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Around 13.8 billion years ago, Ireland is conceived, along with everything else in the universe, in that first spark of creation, the Big Bang. But its path from conception to birth is an incredibly long one, a 12-billion-year gestation in the cosmic womb as the elements which compose it make their way from the bellies of the first stars to the bowels of the Earth via a spectacular series of stellar collisions and explosions. Finally, around 1.8 billion years ago, in a blaze of fiery creation, the first rocks of Ireland are born into the world as part of a chain of volcanic islands which subsequently collide with the coast of an ancient megacontinent composed of large parts of North America, Greenland, Siberia, and northern Europe. Thus is the infant Ireland delivered into the arms of its mother continent, taking its place beside Scotland on a continental margin closest to what is now southern Greenland.

For the next billion years and more, Ireland undertakes a breathtaking journey across the face of the Earth, becoming a tiny province of three true supercontinents, with Columbia forming 1.6 billion years ago, Rodinia one billion years ago, and Pannotia 650 million years ago. This dance of the continents sees Ireland at times flirting with the equator, at others well north of it, and by around 600 million years ago so far south that it would be part of Antarctica today. Indeed, for large swathes of this vast expanse of time, Ireland lies far to the south of those quintessential southern continents of our modern world, Australia and Antarctica, and even becomes far colder than the latter when it is entombed in ice during the first Snowball Earth episode around 710 million years ago. Also, though throughout this time Ireland faithfully maintains its original continental alliance with North America and Greenland, it also forms a long-lasting association with a large block of South America. But as amazing as all these events are, they are eclipsed by the end of this time by an even greater one – the rise of another Ireland.

Whereas the first Ireland will eventually grow to account for most of the northern half of Ireland, this second Ireland is composed of the island's southern half. Mirroring its northern counterpart, it rises in a pillar of fire to become part of a chain of volcanic islands, albeit in this case one which eventually collides with the margin of the emerging Pannotian supercontinent and includes large parts of England and Wales. Sitting in a nook on the Pannotian margin between what is now the northern border of South America and the northwest coast of Africa, this southern Ireland is separated from its northern brother by the 3,000-kilometre-wide bulk of South America, the latter sitting to the west of what is now Peru. But though both Irelands lie relatively near the South Pole and so similarly bear the brunt of the icy ravages of the second Snowball Earth episode around 640 million years ago, the break-up of Pannotia around this time eventually sets them on wildly different courses. 

By 550 million years ago, the two Irelands have become parts of two different megacontinents, with northern Ireland a province of Laurentia, mainly composed of North America and Greenland, and southern Ireland a province of Gondwana, made up of today's southern continents. And, as time passes, they move further away from each other physically and climatically as the slender seaway Iapetus which separates them eventually grows into a mighty ocean, seeing Laurentia surge north while Gondwana drifts even farther south. By around 480 million years ago, the two Irelands sit at opposite ends of a vast ocean thousands of kilometres wide, with northern Ireland occupying a position of around 25 degrees south – a similar latitude to modern South Africa – and southern Ireland one around 60 degrees south, the same latitude as the Drake Passage which separates Antarctica and South America today. But this is all about to change. 

By this time, the great Iapetus Ocean has begun to shrink, setting in train events crucial to the formation of Ireland as we know it. Around 475 million years ago, a chain of volcanic islands which has been drawing ever closer to the Laurentian coast collides with the megacontinent and for 15 million years welds itself to the margin, adding pieces of New England to North America and expanding northern Ireland’s southern borders greatly. This collision also detaches a section of the Laurentian margin and moves it along the coast until it becomes that large swathe of Ireland's west we call Connemara. However, by now a far greater landmass is nearing the Laurentian coast, a micro-continent called Avalonia having rifted from Gondwana and ploughed its way north, its western end composed of the remaining parts of New England as well as Nova Scotia and Newfoundland, while its eastern limb contains parts of northern Germany, most of the Netherlands, Belgium, England, and Wales, and, of course, southern Ireland. Around 420 million years ago, Avalonia finally strikes Laurentia, uniting Ireland as a single land.

From this point onwards, Ireland commences an incredible journey north, voyaging from its position well south of the equator to the place it holds in the northern reaches of the world today. Along the way, its surface is clothed in deserts, rainforests, oceans, and ice, gifting the landscape with some of its most recognisable features, from the sandstone peninsulas of Kerry in the southwest and the limestones of the Burren and those of 'Ireland's Uluru', Ben Bulben, in the west and northwest, to the Ice Age drumlins of the north or spectacular glacial valleys like Wicklow's Glendalough in the east. Continental upheavals also sculpt the landscape, the buckling of the crust in the  northeast around 30 million years ago creating the basin in which Ireland's largest lake, Lough Neagh, now sits, although its ancient incarnation is far larger. However, it is the birth and death of the supercontinent Pangaea that bestows the landscape with some of its most epic features. Its formation over 300 million years ago drives up the peaks of Ireland's highest mountains, the southwest's MacGillycuddy's Reeks, while its destruction sunders Ireland's ancient bond with North America and Greenland as the Atlantic Ocean opens, the final schism occurring just under 60 million years ago and dramatically creating Ireland's most singular feature – seas of lava invading Ireland's northeast to form the iconic columns of the Giant's Causeway.

