As an advocate of space colonisation, I believe firmly in human progress and in the fundamentally progressive nature of the evolution of life.
But with this year seeing the 200th anniversary of the birth of Charles Darwin on 12 February, as well as the 150th anniversary of the publication of his most famous work, On the Origin of Species, on 24 November, I need to clarify how such a concept of progress fits in with the modern Darwinian view that evolution has no direction and no goal.
Natural philosophers as far back as Aristotle believed that the living world had an intrinsic tendency to develop towards ever greater perfection. This is known as "cosmic teleology", or the workings of a "final cause", generally identified with God. It remained the dominant view of biological change until Charles Darwin and (independently) Alfred Russel Wallace introduced the idea of natural selection based on the random variation among individuals in a population. 
In a reaction against the traditional view, modern biologists, most famously Stephen Jay Gould, have denied the validity of any progress in evolution. In Gould's view, we are living in "the age of bacteria" -- "as it was in the beginning, is now and ever shall be", while humans are "a relatively minor phenomenon that arises only as a side consequence of a physically constrained starting point" .
Surely that is going too far? Our present-day world has doubtless progressed in some sense from its state a billion and more years ago, when microbes were the only form of life to be found.
Other biologists do accept the idea of progress to some degree. Richard Dawkins has defined it as "a tendency of lineages to improve cumulatively their adaptive fit to their particular way of life, by increasing the number of features which combine together in adaptive complexes" . Elsewhere he talks of the progressive "evolution of evolvability". And according to Ernst Mayr: "it is quite legitimate to refer to the series of steps from the prokaryotes to eukaryotes, vertebrates, mammals, primates, and man as progressive. Each step in this progression was the result of successful natural selection. The survivors of this selection process have been proven to be superior to those that were eliminated." 
But on the other hand Mayr denies any overall trend towards increasing complexity: "All theories that postulated the existence in all organisms of an intrinsic trend toward greater complexity have been thoroughly refuted. There is no justification in considering greater complexity to be an indication of evolutionary progress." 
How does space colonisation fit in with these definitions of progress? The only way space programmes would be progressive to biologists such as Dawkins and Mayr would be if the successful establishment of permanent settlements on the Moon and Mars was followed by Homo sapiens becoming extinct on Earth, whether through natural disaster or gradual decline.
Earth is unlikely to be capable of supporting multicellular life for longer than another few hundred million to a billion years, due to the gradual long-term increase in solar luminosity. We can therefore argue that our successful transformation to a space-based species would mean that, assuming we have extraterrestrial descendants in a billion years time, their adaptive fit to their cosmic environment will have been superior to that of those of our descendants who remained behind on Earth and perished there.
I find this argument somewhat unsatisfactory, because it assumes we will have descendants in that remote future age, which cannot be proven, and because it depends upon our specific astronomical circumstances.
Is there a more general pattern at work here? I think there is. It can be seen by considering the concept of a design space, which is discussed in detail by Daniel Dennett in his book Darwin's Dangerous Idea, chapters 5 and 6. He does not, however, arrive at the same conclusions as I do.
According to Dennett, there is a single universal design space, and all actual complex phenomena in it are united together . In particular it unites biological design and cultural design: this space contains all the genomes of all the DNA-based creatures that could ever exist, and it also contains all their unconscious products (such as spiders' webs) and their conscious artefacts (such as books about evolution).
I believe Dennett has oversimplifed the structure of universal design space. The actual landscape of all possibilities which exhibit design has what seems to me to be a very specific shape: it consists of a series of distinct domains connected by very narrow corridors.
Consider the relationship between biology and culture. Cultural artefacts can only be produced by a species similar to ourselves, possessing a large brain (over about 800 cc for our body size -- our own adult brains average 1350 cc) and hands capable of grasping and manipulating objects. Even given these attributes, a species will not necessarily develop agriculture, civilisation, science and technology. Homo erectus, for example, a human species closely similar to ourselves, remained on the hunter-gatherer-scavenger-beachcomber level for about 1.5 million years, despite having mastered making stone tools and fire, before dying out.
In other words, to get to where we are now, one of a very small proportion of possible species has to experience a very specific set of environmental stimuli.
Dennett's concept of a universal design space which contains both biological and cultural design is an oversimplification. The reality is that the works of cultural design can only get started from a tiny number of very specific points in biological design space.
I imagine that the same applies to the transition from single-celled to multicellular life. Given the immense span of Precambrian time when the only life on Earth was single-celled -- sometimes clumping together in large masses, but fundamentally incapable of building highly differentiated, coordinated organisms like modern animals -- it would appear that again a very specific conjunction of cell and circumstances was needed.
