air between the stripes that cool the animal down. Improbable as this may seem, the internal temperature of a zebra is on average 3°C lower than that of other herbivores of comparable size. The question is therefore whether this difference in temperature is a selection pressure strong enough to explain the appearance and endurance of these markings.
♥ The second revelation is that the termite colony, several million strong, does not live in the mound, but instead spends its time in an underground nest, where they breed, cultivate fungus and store food. The colony, consisting of around five kilos of termites and forty of fungus, inhales and exhales as much as an animal the size of a goat. The heat and carbon dioxide produced by respiration have to be evacuated and replaced with fresh oxygenated air. The mound plays a key role in this process. It works as a chimney, a passive regulator of heat and oxygen. In other words, it was termites that invented the first bioclimatic dwelling, some 200 million years ago.
..Another possibly analogy for the way termite mounds work is the operation of the lungs. When we breathe in, gas exchange takes place in three phases. In the first air enters the body through the larynx and flows rapidly and in bulk through the trachea. In the third gas exchange takes place not through the bulk flow of air - which the tubes here are too tiny to allow - but through diffusion in the alveoli of the lungs. In between the two the air is subject to the combined influences of the trachea (convective exchange) and the alveoli (diffusion) in a complex process which regulates the link between the two subsystems.
Similar processes may be at work in the termite mound. In the underground maze of sponge-like tunnels beneath the mound the air circulates by diffusion, while above ground the wider passages allow a large tidal flow of air. Between the two an intermediate system controls the exchange of air from one system to the other that ventilates the nest. Precisely how this system functions is still the subject of research in which two main avenues are being explored
The first is that the winds blowing over the termite mound cause the air to be drawn up through the central channel of the mound in a chimney effect. As we've seen, this is insufficient to renew the air in the nest, but it could cause an oscillating effect in the upper air mass which might be enough to mix the two layers sufficiently to have a cooling effect on the nest. This effect in the lungs is known as pendelluft or "air pendulum".
The second hypothesis proposes that the numerous tubes of the termite mound are like a pipe organ. When the wind rushes into them, this musical theory goes, it makes some of the tubes vibrate at very low, infrasonic frequencies. ..This phenomenon is known as acoustic mixing and, if it were shown to be in operation, would be enough to mix the layers of air in the tunnels of the mound.
..Termites are excellent architects and brilliant engineers. They are also good farmers, cultivating a fungus of the genus Lepiota, which they feed with pre-masticated leftover vegetable matter. The fungus then sets about carrying out the delicate stages involved in digesting cellulose, which many termites are incapable of. The termites then consume the sugar supplied by their symbiotic fungus crop. Even this isn't the end of their talents: termites are a keystone species, unique and essential to the ecosystem of the savannah. They mounds accelerate the formation of soil, increase the size and number of the fruits borne by nearby trees, improve the fertility of insects that live in the vicinity, and generally boost primary productivity all around them. The effects can be seen from space.
♥ But antelopes are like sheep. Instead of having one individual volunteering to go on guard duty for the common good, they use the strategy of mimicking their neighbour. "If my neighbour raises his head to look around, I'll have to raise mine in case he's seen something important. If he puts his head down again, that means that he thinks there's no obvious danger, so I can start eating again too." Each individual is torn between the need to eat and the urge to copy their neighbour. This simple copying from one individual to the next triggers waves of vigilance, just like a Mexican wave in the stands at a football match. The appearance of these waves of collective vigilance is one of many examples where complex group behaviours are in fact generated by a very simple rule (in this case, copying), repeated many times at a local level (in this case, between neighbours).
♥ The recipe of obtaining a highly organised school of fish is simple and requires only three ingredients. The first can be called close-quarters repulsion. If my neighbour invades my space, I'll move appropriately so that we keep the same distance apart. The second is long distance attraction. If I am too far away from the group I move in closer again. I must not get cut off from the rest, and I must not get gobbled up by a predator either. These two behaviours are essential to the cohesion of the shoal as a whole. And the third ingredient is copying my neighbour: whichever direction he goes in, I go too. It is this mimicking of alignment along individuals that makes it possible for all the fish in the school to suddenly and very rapidly change direction as one. The movement travels through the group at the speed of the reflexes of each individual fish.
♥ This type of phenomenon, where without conscious planning local interactions combine to form a coherent system, is known as self-organisation.
