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MartinV  Suspended Member (Idle past 5856 days) Posts: 502 From: Slovakia, Bratislava Joined: |
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Author | Topic: Is evolution of mammals finished? | |||||||||||||||||||||||
Chiroptera Inactive Member |
quote: This is not quite true. The Eocene did not suddenly give rise to over a dozen new orders. The linked chart shows quite clearly that these orders began radiating at about the time of the KT-boundary, at the beginning of the Paleocene. It seems pretty straightforward about what happened. A mass extinction emptied a lot of different ecological niches, which the surviving species filled during radiative adaption, perhaps allowing pretty innovated "designs". Once the niches began to be filled, natural selection then intensified, preserving the best adapted of the new designs in the newly opened niches, and by the beginning of the Eocene pretty standard designs (the different orders) had been established. After this point, large scale changes, drastic innovations would move the morphology off of the peak on the fitness graph, so natural selection would then be fairly conservative in preserving those forms that have proven to be highly adapted, and preventing poorly adapted innovations from taking hold in the now crowded ecosystems. My guess is that after human race has run its course, the end result of the mass extinction which we have produced will be that the relatively few remaining species will again undergo radiative adaptation, and we would (if we were around to observe it) the rise of many more new orders. This world can take my money and time/ But it sure can't take my soul. -- Joe Ely
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Chiroptera Inactive Member |
I can't find anything either, but I note that the year in your quote is 1910. Although scientists pretty quickly accepted common descent due to Darwin's efforts, there was a lot of controversy over what role, if any, natural selection played in the process. Darwin's theory is about natural selection -- the common descent part is fairly trivial. It is quite possible that Brown accepted a non-Darwinian theory of evolution.
This world can take my money and time/ But it sure can't take my soul. -- Joe Ely
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Chiroptera Inactive Member |
quote: Davison does that in the essay linked in the OP. The quotes seem to show that Broom may have had some tendencies toward structuralist theories of evolution, but it's hard to say what relative importance Broom felt natural selection had in the process of evolution. At any rate, having supplied evidence that does seem to support the claim, the onus is now on others to read Broom's works to find out if these quotes are taken out of context and to find out what role, if any, he felt natural selection has. -
quote: Darwinian evolution was not the mainstream at that time; rather it was one of many possible theories that were discussed and studied. Common descent was almost universally accepted as a fact; there was still a lot of work to be done to determine the mechanisms of evolution. It is very conceivable that Broom was not a Darwinian, there is no reason to assume that he was Darwinian, and if he wasn't then this would not count as a stain on his professional reputation. Without actual evidence, it is hard to say what Broom believed. Davison supplied some evidence that Broom was not pure Darwinian, and now the onus is on those who would like to show that he was (if anyone really thinks this is an important issue). Maybe he was, maybe he wasn't, but I see no problem right now with the possibility that he wasn't. This world can take my money and time/ But it sure can't take my soul. -- Joe Ely
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Chiroptera Inactive Member |
Broom's evolutionary theory is based on the existence of some sort of 'intelligent spiritual agency' of two types: a) the lower agency, present in animals and plants, of limited vision and limited power, and b) that of a much higher type which has planned and directed evolution (via directing from time to time the former, inferior agencies). Huh. So Broom was a Lamarckian. Interesting. -
quote: What this meant was that among one population of Pakicetus, for example, which were living near a riparian or estuarian environment, those that were slightly better able to make use of the water (for protection or as a source of food) were better able to reproduce and leave behind offspring than those that were better suited for an entirely terrestrial existence. Of this slightly more aquatic version of Pakicetus, those that were ever so slightly more efficient at the use of the aquatic environment were more likely to leave offspring than the less aquatically adapted. After a while, you have an aquatic or semi-aquatic version of Pakicetus. Some environmental change causes the completely terrestrial Pakicetus to become extinct, leaving only the aquatic descendent species. I'm not sure what "more convenient niche" even means. -