However, it is not fire but ice that gifts Ireland with its most defining feature as a land – its status as an island. Towards the end of the Ice Age, the great ice sheets muster one last and terrible advance in the Last Glacial Maximum, which lasts from around 26,000 to 19,000 years ago. At their greatest extent during this time, these ice sheets brutally conquer the entire surface of Ireland, covering it in places to an incredible depth of around one-and-a-half kilometres. As tightly as the ice grips the ground, though, it cannot hold Ireland in its icy grasp forever, and by 19,000 years ago the ice sheets are in retreat and the liberation of the land progresses from south to north, with Ireland beng virtually ice-free 5,000 years later. This collapse of the Irish ice sheet is a thing of catastrophic beauty as it fractures into separate ice domes which criss-cross the landscape to create a great variety of glacial features and eventually surge out through lowland gateways in the west to impregnate the surrounding seas with vast flotillas of icebergs. This demise of its ice sheets not only marks the death of Ireland as an ice-land, of course, but its birth as an island. By around 16,000 years ago, with sea levels rising as deglaciation continues to gather pace, the last thin isthmus connecting southeast Ireland to southwest Britain has been swallowed by the waves converting Ireland into the island which still sits in wave-locked isolation today, a land born of ice and water.

Yet, there is nothing immutable about Ireland's current form, and into the far future it will experience profound changes as it and all the other lands of the Earth are once more drawn back together to create a new supercontinent. There are many competing ideas for just how this will be assembled and what form it will take, but one of the leading models has been named Pangaea Proxima – 'the next Pangaea'. In this view, over the next 50 million years the western half of Pangaea Proxima will be formed as Australia ploughs into southeast Eurasia to become an immense new province of Asia, while Africa will continue its present journey north until it crashes into southern Europe, destroying the Mediterranean Sea and driving up a Himalayan-scale mountain chain in its place, running from southern Europe into Asia. This African uppercut on Eurasia's European chin will also dramatically alter Ireland's place in the world, the resulting clockwise rotation of Eurasia relocating Ireland to a latitude roughly equivalent to that of Iceland today as well as far to the east of where it sits in the modern world, while its orientation will also be drastically changed, its present east coast becoming its south coast. By 250 million years in the future, the collision of Antarctica and the Americas will complete the construction of Pangaea Proxima, with Ireland now lying off the northeast coast of this vast, doughnut-shaped supercontinent.

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Around four billion years ago, or perhaps even earlier, the first form of life on Earth twitches into existence, raising the curtain on a grand evolutionary drama whose latest act is playing out in our modern world, including the lands, seas, and skies of Ireland. This ancient progenitor of every thing that has ever lived, the last universal common ancestor – or LUCA as it is sometimes affectionately referred to – is quite different to what you might expect, not a free-living cell but a kind of living rock that is part of a hydrothermal vent system on the seafloor. In the honeycomb of pores in these hydrothermal vents, a cell membrane does eventually form and life escapes from the confines of its rocky hatchery and ventures into the world beyond. However, by this time one of the greatest divisions in the history of life has already taken place, the flight from the vents involving not one but two groups of microbes who constitute two of the three great domains of life – the bacteria and archaea.

Over the next billion years and more, the archaea and bacteria proliferate in the primitive seas and continue to expand the frontiers for life, including making it to the surface of the oceans and harnessing the power of the sun through photosynthesis. But undoubtedly the event with the greatest impact on the evolution of Ireland occurs just over two billion years ago – a marriage. Some ancient bacterium is engulfed, but not digested, by an ancient archaean, uniting these two venerable lines to create the third of life's great domains, the eukaryotes, which account for virtually all of the large, visible forms of life in Ireland today – from seaweeds to salmon, humans to horses, oaks to octopuses, mice to mushrooms. Over the next billion-and-a-half years, the three groups that all these modern life-forms belong to – the animals, plants, and fungi – diverge from one another and witness the rise in each of their respective ranks of multi-celled life-forms as formerly independent single-celled entities band together. By 500 million years ago, the seas, including those around the two still-separated Irelands, begin to look far more like they do today, filled with predators and prey belonging to the main animal groups which inhabit the lands and waters of modern Ireland, although many of these creatures are still very strange, including trilobites and sea scorpions.

