How Many Friends Does One Person Need? (16 page)

When the last Neanderthal died (probably in northern Spain) less than a thousand generations ago, they had been around as a species for a great deal longer than we modern humans have so far managed. Modern humans emerged about two hundred thousand years ago from the same African root stock as the Neanderthals. But unlike
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the Neanderthals, we remained in Africa until around seventy thousand years ago when there was a sudden exodus across the Red Sea into southern Asia. Modern humans did not reach Europe, where they came into contact with significant Neanderthal populations for the first time, until around forty thousand years ago. When they finally did so, they arrived – as have so many of Europe’s historical immigrants from the Indo-Europeans around six thousand years ago to Attila the Hun and his nomad hordes in Roman times – from the steppes of western Asia. It took us little more than ten thousand years to displace all the Neanderthals from Europe.

The sudden disappearance of the Neanderthals has always piqued our curiosity. Some have suggested that they disappeared because modern humans bred with them – modern Europeans being thus the result of hybridisation between the two species. It’s true that very occasionally you do get the odd Neanderthal-like modern European, complete with barrel-chest, thick neck and heavily muscled legs and arms. But that said, there are too many thin gangly ones who don’t show much of a resemblance, and on the whole this seems a rather implausible explanation. Others have suggested that, on the model of the historical European invasions of the New World and Australia, our ancestors simply slaughtered the Neanderthals because they were in the way or put up a resistance. Alas, we modern humans have rather a bad history of such behaviour, so it’s by no means beyond the bounds of possibility. Others have suggested, in the light of the more recent experience of the South American Indians, that the Neanderthals were wiped out by novel tropical diseases brought from Africa to which they lacked
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immunity. The only fly in this particular ointment is that modern humans didn’t arrive directly from Africa: they came from the east, probably somewhere around the Black Sea, so had been exposed for the better part of thirty thousand years to much the same diseases as the Neanderthals would have had.

Whatever the actual cause of their demise, the Neanderthals probably viewed these darker-skinned immigrants with much the same suspicion that modern Europeans have done in more recent times. That the Neanderthals were light-skinned like modern Europeans received dramatic confirmation from recently published analyses of Neanderthal DNA. Geneticists at the University of Barcelona have managed to extract DNA from a forty-eight-thousand-year-old Neanderthal from El Sidrón in Spain. There they found a variant of the mc1r gene that, in modern Europeans, is responsible for lighter skin colour by suppressing the production of dark melanins in the skin. When copies of this gene are inherited from both parents, the result is the sun-sensitive skins and red hair that have been such a hallmark of our own west-coast island populations. Red-head Neanderthals? That’s a turn-up for the books.

At the same time, it is equally clear from these and other recent genetic studies that Neanderthals shared few of the novel mutations that characterise modern human populations, especially those from the northern hemisphere. It seems that the Neanderthals were not our ancestors, but a separate – albeit closely related – species. Our European light skins and red hair were not the result of our dark-skinned African ancestors interbreeding with Neanderthals, but rather independent genetic adaptations
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to coping with the same problems of life at high latitudes that bedevilled Neanderthals. It’s that old vitamin D problem that we came across earlier.

One reason this must be true is that the genetic evidence has now comprehensively confirmed that the Neanderthals’ ancestors split away from the ancestral lineage that gave rise to us around 750,000 years ago, some time before the lineage that eventually gave rise to the Neanderthals first left Africa in search of a new homeland in Europe. Whatever the root cause of the Neanderthals’ sudden demise some four hundred millennia after arriving in Europe, the one that can now definitively be ruled out is interbreeding with modern humans. The alternatives that remain, however, would seem to be a lot less pleasant to contemplate.
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Species change through the gradual failure of some lineages to reproduce, resulting in a subtle but steady drift in the species’ genetic make-up towards that of lineages that are more successful. Although in most cases these processes are quite slow, an entire species can go extinct catastrophically if none of its various lineages can reproduce fast enough to offset unusually high levels of mortality. There is always a steady trickle of such extinctions over time – there have been literally dozens within our own lineage during the course of our six-million-year evolutionary history. Sometimes, however, environmental conditions conspire to produce a rapid burst of extinctions.

Sixty-five million years ago, a massive asteroid smashed into the corner of Mexico where the Yucatan peninsula now stands. The resulting fireball, combined with millions of tons of vaporised rock thrown up into the atmosphere, brought on a nuclear winter that changed the face of the earth for ever. As the planet slowly emerged from the catastrophe, it was to find that the dinosaurs who had
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dominated the planet for the previous 250 million years were fading fast. The dragon lords of the earth were being replaced by a small and insignificant group of animals –the mammals – that had previously skulked out of sight on the forest floor.

This dramatic turnover in the world’s fauna was the fifth massive bout of extinction in the five-hundred-million-year history of life on earth. Most of these mass extinctions seem to have occurred at intervals of about sixty-five million years. Although their causes seem to have varied, they have typically resulted in the sudden disappearance of seventy to eighty per cent of all the species of animals alive at the time.

So it is, perhaps, no surprise to find ourselves on the brink of yet another wave of extinctions. Although only a relatively small number of species have actually gone extinct in historical times, many are famous for having done so – the dodo of Mauritius and the giant moas of New Zealand are the best known, but the curiously named Miss Waldron’s red colobus from the Gambia and the giant lemurs of Madagascar (some as big as a female gorilla) remind us that even primates are not exempt.

But the figures for actual extinctions give a false impression. Some eleven thousand species of animals and plants are currently listed as being in imminent danger of extinction. The latest estimate is that as many as half of all living species could be extinct within the next century. Sadly, the cause this time is not meteors from outer space or poisoning from volcanic eruptions from within, but – to borrow the Gaelic for a moment –
sinn féin
: we ourselves.

