We have a sample of one modern human civilization, but there are some hints on how likely it was to happen.
Major types of hints are:
- Time - if something happened extremely quickly; or extremely late, it suggests how likely it was.
- Independent invention - something that was invented independently multiple times is likelier; something invented only once in spite of plenty of time, isolation, and prerequisites is less likely.
- Life seems to have developed extremely quickly after creation of Earth. [Origin of life]
- Multicellularity seems to have evolved multiple times independently, at least in animals, fungi, and plants. [Evolution of multicellularity]
- Similar process also happened multiple time on higher level - eusociality developed in aphids, thrips, mole rats, termites, and at least 11 times in Hymenoptera (ants, bees, and wasps). [Eusociality]
- Life did not die out on Earth, or on any particular environment where it previously thrived, in spite of major changes in temperature, composition of atmosphere, and multiple large scale disasters. This suggests life is very resilient. Every time life is wiped out in some part of Earth, it is quickly recolonized.
- Many different lineages of animals developed societies. [Social animal]
- Many different lineages of animals developed communication. [Animal communication]
- All transitions from Middle Paleolithic onwards happened relatively fast to extremely fast on evolutionary scale. [Paleolithic]
- Invention of Mesolithic and Neolithic culture including agriculture, bow, boats, animal husbandry, pottery were all invented multiple times independently, in Afroeurasia, and Americas. [Stone Age]
- Likewise many of latter inventions including metallurgy, writing, money, and state were developed multiple times independently.
Data against:
- Universe is not filled with technical civilizations. Some (dubious due to zero empirical evidence) models suggest once such civilization develops anywhere in the galaxy, it is very likely to colonize the entire galaxy in relatively short period of time. As it didn't happen, it's a strong evidence that there are very few, perhaps no, advanced technical civilizations in our galaxy; or anywhere else in the universe if our galaxy is a good representative. [Fermi paradox]
- Life can survive in a very wide range of circumstances, so there are plenty of places where we might expect to find life if its development was also likely. Mars, Venus, moons of Jupiter and Saturn, and perhaps some other places just in the Solar System might be sufficiently friendly to life. Yet, as far as we know, none ever developed in any of them, what puts strong limits on inevitability of life. [Extremophile]
- In spite of all the theories proposed, we know of no mechanism under which creation of life seems even remotely plausible. Somewhere between the primordial soup (or equivalent) to the first replicator with reasonably stable heredity and metabolism (or equivalent), there's a large number of unknown steps of unknown but most likely extremely low probability. [Origin of life]
- Nervous system evolved only once, about 3 billion years after life started, and nothing analogous to it ever evolved in any other lineage. [Urbilaterian]
- It took life 3 billion years to reach stage of reasonably complex animals, what suggests it is not very likely. [Cambrian explosion]
- Almost all animals seem to have very low encephalization quotients, suggesting that high intelligence is unlikely to develop. The only two major exceptions are primates and dolphins. [Brain size and EQ]
- Anything resembling human language developed only once. [Origin of language]
- It is far from certain, but it seems that Neanderthals had the same capacity for speaking language as modern humans. This pushes development of language very far back, and suggest development of civilization even given language is unlikely. [Neanderthal]
- Transition from animal life to something as complex as early Homo life (Lower Paleolithic), like manufacturing of tools, control of fire etc. seem to have happened only once in history of life, and extremely late. [Human evolution]
- Likewise transitions to Middle Paleolithic, and Upper Paleolithic seem to have happened only once. It could be argued that if it was isolated human populations had chance of developing innovations contained in them independently, but didn't.
- Some inventions like wheel, and iron smelting were invented only once. However by this time the world was going so fast and globalized enough that it's very weak evidence for their difficulty. Inventions later than antiquity also provide little evidence due to little time and little isolation.
To me it looks like life, animals with nervous systems, Upper Paleolithic-style Homo, language, and behavioral modernity were all extremely unlikely events (notice how far ago they are - vaguely ~3.5bln, ~600mln, ~3mln, ~200k or ~600k, ~50k years ago) - except perhaps language and behavioral modernity might have been linked with each other, if language was relatively late (Homo sapiens only) and behavioral modernity more gradual (and its apparent suddenness is an artifact). Once we have behavioral modernity, modern civilization seems almost inevitable. Your interpretation might vary of course, but at least now you have a lot of data to argue for your position, in convenient format.
See Robin's paper on this:
http://hanson.gmu.edu/hardstep.pdf
If a step is extremely hard (and thus astronomically unlikely to occur in the lifespan of a planet) then we should expect to see it taking a length of time comparable to typical planetary lifespans divided by the number of steps.
The last two steps occurred suspiciously quickly to be super-hard, and the independent clusters of mammalian braininess in cetaceans and primates [EDIT: (and birds, to a lesser extent)] make the third step questionable too.
Super-difficult life and nervous systems look very plausible to me. A special difficulty involved in the formation of mammals (a feature that predisposed to the later development of intelligent hominids) seems less plausible but not very implausible.