From this time onwards, though, it is not only in the sea that the story of life plays out, as the plants, fungi, and animals begin their great invasion of the land. These terrestrial pioneers leave some very important evidence in Ireland from around the time it unites as a single land, with the tiny, bubble-topped twig-plant Cooksonia present in Tipperary around 425 million years ago, while around 40 million years later a metre-long vertebrate leaves footprints in an ancient flood plain that are now part of the cliffs of Valentia Island in Kerry. The invasion of Ireland by animals and plants is not a straightforward affair, however, in the early stages limited by Ireland's surface being dominated by a vast desert, while around 350 million years ago it is virtually entirely consumed by the sea. But when it re-emerges around 325 million years ago it is bursting with terrestrial life, its journey from the arid subtropics to just south of the equator meaning it is now frequently drenched with life-giving rains, promoting the growth of a vast, tropical rainforest. This ancient Irish jungle is home to a diversity of ancient amphibians, some quite fish-like, others similar to salamanders, albeit with crocodile-like snouts, and some even having a limbless, snake-like form. But the true stars here are the invertebrates, by around 300 million years ago the upsurge in oxygen spurred by the rainforests allowing Arthropleura, a 50-kilogram millipede relative as long as a car, to rule the land, while king of the skies is the seagull-sized dragonfly relative Meganeura

However, this vast rainforest soon disappears, Ireland becoming far more arid as the global climate becomes cooler and drier and the formation of Pangaea locks it into the heart of the supercontinent's northern limb, a thousand kilometres from the sea. In this new, increasingly arid world, the amphibians suffer greatly as their swampy habitats collapse, but by this time new lines of terrestrial vertebrates have arisen that are truly adapted to life on land – the ancestors of Ireland's living mammals, birds, and reptiles. From a common ancestor that emerges around 330 million years ago, two lines diverge around 10 million years later, with the ancient relatives of the mammals on one side and the reptiles on the other. The early forms of both these great lines are very similar, resembling small lizards, and are utterly dwarfed by many of the amphibians they live alongside, but by the early Permian (299–252 million years ago) they have risen to become the mightiest vertebrates on land. But in this game of thrones it is not the reptiles that first occupy the seat of power. Although they will eventually spawn some of the greatest dynasties on Earth in the form of the dinosaurs and their derived descendants, the birds, this is a world ruled by ancient, superficially reptile-like relatives of the mammals. As the Permian progresses, they evolve to become somewhat more mammal-like, but their rule is brought to a brutal end by the worst mass extinction ever, with up to 95 per cent of species vanishing in what is often simply called 'The Great Dying'.

After the smoke clears from this doomsday event, the ancestors of the mammals continue to evolve, and by the end of the Triassic (252–201 mya) true mammals have emerged. However, by this time the reptiles have risen to seize power in a great Triassic takeover and the Age of Dinosaurs has begun. The reptiles rule not only the land but the skies and seas too, with the pterosaurs being the first vertebrates to evolve powered flight, invading skies once the sole preserve of the insects, while a number of great lines have invaded the water. During the Jurassic (201–145 mya) and Cretaceous (145–66 mya) periods, Ireland is joined to Britain a number of times and so possibly home to some of its most fascinating dinosaurs, including relatives of the famous Tyrannosaurus rexDiplodocus, and Stegosaurus, while flocks of pterosaurs darken the sky and massive marine reptiles – some almost as large as a blue whale – rule the waves. As time passes in this ancient world, though, aspects of modern Ireland begin to bloom as the birds take to the sky and the flowers rise and radiate, spreading to the four corners of the Earth in a dramatic power grab within the plant kingdom. But the real harbinger of modernity arrives in a truly terrifying impact of destructive drama, this visitor from the heavens turning the world into a vision of hell and casting many of the great giants into the fires of extinction. Once more the world ends, and once more it is born again.

Ireland, having been swallowed by the sea around 85 million years ago, re-emerges just in time to be engulfed by the conflagration ending the Age of Dinosaurs, which ushers in a new era of 'recent life', the Cenozoic. This era, in which we still live, is often referred to as the 'Age of Mammals', but the rise of the mammals to ultimate power on land does not go uncontested as other animals also eye the terrestrial throne with lusty intent. Over ten million years after the dinosaurs have exited the stage, this contest is still well in the balance, and the ancestors of Ireland's largest modern mammals are far from becoming imposing beasts. By this time, global temperatures are swelteringly high, and Ireland is clothed in a subtropical forest similar to those of Vietnam or Malaysia today. Prancing among the palm trees is the earliest relative of Ireland's horses, Pliolophus, although this dawn horse is no bigger than a fox, while an ancient relative of Ireland's modern cattle and deer, Diacodexis, is barely the size of a housecat. These minnows live in the shadow of monsters, with crocodilians ruling the swamps and possibly even bounding across dry land on long, hooved legs. Even the Age of Dinosaurs does not seem to be entirely over, as the only surviving dinosaurs – the birds – can claim not just bony-toothed giants ruling Irish skies, but man-sized flightless forms like Gastornis rampaging through Irish lands like spectres from a bygone age. Luckily for Pliolophus and Diacodexis, though, this is a herbivore rather than a bloodthirsty killer.