We have been cutting down the world’s forests at such a rate over the past century that some African countries
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now have as little as five to ten per cent of their original forest cover left. What remains of the planet’s forests are being lost as a rate of about eight per cent per decade. It hardly needs rocket science to figure out what that means: it won’t take much more than a century to clean up the rest.

The tragedy that hides beneath these bald figures is brought sharply into focus by the prospects for our clos-est living relatives, the great apes. If you want to see an orang utan in the wild, you’d best book your plane ticket now. The rate of deforestation in their strongholds on Sumatra and Borneo, and the resulting decline in orang numbers, is such that there are unlikely to be any left in the wild in 2015. And the Boxing Day tsunami didn’t help, either: the Aceh peninsula in northern Sumatra, which took so much of the brunt of the human tragedy, was also one of the strongholds for wild orangs. Even before the tsunami struck, the peninsula was estimated to have lost forty-five per cent of its orang population between 1993 and 2000 alone.

The forecasts aren’t much better for their African cousins. The gorilla and the chimpanzee, with whom we shared a common ancestor as recently as six or seven million years ago, will outlive their Asian cousin only by a few decades. A lethal combination of deforestation and hunting to feed a voracious market for ‘bushmeat’ in the cities of central and west Africa holds out a promise of only another twenty to fifty years for most wild populations.

The root cause, in the end, is the dramatic explosion in the human population over the last two thousand years. When Jesus Christ was born, the world’s entire popula-
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tion amounted to about two hundred million people (less than the current population of the USA); today, there are over 6,400 million of us, and we are adding around seventy-four million new ones every year – a baby every three seconds. Most are living in such grinding poverty that they cannot afford the luxury of worrying about conservation. The tree that is still standing quite literally stands between them and daily survival: cut down, it represents money, fuel, food or housing.

Like the proverbial car crash in slow motion, we stand on the edge and watch a disaster unfolding with an apparent inevitability that is difficult to comprehend, let alone do anything about. With or without the Kyoto Agreement, we have to sort out both our insatiable appetite for hard-woods and the demand for new agricultural land. Here, on a global scale, is the same crisis of survival that triggered the emigrations and Clearances from the Highlands and islands of Scotland during the late eighteenth and early nineteenth centuries. But in the 1800s, the emigrants had somewhere else to go to begin a new life. Today, we don’t have that luxury.

Remember the Three Wise Men, and gifts they brought the first Christmas? Gold, frankincense and myrrh? Alas, it seems that had it been this year rather than two thousand or so years ago that they popped down to the local market for a few things to take with them on the way to Bethlehem, one of the boxes carried onto the stage at primary-school nativity plays today by three puzzled waifs might have been very different. We are busily killing off
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the tree that produces the sticky sap that, once dried, we call frankincense. And this has bigger implications than merely for the Magi and a few school nativity plays. Frankincense remains one of the core ingredients for the perfume industry, as well as in its more conventional use as incense. Frankincense production is falling: the sap is becoming harder to get hold of.

Frankincense is produced by a handful of tree species of a small and rather undistinguished kind that grow in the arid zone bordering the southern edge of the Sahara
.
Like many tropical trees, the
Boswellia
exudes a sticky sap when it is cut or damaged. The sap helps protect the tree against desiccation, bacterial and fungal infections and insect predators while the damage is repaired. However,
Boswellia
sap has some unusual properties which set it aside from most other species. The dried sap yields a headily aromatic fragrance that is prized for its perfuming capacities. It was not long before people discovered that sap production could be encouraged by deliberately cutting the tree bark. The sap that oozed out could be collected a few weeks later, and this cycle could be repeated over and over again.

French crusaders were probably responsible for bringing it back to Europe from the Holy Land during the Middle Ages – hence its name, the Franks’ (or French) incense. But it had been used in the Middle East for millennia as a ceremonial and general household incense, as well as in traditional herbal medicines. Incense has been a major industry throughout the tree’s natural range, but especially so in the Horn of Africa and Arabia, probably for as long as humans could light the fire to burn it on.

Alas, there’s no such thing as a free lunch in real life,
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and especially so in the biological world. Sap production is a hugely beneficial capacity for a tree, since it provides protection for damaged parts and so aids recovery and regeneration. But producing the sap is actually very expensive for the tree. It has to take energy and resources away from reproduction the following season in order to do so. Sap, fruits and flowers all have heavy carbohydrate bases, so if the tree is forced to invest its limited carbohydrate reserves in sap, it simply doesn’t have these available for investing in flowers and fruits when the production season comes around with the following rains. The cost to the tree is especially heavy if its sap is harvested during the dry season: it has to draw on its stored reserves of carbohydrates to produce sap since it cannot create new carbohydrates through the natural processes when it is dormant.

In a recent study, Toon Rijkers and his colleagues at Wageningen University, Holland, and the University of Asmara, Eritrea, looked at the regeneration of the frankincense-producing
Boswellia
trees in the Horn of Africa. They found that the more heavily trees are tapped – and in the most intensive harvesting, the wounds are reopened every three weeks throughout the long dry season – the poorer was the flower and seed crop produced the following wet season.

Rijkers and his colleagues also found that heavily harvested trees produced seeds that weighed much less than those produced by less heavily harvested trees. More importantly, these smaller seeds had much poorer germi-nation rates. In experimental tests, fewer than forty per cent of the seeds of heavily harvested trees produced viable seedlings compared to around ninety per cent for trees
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that had not been harvested for more than a decade.

In short, the demand for frankincense has been literally bleeding the trees to death. Unable to seed properly, they have not been able to replace themselves as natural mortality has taken its toll on the adult trees. However, all need not be lost: Rijkers showed that providing the harvesting is done more sensitively and the trees allowed to rest from time to time, they will regenerate well.