Evolution and complexity

I'm new here so I don't know if this has been discussed already. Is there a simple answer to the question of why there are different degrees of complexity in species out there? I mean, there are fish, monkeys, and humans out there; I know they at some point took different paths in evolution but why do some evolve more than others? We have a common root with fish at some point in the past. Why are not fish intelligent (like human inteligence I mean)? This is probably a dumb question but I'd really like to know the answer because I think this is one of the "arguments" against evolution. Thanks!

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but why do some evolve more than others?

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I think you may be making the following mistake in your thinking about evolution. "More evolved" is kind of a tricky idea, and doesn't generally make sense in terms of evolutionary theory. Let me paraphrase your question so it makes more sense in terms of evolution."Why do some creatures evolve differently from other creatures?"Would that be an acceptable substitute question?

Evolution proceeds semi-randomly. The variation in complexity among different organisms is no different than the variation in size, or in color, or in hairiness, or any other trait.There's no evolutionary drive towards complexity. Certain organisms evolved in complex ways as adaptation to environment, but complexity isn't the only way to adapt; it probably isn't even the best way.As much as we tend to think of life on Earth as lions and tigers and trees, etc., the vast, vast majority of life on Earth is still bacteria; algaes, plants insects, and fungi make up almost all of the rest. Complex macrofauna, like you and me and the oak in your front yard? Counts for hardly any of the total mass of living things ("biomass") on Earth. Nobody "evolves more" than anybody else. All living things on Earth have experienced the same amount of evolution. Evolution is not a drive towards a distant goal; it's an explanation of how survival in the here-and-now drives long-term changes in species over time.Evolution is no more a drive towards complexity than it is a drive towards being tall, or having hair, or being fast or strong. Certainly many species evolved those characteristics, but evolution isn't driving everything to be complex, because complexity isn't always a successful adaptation in every environment. It's only an argument against evolution if you don't really know what evolution is. Evolution is the scientific model that explains the history and diversity of life on Earth as the result of natural selection and random mutation.The "diversity" part is important. If evolution does have one long-term effect you could point to in nearly every species, it would be diversity. Evolution says that over time, species will tend to become more diverse. Diverse levels of complexity, like diverse heights, or diverse land speeds, or diverse coloration, are just a part of that increasing diversity.

This might just be a nitpicky, or maybe you did just use poor wording, but: I can't see this as being true.Selective pressure varies on different populations so that some have felt more pressure and changed more. Couldn't you call that more evolved?Think about whales compared to aligators. Whales went from sea to land and back to sea again while gators have been lying in the same ol' swamps fairly unchanged. Couldn't we call the whale more evolved than the gator?

I don't see it that way, I guess. You're just conflating evolution with selection pressure; but those are two different things. Evolution is the result of selection pressure, among other things, but it doesn't follow that more pressure means more evolution.Evolution isn't a thing that you have amounts of. It's the result of species living over time. Since all species on Earth go back to the same individual, they're all the result of the same amount of time, which means that it really doesn't make any sense to talk about who's "more evolved." Not unchanged; just, unchanged recently. You're ignoring the fact that alligators have their own evolutionary history, too. They weren't just created in situ in swamps, after all.But you're privileging recent adaptations over less recent ones without giving any reason for doing so. Ultimately, I think all such attempts to play evolutionary one-upsmanship will be equally specious.

No, I was saying that the pressure causes the change and that the change is evolution.More pressure does lead to more change - when the mutations are there - so I do think that more pressure means more evolution. Heh. When I read that you wrote that all things have experienced the same amount of evolution, I was going to ask how you quantify evolution to know that its the same I'm not considering the "amount" of evolution to be the length of time that the species has been evolving. I see the "amount" of evolution as the amount of change that a species has undergone. Since some species have changed more than others, I'd say that they all have NOT had the same amount of evolution. How so? I don't think I was ignoring that. I had it in mind, at least. And it was part of the point. Gator's evolutionary history is different from whales. Whales have changed more. I don't think it matters when the adaptaion has occured, its about how much adaptation has occured.

Thanks for you comments guys. I think the bottom line was nicely summarized by crashfrog: So for me the conclusion is: more complex != more evolvedI do not think as evolution as a one-brached three with humans on top (with their little crown), although that's a common mistake among many pleople (myself included perhaps). Showing that picture and telling me (or anybody else) that that's the way I probably think is kind of rude. It's ok to be aggresive when you try to make a point but don't ridicule ignorance.Anyways, perhaps a related question then is how two (new?) species can coexist? Let me try to explain. When a mutation occurs and a new species appears by natural selection, doesn't the predecesor ceases to exist after a certain time? How is it possible then to have branching in the tree of evolution?Edited by ircarrascal, : No reason given.

Yeah, but you've just proved that he was right, when you ask: No, why would it? You would only leap to that conclusion because you're still thinking of evolution as a ladder instead of a tree.Here's one of the ways it works. Imagine you have a population of hill-dwelling skroats. (It doesn't matter what a skroat is; assume we're talking about a sexually-reproducing organism.) They vary, individually, like individuals of all species do; because of sexual recombination and mutation, all skroats are not clones.A skroat hunting party (made up of the largest individuals) is on the next hill over when a flash flood happens, cutting them off permanently from the main population. (I guess skroats can't swim.) They settle down and begin to breed amongst themselves. Since they were already the largest skroats, their children are large too. This goes on for very many generations. They accrue mutations that begin to represent substantial changes from the genetics of the "original" skroats.After a thousand years, the lake between the hills subsides. Suddenly it's possible for a skroat to go from one hill to another. But when the two populations meet, they don't recognize each other as mates because the individuals on the second hill are so much larger, and they have other characteristics (like different-colored fur). Moreover, even if they could physically mate, they're genetically incompatible because of all those generations of accruing mutations. Human biologists come by and identify two species of skroat.Splitting populations like that - splitting gene pools - is where new species come from. From the example you can see that Skrotus maximus evolved from Skrotus regularus, and genetic studies would confirm that, and the "original" population of skroats didn't disappear simply because Big Skroats evolved from them. Because your grandparents don't die, and your cousins don't cease to exist, just because you were born.

