The Accidental Species

MISUNDERSTANDINGS OF HUMAN EVOLUTION

THE UNIVERSITY OF CHICAGO PRESS

Contents

CHAPTER 1

An Unexpected Party

Many years ago I was a paleontologist. I studied fossil bones. Each boneis mute testimony to the existence of a life, in the past: of an animal thelikes of which might have vanished from the earth. I gave up being afull-time bone-botherer when I found myself on the staff of Nature, theleading international journal of science.

I was a junior news reporter on a three-month contract. My first assignment,at 9:30 a.m. on Monday, 11 December 1987, was to write abrief piece on new radiological protection guidelines, of which I knewnothing whatsoever. By noon, however, I was to deliver a well-turned,terse, and, most importantly, authoritative story that could stand thescrutiny of Nature's discerning readers.

It wasn't long before I accreted the job of writing Nature's weeklypress release—a document that goes out to journalists around theworld, keen to learn the latest stories from the frontiers of science.Given that, like me, many journalists would be unlikely to understandall the technical details in each paper, my task was to write a documentthat would summarize the essence of each in language that would begenerally comprehensible. It was an enjoyable and mind-stretchingtask. On any given day I might be writing about anything in science,from high-energy physics to the molecular biology of HIV-1.

I also got some practice at writing catchy headlines.

My favorite press-release headline concerned a story about mice aptto lose their balance and fall over. The researchers found a genetic mutationresponsible for this defect. The research was important becauseit allowed an insight into a distressing hereditary disease called Usher'ssyndrome, which is responsible for most cases of deaf-blindness in humans,and which can also include loss of balance. To paraphrase whatthe humorist Tom Lehrer noted about himself, my muse is sometimesunconstrained by such considerations as taste: so my headline was(hey, you're way ahead of me here)

THE FALL OF THE MOUSE OF USHER

A perk of being the press-release writer was to sit on the weekly meetingof editors trying to decide what would be on Nature's cover twoweeks hence. It was here that I first began to appreciate that editorsat Nature are among the first to hear about new insights into the unknown.In 1994, two marine biologists sent us an amazing photo capturedby the Alvin submersible at a depth of more than 2,500 meters.The picture was dramatic, contrasty, and gothic. Picked out in harshspotlights, exposé-style, it showed two octopi, each of a diff erent speciesunknown to science, but both male, and having sex. A colleaguesuggested that this would make an arresting cover picture—another,however, demurred, on the grounds that it was "disgusting." At thispoint I spoke up—I can still hear myself saying the words—"we canalways put black rectangles over their eyes." My mind raced ahead,composing an arresting press-release entry that would be headed withthe line

BESTIAL SODOMY IN THE ABYSS

In this case, taste intervened and I used something less lurid. The picturedidn't make the cover, either.

I mention all this to excuse some of what follows—if I am criticalof journalists and news editors, my criticism comes from experience. Iknow what it is like to work on a story to a tight deadline, and from aposition of relative ignorance. I can also appreciate that the term "missinglink," which seems to encapsulate so much in so little space, exertsan almost irresistible allure, even though it represents a completelymisleading view of what evolution is, how it works, and the place thathuman beings occupy in nature.

In the course of time, I migrated from the news department to the"back half," the team of editors who have the immense privilege of selectingwhich research papers from the stream of submissions will bepublished in the journal. One of the pleasures of the job is receiving thefirst news of important, potentially world-changing discoveries.

An account of perhaps the single most remarkable discovery I'veseen in my career as an editor was submitted to Nature on 3 March 2004.The discovery was of something quite unexpected, opening up unsuspectedvistas on things we didn't know we didn't know, and challengingconventional assumptions about the inevitable ascent of humankindto a preordained state as the apotheosis and zenith of all creation.After several revisions, and much discussion among my colleagues andthe panel of scientists we'd assembled to advise us on the report of thediscovery, the news was published in Nature on 28 October 2004.

This communiqué from beyond the realms of the known came froman international team of archaeologists working in a cave called LiangBua, on the remote island of Flores, in Indonesia. If you want to findFlores on a map, look up the island of Java, and work your way eastward,past Bali and Lombok, and there it is. Flores is part of a long chain ofislands that ends up at the island of Timor, well on the way to Australia,New Guinea, and the Pacific Ocean.

One of the more intriguing questions in archaeology is when Australiawas first settled by modern humans, the ancestors of today's aboriginalpeoples. There is much debate about this issue. Clearly, oneway of illuminating the problem is to search for early modern humansliving in what is now Indonesia, which can be thought of as a series ofstepping-stones between mainland Asia and Australia. That's whereFlores comes in. Archaeologists are interested in the caves of Flores andother islands such as Timor because of their potential to yield remainsof Homo sapiens, modern people caught in the act of heading towardthat distant island continent later associated with cold lager, "WaltzingMatilda," and The Adventures of Priscilla, Queen of the Desert. This is whatdrew an international team of archaeologists to Flores, and in particularto Liang Bua, known as an archaeological site for decades.