In any case, by 35 million years ago, the mammals have seen off the challenges of the great beasts of feather and scale to become the undisputed lords of the land. They have also gone a step further than their ancestors ever did, having overthrown the reptiles in the seas, with the whales ousting the crocodiles to become masters of the deep, eventually invading the waters kissing the shores of Ireland. Even the skies above Ireland speak of the extension of mammalian power on Earth, and though the birds still rule they must share their domain after dark with those 'birds of the night', the bats, who by now have haunted Irish skies for over 15 million years. But though the mammals have clinched victory on land, there is no true peace, and internecine struggles soon intensify in their own ranks, with profound consequences for Ireland's mammal fauna. Just under 34 million years ago, the growth of vast ice sheets on Antarctica causes global sea levels to drop by as much as 55 metres, converting western Europe from an archipelago into an emergent region and opening a gateway to the east as the Turgai Strait – a long, shallow sea east of the Urals connecting the Arctic Ocean in the north to the ancient Tethys Sea in the south – is destroyed. Through this gateway, hordes of Asian mammals sweep westwards into Europe, eventually penetrating its farthest province, Ireland, adding to the turmoil from climate change to bring untold destruction, with around 60 per cent of Europe's mammals suffering extinction in this Grande Coupure, or 'Great Cut'.

Up to this point, Ireland has been home to some fascinating mammals, including ancient relatives of forms only found far from Ireland today, such as the marsupials, tapirs, hippos, and rhinos, and the greatest new Asian arrivals are also relatives of the latter two. A new ruling triumvirate includes rhinos closely related to living forms and two groups of hippo-relatives – anthracotheres, burly beasts ancestral to the hippos, and entelodonts, which look like nasty, supersized versions of Ireland's modern pigs and were once thought to be related to them. Stalking ancient Ireland is the 'hell pig', Entelodon, a cow-sized terror with massive, powerful shoulders and a huge, befanged head with bony knobs which not only scavenges on carrion but sometimes fells its own prey. Other archaic predators also possibly inhabit Ireland during the Oligocene (34–23 mya), including the wolf-sized Hyaenodon and false sabretooth cats, as well as many other strange or exotic animals, including opossum-like marsupial relatives, tiny gliding rodents, and relatives of the raccoons, red pandas, and bears, not to mention ostriches, alligators, crocodiles, snakes, and freshwater turtles. By this time, Ireland has cooled and the subtropical forests have given way to more open woodlands, but the climate is still Mediterranean, fostering exotic elements like palm trees. However, the undisputed rulers here are arboreal titans that still hold the title of 'tallest tree on Earth' today – the lofty crowns of these giant redwoods, Sequoia sempervirens, piercing the ancient Irish sky. 

Oligocene Ireland is not only home to archaic, extinct, and exotic life-forms, though, and living in the shadow of the giant redwoods are also early relatives of many modern Irish mammals. These possibly include hedgehogs and squirrels, as well as Proailurus, the first true cat, which is very like Ireland's living housecats, although it has shorter legs and can be somewhat larger. Advanced, but still small and hornless, ruminants – relatives of Ireland's living cattle, sheep, goats, and deer – are also present, while primitive relatives of the otters, stoats, badgers, and pine martens also inhabit the woodland floors. But it is the Miocene (23–5.3 mya), which truly witnesses the rise of Ireland's modern mammals, although their ancestors are often found far from Ireland. In Asia, the cats diverge into the eight lineages on Earth today, including that of Ireland's domestic cats, while large, horned ancestors of the cattle also arise here, as do the antlered ancestors of Ireland's deer. On the Mediterranean islands, the first forebears of the sheep and goats emerge, while all the way across the Atlantic one-toed horses make their first appearance in North America as do the first direct ancestors of Ireland's living dogs and foxes. This time also witnesses the incredible rise to power of a plant which covers around two-thirds of Ireland today – grass. Having arisen in tropical forests under the feet of the dinosaurs, from the late Oligocene onwards land after land falls to this conquering blade, with open grasslands spreading across the continents. 

