[Nyetan]

Mildly off-topic, but does anyone else find it odd when people wonder what the function of a naturally evolved object is? I mean, you could ask that of a module in some code or a part in a car, but the moving bits in organisms came about through an unguided process, so don't they just do things (some of them well)?

[TeMPOraL]

If you believe "the moving bits in organisms came about through an unguided process" - remember, some people don't, and I suspect a lot of people just sort-of believe - it's still fine to ask what functions those bits perform well and which they don't. It's building a model, just like we build models in physics or chemistry. The function of free electrons in an atom is to let many atoms stick together. In science, it doesn't imply that they were explicitly designed that way.

[derefr]

One succinct way to describe/pattern-match life is "a process that lowers its own internal entropy, by consuming negentropy sources and emitting waste entropy." Which is sort of to say "a process for bringing order out of chaos", but with the much more particular implication of repairing any internal insult that may occur to return to equilibrium. In short: life is that which maintains itself.

With that in mind—and ignoring the fact that things that cause successful reproduction take precedence (so "suicide by mating" is okay)—most everything in a living being has the "function"—at least, in an adaptive environment—of working to lower that living being's internal entropy over some time-scale.

And everything that isn't helping in that function—every part of the system that isn't serving the system—is itself exactly the entropy that a living being, as a system, is trying to either excrete, wall off, bypass, or xenometabolize.

A completely benign bacterium trying to "keep to itself" in a host is, definitionally, still a parasite: its own self-maintenance increases the entropy of its environment, i.e. the host. And most every kind of host (other than the most primitive of marine microflora) has defenses for parasites, even of the most benign variety, precisely because "keeping to oneself" is still a net negative on the host. A body will only tolerate that which offers some form of symbiosis to it—things which aid the body in the goal of maintaining itself, giving back more than they cost to keep around.

(Obviously, I don't mean to suggest a body will figure out how harmful a given bacterium is and decide how much to react to it. But rather, evolution will selectively adapt the host species to defend itself against anything that's a net negative—while not putting nearly as much pressure to create defenses for things that are symbiotic.)

This applies to things besides parasites, too: "vestigial features" usually aren't, but are rather usually still of some minimal benefit: chickens and penguins can't fly, but flapping their wings still assists them in fleeing from predators. A feature that is truly no longer of any benefit to the species costs more to build and more to maintain than it's "worth", and so, if the relevant genome isn't horribly spaghetti-linked, the feature genes will simply become methylated and turned off after a few generations. It's quite accurate to say that any feature, any organ, any chemical in a body is there for a reason—or at least there for a function.

[akiselev]

This is an interesting question that leads down a rabbit hole without a satisfying conclusion. If you think about it, evolution is a process with but one singular purpose: it is the ultimate arbiter, based on the laws of physics, of what objects exist and for how long. Thus one can argue that the function of everything is survival and propagation, from basic subatomic particles to rocks to living organisms to societies and civilizations to entire planets and stars. Unless you assume that there are an infinite number of universes representing an infinite number of variations on the laws of physics, evolution (of anything) is random but not unguided. It's a process thats less like a coin flip and far more like card counting in a black jack game: the next card may be random but its possibilities are very much bounded by the shuffling of the deck and the cards drawn so far.

To put it another way: without a universe there is no possibility for evolution (of anything) so naturally the function and survivability of an object is entirely dependent on the universe it exists in, and thus is "guided" somehow.

Edit: I use very humanizing language but the process of evolution has no external agency and this cannot be emphasized enough. Our language just gravitates toward describing natural selection as if it's guided by a god, and not something as unrelatable as the ultimate laws of the universe.

[beefman]

I think Wolfram makes an interesting point here: much of our morphology is not programmed in our genes, but is rather the result of gene-gene and gene-environment interactions.[1] These are essentially simple computer programs, which can produce a variety of features if only one of them is adaptive, or even if none are. Is it more likely that cheetah spots are precision camouflage, matched to the Savannah, or just the result of the simplest possible local rules for 2-coloring a surface?[2]

[1] recent story here for example https://news.ycombinator.com/item?id=10629731

[2] shown on human forms here: https://vimeo.com/145251635

[duaneb]

Yes, this is the teleological fallacy: assuming an object had some end or function inherently.

[arrrg]

Natural selection very much is a guided process. It is obviously not guided by anything, but it very much is not random or aimless or any of those things.

On the mirco level, sure, it is all of those things, but not when looking at the macro level. I think you might just not understand evolution?

[username3]

Has anyone calculated how long flipping bits through an unguided process would take to evolve a function? It seems unlikely as randomly finding a private key or breaking hashes, but how do they compare and what is it like in terms of computing?

[TeMPOraL]

Evolution is not random. It's very much directed by what we like to call "selection pressures". The whole way this process works is that some outcomes are more likely to survive than others.

[duaneb]

I think the equivalent might be something like a beam search or quantum annealing for highly efficient reproduction (local minimum, not absolute) given a hostile environment; selected individually, it's almost certainly an NP-hard problem. However, I don't think this is a productive way to look at evolution: there is no intention, many different evolutionary processes interleave in complicated ways, and selection takes the entire lifetime of the reproduced life form (which may never end!). So it's much more instructive to think of an ecosystem selecting for minimum entropy, IMHO, which is pretty far removed from the genetic level.

[mtdewcmu]

https://en.wikipedia.org/wiki/Genetic_algorithm

[adrianN]

Check this paper by Valiant https://dash.harvard.edu/bitstream/handle/1/2643031/Valiant_...