Flores, though, is an island of mysteries—for it has been inhabitedfor at least a million years, and not by Homo sapiens. Stone tools havebeen discovered in several places on the island, and their makers areusually thought to have been Homo erectus, an earlier hominin, whoseremains are well known from Java, China, and other parts of the world.The bones of these early inhabitants of Flores have not been found,their presence betrayed only by the distinctive stone tools they leftbehind.

But whoever these early inhabitants were, their very presence is aproblem. In the depths of the ice ages, when much of the earth's waterwas locked up in ice caps and glaciers, the sea receded so far that manyof the islands of Indonesia were connected by land bridges—theycould be colonized by anything able to walk there. Not so Flores: thisremained separate, cut off from mainland Asia by a deep channel. Homoerectus—if that's who it was—must have made the crossing from thenearest island by boat or raft, or, like other animals, washed up there byaccident. Once they made landfall on Flores, there they stayed—cut offfrom the rest of the world for a very long time.

Isolation on islands does strange things to castaways, making themlook very different from their cousins on the mainland. So it was withFlores, home to a species of elephant shrunken to the size of a pony, ratsgrown to the size of terriers, and gigantic monitor lizards that mademodern Komodo dragons look kittenish by comparison.

Such peculiar faunas are typical of islands cut off from the mainlandwhere, for reasons still unclear, small animals evolve to become larger,and large animals evolve to become smaller. Miniature elephants, inparticular, were rather common in the ice ages. Practically every isolatedisland had its own species. The one on Malta lived eye-to-eyewith a gigantic species of swan called Cygnus falconeri, with a wingspanof around three meters. Micromammoths evolved on Wrangel Islandin the Russian Arctic, where they outlived their larger mainland cousinsby thousands of years.

The fate of island faunas was an important consideration for CharlesDarwin, who marveled at the creatures of the Galápagos Islands in thePacific Ocean, when HMS Beagle visited in 1835. Darwin noted that eachisland had its own species of giant tortoise, as well as its own finches—differentfrom one another yet plainly similar to finches from the mainlandof South America. Had some stray finches, once marooned on theGalápagos, evolved in their own way?

The scene is set, then, for Flores, where, at Liang Bua, archaeologistssurrounded by the bizarre sought for something so seemingly prosaicas signs of modern humans.

What they found instead was a skeleton, not of a modern human oranything like one, but a hominin shrunken to no more than a meter inheight, with a tiny skull that would have contained a brain no largerthan that of a chimpanzee.

In some ways the skull looked disarmingly humanlike. It was roundand smooth, just like a human skull, and with no sign of an apelikesnout. In other ways it was a throwback. The jaw had no chin—thepresence of a chin is a hallmark of modern humans, Homo sapiens. Thearms, legs, and feet of the creature were most odd, looking less likethose of modern humans than those of "Lucy" (Australopithecus afarensis),a hominin that lived in Africa more than 3 million years ago. Thebig surprise, though, was its geological age. Despite its very ancient-lookingappearance, the skeleton was dated to around 18,000 yearsago. In terms of human evolution, this is an eyeblink, hardly rating asthe day before yesterday. By that time, fully modern humans, havingevolved in Africa almost 200,000 years ago, had spread throughoutmuch of the Old World. They had long been resident in Indonesia, andindeed, Australia.

So what was this peculiar imp of a creature doing on Flores, seeminglyso out of tune with its times?

Despite the tiny brain, the creature seemed to have made tools. Pinningtools on a toolmaker is very hard (we weren't there to see themdo it), but these tools looked very like those known to have been madeon Flores hundreds of thousands of years earlier, presumably by Homoerectus. The only difference was that they were smaller, as if fitted totiny hands. Had the archaeologists discovered a hitherto unknownspecies of hominin, dwarfed by long isolation alongside the miniatureelephants?

Further work at Liang Bua showed that the first skull and skeletonwere no flukes. The skeleton was soon joined by a collection of morefragmentary remains, though no more skulls. All the remains couldbe attributed to the same species of tiny hominin, and showed its presenceat Liang Bua, off and on, from as long ago as 95,000 years ago (wellbefore Homo sapiens arrived in the area, as far as we know) to as recentlyas 12,000 years ago.

After that—catastrophe. A layer of ash found in the upper sedimentsat Liang Bua indicate that many of the inhabitants of Floreswere destroyed in a volcanic eruption around 12,000 years ago. The calamityswept away the fairy-tale fauna of giant lizards, tiny elephants,and tiny people (though the giant rats are still there, to this day). Morerecent sediments, laid down after the eruption, betray the presence ofmodern humans, their tools, and their domestic animals.