However, it is only sometime after the Miocene that Ireland falls to the conquest of grass or is invaded by many of the direct ancestors of its modern mammals. During this epoch it is still home to many exotic mammals, possibly including rhinos, tapirs, bears, hyenas, pikas, flying squirrels, musk deer, mouse deer, and relatives of the red panda. Yet, some of these groups include some very strange forms, the early hyenas small and quite cat-like, including having retractable claws for climbing trees, the later ones larger, fully terrestrial meat-eaters resembling dogs. Indeed, they are not the only dog doppelgangers in this ancient Ireland, the bears being represented not only by more modern-looking species but by dog-bears, which look and live like dogs, possibly even hunting in packs. Even the relatives of mammals which inhabit Ireland today are strange, and though ever more advanced horses invade from North America, they all retain three toes. Among the strangest mammals in this ancient Ireland, though, are those belonging to fully extinct families, with the lynx-sized Prosansanosmilus being a member of yet another family of false sabretooth cats, the barbourofelids, while the massive Amphicyon giganteus is a representative of one of the greatest carnivore families to ever live, the amphicyonids, or bear-dogs. This 300-kilogram beast looks like a strange mash-up of the great carnivores of our modern world, its bear-like feet, dog-like head, and cat-like body combining to make a creature we could more accurately call a 'bear-cat-dog'.

The very oddest mammals stomping through Ireland's Miocene woodlands, though, are extinct members of the order Proboscidea to which belongs the largest living land mammal – the elephant. Early in this epoch, a great fire building under northeast Africa ruptures the crust, the opening of the Red Sea and Gulf of Aden causing Arabia to divorce itself from Africa and form a new marriage with Eurasia. The associated uplift of Arabia also sunders the marine connection which has long isolated Africa, forging a new landbridge across which advance a parade of proboscideans. By around 18 million years ago, these ancient elephant-relatives have begun to invade Ireland, swiftly becoming the undisputed rulers of its woods. The early invader Gomphotherium is very elephant-like in many ways, most species even being around the size of an Asian elephant, but its head is remarkably different, with a long, low, skull, shorter trunk, and not two but four tusks – those in the upper jaw curving downwards, the lower ones short and straight and projecting from an extremely long lower jaw. If Gomphotherium looks like a modern elephant whose face has been sucked into a vacuum cleaner, though, it is outdone in the weirdness stakes by a similar-sized proboscidean which possibly invades Ireland shortly after it, Prodeinotherium being a member of the deinotheres, those 'terrible beasts' with even shorter trunks and only one pair of massive tusks sweeping directly down from their lower jaws, like a long beard drooping from the chin of an old man.

From the time of their first invasion up to quite recent times, the proboscideans are the true luminaries of the Irish landscape. During the Pliocene (5.3–2.6 mya), for instance, Ireland is the stage for an incredible cast of mammals, at various times in this epoch home not only to modern-looking deer, bovids, and otters, but three-toed horses, rhinos, tapirs, hyenas, red pandas, and even a massive relative of the giant panda, Agriotherium. But standing head and shoulders (and a bit more besides) over all these fascinating forms is one of the largest land mammals that has ever lived, a relative of the American mastodon called Mammut borsoni, which is far larger and more spectacular than its more famous cousin. Average-sized members of this species stand around a metre taller than the living African elephant, and at an astonishing weight of 16 tonnes are almost three times heavier than this largest living land mammal. And projecting from the heads of these colossal beasts are simply the longest tusks of any animal ever, measuring an incredible five metres in length – or as long as a giraffe is tall! Yet, as a new epoch dawns, the Pleistocene (2.6 mya–11,700 years ago), another proboscidean invades Ireland whose line will go on to rule this land as the world descends into an age of ice. This is a true elephant, the mammoth Mammuthus rumanus, the hairless ancestor of a furry behemoth which stomps into Ireland in the late Pleistocene to become its undisputed Ice Age king –Mammuthus primigenius,  the woolly mammoth.

This shaggy giant presides over an Irish landscape in the late Ice Age filled with musk oxen, giant Irish deer, and reindeer, as well as spotted hyenas, wolves, brown bears, arctic foxes, and arctic lemmings, not to mention mammals still found in Ireland today, such as one-toed horses, red deer, hares, and stoats. The woolly mammoth is the most supremely adapted for the bitter cold, though, having a three-layered coat, short tail, small, round ears, a thick layer of fat under the skin, and even a form of antifreeze blood. But even these defences crumble in the face of the icy onslaught that is the Last Glacial Maximum, which sets in around 26,000 years ago. For a millennium the mammoths endure, but the ever-deepening cold soon wipes them from the face of Ireland, never to return. Over 10,000 years later, once the liberation of Ireland from its icy prison has truly begun, a new king ascends to the throne, one with a true crown – the giant Irish deer, whose largest males are not only huge, standing 2.1 metres tall at the shoulder and weighing over 900 kilograms, but have the largest antlers ever, each the length of a man. Around 12,500 years ago this last great king of Ice Age Ireland disappears, and less than a thousand years later the Ice Age itself comes to an end. However, even in our modern world a faint echo of Ice Age Ireland persists, a kingly beast of the frozen north owing some of its genes to the mating of its ancestors with ancient Irish brown bears, meaning this white bear of the Arctic, the polar bear, is at least partly green.