The same applies when one considers the design inherent in planets. Unlike biological or cultural design, planetary design is not cumulative, as there is no process of heredity, except in the very broad sense that later generations of planets have more heavy elements at their disposal than earlier ones. But planets come in a wide variety of compositions, sizes and orbits, and only a tiny fraction of them appear to be suitable for life.
Real planets appear in planetary design space at random, and, so far as we know at present, only a very small fraction of them allow bacterial life to get started. Bacteria populate monocellular design space in a more connected way, but again only a very small fraction fall into the random walk that leads into multicellular design space. Animals, plants and fungi embark on their own chance wanderings through multicellular design space, and only a very small fraction of them hit on the conditions for starting up cultural evolution. (What may lie beyond that we cannot yet guess.)
The structure of universal design space therefore resembles a series of floors or storeys in a very large house. Each floor offers a tremendous amount of room for change and variety, yet is connected to the floors above and below only by a very few extremely narrow staircases.
The floors represent levels in a creative hierarchy. At each level -- planetary, biological, cultural -- different rules apply. But all the levels are inhabited by entities -- planets, genomes, artefacts -- which appear and move around in the design space according to the rules of that space without being able to see where they are going, and only by chance do some hit on the staircase leading to a higher or lower level.
This has the consequence that once a level becomes populated, it tends to stay populated, as the entities which enter it start reproducing and multiplying. As a result, this concept of the structure of universal design space provides a purely unconscious mechanism which ratchets life upwards on a scale of complexity, diversity and opportunity. There is no purposive striving towards a goal, yet the implicit structure of the universe of the possible causes the system to simulate or mimic what we think of as goal-oriented behaviour, though on extremely long timescales.
We have considered the major levels of planetary formation, microbial life, multicellular life, and civilisation. But within some of these broad levels a similar pattern is discernible. Once animals crawl out of the sea to colonise the land, the land tends to stay colonised. If a technological species colonises space, we can anticipate that space will stay colonised.
It appears that the possibilities open to a species such as ours expanding into space are myriad, and the progress so gained is real, but will be realised in practice only through the ebb and flow of chance and necessity.
Perhaps this goes some way towards explaining why our progress has so far been frustratingly slow and badly managed (see items 2 and 3 below for some current instances of this!).
=== References ===
 Ernst Mayr, What Evolution Is (Weidenfeld & Nicholson, 2002), p.82, 213.
 Stephen Jay Gould, "The Evolution of Life on the Earth", Scientific American, special issue "Life in the Universe", October 1994, p.62-69, on p.65.
 Richard Dawkins, Evolution 51 (1997), p.1016, quoted in Mayr, p.215. Mayr adds that other definitions and descriptions of progress can be found in Matthew H. Nitecki, Evolutionary Progress (University of Chicago Press, 1988).
 Mayr, p.216.
 Mayr, p.219-220.
 Daniel C. Dennett, Darwin's Dangerous Idea: Evolution and the Meanings of Life (Allen Lane The Penguin Press, 1995), p.135-144.
The February 2009 issue of Spaceflight magazine contains an update by Philip Corneille on the Spirit and Opportunity Mars rovers, now into their fifth year of operation. They have functioned 20 times longer than their intended primary mission of 90 days each. Spirit has motored more than 7.5 km, and Opportunity about 12.5 km.
Clearly, NASA has proven a valuable technology here which can be applied to exploring more of the enormous variety of surface locations on Mars. One thinks of the immense canyons of the Valles Marineris and the Noctis Labyrinthus, the mysterious pyramids of Cydonia, the giant volcanoes of Tharsis and the floor of the great basin of Hellas, where the air pressure is sufficient to hold liquid water on the surface for a while. All of these await their first close-up inspection on the ground. Surely the future for Spirit 2 and Opportunity 2 is bright!
Turn the pages of the same issue of Spaceflight, and what do we find? A news report on how difficult NASA is finding it to develop a new technology. The budget has overrun again and again, and now the launch has been delayed for two years. What can this exotic new technology be? It is ... a Mars rover.
Yes. NASA has binned the blueprints for Spirit and Opportunity and is literally reinventing the wheel -- or at least, the actuator which turns the wheel. Having developed a system for exploring Mars, proven it, and found that it performs better than expected, NASA has scrapped it and started building an entirely new type of rover to do the same job at greater cost.