The account that reached my desk at Nature made it plain that thediscoverers were as honestly puzzled by their discovery as anyone elsewould have been, in this coal-face confrontation with the absolutelyunknown and unexpected—a new species of hominin that lived untilalmost historical times, but with a weird, antique anatomy and a very,very small brain indeed.

To emphasize the strangeness of the creature, the discoverers gaveit a scientific name that was noncommittal, yet set it apart from anythingdiscovered hitherto. They called it Sundanthropus florianus—theMan from Flores, in the Sunda Islands. However, the panel of experts Icalled on to comment on the draft paper, and to make suggestions forits improvement, pointed out how relatively modern the skull looked—howmuch it looked like our own genus, Homo. One commentator alsonoted that "florianus" didn't actually mean "from Flores" so much as"flowery anus." Clearly, some revision was required.

When the revised paper was published in October, the creature hadbecome Homo floresiensis—Flores Man. The skeleton with its skull wascatalogued as LB-1, but the media were quick to catch on to a suggestionof one of the discoverers that it should be known as the "Hobbit,"after the diminutive hole-dwellers of J. R. R. Tolkien's fiction—thoughwe in the Nature office sometimes referred to her as "Flo" (the skeletonhaving been described as that of a female).

The paper—and the several commentaries that appeared in itswake—saw the Hobbit as a member of a race of humanlike creaturesthat had evolved in isolation, on Flores itself or nearby, perhaps descendantsof the full-sized toolmakers known to have been on Flores for aslong as a million years. If isolation on islands could do strange thingsto creatures as varied as birds and elephants, lizards and tortoises, thereseemed no reason in principle why hominins should be exempt. TheHobbit could easily be seen as a relative of Homo erectus, known from remainson mainland Asia to be almost as tall as a modern human—butdwarfed as a result of isolation, alongside the elephants whose islandit shared.

And then the fun started.

Hardly had the ink dried on the first account of the Hobbit when thebacklash began. Critics were exercised by two particular aspects of thediscovery.

First, that such an archaic-looking creature had existed so recently,in a region already long inhabited by modern humans.

Second, that a creature with such an incredibly tiny brain could havemade tools. The brain was so tiny, even in proportion to the tiny body,that the Hobbit must—the critics reasoned—have been suffering froma physical or genetic abnormality.

Although criticism of the find came in various shades, critics wereunited, more or less, in proposing an alternative scenario for the existenceof the Hobbit. Rather than it being a distinct species, a relic of anolder world preserved out of time, it was a form of modern human sufferingfrom microcephaly, a congenital disorder that produces midgetswith abnormally small heads.

The first objection can be seen as a symptom of human exceptionalism,the erroneous yet deeply ingrained tendency that I seek to explodein this book. That is, the tendency to see ourselves as the inevitable culminationof a progressive trend of advancement in evolution. The discoveryof such a primitive-looking creature living on the same planetat the same time as Homo sapiens challenges that view. It is a perhapsunfortunate fact that the only hominin that still exists on Earth is ourown. This fact rather reinforces the idea that various species of hominin—the"missing links"—each more humanlike than the one before,succeeded one another with the planned inevitability of runners in arelay race, and that it is not somehow possible for several species ofhominin to coexist on the same planet.

It was not always so. As recently as 50,000 years ago, there were atleast four different kinds of hominin on Earth—Homo sapiens in Africa,Neanderthals (Homo neanderthalensis) in Europe and western Asia, andHomo erectus in southeastern Asia, to which must now be added the obscure"Denisovans" from eastern Asia. The addition of a fifth—Homofloresiensis—would, in such circumstances, hardly be a surprise: neithershould it be a surprise were yet more distinct forms of human to be discovered.Indeed, the only period in which only one species of homininwalks the earth is right now. Modern times are the exception, not thenorm.

That different hominins might live together in the same regionshould, likewise, not be a surprise. It is known that various kinds of earlyHomo coexisted with australopiths in east Africa between 2 and 3 millionyears ago, and that humans and Neanderthals coexisted in Europefor at least 10,000 years (between around 41,000 and 27,000 years ago).The survival of Neanderthal genes in the modern human populationshows that the two species occasionally interbred. There can, therefore,be no objection to Homo floresiensis as a distinct species, simply on thebasis that modern humans were around at the same time; nor on the basisthat Homo floresiensis looks too primitive to have survived until moderntimes. As anachronisms go (what people like to call "living fossils"),the Hobbit is hardly a world-beater. Go tell it to the tuatara of New Zealand,the last relic of a lineage of reptiles distinct from a time beforedinosaurs evolved, and hardly changed in its external appearance for250 million years.
(Continues...)Excerpted from The Accidental Species by Henry Gee. Copyright © 2013 Henry Gee. Excerpted by permission of THE UNIVERSITY OF CHICAGO PRESS.
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