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The deepest origins of Ireland’s people lie in an ancient world still ruled by dinosaurs. The rise of the order Primates is the culmination of a series of splits within the mammals which begin all the way back in the early Jurassic, not long after their first appearance on Earth. It is the fiery break-up of the supercontinent Pangaea which sparks the great divergences between the three living mammal groups, with the ancestors of the monotremes –  today's platypus and echidna of Australasia – set adrift on the southern megacontinent Gondwana, while the common ancestor of the marsupials and placentals inhabits the northern megacontinent Laurasia.  By 160 million years ago, the placentals – which account for almost 95 per cent of modern mammal species, including all of Ireland's native mammals and its humans – have split from the marsupials, and from 105 million years ago onwards the four modern placental superorders emerge. The afrotheres, or 'African beasts', (elephants, aardvarks, hyraxes, etc.) diverge first, followed by the xenarthrans (sloths, armadillos, anteaters, etc.), and, finally, 95 million years ago, the final two split from each other, with the laurasiatheres ('Laurasian beasts') on one side and the euarchontoglirans on the other, among whose ranks are the primates. 

This final superorder split is a major event in the evolution of Ireland's people, as it defines how they truly relate to all the other mammals in Ireland and its seas today. For one thing, it means that humans are on the minority side of the mammal divide on the island, the majority of Ireland's mammals being laurasiatheres. These Laurasian beasts account for most of the island’s native land mammals, including, amongst others, the badgers, otters, and foxes, the red deer and fallow deer, the hedgehogs and pygmy shrews, the bats, as well as the whales and seals which inhabit Ireland’s waters, not to mention all of Ireland’s major domesticated mammals – the horses, cattle, sheep, pigs, goats, cats, and dogs. As members of the superorder Euarchontoglires, then, Irish people's closest relatives on the island are not the proud, powerful horses or the superbly-antlered deer, the cunning foxes or those aerial maestros, the bats. Unlike these animals, they do not gallop or rut, slink or soar. In fact, many of them gnaw, scratch, scurry, and squeak, as they include some of the most reviled mammals on the island – rats and mice. As jarring as it may seem, the simple truth is that, along with the rabbits and hares, the closest relatives of Ireland's people on the island are the rodents.

This affinity of Ireland's people with the island's rodents makes far more sense when we consider the earliest forms that gave rise to the primates. After the superorder Euarchontoglires emerges around 95 million years ago, it rapidly radiates into the orders that compose it today, and by 90 million years ago the primate order arises from ancestors possibly resembling a group of rodents which bounce among the branches of Ireland's modern trees – the squirrels. From such a squirrel-like form, the primates evolve the features which characterise modern forms, with forward-facing, convergent eyes, short snouts, larger and more rounded braincases, and flat nails instead of claws on their grasping hands and feet with opposable thumbs and big toes. They also embark on their epic spread across the world. Likely originating in Asia, they surge eastwards into North America and, eventually, on into Europe around 55 million years ago when the blistering temperatures facilitate dispersals across the northern continents, the opening North Atlantic having not yet entirely sundered the landbridge between North America and Europe. Thus do the primates arrive in Ireland and there thrive, peppering its ancient trees and adding their voices to the wild chatter amid the tangle of branches and vines in the canopies of the steamy subtropical forests.

By this time, though, a mighty rift has occurred, the primates having split into the two great branches to which all living forms belong. On one side of this evolutionary partition today lie the lemurs of Madagascar and the small, bug-eyed bush babies and lorises of Africa and Asia, on the other the tiny tarsiers of Southeast Asia and the anthropoids – those 'human-like' primates, the monkeys, apes, and, of course, humans, including Ireland's people. In the hothouse Ireland of the early Eocene (56–34 mya), extinct groups representing both branches abound, the day belonging to primates from the lemurs' branch, and these ancient relatives of theirs even do a reasonable impression of a lemur. However, as the day steadily slips into a deepening darkness and the blazing authority of the sun yields to the softer governance of the moon, these primates recede, the onset of night seeing the forest revived with primates that occupy the same branch as Ireland's modern humans. However, these ancient primates are far different to the people which now call Ireland home. Whereas the lemur relatives in these primeval subtropical forests are themselves small, none bigger than a housecat, they are giants compared to their human-branch counterparts, some of which weigh only 100 grams. Of the living members of their branch, these primates look far more like the tiny tarsiers, having large eyes, short, narrow snouts, and bodies quite well suited for leaping, and their nocturnal feasts consist of course after course of crunchy insects.

