All Astronautical Evolution posts in 2022:

Is Private Space Travel Environmentally Responsible? (April)

How Will the First Astronauts on Mars Spend Their Time? (February)

All Astronautical Evolution posts in 2021:

Questions for Human Analogue Simulators of Mars (December)

Black Arrow and Prospero Fifty Years On (October)

The Inspiration4 Mission Begins to Fill In the Bottom of the Transport Pyramid (September)

Are Richard Branson, Jeff Bezos and their clients real astronauts? (August)

Planetopolis in an Age of Climate Change (July)

Planetopolis (January)

All Astronautical Evolution posts in 2020:

Stellar Engines (August)

Voyage to the Large Magellanic Cloud (July)

Why the Human Exploration of Space? (May)

Artificial Gravity for the Journey to Mars and Return (April)

Cruising in Space (March)

All Astronautical Evolution posts in 2019:

The Destiny of Civilisations – Fire, Iron and Gold (November)

The Destiny of Civilisations – A Problem for SETI (November)

The Holy Grail of Space (October)

Return to the Moon, 50 Years On (August)

The Case for Interstellar Flight (June)

SpaceX Dragon 2 Success (April)

Killing the Doomsday Fallacy (Feb.)

All Astronautical Evolution posts in 2018:

How Far Can We Take the Copernican Principle? (Dec.)

Dawkins and the McGraths: a Biologist versus two Theologians (Nov.)

The Atheism Question (Oct.)

The Religion Question (Sept.)

I, Starship (June)

All Astronautical Evolution posts in 2017:

Scenario Block Diagram Analysis of the Galactic Evolution of Life (Nov.)

Comments by Alex Tolley (Oct.)

Elon Musk’s “Great Martian” (Oct.)

Elon Musk’s Mars Plans: Highlights from His Second Iteration (Sept.)

What is a Supercivilisation? (Aug.)

Quantifying the Assumptions Behind the METI Debate (July)

Five Principles of a Sustainable Manned Mars Programme (June)

Pale Red Dot: Mars comes to Oxford (May)

Back to 2016:

Elon Musk and Mars: Looking for a Snowball Effect (Oct.)

New in 2020:

Download science fiction stories here

AE posts:

2022: What’s to do on Mars?…

2021: New space company Planetopolis…

2020: Cruising in Space…

2019: The Doomsday Fallacy, SpaceX successes…

2018: I, Starship, atheism versus religion, the Copernican principle…

2017: Mars, Supercivilisations, METI…

2016: Stragegic goal for manned spaceflight…

2015: The Pluto Controversy, Mars, SETI…

2014: Skylon, the Great Space Debate, exponential growth, the Fermi “paradox”…

2013: Manned spaceflight, sustainability, the Singularity, Voyager 1, philosophy, ET…

2012: Bulgakov vs. Clarke, starships, the Doomsday Argument…

2011: Manned spaceflight, evolution, worldships, battle for the future…

2010: Views on progress, the Great Sociology Dust-Up…

Chronological index

Subject index

General essays:

Index to essaysincluding:

Talk presented to students at the International Space University, May 2016

Basic concepts of Astronautical Evolution

Options for Growth and Sustainability

Mars on the Interstellar Roadmap (2015)

The Great Sociology Debate (2011)

Building Selenopolis (2008)

A Response to the views of Richard Leakey and
Roger Lewin in their book “The Sixth Extinction”

Stephen Ashworth, Oxford, UK

31 December 2001

From a philosophical point of view, the position of humankind presented in Leakey and Lewin’s book The Sixth Extinction (Doubleday, 1995; Weidenfeld & Nicolson, 1996) is seriously misleading, and therefore their understanding of anthropogenic environmental stress is not correct.

Despite that, most of their claims and arguments – those which deal with purely biological matters – are interesting and relevant. Here are some highlights.

Estimates of the total number of species alive today on Earth range widely between 10 million and 100 million (p.112-13, 117-21, 241; Dawkins gives 30 million in River Out of Eden, p.9). Since the modern system of classification was established by Linnaeus in the mid-eighteenth century, the total number of recorded species (apparently meaning living species) has grown to around 1.4 million, of which more than half are arthropods (insects, spiders and crustaceans). But clearly this is a long way short of the total, especially in poorly studied groups such as bacteria and fungi, and poorly studied regions of the world such as the tropics, where the vast majority of species actually reside (p.113-23).

On the status of Homo sapiens within all this diversity, Leakey and Lewin are ambivalent. On the one hand, humans are “but one of millions of species” (p.71) and our place in the world “an accident of history” (p.231). On the other hand, there is “nothing like us in the rest of Creation” (p.144) because of a trend in vertebrate brain evolution towards greater braininess (or encephalisation quotient, to give it its technical name) (p.91-98). Rather than a smooth increase, this shows up as a stepwise evolution with early mammals (thanks to their development of the neocortex) consistently cleverer than fish, reptiles and dinosaurs; later-evolving rodents consistently cleverer than early mammals; and so on through prosimians, apes, and eventually modern man. Thus in terms of biological computation humans (together with dolphins) are “the pinnacle of evolution”, and Stephen J. Gould’s famous reluctance to credit mental power with much value in the evolutionary scheme of things is rejected. Moreover, given the point of view that brain power is significant, the evolution of a mental capacity and a self-awareness like ours “probably were inevitable and predictable […] We just happen to be the species in which they became manifest” (p.98).

On the evolution of biological diversity, Leakey and Lewin explain how biologists’ views have been changing over the past two decades with the advent of chaos theory and high-speed computer simulation of ecological systems. Through most of the 20th century the view was that individual species prosper if and only if they are more suitably adapted to their environment – “the survival of the fittest” – and that an ecological system as a whole tends towards a stable state in which the fittest species reach an equilibrium – “the balance of nature”. But both of these ideas have turned out to be wrong. Survival or extinction of a species is a matter of luck as much as adaptation, being strongly dependent on the haphazard accidents of history – which other species it happens to come into contact with, in which order different species colonise a locality, and whether, when and to what extent they are affected by random natural events such as climate shifts or the impacts of asteroids from space (chapter 9; also p.230). Furthermore, even an undisturbed ecology does not simply gravitate towards an equilibrium in which different species stabilise indefinitely at their ideal population levels; rather, the populations of different species may fluctuate chaotically due to the complex internal dynamics of the system itself.

