by Ted Dewan
Half die before they reach their first birthday; only 1 in 100 makes it to five, and 15,000 are squashed on British roads each year (down from the mid-1990s peak of 100,000). Road carnage combined with the use of powerful insecticides and the destruction of the grassy field margins that hedgehogs like to nest in make it hard to feel optimistic. Even ‘urban hedgehogs’ aren’t as adept at surviving in cities as foxes. They fall into swimming pools, get puréed by lawnmowers or wedge their heads into food containers and starve to death (McDonalds have now changed the design of their McFlurry cartons to make them hedgehog-proof). Many also die from diarrhoea caused by well meaning humans leaving them bread and milk. The best way to help a hedgehog is not to feed it but to turn it loose in your vegetable patch. A single adult can eat 250 slugs in an evening.
The fox knows many things; the hedgehog, one big thing.
ERASMUS
Ironically, because of their ‘spiny ball’ defence, hedgehogs have very few natural predators. Badgers are the only animals with claws strong enough to prise open a rolled hedgehog, although hungry foxes have been known to urinate on them to force them to unroll. Hedgehogs also have an extraordinary immunity to poison. It takes more chloroform to put a hedgehog to sleep than any other animal of comparable size and they can survive a bite from an adder that would kill a guinea pig in five minutes.
This resistance offers a clue to the strangest of all hedgehog behaviours: ‘self-anointing’, which involves them contorting themselves to coat their own back with gobbets of foaming saliva. Hedgehogs have been observed self-anointing after chewing on the poisonous skin of a toad, thereby creating a toxic mousse for their spines. This makes them even less attractive to predators, but it doesn’t entirely explain why the smell of shoes, cigar butts, furniture polish, creosote, coffee, boiled fish, face cream and distilled water should also stimulate the same behaviour.
The word heyghoge is first recorded in 1450 and this quickly splintered into regional nicknames like highoggs, hedgepigs, hoghogs and fuzzipeggs. Before that, the Anglo-Saxons had called them igl and the Normans, ‘urchins’, after the Latin for hedgehog, ericius. This came from the ancient root gher-, meaning ‘to bristle’ (which also gave us ‘horror’).
An adult hedgehog bristles with over 5,000 spines. They are hollow hairs, reinforced by keratin, the same substance our nails are made from. They are extremely strong; a hedgehog can be picked up by a single spine without it breaking. Considering the physical barrier, hedgehogs of both sexes are remarkably promiscuous, mating with ten or more partners each season and sometimes several on the same night. It is never face-to-face, despite Aristotle’s confident assertions. The male circles a female for hours, snorting loudly until she spreads her back legs, flattens her spikes and points her nose upwards. Copulation is very brief and noisy and, once sated, the male immediately trundles off, taking no further interest in the female or the rearing of his offspring.
Hoatzin
Half-bird, half-cow
Very few birds live by munching on vegetation. It’s heavy, low in energy and slow to digest, not the ideal fuel for flying. But the strange hoatzin (Opisthocomus hoazin) – pronounced ‘watseen’ – of the South American river swamps has actually developed a stomach like a cow’s to cope with its diet of leaves.
The hoatzin’s crop is enormous, fifty times larger than its stomach, accounting for almost a third of total body-weight. And unlike most birds, where it is used for storage, the hoatzin’s crop does most of the digestive heavy work. Like the foregut of a cow, it is full of bacteria and enzymes which break down the cellulose in the leaves. An amazing 70 per cent of the fibre gets digested, but as with cows, this takes time. Hoatzins take two days to digest a meal, the slowest of any bird.
The downside of eating like a cow is smelling like one, which is why the hoatzin is known as the ‘stink bird’. The manure-like pong is produced by fermenting fatty acids in the crop and has kept them mostly out of the human food chain, although their eggs are eaten. The intrepid American ornithologist William Beebe cooked and ate a hoatzin in 1909 and declared it ‘clean and appetising’. More recently, microbiologists have studied the crop bacteria because of its ability to neutralise poisons in the toxic foliage the bird eats. Transferred to cows and goats, these might allow them to graze on a wider range of forage, with an enormous increase in yield.