For many millions of years, both of these primate groups bound and leap through the branches of Ireland's ancient forests, sailing over the heads of everything from giant birds to crocodiles to tiny horses, but as the Eocene gives way to the Oligocene (34–23 mya), the long reign of these arboreal kings comes to a crashing end, as the downturn in climate sees their dense, subtropical forest strongholds fall and be replaced by more open woodlands. The end of the primates in Ireland, then, is part of that terrible European extinction episode the Grande Coupure, with the twin terrors of climate change and competition with Asian invaders wiping many mammals from the face of Ireland. But though this 'Great Cut' severs the tale of primates in Ireland for millions of years to come, in faraway lands the evolutionary story of Ireland's people continues, by this time some fundamental divergences of living groups having occurred on the human branch. In the early Eocene, around 50 million years ago, the first primitive tarsiers arise in Asia, and by the end of the epoch monkey-like anthropoids throng the branches of the lush forests of North Africa and even South America, the ancestors of the New World monkeys having split from the ancestral group of the Old World monkeys and apes and somehow journeyed from their African homeland to the ancient forests of Peru – the earliest anthropoid in the New World being the small tamarin-sized, 36-million-year-old Perupithecus.

So, by the early Oligocene, the New World monkeys have split from the Old World monkeys and apes, but only later in the epoch will these latter groups diverge from each other in Africa, and only far later again evolve their modern, specialised forms, leading to the baboons, mandrills, macaques, etc., on one side, and the gibbons, great apes, and humans on the other. Thus, at this time, Ireland's people and all their ape and Old World monkey relatives are still represented by a single form, a vision of this common ancestor provided by a tree-dweller in the forests of the Fayum in northern Egypt known to be a member of their ancestral group – Aegyptopithecus, the 'Egyptian monkey'. At six-to-eight kilograms, Aegyptopithecus is the size of a large housecat, and has a general monkey-like form, including the possession of a long tail, and runs and leaps through its forest home on the tops of branches using its palms on all fours. In basic form, then, the common ancestor of the apes and Old World monkeys probably looks much more like the latter, and this is also true of the earliest members of the ape line even after they split from that of the Old World monkeys. In the trees of Tanzania 25 million years ago, the first ape, Rukwapithecus, lives alongside the first Old World monkey, Nsungwepithecus, and both look very similar, being roughly 12-kilogram, monkey-like forms. However, as we enter the Miocene (23–5.3 mya), the apes set out on a spectacular evolutionary journey, by the epoch's end producing forms much closer to Ireland's people.

Whereas today the Old World monkeys can boast around three times the number of the apes' roughly 20 species, during the Miocene the apes are ascendant and this is their golden age. In East Africa 20–17 million years ago live a wondrous variety of apes, some as small as a housecat, others as big as a male chimpanzee, and one of the best-known forms is the 15–30-kilogram Ekembo. Although still quite monkey-like in form, Ekembo resembles modern apes in some crucial ways, having lost its tail and evolved more ape-like teeth and a brain as large as that of the smallest living ape, the gibbon. But while Ekembo and its kind lie outside the living radiation of apes, soon forms turn up which are closer to Ireland's people both evolutionarily and geographically. By 17 million years ago, the quest to turn the world into the planet of the apes has begun, the apes colonising Arabia first and then Europe, following the shorelines of an ancient inland sea to invade subtropical forests not far from Ireland, in southwest Germany. Here lives Griphopithecus, a roughly 50-kilogram ape that still looks quite like Ekembo but has teeth more like those of the great apes – the orangutan, gorilla, chimpanzee, and bonobo – and is possibly a primitive member of the family we share with them, Hominidae, which is no longer restricted to just the members of the human line as it once was. As the Miocene progresses, though, apes appear in the forests of Europe that are, incredibly, perhaps even more closely related to the people of Ireland.

By around 14 million years ago, the family Hominidae has split into two groups: the pongines, whose only living member is the orangutan, and the hominines, today represented by the African apes (the gorilla, chimpanzee, and bonobo) and humans, including Ireland's people. But while the pongines rule Asia, from Turkey to Thailand, the hominines' stronghold is Europe, which is home to a number of forms resembling modern African apes. Dryopithecus, the first of these 'African apes' of Europe, lives in northern Spain and southern France over 12 million years ago and looks like a strange mish-mash of living African apes, being chimpanzee-sized with a gorilla-like face. Around two million years later, a number of Dryopithecus's descendants appear across Europe which display even more features allying them with living African apes, and altogether these dryopithecins raise the fascinating possibility that the first hominines arose in Europe and from there migrated to Africa to give rise to the gorillas, chimpanzees, bonobos, and hominins, the group exclusive to humans and their ancient kin. One dryopithecin, the 30-kilogram Danuvius living in the Bavarian forests 11.6 million years ago, possibly provides a glimpse of the common ancestor of the African apes and hominins, combining African ape-like arms and hands for hanging from branches with more human-like legs and feet for walking upright upon them, while some have even argued that the 7.2-million-year-old Graecopithecus from Greece is not only a hominine but a hominin!