Not neccessarily.A speciation event usually occurs when the two populations become isolated. The new species doesn't always replace the old one.However, when a species is gradually evolving, it is constantly replacing the old versions of itself. This isn't a speciation event though.For example, take one population of sheep. Have a flash flood that produced a river that divides them that they cannot cross. Over time the two populations will be different from each other. When they become so different that they cannot interbreed genetically (not because of the river) then they have become two seperate species, but one did not replace the other.If we have one population of sheep that is changing over time and at some point in time it is different enough that it would not be able to reproduce with what it was a very long time ago, it is a new secies that has replaced the old one. We just have one contiuous population instead of the two.Make sense?

Lol! I guess if you hang out here long enough you know all of the "official" examples for stuff, huh?

I'm just disappointed that you beat me to it I actually read the "sheep and river" story in a biology textbook, IIRC.But, yeah, that's the 'official' example that you, and I, see tossed around everywhere.

Crashfrog already pointed out the reason why different species of the same branch can coexist. I just want to clear some misunderstanding that I sense in you.I think you think a speciation event takes place overnight via a single dramatic mutation. This is the most common misconception among people who don't know anything about evolution.Permit me to bring in the a few examples to make this easier for you.The human history can be divided up into ages: stone age, bronze age, iron age, ect. Your assumption that a single dramatic mutation bringing in a new species over night is like saying in such and such date the world in one voice decided to change from the bronze age to the iron age.It doesn't make any sense that such change occur over night with every civilization on earth being in sync with each other.The reality is that little by little the tools in each civilization became more advance. Little by little, people discovered how to extract iron from the ores. Little by little, people discovered that iron was a lot stronger than bronze. Little by little, nations began to switch their weapons from bronze to iron. Little by little, changes were made in the cultures.The transition literally took thousands of years.The same could be said about speciation, except in a much longer period and much grander scale. Little by little, mutations are accumulated within a population that distinct it from the rest of the species. Over the course of millions of years, a population may become different enough from the rest of the species that it could be labeled its own species. The transition took place over millions of years. There was no one date when the entire population decided "ok, let's be our own species!"With this regard, can you think of any reason why the parent species and the daughter species can't coexist at the same time if not in the same niche?

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I do not think as evolution as a one-brached three with humans on top (with their little crown), although that's a common mistake among many pleople (myself included perhaps). Showing that picture and telling me (or anybody else) that that's the way I probably think is kind of rude. It's ok to be aggresive when you try to make a point but don't ridicule ignorance.

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It was not meant to be rude. As you say, it is a common misconseption. The use of the phrase "more evolved" threw up a little red flag that you might have the misconception. My only intention was to find out your actual position, not to imply that you had a specific position.

And selective pressure also causes stasis (ie, no change) and the more pressure also leads to more stasis.I don't think we can equate evolution with change, but rather with adaptation. If a population is not well adapted to its environment to start with, then selective pressure would result in change. But if a population is already well adapted to its environment, then selective pressure will act to resist change and hence keep the population in stasis.So how does evolution know to change gears like that? Like the thermos, which keeps hot things hot and cold things cold. How does the thermos know which is which? It doesn't. All the thermos does is block the transfer of heat in either direction and the "keeps hot things hot and cold things cold" effects are the natural consequence.A thought experiment suggested by a 1980 Science article on the conference where punctuated equilibria was introduced. Picture a population as a bell curve with the horizontal axis representing the genome and the vertical axis the number of individuals possessing that genome. Most of the population will be clustered around a mean (read "average") genome. The wider the curve the more diversity the population has. Now also picture that for the environment there exists some ideal genome with which the population would be optimally adapted; actually there are probably several such "ideal" genomes, with some being more ideal than others but each being just fine. Next picture reproduction being represented by the drawing of a new bell curve which would be larger than the parent curve, exist around pretty much the same mean genome as the parent curve, and be spread out wider (more diverse) than the parent curve. Then that new generation undergoes selection in that not all the children will survive to reproduce.What I see happening in the selection step is that the portion of the child curve which is closest to an "ideal" genome will have a higher percentage of survivors than will the portion(s) farthest away from an "ideal" genome. Over generations, this will result in the bell curves' mean genomes to shift towards the closest "ideal" genome. This will have one of two different outcomes, depending on where the population is positioned on the horizontal axis.If the population is not on an "ideal" genome, then selective pressure will cause it to shift towards the closest "ideal", thus resulting in change. This is what people commonly regard as evolution meaning change.But if the population is already on an "ideal" genome, then selective pressure will cause it to stay there, thus resulting in stasis.What I see as the effect of greater or lesser selective pressure is that the population would possess less or more genetic diversity. A high degree of selective pressure would result in a narrow bell curve clustered tightly about the ideal genome, whereas a low degree of selective pressure would allow for a much wider distribution about the mean, which would not necessarily need to be centered about an ideal. An effect of this is that generalized species will tend to have higher genetic diversity and be able to weather through changes in their environment, whereas specialized species that are finely tuned to their environments will have less genetic diversity and will most likely not be able to survive changes in their environments.