What of the human impact on Earth’s biological diversity as a whole? The picture presented by Leakey and Lewin is that, if current trends continue, as a direct and indirect result of human activities we may expect the total number of species on Earth to be cut to somewhere around one-half of its pre-industrial level by the end of the 21st century (p.233, 235). There is room to quibble over the exact value, both because the total number of species alive up until the industrial revolution is not known to within an order of magnitude, and because the fraction of that number which have already been lost and the fraction currently at risk can only be crude estimates. But since the majority of species live in tropical forests, which are being felled at a considerable rate by human developers, it is clear that those fractions must be large ones, and so on this basis Leakey and Lewin advance their fundamental claim: a sixth mass extinction of species is under way, and Homo sapiens is the agent which is causing it.

This claim is by no means universally accepted, even among experts in the field. For example, David Jablonski of the University of Chicago recently wrote:

The direct comparability of the Big Five mass extinctions to present-day biodiversity losses remains unclear. Although present-day losses are severe and appear to be accelerating [ref. supplied], they have yet to approach the scale of the Big Five extinctions of the geologic past. For example, the K-T extinction removed 50% of the marine bivalve genera globally [ref.], and 97% of the photosymbiont-bearing coral species (and 83% of those genera) [ref.], and the sampling biases inherent to the fossil record virtually require that these victims were drawn from the more abundant and widespread components of the biota [refs.]. Viewed in this light, these are shocking statistics that exceed even the most severe estimates for present-day losses, although long-term projections eventually can approach such magnitudes. Further, over the past 2,000 yr species-poor clades and geographically restricted species have been the overwhelming majority of losses [ref.], corresponding to an intense version of the “background extinction” regime rather than the mass extinction selectivities of the fossil record.

Even so, Jablonski goes on to assure his readers that he does not wish “to belittle the violence being wrought on today’s biodiversity” by human activities. And he is clearly sympathetic to the claim that a worsening human impact in centuries to come could well come to rival the Big Five mass extinctions. (From a paper presented at the National Academy of Sciences colloquium “The Future of Evolution”, held 16-20 March 2000; reprinted in CCNet 65/2001, 9 May 2001; published in Proceedings of the National Academy of Sciences of the USA, vol. 98, issue 10 (8 May 2001), p.5393-98.)

Without quibbling too much about definitions, clearly we can say that species are being made extinct by human pressure, and in considerable numbers. What are we to make of this situation, what can we say about mankind’s place in the terrestrial ecology, and what does it mean for the future? Leakey and Lewin discuss these questions in the final section of their book.

Richard Leakey in particular is a specialist: a scientist and conservationist immersed in the study of biology in general and human evolution in particular. He is therefore not necessarily the best authority for an overview of what it all means.

As noted above, Leakey and Lewin describe humans as “but one of millions of species”, our place in the world as “an accident of history” (p.71, 221, 231). Both of these statements are obviously true. But the authors clearly intend them to be understood as meaning that we are no more than one of millions of species, our place in the world no more than an accident of history. As they admit, this sort of view of ourselves is not reassuring (p.8) and requires us to discard “many comforting notions about our place in the universe of things” (p.223, 226).

They make a number of specific claims which I would like to refute. In doing so, they cast the central theme of their book – the extinctions of other species by human agency – in an erroneous light, and this too I wish to correct.

But first let me say that I do agree with Leakey and Lewin on the crucial moral point: yes, it is good and right that we humans should document the incredible variety of living things on Earth (see p.123), and it is good and right that we should be concerned about its destruction and should attempt to preserve species and ecosystems wherever possible (see p.209, 253). I agree wholeheartedly with their desire to save species from destruction – but not for the reason they give, namely that we are “on an equal footing with each and every other species here on Earth” (p.253) – clearly we are nothing of the sort! – but for a completely different reason: that I believe such a concern for the living environment is firstly an indispensable step forward in our own moral evolution, and secondly an indispensable preparation for our future role as, not destroyer, but creator of new ecologies in colonies in space and on other planets.

Ah, other worlds! Leakey and Lewin have a view on them (p.252):

There are those who cling to the idea that we can escape this end, too [the end of all life on Earth due to the Sun heating up as it ages], by recourse to space travel and colonization of other planets, in which case it matters little what damage we inflict on the one planet we know can support us. Both [beliefs: that we can survive until the death of the Earth, and that we can survive that death, too] are flights of fancy, born of the arrogant belief that Homo sapiens is separate from and above the rest of the world of nature, and a belief in our invincibility. If we learn anything from a scrutiny of life’s history and of the dynamics by which species thrive collectively, we learn that neither is true.

Unfortunately none of these claims are discussed in any further detail, so Leakey and Lewin’s reasons for making them are not revealed.

Their view of our long-term future should be taken together with the authors’ prediction that Homo sapiens too will one day be extinct: “There is a certainty about the future of humanity that cheats our mind’s comprehension: one day our species will be no more” (p.224, repeated on p.236, 245, 249, 251, 252). They are so keen to put this point across that they twice allow themselves the luxury of blatant overstatement. They write: “There is no reason to think that the one- to ten-million-year average life span that applies to other species should not apply to our own” – yes there is: technology; comparing technological species with non-technological ones is not comparing like with like, for how many of those have engineering access to their own genome or to the universe of matter and energy beyond the Earth’s confined biosphere? and how many have foreknowledge of their own likely mortality? Again, the authors write: “If there is one certainty that we can derive from an understanding of life’s flow and the forces that shape it, it is that one day we and our descendants will be no more, and the Earth and its inhabitants will go on without us” – and our descendants? Since when has it been possible to predict that a species will die out without first producing at least one daughter species? What exactly does past history tell us about the fate of technological species? – clearly, it tells us nothing at all!