..To sum up, the recipe for self-organised collected behaviours goes as follows. First, a large number of individuals must copy each other blindly or be moved by the same motivations. Second, a set of simple rules must define their behaviour with regard to their near neighbours. And lastly, there must be thresholds defining the point at which feedback loops will be triggered. The general idea, therefore, is that apparently complex behaviours are no more than the results of numerous simple interactions. Just as some patterns of human behaviour that look complex can be explained by a handful of simple rules that don't require the existence of a large brain.
Collective behaviours are very simple to produce, especially when the individuals in the group are broadly similar. They are so simple, in fact, that they are everywhere. Here are just a few examples to think about: traffic jams; stock market crashes triggered by copycat sell-off trading; fireflies that coordinate their intermittent flashes; and, of course, the synchronisation of elements in ecosystems or catastrophic shifts...
♥ He is a seaman, certainly, but he is also keen on statistics and a convinced democrat, and he decides to call together a group of 101 passengers, including you, and ask you all to vote on the direction he should steer the ship, to port or to starboard. When you have all voted, he will follow the majority decision, without question. Naturally, each individual passenger is pretty poorly equipped for making this sort of choice, so let us say that he or she will have a 40 per cent chance of getting it wrong. In other words, each passenger might almost just as well toss a coin, which would have a 50 per cent chance of getting it wrong. The captain watches through a haze of alcohol as you wrestle over which way to vote. And there is no conferring with your neighbours, this is a secret vote. It is nerve-racking: you are convinced the ship will smash into the iceberg and it will all be your fault. While you are pondering over the litany of accumulated errors of judgement that litter your wretched existence, the captain explains that if you are a state it is because you are rubbish at statistics. You struggle to see what this has to do with it; you think it is more a matter now of how good you are at swimming. So he explains:
If every passenger has a 40 per cent chance of getting it wrong, that means he or she also has a 60 per cent chance of getting it right. In this case, it's as if you took a coin that's slightly weighted on one side, so that it has a 10 per cent greater chance of falling one way than it would by pure chance only, and tossed 101 times. In the end, the number of votes the passengers cast for "port" or "starboard" is in fact described by a binomial law, the same law that predicts the results of tossing a coin a few times. All you have to do is apply the binomial formula. The result is that ninety-nine times out of a hundred, the majority in a ballot of 101 votes will be right.
..Let us return to the ability of groups to get the right answer, even when they are made up of a random mix of individuals. Francis Galton tested it in a "guess-the-weight-of-an-ox" game he set up at an agricultural show in Plymouth in 1906. He observed that none of the 800 people who took part got anywhere near the ox's actual weight if 543.4kg but, when he took an average of their guesses, he got a result of 542.95kg, or a mere 450 grams short of the bull's true weight - an almost uncanny degree of accuracy. A century later, in 2007, Scott E. Page published an article demonstrating that for the end result of such a consensus to be accurate, the individuals in the crowd have to express a diversity of opinion. He described his theorem in the following equation:
Collective error = average error minus diversity
To reduce the collective error, you can either reduce the error of each individual, or increase the diversity of the individuals.
♥ ..when bees establish a new colony they carry out a dance indicating the direction and distance of the site that has been voted for. Buffalo herds show a similar effect when they move off to a new site: when a buffalo wants to show her preference, she stands up and positions her body facing in the direction of the spot she favours, makes a show of raising her head, and then lies down again. Several other females "vote" in the same way for their preferred direction, and the herd will then set off in the direction that is the average of all the individual votes, calculating the angles with tremendous precision to within plus or minus three degrees of the mean vote). A fine example of democracy in action. In cases where two separate directions are chosen, the herd splits in half.
In different animal species there are all sorts of votes: a straight majority (red deer and gorillas), an average vote (buffalos), and a quorate decision by a key minority (bees). The theory behind collective decisions posits that gaining a consensus is one of the most effective ways of maximising the accuracy of the end decision by means of "collective wisdom", and of minimising the risk of extreme decisions. In theory, no group should accept a despot unless there is a very large discrepancy between the information possessed by the despot and that possessed by the rest, and it is only in this situation that "following the leader" becomes the most favourable option and therefore the one selected by evolution.
♥ In the 1950s the Polish-American psychologist Solomon Asch devised an experiment to demonstrate this phenomenon. He showed a diagram to his students, and asked them to pick the line in the right-hand section that matched the one in the left-hand section, telling them that it was an experiment to do with optical perception. When the students were on their own, they gave the right answer, line C, in 99 per cent of cases. But Asch was interested in the results of peer pressure, and did the experiment again with student stooges in which the unsuspecting student who was being tested was unaware that the other students in the room were stooges instead believing that they were also undergoing the vision test. The planted students and the guinea pig were seated round a table, and each in turn gave their opinion out loud. Asch had asked his actors to give systematically wrong answers. The guinea pig was among the last to give his verdict. The results were clear: three-quarters of the students tested allowed themselves to be influenced at least once, giving the same answer as the others even though they knew it was wrong. (There may be a lesson here for all of us.)