Despite being rather tame, hoatzin get stressed by tourists. Colonies that are visited regularly produce double the level of stress hormones and lay a third fewer eggs.
They are very social birds, living in groups of five to fifty, and are about as large (and clumsy) as chickens. Their weight makes them poor flyers and they spend three-quarters of their time just perching, spreading their feathers to soak up the sun and digesting their toxic breakfast. They look rather prehistoric, with shaggy russet and light brown feathers, a bright blue face, piercing red eyes with large eyelashes and a spiky head crest. They are noisy, too: continually grunting wheezing, and hissing.
What is a hoatzin? Taxonomists still can’t agree. Even with genetic analysis they don’t quite fit into any of the existing bird families. For a long time they were classed as game birds (uazin is the Aztec name for pheasant), then as cuckoos and more recently as doves. Now, most reference sources list them, aardvark-like, as a single species in their own order, the Opisthocomiformes – ‘ones with long hair behind’, referring to their large crest.
A BUMPER CROP
Their chicks share a feature with the fossil proto-bird, archaeopteryx: the first two ‘fingers’ of the wing form into two claws. If disturbed, chicks as young as three days old will leap into the water, and clamber back through the branches to the nest using their claws like small monkeys. It’s unlikely that the claws are a prehistoric survival; they are just another odd adaptation to life in the swamp, and disappear as the birds grow older.
Horse
Made in America
The horse, like the dog and the camel, first carved out its evolutionary niche in the North America of 50 million years ago. In those days, it scampered around the rainforest eating fruit, much as its relative the tapir still does today. But as the planet cooled, and the forests were replaced by vast grass-filled plains, the American proto-horses diversified and adapted themselves to the new environment, eventually crossing the Bering land-bridge into Asia. All our breeds of domestic horse are a single species, Equus caballus, descended from these American immigrants; only one wild horse, the Mongolian Przewalski’s horse (Equus ferus przewalskii) has survived.
Many cultures still eat horse, especially Kazakhs, who even eat horse rectum, and the French, whose preference allegedly dates to the Battle of Eylau in 1807, when Napoleon’s surgeon-in-chief advised the starving troops to eat dead battlefield horses.
Horses are animals of the steppe, and many of the adaptations that allowed them to thrive in an open landscape of rough grass continue to affect their behaviour today. Poor diet requires a large digestive tract, so they grew larger. Because they aren’t ruminants, horses depend on lots of small meals, to maintain energy levels, rather than one large feast. They are ‘hind-gut fermenters’, absorbing nutrients through their intestines rather than their stomachs, so a change in diet can cause serious problems: over-rich pasture, mouldy hay and unfamiliar or toxic plants can cause colic, or even death. Horses are prey animals: the best defence on the steppe is to run faster than your predator. Hence they have the largest eyes of any land mammal, arranged to give them almost 360? vision. Anything unfamiliar (like a plastic bag) triggers the flight response. Also, because endurance is more important to survival than initial speed, horses’ legs became longer and more powerful, but took time and space to reach top speed. Most humans can beat a horse from a standing start over 50 yards.
This might explain why most of our early interaction with horses seems to involve us killing them for meat. The oldest European hominid fossil, 500,000-year-old Boxgrove Man, was found next to a butchered horse. In their original homelan
d of North America, the native horse was hunted to extinction by the end of the last ice age. It wasn’t until Cortez and his Spanish troops arrived in 1492 that Native Americans met their first modern horse. They called them ‘big dogs’, quite reasonably, as they had relied on dogs for transport until then.