At any rate, let us summarise these claims which Leakey and Lewin would have us believe:

(1) Colonisation of lifeless planets by a technological species is impossible (“flights of fancy”), for reasons unknown or unstated.

(2) Those who promote interplanetary colonisation care little what damage is inflicted on the Earth’s biosphere.

(3) Those who promote interplanetary colonisation believe that Homo sapiens is “separate from and above the rest of the world of nature”.

(4) One day, within the next several million years, Homo sapiens will be extinct, and (apparently) will not leave a technological successor species, or indeed any successor species at all.

(5) We must cease “to degrade the wondrous diversity of life upon which we depend for our survival and our soul” only because we have in some sense a moral duty to do so (p.252-53). In the long run, “it matters not at all” (p.247): whether we respect our natural environment or destroy it will have no long-term practical consequences, looking on a scale of ten million years or more into the future (p.253).

(6) (By implication:) one day in the distant future (a billion years or so ahead) all life on Earth will be destroyed in a final mass extinction caused by solar expansion, and the universe will go serenely on its way with no sign that terrestrial life had ever existed. By that time, the actions of human beings a billion years earlier – and of all life on Earth – will have left no consequences whatsoever and will be wiped permanently from the memory of the universe (unless one believes in a spiritual realm outside our material universe, something the authors seem to hint at in their references to the “human soul” on p.144, 248, 252).

Fundamental to Leakey and Lewin’s viewpoint is the idea that the sixth extinction is a totally destructive event, with no creative aspect to it. Yet with regard to earlier mass extinctions they approvingly quote David Raup’s observation (p.229): “Extinction, and especially mass extinction, can be seen as a vital ingredient in the evolution of complex life as we know it.” Furthermore, they report (p.23-24) that the advent of the Ediacaran fauna, the world’s first known multi-cellular animals found in deposits 670 million years old, was itself the cause of a mass extinction: “some 75 percent of the species of single-celled organisms that constituted the living layers of stromatolites became extinct, victims of grazing by the new big boys on the block.” The lesson is clear: destruction and creation go hand in hand. Is this true of the sixth extinction? (an issue which Leakey and Lewin do not address in their book).

In order to answer this question, it will first be necessary to consider the biological function of a species which evolves in an ecology along with other species. Its most general functions are clearly both to maintain its position and to increase its numbers and its range – and thus its future chances – by colonising its own ecological niche efficiently and adapting to others if it can, thus engendering daughter species. In the process it does work on its environment: rock and dust are transformed from dead regolith to living soil, an inert carbon dioxide atmosphere is transformed into a chemically active one with a high content of free oxygen. This is what living organisms do; they do it because it is physically possible and because lineages which succeed in doing so prosper at the expense of those which do not.

If we lift our sights from our Earthbound situation and consider the universe at large (perhaps more difficult for biologists, unless they have an interest in exobiology – the speculative biology of extra-terrestrial creatures), we see gargantuan flows of energy from the almost uncountable myriads of stars, and indications of planets and interplanetary dust in orbit around some of the nearer ones. Matter and energy are basic to life. Life on Earth exploits the fact that we have here just the right amount of energy illuminating a world with just the right material composition. But the universe also offers a great number of potential, though currently unoccupied, ecological niches.

This suggests another question: if – in the natural course of promoting their survival and extending their territorial range – living creatures were to move from an ideal environment such as Earth to a less ideal one – Mars, say – how could they achieve this?

Note that I am not suggesting any underlying rational purpose – an anthropomorphic Evolution consciously planning its next step as a human engineer or general might. I am merely asking about the bounds of the possible: is it actually possible for living creatures to colonise a world like Mars? Does Mars offer a potential ecological niche to any imaginable form of life?

The answer has come increasingly into focus over the past century or so: a technological species such as our own at its present stage of development should have little difficulty in establishing itself on such a world. We could enclose large areas under greenhouse roofs to support a diverse Martian ecology which would in turn support our own existence, and in the long run (on the human timescale, but the very short run in geological terms) make planet-wide changes such as thickening and warming the atmosphere to allow running water and unprotected plant and insect life on the surface. But a non-technological species – of bacteria, say, propelled to Mars on a chunk of rock blasted off the Earth’s surface by a colliding asteroid, as is believed to happen occasionally – could do very little by contrast because the conditions are too hostile. The present-day Martian surface remains completely unsuitable for multi-cellular life and it is doubtful even whether single-celled organisms live below the surface (a question which may not be resolved until human explorers have made extensive investigations on site). Yet from the point of view of life, Mars has the least inclement surface conditions of any planet in our solar system, other than Earth.

It is perfectly possible, then, that the “flight of fancy” of Mars colonisation may become reality within say the coming half millennium or so (the first astronauts could be standing on the surface within ten years of anyone’s deciding to send them; the first voyage to the Moon only took a little over eight years from the moment of decision, and we are technically far closer to Mars today than we were to the Moon in 1961). Given that it is indeed possible, will it in fact ever happen?

The answer is in front of us. Terrestrial evolution has in fact produced a technological species; that species has in fact developed spaceflight and related technologies needed for planetary colonisation such as nuclear and genetic engineering; it supports institutions which are in fact preparing for manned missions to Mars, extended stays on that world and even terraforming.

This suggests the following conclusion: viewed in terms of biological evolution, the special and unique function of Homo sapiens, shared by no other species, is its capability to develop science and technology and use them to enable life to expand its range from one world to many. In other words, if we consider the whole of Earth’s biosphere as a single living entity and call it Gaia (after James Lovelock), then Homo sapiens – with all its propensities to invent technologies, industries, market capitalism and books about the evolution of life – Homo sapiens is Gaia’s reproductive system, her method of spawning extra-terrestrial daughter ecologies and so, like an individual creature, prolonging the success of her kind beyond her own individual death (a view first suggested, to my knowledge, by Michael Allaby).