In addition to steps that are hard in the sense that they can take a long time, there may also be tricky steps -- ones that have a finite window of opportunity before being precluded by some other version of events. I don't have a good enough theory of the development of civilization to defend any candidates in history, but here's a paleontological candidate:
Consider that animal lineages readily lose limbs but, once lost, almost never regain them (many-legged arthropods to six-legged insects, four-legged reptiles to two-legged birds and no-legged snakes, but no reverse transitions; the reasons for this are easy to understand in terms of the requirement of evolution that intermediate forms be advantageous). It is also clear that animals can get by well enough with two legs, but sparing two of four for toolmaking has always been a problem, let alone sparing two of two. Finally, it is clear that four legs over two is not necessarily enough advantage to displace an entrenched competitor.
The four-legged lungfish that became the ancestor of amphibians could not of course have known its distant descendents would need two spare limbs for toolmaking. If it had been delayed until a two-legged lungfish had taken the niche... it is not certain that the ultimate development of civilization would have been rendered impossible, but it is at least plausible.
One question we need to ask about the question of time is what sort of process leads to each breakthrough.
Is it more like buying a lottery ticket with every generation, or is it like saving until you have enough money to buy the next step?
It may well be that the Cambrian explosion was the result of 3 billion years of small improvements and would have been impossible at 1 billion years.
The history of invention in human history seems to work more like savings -- as soon as sufficient progress has been made, the breakthrough happens independently.
There's a problem in independent invention in evolution as well--once the first evolution takes place that niche is occupied. An independent invention may be beat out for resources by the more polished first-mover. Short-lived species leave very few fossils.
Something at least remotely analogous to the nervous system seems to have evolved in some plants, which use cells with something like action potentials to drive rapid movement or rapid changes of chemical behavior in response to environmental stresses.
Bats also have high encephalization quotients, and corvids seem to have the sorts of behaviors characteristic of high encephalization quotients, though both may be too absolutely small to become civilized absent unusual environmental conditions.
The latter three items all seem sufficiently rapid to provide l... (read more)
There were wheels in the western hemisphere before the arrival of the europeans, but they were only used for toys. No one seemed to guess that they might be useful. But if they'd had more time....
ETA: perhaps I should cite Diamond here in case anyone wonders where this factoid comes from. It's from "Guns, Germs, and Steel".
This isn't really true. Only organisms with mitochondria developed multicellularity. Mitochondria are the hard part.
Similarly, it would be more informative to say that Hymenoptera developed a particular pattern of chromosomal inheritance once, and that led to 11 different types of eusocialism.
Re: abiogenesis. You say:
For a plausible mechanism, see this video. (It starts with anti-creationism stuff; skip to 2:45 to watch the science.)
Our observations are biased because anything that occurs multiple times is very easy to see but something that occurs only once could be completely missed as an essential step towards civilization because we assume it was inevitable.
AK's Rambling Thoughts has an interesting post on the originas of bilaterians (as well as eukaryotes and life in general).
From Science, July 3 2009, p. 24-26, "On the origin of the nervous system":
... (read more)Be careful of anthropic bias here. Taken alone, the argument "life did not die out on Earth" is invalid because if it had, we wouldn't be here. However, the second point, that when some evolutionary niche is wiped out it is quickly col... (read more)
One thing that caught my eye is the presentation of "Universe is not filled with technical civilizations..." as data against the hypothesis of modern civilizations being probable.
It occurs to me that this could mean any of three things, which only one of which indicates that modern civilizations are improbable.
1) Modern civilizations are in fact as rare as they appear to be because they are unlikely to emerge. This is the interpretation used by this article.
2) Modern civilizations collapse quickly back to a premodern state, either by fighting a v... (read more)
One other thing an advanced technological civilization seems to need is concentrated energy. We're highly dependent on coal and oil. At this stage, nuclear could be substituted, but I don't know that there would have been enough slack for the research to get nuclear without the fossil fuels.
It seems plausible that any planet which has had extensive life for long enough to develop intelligence would also have fossil fuels, but that's pretty vague. It doesn't guarantee that the fossils don't get dispersed, eaten, or end up too deep to be easily accessible.
I'... (read more)
No we're not. The data is clearly against this theory.
Coal was barely used until 1800s, early industrial revolution machinery used wood (indirectly solar power), charcoal, and river flow (indirectly solar power) instead. Oil didn't matter much until 1950s.
Amount of solar energy Earth receives annually is 3,850,000 EJ (and if we ever needed more there are ridiculously higher amounts of solar energy available is space). Human primary energy use is 487 EJ, or 0.01% of that. That's of course only because we conveniently don't count solar energy used to grow our food, and heat our planet - otherwise it would be fair to say human civilization uses 99.99% solar power (via photosynthesis, heating, water flow, wind etc.) and 0.01% all the other kinds of energy like fossil fuels, nuclear, geothermal etc.
We know fossil fuels were not necessary for industrial civilization because by the time we started using them we were already had industrial civilization. That's as good a proof as it gets.
History of ferrous metallurgy History of coal mining History of petroleum Solar energy
EDIT: Also, long before railways, river transport, and long distance sea transport were extremely common. If some place ... (read more)