♥ Female elephants live with their young, separately from the males, in groups ruled by a dominant female, the matriarch. She is also usually the oldest in the group and, since elephants can live to the age of sixty or seventy in the wild, she is generally a highly experienced individual who knows how best to lead the group through the perils of the savannah, including predators, family and drought. When researchers used loudspeakers to broadcast the sound of lions roaring to groups of elephants led by matriarchs of different ages, they found that the older the matriarch, the more quickly and accurately the herd reacted to simulated danger. A veteran matriarch was able to tell the difference between the roars if lions and lionesses, and gave particular attention to the former, which was not necessarily the case with the younger ones.
♥ There are also many examples of hierarchical social structures, some occurring when certain individuals are more experienced than others (as among elephants), or are better equipped to resolve conflicts within the group either because they're more powerful (as in chimpanzees) or have the most pressing needs (as in zebras). However, not all despotic regimes among animal species can be explained so easily. The different kinds of social organisation among animals are the subject of much contemporary research in behavioural ecology, some of which may occasionally throw an oblique light on the variety of social and political systems we humans enjoy, aspire to, or put up with.
♥ Males of the topi antelope species found in Kenya manage to persuade any females that might be thinking of making a break for freedom to stay quietly at home in their harem. And not only that: they do not just prevent them from leaving, they also take advantage of the opportunity to copulate with them. How?
The answer is simple: when a female threatens to leave his territory, the male raises the alarm with a special snorting sound that he generally uses only to warn of the presence of a predator lurking in the long grass. The male is an accomplished actor, and he gives a convincing performance, striking a pose to signal danger in the direction in which the female is heading, complete with fixed stare, pricked ears and muscles tensed for take-off. The signal could hardly be clearer. The female panics and rushes back to the heard, and in one case out of ten the male will take advantage of this to copulate with her.
♥ Navigating by the sun? Easy. By the stars? Not so easy. In fact, only a handful of species are known to be capable of doing it: common seals, blackcaps, black flycatchers and, of course, humans. But by the Milky Way? Currently only a single species has shown it can pull it off - the dung beetle.
..We know this because in 2013, Swedish and South African researchers carried out an intriguing experiment in the grasslands of Africa. They covered the heads of some nocturnal dung beetles with tiny masks, then compared the trajectories of these "blind" beetles with others whose vision remained unimpaired. The results were very clear: the unmasked beetles headed straight for their destination, while those fitted with masks went round and round in circles.
The researchers then performed the experiment again. But this time they did it in a planetarium, where they could simulate night skies that were either starry or completely dark, and with or without the Milky Way; basically, the scientists had fun creating a range of conditions in order to test how the dung beetles used light to guide themselves across the savannah on moonless nights. The results observed in the planetarium matched those in the field: even when they had only the Milky Way to guide them, the dung beetles still managed to crawl in a straight line.
Intriguingly, when deprived of visual cues humans, too, go round in circles. In 2009 experiment, volunteers were blindfolded and asked to walk in a straight line. Some people ended up walking in circles, some of which were very tight, less than twenty metres in diameter, others wove an erratic route; all of them, however, were quite convinced that they were walking in a straight line. The authors of the research also showed that on moonless nights, even when not blindfolded, their human subjects went round in circles. Which just goes to show that when it comes to navigating by the stars, dung beetles are cleverer than people.
♥ Elephants are cloaked in myth: their memory is fabled, their intelligence is celebrated, and they are believed to mourn their dead - grouping together in graveyards - and to be frightened of mice. As is often the case, these myths contain both truths and falsehoods (elephants are not afraid of rodents and they do not have graveyards, for starters).