We may go even further. With the evolution of Homo sapiens, a totally new creative process has appeared in the universe, one which has appeared, so far as we can tell, for the first time ever. This process is rational, conscious thought and its application to manipulating the material world. It is the first appearance of an entirely new creative principle since, billions of years ago, the first biological cell introduced metabolism and heredity.

The creative potential of rational thought is obvious: to spread life beyond its only known point of origin and onward, throughout the universe, thus ensuring its long-term survival beyond the death of Earth itself, a billion years or so in the future, and the death of the Sun, five or six billion years ahead – ensuring it for at least some thousands of billions of years into the future. Its destructive potential is equally obvious, though limited in extent to only a single planet: to destroy itself (through nuclear war or over-pollution) and a sizeable fraction of other species at the same time. Yet there is no creation without a destructive backlash, as we saw with the Ediacaran creatures whose advent “wreaked havoc among the existing communities of microorganisms” (p.23), and as was the case with the “leap in encephalization” which occurred in mammals under the environmental stresses they experienced 65 and 35 million years ago (p.95-96) – apparently the dinosaurs had fallen into a rut of very slow innovatory change, and a catastrophic external stimulus was necessary before the leap to large-brained animals became possible.

The important point is that if a mass extinction is happening now, it is only one side of the story: it is balanced in the scales by the billions of inhabited worlds, each with their own diverse ecologies, which will be the consequence of the successful colonisation of space by Homo sapiens. Destruction and creation go hand in hand.

The next thousand years will be crucial: it will be then that success or failure will become apparent, with colonies of life taking root – or failing to take root – beyond the confines of Earth, just as, half a billion years earlier, multi-cellular creatures emerged from watery environments to colonise the land.

This is not to imply the least disrespect for Earth, any more than any child should feel for its own mother. Let us disown and demolish the malicious accusation, repeated by Leakey and Lewin (let us hope, unthinkingly), that space exploration and colonisation are in any way compatible with an irresponsible attitude to Earth’s ecology! The exact opposite is the case. Some of the words of the astronauts themselves are quoted in Frank White, The Overview Effect (Houghton Mifflin, 1987); thus Gemini and Apollo astronaut Michael Collins wrote (p.202, 203):

I think the view from 100,000 miles could be invaluable in getting people together to work out joint solutions, by causing them to realize that the planet we share unites us in a way far more basic and far more important than differences in skin color or religion or economic system. The pity of it is that so far the view from 100,000 miles has been the exclusive property of a handful of test pilots, rather than the world leaders who need this new perspective, or the poets who might communicate it to them.
When you are sixty miles away [from the surface of the Moon], you realize we are really lucky to be living on Earth. You sort of have to see the “second planet” to appreciate the first.

Again, Shuttle astronaut Ronald McNair wrote (p.243):

Truly there is no more beautiful sight than to see the earth from space beyond. This planet is an exquisite oasis. Warmth emanates from the earth when you look at her from space. I could no more look at the earth and see anything bad than I could look at a smiling little girl or boy and see a bank robber. It’s impossible to see anything but goodness. My wish is that we would allow this planet to be the beautiful oasis that she is, and allow ourselves to live more in the peace that she generates.

The overwhelming experience of astronauts and cosmonauts is one of awe at the place of Earth in the universe and concern for her welfare on ecological, political and spiritual levels. Russell Schweickart (White, p.201) called it the “Cosmic Birth Phenomenon”. Eugene Cernan (White, p.206-207), wrote: “You wonder, if only everyone could relate to the beauty and the purposefulness of it, the reality of the infinity of time and space, how our star moves through time and space with such logic and purpose. It wouldn’t bring a utopia to this planet for people to understand it all, but it might make a difference.”

Space travel, therefore, promotes precisely the enhanced awareness of Earth which our planet so urgently needs, and the allegation that it has anything in common with a careless or destructive attitude towards its delicate ecology is mean-spirited and contradicted by the truth.

Let us now return to the claims from Leakey and Lewin’s book referred to above. In light of the astronautical evolution of life into space, under way right now, we may make the following corrections to their claims, point by point.

(1) Colonisation of lifeless planets by a technological species is physically possible, and in the case of early 21st-century Earth seems likely to begin in earnest within a few decades. It will exploit the similarities between Earth and Mars, and harvest the vast resources of asteroids and solar energy.

(2) Any new ecology independent of Earth, set up by technological man on a new planet or orbiting space platform, must of necessity take Earth as its model. In addition, the engineers building it will be concerned to achieve a system that works with minimal mechanical support (hence less likelihood of breakdown and the more efficient use of energy) and which provides pleasant Earthlike conditions for the benefit of the human colonists. For both these reasons a parochial commitment to one ecology or another would be a strange attitude; rather, those who strive for a healthy ecology on Mars will make common cause with those who do likewise on Earth; those who would trash Earth will certainly be seen as having the wrong attitude on Mars as well. In addition, as we have seen, there is a sense of wonder at the place of life in the universe which is strongly inspired by viewing our Earth in its true cosmic context at first hand.

(3) Those who promote interplanetary colonisation are hardly likely to imagine that they are “separate from and above” the rest of nature. It is far more natural and rational for them to see themselves, as outlined above, as a new evolutionary departure, one as important to the future of terrestrial life as once the first multi-celled creature was, or the first creature to evolve a distinct nervous system. Living surrounded by a black sky or on a rocky wasteland of a world only intensifies one’s sense of belonging to Earth, as the comments of astronauts quoted above demonstrate.