ASLEEP ON THEIR FEET
No one can quite agree when we first started riding horses as well as eating them. They were probably domesticated independently many times and in many places, but the earliest known evidence points to the Ukraine around 6,000 years ago, which is several hundred years before the oldest known wheel. It was one of the great breakthroughs in human history (and an evolutionary meal ticket for the horse). Suddenly, we could travel huge distances quickly and wage wars of unprecedented scale and savagery.
As well as being useful and nutritious, horses acquired huge symbolic value, and were worshipped all over the ancient world from China and Mongolia to ancient Egypt and Celtic Europe. Their importance in this regard has never waned, even as their role in combat, agriculture and transport has diminished. In the UK and US alone, there are 10 million horses ridden for pleasure and profit, creating an income in excess of £60 billion, a figure which outstrips the gross domestic product of most of the world’s poorest nations.
Human
The storytelling ape
What Darwin suspected, our DNA has confirmed: we are remarkably similar to our primate cousins – we share about 97 per cent with gorillas, and over 98 per cent with chimps, although the developmental difference those very particular genes makes is clearly evident. (Interestingly we are ‘hairier’ than chimps, having more follicles, but their hair is thicker and longer.) The physiological differences are small: our hands are able to make two grips that a chimp can’t; from this one modification all our manual dexterity has flowed. Combined with a gradual preference for walking on our hind legs (which still causes us physical difficulties), it’s not impossible to see how freeing our hands also freed our minds. There is strong evidence pointing to language – the greatest of all tools – having evolved as gesture before it became speech. Culture started with our hands as well as our brains.
Human beings, who are unique in having the ability to learn from the experience of others, are also remarkable for their apparent disinclination to do so.
DOUGLAS ADAMS
Why did it take us so long after we had grown our large brains and smart hands to start daubing walls, carving objects and telling stories? No one knows for sure what caused the so-called ‘great leap forward’ but the astonishing homogeneity of Homo sapiens’s DNA suggests that humans went through an ice-age ‘bottleneck’ around 70,000 years ago, with our population being reduced to a few thousand individuals. Life must have been tough for a long time but gradually as these pockets of humans interacted and grew larger, social relationships would have developed, tasks would have been shared and campfires lit. Among monkeys and primates, a larger social group leads to greater intelligence. Imitation, communication, learning, problem-solving are all products of primate social interactions. Among humans, it seems reasonable to suggest that these interactions selected for language. It’s a self-reinforcing cycle: once it starts, it snowballs.
WHERE ALL THE TROUBLE STARTED
And where has the great leap taken us? We have jumped free of evolution. If we were to live in tune with the distribution curves that apply to other species, our total population would be fewer than a million. If we used primates as a guide, our communities would each be 150 individuals: large enough for breeding, small enough for there to be there are no strangers, with little crime or cheating.
But we human primates have used our brains and hands to transform the world, before our DNA could change us. We have swapped biology for history, nature for technology. The fact that you’re reading this book is singularly extraordinary. You have learned a complex language, and can interpret meaning in its written form. But now this very ingenuity is creating its own limits. The animals and plants we have domesticated are so lacking in genetic diversity they are falling prey to new diseases. Globalisation means that at any one time half a million people are in the air, and millions more are on the move, their bodies and suitcases full of organisms hungry for fresh habitats. Cities – our greatest invention – are choking the planet’s skies and threatening the delicate balance of climate which makes life possible.
All human cultures tell the same stories – of the man punished for stealing fire; of the flood that sweeps away all we have built. Only stories, and the imagination that feeds them, may be strong enough to save us from the endless ingenuity of our hands.
Hummingbird
Tiny genius
The smallest bird of all is the bee hummingbird (Mellisuga helenae) and it weighs less than a penny. Despite being not much more than feathered wing muscles, the 320 species of hummingbird carry a huge amount of cerebral firepower. Relative to body size, their brains are twice as large as our own and this helps them do a number of things beyond the scope of larger animals.