quote: There were probably many empty niches in the oceans -- I believe that the KT-extinction hit marine life harder than land life, but I'm not sure. At any rate, some niches were filled by land animals adapting to the seas, and other niches were filled by sea animals who likewise adapted to the newly opened environments from different niches. I bet that in examining the fossil record one would see an increase in new orders in all surviving classes at this time, including among fish, crabs, and whatever. -
quote: Maybe the niches were already filled. There was no more room for new entrants. -
quote: Sure. If like Broom
Broom's evolutionary theory is based on the existence of some sort of 'intelligent spiritual agency' of two types: ... b) that of a much higher type which has planned and directed evolution.... one has an a priori commitment to some vague Lamarckian force that compels species to evolve in particular directions, then I can see how this is difficult to understand. But in the absense of anything forcing evolution, particular in the absense of anything forcing evolution in a particular direction, why should they evolve into a more aquatic species? Presumably they do quite well the way they are. Those better adapted to a more purely aquatic life would not fare as well as the present pinnipeds, those better adapted to a more terrestrial environment would not do any better either. -
quote: Sure. It can be. In fact, pre-Darwin that is what naturalists believed that natural selection did. Before Darwin it was believed (at least by the functionalists) that each species was already perfectly adapted to its environment, and that therefore any variation off of the archetype would be less adapted and removed by natural selection. In fact, one of the biggest obstacles to Darwin's theory was that people had a difficult time imagining natural selection as positive, creative agent as opposed to the traditional view of it being a negative conservative one. And it makes sense. Imagine the graph that measures "fitness" as a function of "morphology". If a species is already at a local maximum, then any change in morphology will make the individual "less fit", and natural selection will remove it -- hence natural selection will tend to prevent evolution. But a change in the environment (like a mass extinction) will change what is considered "fit" -- it will take the species and plop it right on a new and different graph, not necessarily at a peak. Now there is a direction "up" and variations in morphology that are in this direction will be selected for; we will now see evolutionary change. This world can take my money and time/ But it sure can't take my soul. -- Joe Ely
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Chiroptera Inactive Member |
quote: Because you don't know what Lamarck's theory was.
Broom's evolutionary theory is based on the existence of some sort of 'intelligent spiritual agency' of two types: a) the lower agency, present in animals and plants, of limited vision and limited power, and b) that of a much higher type which has planned and directed evolution (via directing from time to time the former, inferior agencies). This is a pretty good, but short, description of Lamarck's theory. Except that he felt that the two agencies could be explained through naturalistic means rather than "intelligent spiritual" ones. The acquisition of acquired characteristics was a common belief at the time, shared by Darwin as well, and was accepted as "folk wisdom" until modern genetics showed it to be wrong. -
quote: So "there might be no vacant niches" becomes "land mammals did push back all species". Anyway, as long as there might be vacant niches, then there would be no other species to be "pushed back" and natural selection has not been discredited as an explanation for the observed phenomenon. -
quote: So go read up on the evolution of post-KT marine life and report back to us on what you find. -
quote: Maybe. But as long as "maybe not" natural selection has not been discredited as the best explanation. -
quote: Maybe. But as long as there is a "maybe not" natural selection has not been discredited as the best explanation. -
quote: Cool. So we can both write our own science fiction books without fear of plagiarizing each other. This world can take my money and time/ But it sure can't take my soul. -- Joe Ely
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Chiroptera Inactive Member |
quote: That's a good question. When people play pachinko, why does one person's ball fall more or less straight down, while another person playing the exact same machine see her ball bounce all the way over the side? Yet, despite not being able to answer even such a basic question, no one doubts that the motion of the ball is basically described by Newton's simple laws of motion. I don't know why you want do doubt Newton's laws just because I cannot describe exactly the path of a pachinko ball. Evolution is governed by the environment. The environment contains lots and lots of factors that will influence the evolution of a species. Crocodiles that were too far from the "basic crocodile form" didn't survive to leave offspring. Why? Maybe the right mutations didn't occur that would have given them a survival advantage. Maybe the KT-extinction did not change the shape of the "fitness vs. morphology" function. Why did Pakicetus evolve toward an aquatic environment? Well, evidently some Pakicetus had a mutation that allowed a more efficient use of a more aquatic environment, and these Pakicetus were able to thrive. Just like the pachinko ball, that is pretty much all we can say. -