(4) Certainly one day Homo sapiens will be extinct. But that is not an interesting question; rather we should ask: what will Homo sapiens evolve into? On present showing, our daughter species – call it Homo astronauticus or Homo technologicus – will not resemble any species so far seen. It will be a fusion of biology and technology, probably retaining a biological brain for a while (our brains are analogue devices with chaotic architecture; modern computers are digital and precisely designed; the two are clearly complementary) but with instant electronic communication among all individuals on a given planet, and so accustomed to extra-terrestrial habitats that it will no longer draw the popular but artificial distinction between the “natural” and the “artificial”. Individuals will probably enjoy near-immortality. The species and its descendants will spread throughout the Milky Way galaxy over some tens of millions of years. They will colonise a vast number of ecological niches in planetary systems which are totally inaccessible to pre-technological life, creating an unprecedented variety of different habitats, some on existing lifeless planets, some on freely orbiting space platforms, and themselves evolving in a variety of different directions among their far-flung branches. As in the recent past, scientific and technological progress will go hand in hand with progress in realms economic, political, artistic and moral, and will also create agonising new problems we can hardly guess at today. Due to its wide range technological life will quickly become indestructible, though many individual branches will certainly wither and die and have to be recolonised from neighbouring systems. – This, obviously, is a speculative potential future; for the next thousand years or so, before large-scale interstellar colonisation begins, technological life will remain vulnerable to disaster, collapse and extinction.

Homo astronauticus may not evolve in quite the haphazard fashion of its purely biological predecessors; rather some changes to its genome could be deliberately engineered and integrated with the non-biological, technological changes taking place at the same time. This is because technical evolution takes place at a rate many orders of magnitude faster than biological change. Thus biological evolution could be leading to a new kind of evolutionary level altogether, just as, long ago, stellar and planetary evolution set the stage for biology to begin. This is not to say that genetically engineered humans are likely to appear on the streets tomorrow, but rather that over periods of even hundreds, let alone millions, of years some sort of convergence of genetic science, information technology, medicine and human procreation seems both natural and inevitable – provided that technological civilisation continues to prosper and grow. That presumption, of course, is one with with Leakey and Lewin disagree.

(5) In the long run of millions of years, therefore, decisions taken now by powerful individual members of Homo sapiens will influence the future evolution of life and habitation of the galaxy to an enormous extent: on one hand a galaxy teeming with life; on the other, one as barren as it is today, perhaps with little splodges of bacteria eking out a precarious existence here and there; on the third hand (obviously an alien physiology) a galaxy teeming with life, but life derived not from Earth but from some other closely Earthlike world, if any such exists – we do not know whether one does exist or whether conditions there are conducive to the evolution of an intelligent technological species. Therefore on the long-term view the successful transition of Homo sapiens from a planetary species to an interplanetary and ultimately an interstellar one should be seen as the topmost priority, more important even than saving other threatened species on Earth. That said, it remains true that an enhanced sensitivity to other species and the preservation of their habitats are themselves important elements, on both the moral and the practical level, in preparing to build extra-terrestrial analogues of those habitats.

(6) On the longest possible view – that which peers uncertainly into the mists of billion-year swathes of futurity – Leakey and Lewin’s sixth extinction should be seen as the downside in an audacious new evolutionary departure in which life’s survival of the destruction of Earth itself is the prize at stake.

It will be noticed that this reinterpretation of the role of Homo sapiens completely changes one’s intellectual view of the sixth extinction, though of course on a practical level it strongly supports the conservationist case.

Leakey and Lewin present it as a moral issue: we are the collective “culprit” (p.254), we have a moral duty (why?) to amend our lives and those of our struggling conspecieates in the poorer tropical countries. This is not quite right. What an individual does with his life is a moral issue. But if we follow Leakey and Lewin’s exhortation to consider Homo sapiens as one species among many, the logical conclusion is that the sixth extinction is itself a natural event, the inevitable outcome of an unprecedented evolutionary experiment. We have no more need to accept moral blame for the loss of the Centinela ridge or the Lake Victoria species (p.242-43) than if they had been blotted out by the hazards of asteroid impact or continental drift.

Rather than bemoan “our” culpability and denigrate our position in nature, I would prefer to see people welcome the opportunity for moral and scientific growth that the present stressful situation offers. We should see it as our business to become efficient stewards of ecosystems, present and future. And we might also remember that, if human civilisation continues to grow, the sixth mass extinction could also be the last.

Again, we need feel no sense of shame about new technologies – be they nuclear fusion, genetic manipulation of plants, animals or even ourselves, a brain/computer interface, an artificially constructed ecosystem or whatever it may be. According to Leakey and Lewin’s account, “unfortunately” we have collectively exploited Earth’s resources “in unprecedented ways”; they seem not to understand that exactly this is our evolutionary specialisation; they comment sadly that while we are “a single, sentient species consciously pursuing its own material goals” (and what species ever pursued other goals?!), dramatic change only seems to be acceptable when wrought by “countless, non-sentient species, collectively and unconsciously operating new metabolic pathways” (speaking of the photosynthetic algae which transformed Earth’s atmosphere over a period of some two billion years, p.232-33). This is surely an accidental slip on their part? Earlier in the book the authors were concerned to explain the dynamic nature of life; they ranged freely up and down the great staircase of major evolutionary developments; yet now when confronted with the latest example of dynamic change, more explosive than even the Cambrian and Ediacaran revolutions – “a frenzy of evolutionary innovation” (p.16), a grand “evolutionary experiment” (p.24) which “wreaked havoc among the existing communities” (p.23) – they seem unable to recognise it for what it is and slip (surely unconsciously?) into the view that evolution ought really only to be allowed to work on million-year timescales, and the appearance of a new creative process that operates about a million times faster is somehow not proper evolution at all but merely “an environmental abnormality” (in the words of Edward Wilson, quoted on p.233).