LICKING NOT SUCKING
Like us, they have a precise sense of time. The Rufous hummingbird (Selasphorus rufus) remembers not only where its food is located, but also when it last fed there. It will leave flowers enough time to fill up with nectar before revisiting them. Hummingbirds are also one of only six groups of animals that learn how to communicate vocally, rather than just through instinct. Humans, whales and bats do this, but among other birds, it is only the parrots and songbirds that learn by imitation. Special structures in the frontal lobes of the brain control vocal learning, and this skill seems to have evolved independently in all three bird groups. For hummingbirds, it is driven by the need to maintain strict territorial control. Their nectar-licking lifestyle requires so much energy that keeping the neighbours away from the food supply is essential to survival. Singing is the most efficient way of doing this.
Their unique ability to feed from flowers while hovering also requires special brain adaptations. They can see much further into the ultraviolet spectrum than other birds (perhaps to help with flower recognition) and have a large section of brain dedicated to the visual adjustment that allows them to focus, despite the airflow created by having wings that beat up to 200 times a second. This also creates astonishing physical demands, so as well as being clever, hummingbirds have the largest heart relative to size, and the fastest metabolism, of any animal. In a single minute, their hearts can beat up to 1,200 times and they may take as many as 500 breaths.
The craze for hummingbird ‘skins’ for hats and bags peaked in the late nineteenth century: one London dealer imported over 400,000 in a single year. Many unrecorded species were hunted to extinction until it was finally made illegal in 1918.
Their flying technique is closer to a bumblebee’s than to that of other birds, with ball-and-socket shoulder joints allowing their wings to rotate 180 degrees in all directions. As they hover the wingtips move horizontally, tracing a figure-of-eight pattern rather than up and down, as with most birds. This means they can generate lift on both strokes, enabling them to fly forwards, backwards, and even upside down. To keep this up, they need to eat at least their own body-weight in nectar (for energy) and insects (for protein) every day. That means visiting an average of 1,500 flowers. Because this generates so much liquid waste, hummingbirds are continually dripping urine.
Their tiny feet are useless on the ground so they spend three-quarters of the day perching to save energy. At night, some species go into an energy-efficient torpor – a kind of mini-hibernation – where their metabolism plummets and their body temperature almost halves.
Hummingbird feathers come in two basic colours: reddish-brown and black. The amazing range of colours we see is caused by granules of melanin and tiny air bubbles in the feathers that refract light to create a metallic sheen. Light must shine on an iridescent feather at the correct angle, or we only see the dull ‘pigment’ colours.
Hyena
Girls on top
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nbsp; The female Spotted hyena (Crocuta crocuta) carries something between its legs that continues to baffle and fascinate biologists: a clitoris that matches the male’s penis in shape, size and erectness. Its vagina is fused shut, so it uses this one organ to urinate, mate and give birth. How and why it has evolved may seem hard to fathom, not least because giving birth often results in painful tearing which kills one in ten mothers and often suffocates the first-born cub, whose umbilical cord is too short to negotiate the elongated birth canal. The usual assumption is that testosterone ‘leaks’ from male siblings in the womb, dousing the females, as sometimes happens to produce ‘butch’ female mice. But there is little evidence for this in spotted hyenas, and all females are similarly endowed.
The ancient Egyptians trapped hyenas as pets and fattened them for the table. In the Ethiopian city of Harar, ‘hyena-men’ still feed on wild hyenas at dusk, holding the meat in their mouths.
The key is social organisation. Hyenas live in female-dominated societies, where every member in a clan has a precise hierarchical rank, with females being senior to males, and the female rank being inherited through the mother. This matriarchal social structure rivals those of the higher primates in complexity. In hunting terms, it delivers numerous benefits. A clan will chase their prey for miles, if necessary, until the target animal simply gives up. At that point the hyenas tear into its belly and legs, starting to eat it while it is still alive. This requires co-ordination and planning, but, above all, tremendous aggression. That’s where the testosterone comes in handy. From birth, spotted hyenas are programmed to fight and a cub will often kill its twin (they are born in pairs) to establish dominance.