Nice argument.
It seems to me that we may have some semantics issues around evolutionary concepts like '
direction' or '
push toward', but not around '
highly evolved' or '
complex organisms'. You consider such development to be entirely coincidental in that it's not directed, and I wonder whether that stance can be maintained unqualified in situations where fewer than all possible niches are occupied, and possibly even when they all are.
I don't consider them entirely coincidental; natural selection is a non-random process. I do consider them unguided. In an ecosystem where organisms filling a particular niche have been wiped out, you will often find other organisms adapting to fill that niche; that's why convergent dimorphism (similar looking animals with similar behaviors but vastly different evolutionary heritages) are so common.
The place it runs off the rails is in thinking that evolution is goal-directed or that a particular type of complexity is inevitable. Humans tend to see evolution as a progression from simpler organisms at the bottom to us at the top. That's absolutely not the way it works. In fact, were humans to be suddenly wiped out tomorrow, it's quite likely that our level of sapience, with our enormous brains and abstract language and sophisticated tool use, might never appear again.
I'm not valuing one niche over another, I'm just observing that life on earth started out with minimal variety and complexity, and developed to include greater variety and complexity, and that once more complex systems appear they have reappeared in a variety of forms and niches. Not the other way around, although it may seem that way when viewing isolated time periods along the way. I was primarily referring to this overall sequence, which is arguably consistent, and perhaps inevitable, although the latter wasn't my point.
The overall development of a wide variety of complex organisms certainly looks inevitable from our perspective, since we live in an ecosystem dominated by an explosion of extremely complex forms.
But consider the fact that for
more than half of the history of life on this planet, there were only single-celled organisms.
It's likely that had cyanobacteria not developed photosynthesis, there would
still be nothing but single-celled organisms. The development of photosynthesis, which (unlike developments like the eye or venom or other sophisticated adaptations) appears to have happened only once, poisoned the air with toxic oxygen and wiped out every species of life on the planet with only a couple of exceptions; but that toxic, highly reactive, corrosive oxygen also enabled the development of cells with rapid metabolisms, better able to develop the complexity we see today. And photosynthesis provided a way to power all those new types of life.
Without that development, it's possible the planet might have gone through all its days and never produced anything as complex as a jellyfish, much less a vertebrate. So in that sense, complexity isn't inevitable.
Now that it exists, of course, it is inevitable in the sense that if a complex species goes extinct, another will arise to fill its niche. But it's not inevitable that any PARTICULAR adaptation--sapience, for example--will arise.
If evolution of certain organisms (like insects) is especially active (read: fast), it's usually because evolutionary pressure and with it speciation increases in species with stricter adaptation to smaller niches, which are both more frequently subject to as well as more sensitive to changing conditions. Brains may increase niche-manipulation abilities, which in turn may deflect (part of) evolutionary pressures. Since pressure, and more specifically its release, implies direction, this deflectional bias can be seen to provide a directional advantage, which given proper circumstances will generate new candidate species. I suppose we can argue about the level of such 'direction' (e.g., overarching or incremental), and (to a lesser extent) about the applicability of 'inevitability' here.
Part of the issue with this conversation does seem to be in poor definitions of words like 'balance,' 'complex,' and 'direction,' of course.
We think of things like convergent dimorphism as being inevitable, and in our particular situation with our particular biosphere they (to some extent) are. But think about how many of the evolutionary adaptive pressures
are the result of other organisms. Go back all the way to the start, and begin again with the first self-replicating molecules, and the tape won't play out the same way. We might never get multicellular organisms. If we do, we might never get vertebrates. Even if we get those, we might never get land-dwelling vertebrates. Organisms evolve to fill niches, but those niches are peculiar to the particular biosphere. Different biosphere, different niches. Different niches, different evolutionary pressures. Different pressures, different results.
Even the flow of water on this planet is influenced by biology; the patterns of large rivers seem to have developed as a result of the way vegetation evolved on this planet. Change that, and you change the course of evolutionary history.
Hell, it gets weird even if you think about what we all believe to be true: large vertebrate predators preying on large vertebrate prey animals.
The standard narrative, taught in schools and talked about on television, is that predators prey on the weak and sick prey animals, culling the herd and keeping it healthy. It makes sense to us. It's easy to grasp. But we're learning that it absolutely, positively isn't true.
The book
Parasite Rex I mentioned earlier talks about how the predator/prey relationship is driven far, far less by the population dynamics of prey animals than we ever realized. Instead, it is driven almost entirely by parasites, which modify prey animals to make them more likely to be caught by predators and modifies predators to make them more likely to target infected prey animals.
The
toxoplasma parasite infects rats and changes their brains to make them unafraid of cats, making them easier prey for cats. It does this because it can only grow in rats, but it can only reproduce in the bodies of cats. There is a fish parasite that leaves the fist healthy and strong, but changes its behavior so that it becomes easier for birds to catch. An infected fish is
thirty times more likely to be caught and eaten by a bird than an uninfected fish. (Imagine what wuld happen to the population of predatory birds if they had to work THIRTY TIMES as hard to catch fish!)
Even with large-scale macrofauna, this is the case. The cycle of predation of wolves is driven by another parasite that grows in the body of moose and breeds in the body of wolves. The infected moose are not weaker or sicklier than uninfected moose; if the parasite sickened or killed the moose, it would die too. Infected moose are just as strong and just as healthy...but the parasite changes their behavior so that they are less prone to run away from wolves, by changing their response to fear. They become clumsy and slow when they're afraid, and the wolves catch them more easily.
This increased availability of food makes a moose population better able to support more predators like wolves. The so-called "balance" between predator and prey populations that we have all heard about on TV is orchestrated by parasites, more than by
any other single factor. When the parasites change, the "balance" changes.
That's why I say there is no such thing as "balance." It changes constantly. Year by year, month by month, sometimes week by week, the variables change and the so-called "balance" changes. That's not "balance" in any sense of the word that I understand; that's an ever-changing cycle of boom and bust that can and very, very often does lead to extinction. (If nature is in "balance," then so is the stock market!)
Of course, when focusing on the fraction of life forms with complex brains and certain associated behaviors, we're disregarding the vast majority of organisms on earth. On top of that, we don't yet have much in the way of well described and comprehensive examples of a putative complex brain effect of the kind presented by Homo sapiens, since it is a relatively recent phenomenon with a long and as yet incomplete incubation time on the only planet we know to harbor this variety of life. And, to tie this back to Jon's original post, we may never know, if this experiment self-destructs before it runs its course.
Most of nature's experiments self-destruct. That's kind of how nature works. We see cycles of mass extinctions, then explosions of diversity, then mass extinctions...even without outside calamities like meteor hits. This is exactly how nature works!
Ideas like "increasing diversity of life is better than decreasing diversity of life" and "extinction is bad" are HUMAN ideas. They are not "natural" ideas. It is meaningless to talk about nature being "better off" without humans; as far as nature is concerned, there IS no "better" or "worse". It is only humans who have those values. No other species do.
It's also a mistake to think of humans as "bad for nature" but things like cyanobacteria, which exterminated far more species than we could ever do even if we were to deliberately try to kill everything, as "natural". Cyanobacteria are natural...
and so are we. We are not separate from nature. The same natural processes that gave rise to cyanobacteria--and wiped out almost all other life on the planet--also gave rise to us. If it is "natural" for things like the oxygen extinction to happen but "unnatural" for things like anthropic extinction to happen, someone is hanging on to a whole lot of cognitive dissonance...
There is one thing that does make us special. We can have the power to wipe out another species and then choose not to. We have, from time to time, done that. No other organism in this planet's history can say that.
