So I figured, but had to ask. Doesn't seem right for things to turn back into their worse forms, now that I think of it. Thanks for the explanation.
It's more that you can't say one thing is worse or another better. At least not in a technical sense. Things just change. And if something is relatively worse in a given environment, we say it's less fit, but the idea that it's somehow turned around doesn't match how the process worked. It always goes forward.
Evolution means change.over generations. So biologists would describe this as the species evolving to be less fit. From the perspective of our thread, the key thing is that the arrow always goes forward, and change as we follow things forward is evolution. Putting this yet another way, a set of mutations is incredibly (astronomically) unlikely to be reverted back to the ancestral state. Reversions do happen, but it would be basically impossible for a group of more than two or three mutations to spontaneously revert. If this weren't the case maybe devolve would be a technically useful idea. But thermodynamics being as it is, reversion is super rare. So species are always going forwards, with each new generation basing itself off the last, and no real opportunity to go backwards. I hope this is at least interesting because I am tired and it is coming out messily.
It's an explanation, but it's not correct. Any given feature is equally likely to become more or less complex over time. That's the entire premise of variability. The reason that we see more complexity with time is that there is a lower limit on how complex an organism can be, but there is no upper limit. So, statistically speaking, over time the average tends to be more complex. However, complexity has a high cost (in terms of energy usage), so where lower complexity is possible without sacrificing fecundity (as in the cave example I gave above), it will likely be favored. Don't fall into the trap of teleology, although it's easy to do (as we all think the world "wants" us to be here). The arrow of time moves forward, but the arrow of evolution doesn't exist. Full stop.
| The arrow of time moves forward, but the arrow of evolution doesn't exist. Full stop. Evolution is the change in heritable traits over successive generations. A situation where this stops is as impossible as one which it goes backward. It may go really, really slowly, but the second law of thermodynamics means it will continue. As such, I don't think there's anything wrong with understanding evolution as a ceaselessly progressing pattern. The idea that evolution could go backwards (devolve) is flawed and confuses the idea of evolution. We can only go backwards if time goes backwards. There is no underlying "fundamental" or "less-evolved" entity that can be reached from the present state by un-doing the steps that got us to the present. To reach a past state, a species must start from the present, so it is still evolution.
You're misunderstanding both natural selection and the 2nd law. That phenotypes can get more or less complex with equal probability has nothing whatever to do with the 2nd law. I believe you're conflating specific polymorphisms (which are invisible to the environment) with phenotypic variation (what natural selection actually selects for). Of course the probability that a specific mutation will occur "backward" is vanishingly low, but that's not what "evolution" is. Understanding evolution as ceaselessly progressing is not just incorrect but scientifically dangerous, as it implies that there's a directionality to the process. There isn't. There are stochastic changes that from time to time become beneficial to survival.
The entropy of things increases over time provided their size remains constant. This says nothing about the complexity of phenotypes, but it does suggest that it is unlikely for the same phenotype to be reproduced by a "devolving" process in which all the physical things on which the phenotype are based revert. Because life isn't a closed system (there is always energy in and out) the second law applies with a caveat that the flow energy can be used to maintain the state of the system. However, unless there is infinite energy available this won't be a perfect process and things will tend to change. I think we are talking past each other because I am focusing on genomic evolution and you are thinking about it from a phenotypic perspective. If we ignore that genomes determine phenotypes, and look at evolution as a progression through various phenotypic states then it is more comfortable to say that there is no direction to the process. To me, evolution is a physical process, but I think you have a different perspective. I also don't think you're wrong or I'm right--- my focus here was just to describe why "devolve" is not a technically rigorous concept!
"Devolution" is definition in biology. It's not a concept. It means the losing of previously evolved structures. As a definition it can't be incorrect, it can only be shown to exist or not it exist. It happens frequently, as a matter of fact. Again, the 2nd law doesn't apply in any way that it doesn't already apply to any other aspect of life. I don't know what this means. Of course it's physical. Organisms are made, destroyed; they eat, make new organisms along the way. There's an underlying molecular biology to it all, but all the processes at every level are physical.To me, evolution is a physical process, but I think you have a different perspective.
| "Devolution" is definition in biology. It's not a concept. It means the losing of previously evolved structures. As a definition it can't be incorrect, it can only be shown to exist or not it exist. It happens frequently, as a matter of fact. Again, the 2nd law doesn't apply in any way that it doesn't already apply to any other aspect of life. There is no "devolution" which is not more generally understood as "evolution". It can be confusing for people to talk about something devolving because it implies a hierarchy to evolution, and furthermore that we can "go backwards" down this hierarchy. In saying that evolution is always progressing, I'm just stating a physical fact. We can't become our parents or ancestors. To do so, there would have to be some process that remembered how they were and undid all the changes to our genomes that accumulated over time. The only way that we may begin to look like our ancestors is through the continued process of evolution.