Of course, our authors may have committed themselves to the view that all really fundamental change lies in the past. They write (p.25, 27): “The Cambrian explosion half a billion years ago was a burst of evolution unprecedented in the history of life and, as we will see, has not been repeated since. [...] The Cambrian explosion should therefore be recognized as special not only in the intensity of innovation over so short a period of time, but also in its remaining unmatched, or even approached, in fecundity.” And yet they also say, of a post-human future (p.251): “who knows what evolutionary novelties may emerge?” Quite so.

Let us move on to consider the thought-experiment suggested by Simon Conway Morris and Stephen J. Gould and mentioned here also (p.33-36, 226-27): supposing the Earth were recreated in its early form and life allowed to evolve from primitive beginnings once again, would it follow the same pattern of development? would the same phyla – the same basic body plans – survive the Cambrian explosion and subsequent winnowing out? would dinosaurs appear again, to be succeeded by mammals? and would the inevitable, predictable result be the appearance of Homo sapiens? – or might it go off in another direction altogether?

Here our authors concur with Gould. Under the old, Darwinian, gradualist paradigm in which the survival of the fittest produced the best-adapted species living together in harmony in the balance of nature, the pattern of life’s evolution appeared almost mechanistically predictable, modern man its inevitable product. But the new ideas of the last twenty years or so have changed all that: the rise of chaos theory; the discovery of an iridium anomaly at the boundary between the Cretaceous and the Tertiary periods and a giant impact crater off the coast of Yucatan; the re-examination of the strange fossils from the Burgess Shale. Species survive as much through good luck as by good adaptation; every so often Earth is convulsed by a catastrophic impact with a piece of celestial debris; and in general the role of random chance and historical contingency is so great as to force one to conclude that our favourite species is no less and certainly no more than “a mere accident of history” (p.221).

Not so fast. That conclusion is true in one sense, but perhaps not in another.

Of course we all know about the butterfly effect. We are all sophisticated enough by now to realise that the first fish to crawl out of the sea has only on a whim to turn left instead of right to completely transform the flora and fauna ten million years down the line. But is this the most interesting conclusion?

Let us try re-stating that thought-experiment in more general terms: supposing life were allowed to evolve from primitive beginnings once again, would it follow the same general pattern of development? Would it kick off in aqueous environments, thence evolving multi-cellular creatures which colonise the land and the air, thence producing a creature – any creature – with the brains and the hands to invent technology, thence becoming the instrument through which the planetary ecology reproduces itself?

The interesting point is not whether, starting with an identical clone of the early Earth, we can develop another Homo sapiens accurate down to the last freckle and the last French irregular verb. It is whether biological evolution is intrinsically progressive or not. If so then, whatever basic phyla are thrown up in the leap to multi-cellularity, the sheer physical restrictions within which any creature has to operate – the need for food, the mechanics of walking, the chemistry of air and soil and so on – will cause them to stumble across certain complex solutions to the problems of living, including brains, hands, and the mastery of fire. But if not, then no overall pattern of development is likely to appear more than once.

There is enough diversity among living creatures on Earth to answer this question. Certain features do indeed evolve over and over again in different groups. Eyes evolved independently more than forty times – in fish, arthropods, molluscs and so on (Richard Dawkins, River Out of Eden, p.91, 96). Wings have evolved independently in insects, fish, dinosaurs, birds and mammals. The organisation of a multi-cellular animal into distinct bodily organs, resulting in the appearance of a specialised nervous system and ultimately an intelligent brain, is another universal. Of course none of these things have yet appeared in the plant or fungi kingdoms. Is it possible to have a world inhabited by plants and fungi alone? If such a world were a close copy of Earth it would then have major ecological niches left unoccupied, especially as its only living creatures would represent a vast untapped food source. Surely this seems an unlikely outcome – though only extensive surveys of Earthlike planets elsewhere in the galaxy can prove whether such ecologies are possible in practice. Such explorations will probably be made over the next few thousand years. Meanwhile, the situation on Earth suggests strongly that if an ecological niche exists, a creature is very likely to evolve to take advantage of it. Gould’s description of the early Cambrian echoes this view (p.28): “Ecosystems had room for everything – crawlers, walkers, burrowers, slurpers, predators, you name it – and life responded with unparalleled seizure of the opportunity.”

Again, Homo sapiens appears to be the only species ever to have evolved the arts, sciences and technologies of civilisation. Does that indicate that – unlike the evolution of eyes – rational intelligence is a spurious one-off? Not necessarily, partly because intelligence depends upon the prior existence of a species with eyes, hands and brain and must therefore come later in evolutionary history, and partly because the first successful technological species tends to destroy any potential competitors in a brief instant of evolutionary time.

At any rate, for all the uncertainties we can at least state with confidence that the living world we know is set up in such a way as to explore a huge variety of different ways of living, and it is prevented from falling into a rut by periodic catastrophes on a hundred-million-year timescale. We have no definite grounds for believing that any intelligence lies behind this fruitful arrangement (divine or other). On the other hand, it is clear that if some creative evolutionary development is lurking somewhere out there in the invisible space of future possibilities, an ecology such as that of Earth is well-organised to eventually stumble across it.

An identical clone of Earth would not in a million tries reproduce Homo sapiens. But we may expect that it would quite frequently produce some mobile, intelligent, land-dwelling animal with hands and eyes and both the desire and the ability to explore beyond its planet of origin, prolonging its own survival and that of life in general by an incalculable factor, and presumably transforming itself into a biological/technological hybrid in the process.

In our own case, it is reasonable to say that life on Earth has reached the culmination of its development in Homo sapiens – not merely because we have a higher encephalisation quotient than any other animal, as Leakey and Lewin argue (p.97-98), but because our braininess, combined with other critical factors, is sufficient to launch us into the technological age and hence onto voyages of both interplanetary colonisation and genetic experiment, at which point the whole character of biological evolution is transformed.