quote: Huh? You mean the subsequent evolutionary history of life was already written in the first cell three and a half billion years ago? How does that work? This world can take my money and time/ But it sure can't take my soul. -- Joe Ely
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Chiroptera Inactive Member |
quote: You seem to have an unhealthy obsession with crocodiles and sharks. Is this a national trait because Slovakia is landlocked? I suggest you try to make it to the Mediterranean on your next vacation. Even if you are too scared to go into the water yourself, go to the beach anyway just to watch the people. You will see lots of people playing in the water without being eaten by crocodiles and sharks. Even today, we have lots of aquatic and semi-aquatic mammals -- whales, manatees, seals, nutrias, and otters -- all living in the water. Some of these avoid being eaten by crocodiles and sharks, and others manage to survive despite occassionally being eaten by crocodiles and sharks. So what is the problem with paleocene and eocene mammals living in or near water? And what prevents some sort of direct evolutioned mammals from facing the same crocodile and shark problem? I don't think a crocodile will care much whether amulocetus evolved due to natural selection or through some sort of directed evolutionary process. A meal is a meal. Whatever prevents an directed evolutioned ambulocetus from being eaten by a shark will also prevent a naturally selected ambulocetus from being eaten by a shark. -
quote: Heh. Heh heh heh. Hee hee hee hee hee hee hee hee hee. BWAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHA! - Okay, so we're taking about some sort of New Age woo woo. That's fine, I just want to make sure we aren't talking about science any more. - But let's make sure I got this straight. You want to believe in some sort of directed evolution, so you have to come up with a "problem" for natural selection. The "problem" that you came up with is that the world is filled is demonic ravenous crocodiles and sharks that will gobble up anything that so much as touches water. But there is that magical spirit that not only forced mammals to evolve, but it also protected them from crocodiles and sharks. But this magical spirit has run out, so not only do mammals not evolve anymore, but they are now all being eaten by crocodiles and sharks and that is why they are endangered. Uh-huh. Thanks for sharing. Actually, if their god makes better pancakes, I'm totally switching sides. -- Charley the Australopithecine
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Chiroptera Inactive Member |
quote: Birds and crocodiles are the surviving branches of the archosaurs (which also may have included the pterosaurs. During the Permian, the therapsids were the most dominant land form. Then the PT extinction event (the worst that is known) allowed the archosaurs to become dominant; the extinction event that marked the end of the Triassic allowed one particular branch of the archosaurs, the dinosaurs, the opportunity to become dominant, and the the KT extinction then allowed one particular branch of the therapsis, the placental mammals, to once again reclaim their ancestor's place as the dominant land form. Added by edit:As far as the warm-blooded croc thing, I found this abstarct: We present other evidence for endothermy in stem archosaurs and suggest that some dinosaurs may have inherited the trait. I also found an old Pharygula article that I remembered spoke of this. Edited by Chiroptera, : No reason given. Actually, if their god makes better pancakes, I'm totally switching sides. -- Charley the Australopithecine
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Chiroptera Inactive Member |
quote: Oops. Not quite. Crocs are close cousins to dinosaurs, sharing a common ancestor that they do not share with any other living taxon. But I am mostly responding because I found something cool on the Wikipedia article:
Wow! How cool is that! Actually, if their god makes better pancakes, I'm totally switching sides. -- Charley the Australopithecine
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Chiroptera Inactive Member |
quote: I was wondering when someone was going to bring this up. The fact is, a niche does not exist until there is a species that is actually occupying it. I realized that potential confusion that could arise using these terms carelessly, but I did so anyway. Sorry about that, folks. Actually, if their god makes better pancakes, I'm totally switching sides. -- Charley the Australopithecine
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Chiroptera Inactive Member |
quote: Would three years in Africa on the equator count? There were crocodiles in some of the rivers. Sometime people got eaten. Sometimes they didn't. People, and animals, can use the rivers and only be eaten on occassion. Same with the oceans. Seals manage to survive as a species even though a few get eaten by sharks. The fact that completely non-aquatic deer can drink out of a river without being eaten to extinction, the fact that manatees can live in swamps without being eaten to extinction, and so forth shows that prey animals can coexist in the same environment as predators. In fact, if they couldn't the predators themselves would become extinct. So I see no reason why the transitional forms between, say, pakicetus and modern whales couldn't coexist with crocodiles and sharks; other animals manage to do it. -