..Since 1993 the English animal behaviourist Karen McComb has worked in Amboseli National Park in Kenya, studying cognition and communication in elephants. Her remarkable findings include not only the adaptive value of age in the leadership of elephant matriarchs, but also the discovery that elephants are capable of distinguishing the ethnicity of the humans with whom they share their living space. It was known that elephants reacted more powerfully and negatively to the clothes worn by Maasai people than to the clothes worn by Kamba people. In an experiment using concealed loudspeakers in the field, McComb played sound recordings of human voices to groups of elephants. The same phrase - "Look, look over there, a group of elephants is coming" - was said first in the Maasai language and afterwards in the Kamba language. Obviously, the elephants could not understand the words, but nonetheless the researchers observed very different responses from them according to the language they were being spoken in. The Maasai people, who raise livestock, regularly come into conflict with elephants and sometimes hunt them. The Kamba, by contrast, are agriculturalists who have less quarrel with elephants, despite the damage they sometimes do to crops. The fact that the elephants reached strongly to the phrase when spoken in Maasai demonstrated that they were able to distinguish between the two languages, and that they associated Maasai people with potential danger. When they heard the Maasai recording, they displayed classic responses to the possible presence of a predator: bunching together in a group with tusks pointing outwards; using their trunks to sniff their surroundings, urgently searching for information about the predator; or simply stampeding in the opposite direction from the loudspeakers.
..In Amboseli, McComb also explored whether elephants could distinguish between men and women. In theory, elephants should react different to the presence of men, who hunt them, and that of women, who do not. And indeed this turned out to be the case. The next question to investigate was how the elephants managed to tell the difference. The researchers tested the hypothesis that they could tell women's voices from men's by their higher pitch. By adjusting the recordings so that both the men's and the women's voices were pitched at the same level, and then running the experiment again, the scientists obtained results that were startling: even when the pitches of the male and female voices were levelled out to the point where we would generally find them indistinguishable, the elephants could still tell the men's voices from the women's, and reacted negatively to the men.
..Worldwide, the ancestors of elephants have been hunted for millennia. For 780,000 years, and throughout their range, which coveted most of Europe, Africa, Asia and the Americas, the ancestors of elephants died out whenever members of the genus Homo settled in these regions. Humans (Homo sapiens) played their part in this, of course, but so also did Homo erectus and Neanderthal man, Homo neanderthalensis. The early elephants were safe only where the human population was too small to hunt them to extinction. They therefore had every reason to associate humans with danger.
..The elephant calls that are audible to humans have vocal range of over four octaves. However, elephants also communicate by means of sounds that we cannot hear - infrasound.
Elephants can emit very low-frequency rumbles, at between ten and forty hertz, which are transmitted partly through the air and partly through the ground, forming a seismic signal: they can communicate with each other by sending and receiving seismic waves. The ground is a good vector for communication, as in comparison with the air it is relatively little used by either animals, and vibrations that are transmitted through it are subject to relatively little interference. As the ground is denser than air, underground vibrations can travel long distances: the percussive force of 75kg man jumping up and down has been recorded a kilometre away, while the steps of an elephant weighing three tonnes can travel over thirty-six kilometres. Elephants send and receive rumbles through the ground through their front feet, which have fatty pads on their soles to help detect seismic signals and to improve their quality: each cushion acts as a sort of lens for seismic vibrations, and this mechanism enables elephants to increase their sensitivity and pick up as many signals as possible.
Once received, the vibration is then transmitted up the leg bones to the shoulders, and on to the middle ear. Elephants therefore listen to the ground in the same way as we listen to the air. Among the network of earthquakes that rumble across the savannah, elephants can recognise warning noises from members of their family group, identity where the seismic wave is coming from, and quickly assume a defensive position if necessary.
♥ The honey badger (Mellivora capensis) is a small, member of the Mustelidae family, which also includes weasels and otters, and is found in regions stretching from Africa to India. It is fairly unimpressive to look at: the largest males measure at most a metre in length (tail included) and weigh no more than 15kg - not much more than a poodle. Hardly enough, you might think, to be the scourge of the grasslads, randomly terrorising, impaling and slaughtering other animals at random, and pillaging their prey, offspring and food.
If Genghis Khan had ordered some evil genie to conjure up a genetically modified attar pet that was a sadistic hybrid of a great white shark, a grizzly bear and a giant squid, it would have nothing on the honey badger. Since 2002 the honey badger has regularly won the accolade of "the world's most fearless creature" in the Guinness Book of Records. It has been spotted stealing prey from leopards, fighting with the most venomous snakes in Africa and attacking an elephant - all five tons of it - by its trunk. No problem.
When attacking large animals, honey badgers are reputed to aim for the scrotum. ..The honey badger aims at the testicles and waits for the poor beast to bleed to death. It can take this cavalier attitude to apparently uneven odds because it boasts a range of adaptations. These include:
- a thick, rubbery skin
- a resistance to snake venom
- a highly developed intelligence
- a reversible anal pouch
- staggering levels of aggression
..Puff adders are the deadliest of all African snakes. Yet a male honey badger has been filmed attacking a puff adder and being bitten by it (and thus injected with its deadly venom). The honey badger then rips the snake to death with its teeth before keeling over - only to regain consciousness a few hours later and tuck into its hard-won meal, looking none the worse for wear. Biologists are trying to understand the molecular mechanism honey badgers use to protect themselves from snake venom.