Looking further afield, we might expect life to have begun independently on many worlds in our galaxy. But the pattern in which single-celled organisms produce an oxygen-rich atmosphere and multi-cellular life, which proceeds from the seas to the land, to intelligence and technology, requires quite stringent conditions which are at present poorly understood. Clearly a planet with too much water will not have much chance to develop biological diversity on land (and no water-dwelling species, no matter how bright, can venture into the technological age because it can never master fire). A closely circular orbit with long-term stability, and a long-lived central sun, are also vital. But was the presence of the Moon – a fortuitous chance above all others – necessary to stimulate life’s appearance? How delicately in fact has Earth been balanced between runaway ice age and runaway greenhouse? Again, detailed examination of Earthlike worlds in many other planetary systems is needed.

The pattern we may expect to see is therefore one in which many planets have single-celled organisms, but the further along the developmental scale towards intelligence one looks the fewer planets will be found to have reached that stage – partly through lack of the physical resources to achieve it, partly through having had insufficient time to explore the possibilities thoroughly enough.

The general scheme is uncontestably progressive in terms of a hierarchy of levels of creative development. Given simple, prokaryotic cells, we know that there is at least one evolutionary pathway to complex, eukaryotic cells, given which there is at least one route to multi-cellular creatures, given which there is at least one route to intelligent creatures with arts, sciences and technologies, given which there is at least one way in which a planetary ecology can reproduce itself. Why such pathways exist in the abstract design space of potential evolutionary development is a deep mystery, but we know that they do exist and have (all except the last one) been travelled in reality at least once!

But does this prove that an intelligent technological species must always remain possible after that first explosion of multi-cellular life? In the Cambrian lakes and seas a wide variety of different phyla were possible. But are they all equally suitable for development, hundreds of millions of years down the road, into large-brained land-dwelling animals? Perhaps many of them preclude such a possibility. None of Earth’s arthropods or molluscs have come anywhere near such an outcome. Clearly, creatures with an internal skeleton have an inbuilt advantage over those with an exoskeleton or with no hard body parts at all. Perhaps of all the phyla present or likely in such a multi-cellular blossiming, only one or two – such as the vertebrates – are physically capable of engendering a species anything like our own?

This is a point of detail, not of principle. We know that the abstract design space of potential life is structured in a hierarchy of creative levels: single-celled, multi-celled, technological, and maybe more undiscovered levels beyond our own. We know that there is at least one door at each level which offers access to the next. We know that these doors, which I call “creation gates”, have to be stumbled upon by trial and error, yet within the lifetime of an Earthlike planet there is time for that to happen. How often it happens is a question of detail: it depends on how often the right environment appears (with liquid water), how much external stress (from asteroidal debris or stellar radiation) that living world is exposed to, and also how often a Cambrian flowering of multi-cellular creatures throws up at least one phylum with a design tolerant of adaptation into a large, mobile, land-dwelling creature with specialised hands and brain; or conversely, how often all evolutionary pathways through the next creation gate are accidentally blocked off. Clearly, Homo sapiens is a rare bird. But the universe only has to produce such a species once.

Despite all the uncertainties, therefore, Leakey and Lewin’s stress on humanity’s emergence as being “a contingent fact of history” which could easily have been very different – while it is trivially true if “us” is understood to mean “us as we are now, exact in every detail” – is clearly quite false if it is taken to mean “an intelligent species with civilisation, the arts and sciences, and technology”. We are not a freak of nature – as Leakey and Lewin clearly imply with their assurance (p.252): “one day we and our descendants will be no more, and the Earth and its inhabitants will go on without us” – we are not an intellectual peacock, a natural curiosity with an over-developed cerebral appendage which arrogantly struts the stage for a while before it soon vanishes again. Rather it is merely stating the obvious to assert that if the growth-oriented portion of mankind continues on its present course for just one more brief millennium, it will transform the whole business of evolution both by integrating biological change with conscious design and by radiating from a single planetary oasis to many.

Therefore our existence as intelligent beings is only an accident of nature in terms of the detailed history of events which brought us into being. At a deeper level it is no accident, but a necessary, though utterly unpredictable, consequence of life’s restless exploration of all the possibilities open to it in an environment which allows those possibilities to be realised.

Had the Yucatan asteroid missed striking Earth 65 million years ago a dinosaur species might have hit the jackpot instead – the descendant of a genus such as Deinonychus, Stenonychosaurus, the Raptors or the Saurornithoides, which exhibited a relatively large braincase by dinosaur standards, stood around two metres tall on its two hind legs, had its fore-legs ready for use as hands, and a complex social life. It could have been an arthropod species, or one derived from one of the vanished phyla of the Burgess Shale such as Anomalocaris or Opabinia – after all, the Burgess animal from which we are believed to be descended, the tiny wormlike Pikaia, looked completely unlike any mammal, let alone a human.

If it is true that the losers in the Cambrian lottery, which to us today “seem like something out of science fiction” (p.31), really were as well-adapted as the winners, as Conway Morris and Gould assert, then it is surely possible that at least some of them could, on a different throw of the dice, have become ancestor to an intelligent high-tech species. Not Homo sapiens, but some variant of Anomalocaris sapiens or Opabinia sapiens would have become a potential destination through the labyrinth of biological design space, and given enough time and a fair wind there would have been a good chance of one of these species stumbling into reality during Earth’s lifetime. A game of chance it may be, but the prizes are real enough, and are the same every time the game is played.

When I say “prize” I do mean something to be greatly desired: a creative leap, a new evolutionary game, a broader set of wonderful possibilities. This is of course something of a subjective view. It would be logically possible to hold the opinion that no further evolutionary leaps are in prospect, that the hierarchy of creative innovations has already topped out, and life has no further business in hand but to adapt to the ever-shifting sands of climate and ever-shuffling permutations of species while waiting patiently for its irrevocable doomsday, when an old and angry Sun finally blots it out of existence forever.