In the words of Alan Stern, former associate administrator at NASA, writing in the New York times on 24 November 2008:
A cancer is overtaking our space agency: the routine acquiescence to immense cost increases in projects. Unmistakable new indications of this illness surfaced last month with NASA's decision to spend at least $100 million more on its poorly-managed, now-over-$2 billion Mars Science Laboratory. This decision to go forward with the project, a robotic rover, was made even though it has tripled in cost since its inception, it is behind schedule, there is no firm estimate of the final cost, and NASA hasn't disclosed the collateral damage inflicted on other programs and activities that depend on NASA's limited science budget.
Read the full article here.
Clearly, NASA places a very low priority on Mars exploration in comparison with funnelling public money into high-tech jobs on Earth.
Two designs for outer planet exploration probes are currently under consideration by ESA and NASA, with the aim of following up the highly successful missions of Galileo and Cassini/Huygens. They are the Europa Jupiter System Mission (aka Laplace) and the Titan Saturn System Mission (aka Tandem). But despite their obvious similarities, only one will be approved, according to BBC news.
The winner is to be announced this month (February). But the BBC reporter, Jonathan Amos, cautions: "The mission [...] may never fly if the agencies decide there are other space missions in their future portfolios that they consider to be a higher research priority." Meanwhile, at the IAC in Glasgow, ESA science chief David Southwood described the competing mission plans as being engaged in a "fight to the death" (Spaceflight, Dec. 2008, p.461).
Surely this is another case of spending money first, exploring the planets last?
Surely the first criterion that any credible outer planets design should satisfy is that the same basic system must be versatile enough to support missions to all four giant planets, as well as to other targets in the outer Solar System? Otherwise follow-on missions will require expensive redevelopment, greatly reducing the value for public money they represent.
As with Mars, the list of interesting targets is a long one. For a start, we should place orbiters around all four giant planets and their six major satellites, plus Titania, plus Pluto, and in addition send probes to rendezvous with both groups of Jupiter trojan asteroids, adding up to a total of 14 initial missions. Smaller moons such as Enceladus, Iapetus and Miranda would also repay closer study, not to mention Kuiper Belt Objects beyond Pluto. And we need to add in atmospheric probes for the giants and landers for the major moons before this phase of the reconnaissance is complete.
At the current rate of one outer planets probe per decade (Galileo in the 1990s, Cassini in the 2000s, Juno for the 2010s, Laplace or Tandem for the 2020s), these worlds would take a couple of centuries to explore with just one dedicated probe each.
But does exploration of our Solar System have to proceed at such a snail's pace?
Suppose that probes were launched more frequently, say one every two years? We could envisage an international consortium building the probes to a standard design on a continuous production line and selling them to NASA, ESA, Roskosmos and other agencies as required. Such commonality of design would keep the cost per probe low. By avoiding the temptation to optimise each spacecraft for each mission, the amount of science done per mission is reduced, but the amount of science done per dollar or euro -- and especially per year -- is surely greatly increased (though it would be nice to have further analysis to quantify this tradeoff).
The amazing thing is that NASA seems to have arrived at a concept similar to this (though not internationalised) in its 1983 Mariner Mark II programme.
According to Wikipedia, the intention was to have a series of space probes to follow up the very successful Mariner series. They were specifically for the outer Solar System, therefore technologically compatible. The first two missions planned in the series were Cassini and CRAF (Comet Rendezvous - Asteroid Flyby). The costs were supposed to be kept down to $400 million through commonality. Presumably missions to the other outer planets would have followed, instead of today's irrational strategy of playing off expensive one-off Jupiter probes against expensive one-off Saturn probes.
Then Congress cut the funding, and CRAF was sacrificed. In order to save Cassini, it was (according to Wikipedia, which is not always accurate) significantly redesigned in order to reduce total programme cost. As a result Cassini was slimmed down from a $400 million mission to ... a $3.4 Billion one !!! (total programme cost given by Astronautix.com).
In other words, it's the same story as with the Mars rovers: costs rocketing up out of control, exploration going ahead at a crawl, if at all. Clearly the story of Mariner Mark II's transmogrification into Cassini sets the scene for today's planetary exploration landscape.
One can only wonder in amazement whether these programmes are managed by the same people who flew men to the Moon in the 1960s!
Mariner Mark II was replaced (says Wikipedia) with the Discovery programme, and an article in the Dec. 2008 Spaceflight magazine (p.467) puts the cost of Discovery missions at $400 million (i.e. lower cost than the same figure in 1980s dollars). Current Discovery probes are Dawn (to Ceres and Vesta) and Grail (lunar gravity probe, launch in 2011).
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