Honey badgers are clever. In Ranthambore National Park in the Indian state if Rajasthan, one was filmed trying to catch a kingfisher chick that was trapped high up and out of reach: it rolled a log to a point where it could stand on it to reach the chick. This use of an improvised tool signals a developed intelligence.
..In addition to its arsenal of long claws, sharp teeth and a tank-like profile designed for head-butting, the honey badger also possesses another weapon: a reversible anal pouch that when deployed gives off a suffocating, corrosive stench. This scent gland (a deceptively anodyne term in this case) has been said to help to neutralise the angry African bees when the unwelcome intruder smashes its way into their colonies to gobble up their young. The honey badger is also one of the few mammals capable of running backwards.
♥ Rafiki lives in a large baobab tree, and is referred to an "an old baboon". Yet his colourful markings show that he is clearly a mandrill (Mandrillus phinx), a species that lives largely in the tropical rainforests of equatorial Africa. The Lion King takes place in the grasslands of Kenya on the other side of the continent.
..Scar is the embodiment of perfidy and aggression; Mufasa personifies peace and wisdom. Recent research has confirmed a link between coat colour and behaviour: in some species darker individuals are more aggressive and in lions mane colour can indicate levels of testosterone and aggression. We await studies to show whether males with dark manes are also crooked and devious.
..The spotted hyena is, in fact, a highly social species with a complex language composed of many different calls. The dozen or so different calls that have been identified are used in a variety of contexts: as a warning of an imminent attack, in encounters with other hyenas, as a sign of submission, and so on. The "chuckle" is just one of these calls. As a response to aggression from another individual, it basically means, "Leave me alone!" Not really a laugh then. ..In fact. spotted hyenas are excellent hunters, and most of the meat they consume is from prey they have hunted themselves. Scar is right when he says that it is the lionesses' job to do the hunting. But the kings of the jungle are more than happy to feast on carrion, and will push other predators off their kill in order to steal it from them. Actually, lions are bigger scavengers than hyenas.
..So far so good, except that elephants don't have graveyards. This myth has probably arisen from two observations. Elephants, like humans, are attentive to their dead. They often linger over their bodies: there are many stories of elephants spending several days beside other elephants' corpses, and even covering them with branches. The bones of several elephants are sometimes all found in the same place, as though they had gone to a single spot to die there together.
The reality is simpler: elderly elephants tend to die near waterholes where they are drawn to soothe their aged bodies with the water and to feed on the water plants that are softer for their toothless jaws to masticate. The old elephants can get stuck in the mud around the waterhole and there, either because they are unable to free themselves or because they are so weak that they lose consciousness, they die.
..The animals in the film must have short memories: they have forgotten that the dry season comes every year and that during the dry season the grasslands become parched. Some countries in sub-Saharan Africa experience no rainfall at all for six or eight months of the year. Plants dry up and wither to reveal the bare soil (which in many southern African grasslands is sand), and may then spontaneously ignite, filling the air with smoke and turning the sky a distinctive purplish grey. In a particularly fierce dry season, some herbivores may perish. In short, the phenomena of "ruin and devastation" that are attributed to Scar's despotic regime are just part of the annual cycle of the seasons of which animals in the wild tend, for obvious reasons, to be keenly aware.
..Shock revelation: Nala and Simba have to be related to each other. At best they are cousins. At worst they are half-brother and half-sister. This is the way a pride of lions works: there may be one dominant male or a coalition of two, and these males monopolise the reproductive rights of many females. The other males are either too young to rival them, or are expelled from the pride's territory. In the case of a coalition, two brothers will form an alliance to force another dominant male out of his territory, and will then share his reproductive rights between them. This is the most logical explanation for Scar's presence in the pride: he and Mufasa must have established a coalition. Yet Scar does not seem to be particularly fulfilled sexually, as Mufasa appears to monopolise the females (and Scar feels understandably aggrieved). There is, therefore, good reason to suppose that Mufasa has fathered all the cubs, Nala and Simba included. So Nala and Simba are most probably half-brother and half-sister, and their family tree risks containing record levels of inbreeding, and of producing baby lions displaying a wide range of recessive disorders and birth defects.