Such a view would be consistent with the popular rejection of technology as “unnatural”, and the yearning for a simpler way of life. This ethos clearly regards the triumph of civilisation with horror: a comforting natural world is uprooted to make way for deserts of steel and glass, concrete and asphalt – a barren technoscape which crushes the soul and enslaves its inhabitants, the living spirit reduced to a mindless cog in some terrifying machine. Surely this is not life at all but a cancerous growth! a disastrous holocaust! some evil force of darkness! Even the broken, parched face of the Moon would be a thousand times better off to remain as it is than to be forced to endure such nightmare pollution!

Since the other planets can only be reached by spacecraft, which represent the acme of technological civilisation, it follows that planets on which life has failed to evolve from primitive single-celled beginnings can only be colonised by an unnatural machine-existence unworthy of the name of life. Therefore those planets can never be colonised by terrestrial life worthy of the name and must remain forever as they were created, as God intended them to be – this, at any rate, seems to be the position of the anti-technology ethos.

To their credit, Leakey and Lewin do not launch any such attack on the modern world. Yet they clearly have a sneaking sympathy for it. Leakey describes his childhood experiences of the wild and what they mean for his personal philosophy (p.142-44), a feeling which Edward Wilson called biophilia: “the innately emotional affiliation of human beings to other living things”. Leakey believes this is the legacy of over two million years of evolution of the genus Homo, when our ancestors were hunter-gatherers in intimate lifelong communion with wild nature, especially the East African savannah. No doubt he is right.

Yet when he quotes the words of American Indian Luther Standing Bear to the effect that humanity is one with the soil and with all living, growing things, and contrasts them favourably with the reprobate attitude of modern Western culture which prefers to emphasise “the promise of worlds beyond our own planet or solar system” (as if these were opposites!), one wonders whether he thinks civilisation was really worth the effort, whether it was really worth the sacrifices, both human and non-human, that continue to be made towards its growth.

I am sure that biophilia is real, and that many or most people are susceptible to its claim on their affections. But that is not to suggest for one moment that humans would be better off abandoning their cities and going back to a village lifestyle – even if that were possible without a calamitous destruction of human life. We are city people born and bred, we would be lost without our Internet connections, supermarkets, running water, mains electricity, libraries, cinemas, hospitals, dental clinics, television shops, video hire, Chinese takeaways, wine shops, refuse collection, motorways, airports, and so on.

What biophilia does mean is that we are probably capable, in the long run, of learning to balance our own needs with those of the rest of nature. But this cannot happen overnight, partly because the most threatened areas, in the tropics, are under the axe of some of the poorest people, while being able to consider our impact on the natural world is a middle-class luxury. Therefore conservation must go hand in hand with global development, as Leakey is well aware. A huge number of species will inevitably be lost – just as they were when the first multicellular creatures evolved. An evolutionary leap of a similar magnitude is under way today, therefore the stress on the system cannot help reaching a similar pain level. Humans are beginning now to think about that global trauma and sometimes to act towards alleviating it, as Leakey himself has done, but we did not design the evolutionary scheme and we should not blame ourselves for deaths we cannot avoid.

What biophilia also means is that when representatives of Homo sapiens travel to Mars and elsewhere in the universe and begin to dig in there, they will begin not only to humanise the extra-terrestrial desert but to vitalise it in the name of all Earth’s ecology. If we are as deeply imbued with a love of living things as Leakey believes, perhaps that could be nature’s way of ensuring that nothing of value to the health of the growing off-Earth ecology is left behind.

Love of Earth’s diversity and love of the potential new diversity of life on planets colonised by man are in no way opposites – rather they are two complementary sides of the same awakening of conscious purpose into the universe.

On the broad, system-level view, destruction and creation are in no way opposites – rather they are two alternating winds in the storm of evolutionary change. Earthlike planets are only possible because of the explosive death of earlier generations of stars; conscious intelligence is the offspring of occasional catastrophic annihilations of species; civilisation, democracy, wealth and the leisure to think are the sequel to a chronicle of war, torture, slavery and famine; technological success is forged in failure – the Titanic, the Hindenburg, Thalidomide, radium poisoning. The realistic view of humanity’s future is one in which both pessimism and optimism coexist symbiotically in creative tension: nuclear energy offers the fear of radioactive fallout and of all-consuming war versus the promise of a living solar system and flight to the stars; genetic science offers the fear of unstoppable superbugs and freakishly frankensteinian monsters versus the promise of engendering a race of angels. Both great fear and great hope are fully justified – their amalgam is courage.

One day living creatures will spread among the stars of the Galaxy on Daedalus-wings of conscious design. Their eyries will perch on hitherto silent worlds; their dams will harvest the inexhaustible floods of starlight. If Homo sapiens fails, some other species will eventually succeed in aeons to come, whether from Earth or the progeny of another world – this is as reliable a prediction about the future path of evolution of life as can ever be made. It will happen because it is physically possible and because species which do so (together with those they take along with them) will prosper at the expense of those which do not. It will happen because birds build clifftop nests and beavers dam rivers, because ancient Mesopotamia piled up ziggurats and medieval Europe raised gothic cathedrals. It will happen because most of the ecological niches in the universe are hidden behind a creation gate to which only technology holds the key, and because technology itself is a natural – though rare – offspring of biology.

In contrast to Leakey and Lewin, therefore, I propose that we should enjoy a more satisfying view of our present role in the evolution of life and the creative opportunities open to us and to our descendants. At the same time we should not lose awareness of the damage and the risks involved. But the prize is far too great for us to renounce industrial civilisation even if we were able to. We are no mere “environmental abnormality”; we are here for a purpose; we are what nature has been working towards – unconsciously, unknowingly – for billions of years. With this confidence in the rightness of our existence, our continuity with the rest of the natural world and our significance for its future development, we can surely afford the generosity of spirit required to limit today’s damage to Earth’s biodiversity while at the same time pursuing our material goals – those of life itself – with vigour.