This is a very controversial claim but, if true, obviously has seismic implications for our understanding of the origins of Ireland's people, meaning their roots not only as hominines but as hominins may lie in Europe rather than Africa. Whatever the truth of all this, by around seven million years ago the story of Ireland's people shifts to Africa, the first forms more generally agreed to be hominins appearing at the same time as the dryopithecin apes vanish in Europe. Between this time and around five million years ago, three hominins are known: Sahelanthropus ('Sahel man') in Chad in Central Africa, and Orrorin ('original man') and Ardipithecus in Kenya and Ethiopia, respectively, in East Africa. Although roughly chimpanzee-sized and still bearing many features related to a life in the trees, all three also display features related to upright walking on two feet as well as reduced upper canines in males, which are hallmarks of hominins. With the rise of Australopithecus just over four million years ago, we see the hominin body plan beginning to display an even greater commitment to life on the ground, for instance, the feet being less hand-like as the big toe is aligned with the rest of the toes as in a modern human foot rather than being ape-like and divergent as in Ardipithecus. But it is only with the rise of Homo erectus in South Africa two million years ago that we see the body form of Ireland's modern people truly emerge, many of our characteristic traits related not to upright walking but to a more dynamic form of locomotion – long-distance running .

However, Homo erectus resembles modern Irish people not only in body but in brain. Whereas a chimpanzee-sized brain had arisen in the early pongines and hominines, no enlargement is visible in the earliest hominins, and only a slight one in Australopithecus, but in early Homo, and especially Homo erectus, we see the first appearance of brains that are two-to-three times larger than that of a chimpanzee. With a body and mind suited to exploiting the open grasslands spreading across the continents, Homo erectus soon surges beyond the confines of its African homeland, and by 1.8 million years ago it is in Dmanisi, Georgia in western Asia, right on the doorstep of Europe. Over the next million years, Homo erectus and its daughter species forge a path into western Europe, and by 850,000  or possibly even 950,000 – years ago, humans appear for the first time in that land just to the east of Ireland, Britain, footprints found in eastern England from this time possibly belonging to Homo antecessor. From this time onwards, Britain is inhabited by various Homo species, among the highlights of these later occupations being the powerful hunters at Boxgrove in southern England around 500,000 years ago and the Neanderthals known from the southern half of Britain from around 60,000 years ago. But if any of these ancient humans also invade Ireland they leave no trace of their presence, the earliest evidence for humans in this land coming from a new species  our species, Homo sapiens.

This species, to which all the people of modern Ireland and the rest of the world belong, rises around 300,000 years ago in Africa, and by around 60,000 years ago its members have emulated their grandmother species Homo erectus by breaking out of Africa and invading the surrounding continents. Meeting the Neanderthals in western Asia, interbreeding occurs, the traces of which are still found in the genetic makeup of many Irish people today, who have around two per cent Neanderthal DNA. By around 47,000 years ago, our species begins its great invasion of Europe, but the first phase of this invasion fails without issue and it is only from around 37,000 years ago onwards that Homo sapiens populations appear that are among the ancestors of modern-day Europeans. Before long, these people have made their way to the very western lands of the continent, leaving the very first evidence of a human presence in Ireland in the form of a butchered reindeer bone dating to around 33,000 years ago. But these first inhabitants of Ireland differ from many of its modern people in one very striking way, their more recent African ancestry still evident in their darker skin. By the time these early Europeans arrive in Ireland, though, their new home has begun to turn against them as the continent descends into the brutal cold of the Last Glacial Maximum (26,000–19,000 years ago), and while humans return to Ireland yet again just under 13,000 years ago, they are once more wiped from the land by a vicious cold snap closing out the Ice Age.

Around 11,700 years ago, the Ice Age ends, but it is only about 1,500 years later that Ireland is settled by humans anew. Like those before them, the African ancestry of these people is still obvious, but by this time Europeans have also evolved lighter eye colours lending these early Irish a striking combination of darker skin and blue eyes. For 4,000 years, these ancient hunter-gatherers enjoy their splendid isolation on the island until a new wave of migrants arrive with a new way of life – farmers. From their homeland in the Near East, these lighter-skinned farmers seize Europe in a great westward sweep, reaching the shores of Ireland around 6,000 years ago. For the next 1,500 years, they profoundly alter the fabric of the Irish landscape, building houses, clearing fields, and erecting great monuments, not least the peerless passage tomb Newgrange. By the time this great tomb is raised, the fabric of their society has also changed, incestuous elites having risen to monopolise power to reign like the pharaohs of Egypt. But these god-kings' rule does not last, around 4,500 years ago a new invasion from the east deeply changing Ireland as Bronze Age migrants from the eastern European steppe bring not only metal to the island but the first Indo-European languages – the linguistic pool from which the first form of the Irish language will arise. Later times will see yet more great invasions of the island, from the Vikings to the Normans to the English, and the arrival of Christianity, but as a land, a people, a culture, Ireland has already become truly Irish.