The Crater lions of Ngorongoro Conservation Area are a good illustration of this effect. The Ngorongoro Crater, the largest extinct volcano in the word, supports an isolated population of closely related lions, recently reconstituted from a mere handful of individuals and forming what is known as a genetic or population bottleneck. The effects of this inbreeding can be seen in the males, with nearly half of their sperm displaying abnormalities. Behold the future that awaits Simba and Nala's offspring.
♥ In the Hwange, another measure was quickly adopted. The park had no natural surface water: to remedy this, boreholes were drilled in order to pump water up from deep underground, so that the man-made waterholes were kept full of water even at the height of the dry season. As a result, the animals in the park no longer need to migrate to find water; now the have as much as they want in situ. By changing one of the parameters of the habitat, humans have ended migration among the animals. In the Hwange, this has led to an appreciable growth in the elephant population: now baby elephants no longer die of thirst on the perilous journey to the Okavango Delta, and the local population has probably increased to over 40,000. Throughout the dry season the diesel pumps hum away, bringing water up to the surface for animals that have become a settled population.
♥ Many bird specie incorporate coloured plastic detritus when building their nests, using the bright colours as signals to neighbouring birds or to attract females. Among territorial birds such as the black kite (Milvus migrans), the largest individuals with the best territories use more plastic in their nests than weaker individuals with less desirable territories. This eye-catching display reduces conflict: each individual can size up a rival's strength at a glance, and so avoid getting into fights in which they are likely to be beaten. Any weak bird that tried to cheat by adding plastic to its nest would run the risk of getting into a potentially lethal fight with a stronger bird. The plastic detritus serves as a visible indicator of an individual's status, so reducing territorial conflicts.
House sparrows (Passer domesticus) incorporate cigarette ends in their nests, where the residual tobacco acts as a powerful insecticide to protect their chicks form parasites. Birds in the wild use sprigs or aromatic plants such as thyme in their nests as an antiseptic and a deterrent against parasites, and it appears that cigarette ends make an effective urban substitute. The tobacco plant originally used nicotine as a protection against leaf-eating parasites: when sparrows use cigarette butts in their nests they're exploiting nicotine's original function. Better still, the BBC filmed crows in a Japanese city dropping tough-shelled nuts from overhead wires on to a busy road, so that passing cars would crack them open as they drove over them. The birds soon worked out that if they did the same thing on a pedestrian crossing and waited until the light turned red and stopped the traffic, they could collect the nuts at their leisure without running the risk of being run over.
A recent study suggests that birds feeding on roads somehow know their speed limits. Researchers from Quebec drove at different speeds on a variety of roads in western France. Whenever they encountered birds on the road, they measured the distance between their vehicle and the bird at the point at which it decided to fly off. The results were startling: the distance was not related to the speed of the car, but rather to the speed limit in force on the road in question. On a road with 90kph limit, for example, their research showed that birds will generally fly off when a vehicle is seventy-five metres away from them, and this distance remains constant whether it be a tractor chugging along at low speed or a high-powered car in a hurry travelling at twice the limit. In the former case the birds will take off earlier than they need to; in the latter case they will be much too late, as at that speed the car will cover seventy-five metres in one and half seconds. Does this mean that birds have learned to read road signs? One rather doubts it. Another explanation is that birds learn to work out the average speed of passing vehicles: on any road there will be some drivers who drive a little over the speed limit and others who drive a little under it: their average speed will therefore be close to the speed limit, and it is this average that birds "know" as they peck away in the middle of the road. Drivers with experience of less intelligent bird behaviour may think more work needs to be done on this intriguing phenomenon.
♥ In the grasslands, the most heinous example of this is found in the link between trophy hunting and infanticide in lions. Lions live in a social system in which one male may monopolise the reproductive activity of five or six males. The position of the older males is constantly being challenged and usurped by younger ones, and a male lion has an average window of two years for reproduction - the time between his becoming strong enough to unseat another male and becoming too old to resist being ousted in his turn. The lionesses are not sexually receptive as long as the are rearing a litter of cubs, so when a young male overthrows an older male in the pride, he also kills all the cubs. Once the females have lost their cubs, they become receptive once more and ready to mate with the new male. Although the lionesses are ferocious in defending their young, it is estimated that a quarter of all lion cubs that die in their first year are killed by an incoming male.
♥ From an impartial and objective viewpoint, humans can be considered as a species that exerts a major influence, consuming resources but also making new ones available. It is always useful to remind ourselves that this state of affairs is not entirely new: it is nearly 30,000 years since the first domesticated animal, the dog, was genetically selected by humans, and at least 60,000 years since humans started using forest fires as a way of making hunting easier and changing the biodiversity in a particular area, long before the invention of agriculture - so-called "fire-stick farming". By setting more recent events in this context, we may be less tempted to consider all human impact as "unnatural", and as antagonistic to the "virgin" state of what we imagine to be pristine, untouched nature. From the beginnings of human history, we have shaped our environment and been shaped by it, modifying the behaviours of the species we share our lives with and being modified by them. The difference today is simple one of scale.