quote: I'm not sure why you think that crocodiles should have grabbed up all the good niches (uh-oh, there's that word again) before ambulocetus had a chance to evolve into them. -
quote: Is there any, like, evidence that this can happen? You know, assuming we're going to pretend we are still talking about science? -
quote: Heh. Except the Darwinist fairy-tale of "natural selection" has been verified to be a real phenomenon in the real world. Unlike your "magical spirit force", the motivations for which I am still trying to understand. Actually, if their god makes better pancakes, I'm totally switching sides. -- Charley the Australopithecine
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Chiroptera Inactive Member |
quote: Was? It still is. The KT-event emptied a lot of niches. There was a lot of opportunity for dramitically new (at least new to the surviving species) ways of utilizing available resources, resources that suddenly became available to the surviving species (but were previously unavailable because they were being utilized by other species that were now extinct). So, right after the Cretaceous, a series of mutations that would, over time, lead to a profound morphological difference could possibly result in a new viable species. However, by the late eocene the new opportunities had either been already filled by new species adapting into them, or closed as the new species created new ecosystems where the potential niche could not be realized. In this situation, natural selection would not, in general, result in profoundly new morphologies. First, because the new species had fully adapted to the newly established ecosystems so that small morphological differences from the average population norm would be less adapted to the lifestyle in which the species had adapted. Second, if the small changes made the individual better adapted to take advantage of a different set of resources, by this time those resources were already being utilized by a better adapted species. So in this case, natural selection would act as a relatively conservative force. Actually, if their god makes better pancakes, I'm totally switching sides. -- Charley the Australopithecine
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Chiroptera Inactive Member |
quote: Yes, you keep saying that. Yet you haven't really explained why this is questionable. You also haven't explained why you find the conception of a vaguely defined, unobservable "spirit force" to be reasonable. Edited by Chiroptera, : clarity Actually, if their god makes better pancakes, I'm totally switching sides. -- Charley the Australopithecine
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Chiroptera Inactive Member |
quote: Heh. Ain't that the truth! -
quote: Yes, I realize that this is one of the things that Martin has been saying. But I wasn't sure why Martin feels this way. This is why I was trying to get him to explain how his magically, spirit driven transitionals would have had any better chance at surviving than naturally selected transitionals. Unless Martin is an all-at-once saltationist -- as you say, it's not really clear what he is trying to say. -
quote: An even better point. Thanks. -
quote: It seems naive to me to assume that "all water species are basically the same" or that "all water niches are basically similar". I don't buy into the notion that somehow crocodiles and sharks were in any better position to take advantage new opportunities afforded by the KT extinction than terrestrial mammals were. But if you think it's partly insoluble, maybe I'm wrong. -
quote: This may be close to what I was trying to get at in my pachinko example. Why does one ball travel more or less straight down, while another bounces all the way over to the side? If they were both subject to Newton's laws and gravity, then wouldn't we assume that they both would take the same paths? I guess there must be some sort of "spirit force" that guides the balls in a pachinko machine. But in reality, we do recognize that Newton's laws are responsible. It's just that an exact calculation of the paths would require us to know a huge amount of data to great precision -- just hitting a peg just a little bit differently will create a whole different path. In the same way, predicting how real species evolve (or do not evolve) in real ecosystems would require a great knowledge (with great precision) of all the factors in an environment, as well as exactly which mutations will arise. Furthermore, there may be developmental constraints as to what paths are even potentially possible. Actually, if their god makes better pancakes, I'm totally switching sides. -- Charley the Australopithecine
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Chiroptera Inactive Member |
quote: Indeed. Not much of a problem at all, actually. Actually, if their god makes better pancakes, I'm totally switching sides. -- Charley the Australopithecine
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