Darwin and evolutionary progress to the starsby Stephen Ashworth
|
| Hasn’t our present-day world progressed in some sense from its state a billion or more years ago, when microbes were the only form of life to be found? Won’t a future constellation of many inhabited planets be a great advance over the single one of the present? |
In a reaction against the traditional view, many modern Darwinian biologists, most famously Stephen Jay Gould, have denied the validity of any progress in evolution. In Gould’s view, writing in Scientific American, we are still 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” (October 1994, p.65).
Surely that’s going too far? Hasn’t our present-day world progressed in some sense from its state a billion or more years ago, when microbes were the only form of life to be found? Won’t a future constellation of many inhabited planets be a great advance over the single one of the present?
Some biologists, including Ernst Mayr and Richard Dawkins, do accept a qualified idea of evolutionary progress. But in his book What Evolution Is, Mayr denies any overall trend towards increasing complexity: “All theories that postulated the existence in all organisms of an intrinsic tendency towards greater complexity have been thoroughly refuted” (p.220).
Dawkins, however, does identify a trend of growing complexity by taking an overview of life on Earth. In his book River Out of Eden, he mentions that a star can explode as a supernova, and adds that another type of explosion is also possible: instead of going supernova, it—or rather one of its nearby planets, powered by the energy of the star—can “go information”, in a process he describes as a “replication bomb”.
This information or life explosion works its way up through a number of distinct thresholds, which Dawkins enumerates, starting with the appearance of molecular replicators, which later begin making cells to live in (genes living inside their phenotypes). Later still the many-cells threshold is crossed, then the nervous system threshold, and so on.
He does not know how the information explosion will end. He conjectures (p.158): “Presumably it eventually fades away like a supernova, but we do not know how far it typically builds up first. Perhaps to a violent and self-destructive catastrophe. Perhaps to a more gentle and repeated emission of objects, moving, in a guided rather than a simple ballistic trajectory, away from the star into distant reaches of space, where it may infect other star systems with the same tendency to explode.”
In stark contrast to Gould, Dawkins allows Homo sapiens a key evolutionary role (p.159): “We humans are an extremely important manifestation of the replication bomb, because it is through us—through our brains, our symbolic culture and our technology—that the explosion may proceed to the next stage and reverberate through deep space.”
So although the universe has no intentions, no purpose, and no guiding divine hand, at least one prominent Darwinian thinker is prepared to allow that space colonization would be a logical continuation of the pattern of the evolution of life on Earth so far.
I should like to add a further perspective on the thresholds of Dawkins’s replication bomb, using the concept of a biological design space, which is a major theme in Daniel Dennett’s book Darwin’s Dangerous Idea. A design space is an imaginary domain containing all possible permutations of complex objects (living creatures, artifacts, etc.) that exhibit the kind of structure we may broadly think of as design.
According to Dennett, there is a single universal design space, and all actual complex phenomena are found in it. 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 artifacts (such as websites about space exploration).
I believe Dennett has oversimplified 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—the corridors corresponding to Dawkins’s thresholds.
Consider the relationship between biology and culture. Cultural artifacts can only be produced by a species similar to ourselves, possessing hands capable of grasping and manipulating objects, and of course a large brain—over about 700 cc for our body size, representing the watershed between Australopithecus and Homo (our modern adult brains average 1,350 cc).
Even given these attributes, a species will not necessarily develop agriculture, civilization, science, technology or spaceflight. 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. The reality is therefore that the works of cultural design can only get started from a tiny number of very specific points in biological design space.
| Once animals crawl out of the sea to colonize the land, the land tends to stay colonized. If a technological species colonizes space, we can anticipate that space will stay colonized. |
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—certainly for surface life.
Real planets appear in planetary design space at random, and, so far as we can speculate 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.
The structure of universal design space therefore resembles a series of floors 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, artifacts—which appear and move around in the design space according to the rules of that space without being able to see or control 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 that ratchets life upwards on a scale of complexity, diversity, and opportunity. There is no purposive striving towards a goal, no designing intelligence, yet the implicit structure of the universe of the possible causes the system to simulate or mimic what we may think of as goal-oriented behavior.
We have considered the major levels of planetary formation, microbial life, multicellular life, and terrestrial civilization. But within some of these broad levels a similar pattern is discernible. Once animals crawl out of the sea to colonize the land, the land tends to stay colonized. If a technological species colonizes space, we can anticipate that space will stay colonized.
Many of us—myself included—foresee our imminent transformation into Homo astronauticus. Just as Australopithecus evolved the new genus of Homo when, two million years ago, our ancestors freed themselves from dependence on the African forest, so emancipation from dependence on planet Earth will have at least as great a biological effect.
But that process is still an evolutionary one, not one under anybody’s rational control. Rather it remains, like our emergence from Australopithecus, a function of chance and necessity—for which in today’s situation read the unpredictable currents of politics, economics, technology, and culture.
Yet, assuming we make it, the progress will have been real, and is likely to be permanent.