♥ The Dust Bowl is the name now given to the period in the 1930s when dust storms ravaged the North American prairies. The storms would blow up suddenly after a severe drought, in an environment that had been farmed intensively for many years. The spread of the tractor and of deep ploughing (combined with a lack of understanding of the local ecology) led to the systematic destruction of the deep roots that had previously stabilised the sandy soils of the arid plains. In the absence of the native grasses that historically maintained levels of humidity and bound the soil together, billions of tonnes of loose silt and sand were picked up and carried away by the fierce summer winds. The effects were felt in winter too: in 1934-5, red snow fell on New York, coloured by dust from the middle of the continent. On 14 April 1935, known as "Black Sunday", dust storms swept right across the Great Plains from Oklahoma to Texas, whipping up 300 million tons of dust and sand and creating the first ecological refugees in American history. During the 1930s, some two and a half million people who had lost their livelihoods because of these "black blizzards" abandoned the Great Plains and made their way to the coast to look for work, and especially to California - as described by John Steinbeck in The Grapes of Wrath. This desertification shows that major environmental changes can sometimes take place within the space of just a few years.
..The American Dust Bowl created a desert of such stability that more than 200 million trees had to be planted to make the Great Plains once more fit for agriculture.
♥ ..3.6 billion hectares are currently suffering from desertification around the planet, representing over a third (36 per cent) of its exploitable land.
..When an area covered by trees dips below a critical threshold, it is often observed that the ecosystem suddenly collapses and the trees disappear: this is desertification. Desertification is a catastrophic transition: the transformation of a landscape from patchy trees to desert can be brutally sudden. By contrast, returning in the other direction - that is, reducing the degree of aridity to a level far lower than that at which the transition took place - is a much longer, slower process. There are two feedback loops, one favouring plant growth and the other reducing it. When the level of vegetation dips below a given threshold, the former grassland quickly turns to desert. When the ingredients are all in place, namely:
- two stable states: with vegetation (savannah) and without vegetation (desert)
- external conditions of aridity that exceed a given threshold and
- domino effects that increase the speed of reaction,
♥ If we examine the ecosystem in more detail, we see that the trees encourage the presence of water in their immediate vicinity by providing shade, while their roots reduce evaporation and increase local humidity. In other words, when there is very little water available, the only place were trees can grow is next to other trees. This is the reason why, when water is scarce, they form small patches of green in an otherwise bare landscape: they have to live in close proximity in order to survive. In short, the more trees there are, the more trees there are likely to be. Conversely, the bare areas are extremely arid and are eroded by the wind: as soon as there are no more roots to bind the soil, the last nutrients vital for the establishment of new plants are quickly blown away, making it even more difficult for new shoots to grow. In short, the fewer trees there are now, the fewer trees there will tend to be in the future.
♥ The Sahara offers an example of an even more spectacular transition. Just over 5,000 years ago it was a great plain with forests and lakes. Then changes in the amount of sunlight absorbed by plants and the amount reflected back into space, which had been at work for millennia (and is now known as radiative forcing) may have crossed a threshold, triggering a snowball desertification effect that created the largest hot desert in the world. Exactly why the Sahara should have changed so dramatically is, as yet, uncertain.
♥ Some of the most important episodes in our evolutionary history have played out in the grasslands of Africa. One of the most significant was the transition from quadrupedalism to bipedalism, which took place in East Africa some four million years ago. By getting up on two legs, our ancestor Australopithecus could see further, walk for longer and use their hands more freely. The fossil remains of various species of Australopithecus have been found in a strip stretching from the Sahel to South Africa, and palaeontogolists have given affectionate nicknames to the most notable individuals: Lucy (Australopithecus afarensis), discovered in Ethiopia in 1974, needs no introduction, and there are also Abel (A. bahrelghazali), found in Chad in 1995, and Mrs Ples (A. africanus), discovered in South Africa in 1947.
♥ Whenever it first developed, the ability to cook had numerous repercussions: cooking softened foods, made the nutrients they contained more easily available and reduced the time needed for chewing and digestion. A morphological effect of this was a reduction in the size of teeth, while the fact that less time was spent chewing food freed up more time and energy for doing other things such as making tools, interacting socially, or even migrating across the landscape. The brain of Homo erectus was appreciably bigger than that of their ancestor Homo habilis (with a volume of 980cm3 as opposed to around 600cm3), and some individuals had brains approaching the size of human brains today (1100cm3). The cooking of food could well be responsible for this growth in skull size: of all our organs the brain is the one that consumes the greatest proportion of our energy with almost a fifth going to power brain activity; the increase in resources provided by cooking was able to support the energy requirements of a larger brain. Homo erectus made good use of this added brainpower, leaving Africa and its grasslands behind to spread all around the Mediterranean coast or as far as Asia.
♥ Our ancestors were members of the Homo erectus species who stayed in Africa and did not travel. As time went on, a new species emerged: Homo sapiens. The oldest Homo sapiens fossils so far discovered were found in the Omo Valley in Ethiopia, and date from 195,000 years ago. However, recent scientific research places the origins of our species considerably earlier, at 340,000 years, almost doubling its age.
♥ The Aka people are a pygmy tribe who form one of the oldest branches of humanity, having split off from other humans some 70,000 years ago, in the area now occupied by Cameroon in Central Africa. At the same time, the human population in the Horn of Africa, the ancestors of all non-African humans, were setting off on their great voyage from Africa and reaching the Arabian peninsula. The pygmy peoples, meanwhile, became specialists in living in Africa's equatorial rainforests, and for a long time it was thought that they remained genetically isolated from other populations. But recent studies show that to this day the genome of these pygmy peoples contains a fragment inherited from other very early human populations that are as yet unknown. At the point when this hybridisation took place, these mystery populations were so different genetically from the pygmies that they may even have constituted a different species of the genus Homo. The pygmies must have interbred with this ancient people some 40,000 years ago. Although as yet we have no fossil record of these people, they left their imprint on the pygmies' genome.
The pygmy peoples are not unique in this respect: extensive genetic research and the examination of ancient DNA have uncovered at least two other hybridisation events involving human populations and another species of the genus Homo. The event that has been most written about is without doubt the hybridisation between Homo sapiens and Neanderthal man: we know now that on average 3 per cent of the genes of non-African humans (whose ancestors left Africa 70,000 years ago) is inherited from Neanderthal man. Whether this means that Neanderthals were technically a different species is still a matter of debate. Such hybridisation events are highly significant, as we known that many genes we inherited from these vanished relatives are now under strong selection, meaning these are useful genes on which we depend for our survival. Some of them are immune genes, other are related to resistance to ultraviolet rays, and others again are linked to keratin, the protein that forms an essential part of skin and hair. It may not be all good, however, as it has recently been suggested that some of these Neanderthal genes may be associated with mental health problems. Finally, up to 6 per cent of the genes in the genome of many populations of South-East Asia and Oceania come from another, deeply mysterious group, known only by the name of the cave in Siberia where a handful of their bones have been found - the Denisovans. As yet we known little of these extinct relatives, but one thing we do know for certain: our history is one of hybridisation.
♥ The creation of the Hwange National Park in Zimbabwe in 1920s involved the displacement of the indigenous human populations, who were pushed out to the less fertile lands that surrounded it. Some researchers have calculated that in Africa alone fourteen million people have been displaced in order to create national parks and reserves.
♥ It has become generally accepted that an unbridgeable divide exists between "nature" and humans, with the latter being condemned as incompatible with the survival of the former. This viewpoint, which has driven the politics of conservation throughout the twentieth century, is now being challenged by an alternative view, which proposes that humans are capable of living in habitats rich in biodiversity without destroying them. First came recognition of the existence of "traditional ecological knowledge" in numerous human cultures, highly developed systems of understanding that are often possessed by societies that inhabit environments rich in biodiversity. Then a series of historical and archaeological studies showed that many ecosystems once believed to be fundamentally natural were in fact the result of human interaction going back over millennia; these included not only the grasslands of West Africa but also areas of the Amazon rainforest and African equatorial rainforest, which until then had been thought to be virgin. The vogue for creating nature reserves sealed off and hostile to all human activity appears to have lost its impetus, perhaps because by definition they're not tourist-friendly. The current emphasis is on involving local populations in the protection of threatened species, an approach to conservation that, if it works, is likely to be more effective in the long term that measures imposed from outside.
..The grassland ecosystems are particularly pertinent for a consideration of the complex interactions between ourselves and other species. We have lived in these environments for a very long time, and their current desertification poses a major ecological challenge. Our most appropriate response must surely be to accept our responsibilities and to protect the grasslands just as we protect our own dwellings so that both can coexist, as in fact they have done for a long way back into history.