Evolution - small to big?

Yeah. It was message 2 I was replying to.[This message has been edited by crashfrog, 09-06-2003]

Well, if you see the topic as being about old earth creationism, then you're right. It would take too many generations in an oxygen tank to produce strong results. Message one could be OEC or YEC, but message 2, to which crash responded sure seems YEC-ie to me. Maybe I've just seen the 'oxygen in the air pre-flood made things big and they lived a long time too' argument one too many times.------------------
No webpage found at provided URL: www.hells-handmaiden.com

Though you did qualify your statement by saying "sometimes" the fact that small and large species of sloths, elephants, etc. lived contemporaneously argues against oxygen as the main factor in determining size. By the same arguement why arent minke whales as large as sperm whales or blue whales? Presumably there are not locallized areas of higher oxygen content exactly where these different species exist since in some cases their ranges overlap.I don't really see a tendency in evolution regarding size...mammoths (my favorites) varied over time in size getting bigger and smaller depending on the time with Mammuthus columbi being absolutely enormous and M. primigenius smaller than modern African elephants.If the argument is that dinosaurs, extinct mammals etc. are big versions of modern taxa as a result of different oxygen levels, then how does one explain that some modern species are larger than their ancestors while others are smaller..i.e. no generalized trend.

It think it was in one of Gould's essays that it was pointed out that the apparent evolutionary path of small to large and simple to complex is an illusion. If you assume the existance of a "wall of simplicity" - the simples (and almongst the smallest) viable life-form, and evolutionary path must be to more complex and larger. This results in filling the ecological niches and leaving open only those useable by larger and more complex species.As has been pointed out there are many examples of, when new niches are opened up, of evolution into smaller forms. Another example is the size of sabre-toothed tigers tusks. They fluctuate in size from species to species with no discernable time trend, probabally in response to the current prey. For complexity, there are plenty of examples ogf animals simplifying, e.g. parasistes losing the ability to survive independently of their hosts, snakes losing legs, cave animals losing eyes.Edited to add: This belief was held by many scientists in the late 19th/early 20th century, so quotes can be found to support it, but the idea is wholly discounted now.[This message has been edited by MarkAustin, 09-09-2003]

I have been trying to find some info, on the variation of atmospheric oxygen content through geologic time - not much sucess.The below cited is something I did find.
http://www.sciencedaily.com/...ases/2000/03/000308081611.htmI have been speculating that there was a significant rise in atmospheric oxygen during the Mesozoic (aka "Age of Dinosaurs"). Part of this line of thought was the prominent existance of coal created in the Carboniforous (sp?) period of the late Paleozoic. I was thinking that the great removial and burial of carbon might result in higher atmospheric oxygen levels.Of course, the Mesozoic "Age of Giants" was preceded by the great extinction at the end of the Paleozoic.Mostly just some speculations on my part. I haven't been able to track down much at all in good specific information.I do suspect that the Triassic and/or Jurassic did have higher oxygen concentrations, but again I concede not having tracked down supporting information.I might be babbling,
Moose

Evolution does not state that an animal has to evolve from small to big. Evolution occurs to benefit the survival of an animal. I think a lot of people comprehend evolution as some magic process that magically changes animals. Evolution happens because of natural selection. If the environment all of a sudden becomes unsuitable for a large animal, the larger ones will start dying off, leaving only the smaller variations to breed. As most people know, most animals do have traits that create a lot of variance in size within a single species. Take the guppy for example, which lives in South America.Guppies that live in an area with no predators will tend to grow quite large, because they dominate the smaller ones in the group. However, if you all of a sudden add a predator that prefers to eat large guppies, then the small ones will have dominance over the large ones. This eventually forms the guppies into two quite distinct groups. Mate these two groups together, and you won't get a medium sized guppy, you will recieve a guppy that is either small, or large, depending on which trait is dominant. And no, this does not necessarily have to happen of thousands of years, it has been done in about 10 years under scientific observation.

Among others, Robert Wright pointed out that Gould's notion of nondirectionality is a confusion of a few different concepts. Many here have said, quite correctly, that evolution does not always favor the bigger or most complex organism, and there is support for lineages where the descendents lost size or complexity due to environmental pressures. However, the fact that there has been an increase in the average complexity of all life on Earth is pretty irrefutable.Another subject mixed into this matter is Gould's notion of 'contingency,' which I believe he overemphasized. He always said that humans were lucky winners in the evolutionary game, and that's certainly true. However, I'm one of the people of the opinion that intelligence of some kind was as inevitable an outcome of the evolutionary algorithm as, say, the existence of sight. Is 'directionality' in these terms just groundless speculation?------------------
I would not let the chickens cross the antidote road because I was already hospitlized for trying to say this!-Brad McFall

But, as Gould points out, that is a necessary consequence of life starting near the wall of lowest possible complexity. What Wright's article adds to the dunkard's walk analogy is the "rachet" caused by an environment that "holds onto" complexity once it is reached. However, he simply states that this is the case. I don't see any reference to evidence for it but it does have a certain intuitive appeal. This still leaves us with a drunkard walking randomly but now he is accompanied by others who like to lean on the wall and push him away from it. It is still for the most part a random walk.In addtion, a point that Gould makes is that the apparent complexity of life could be taken as simply an artifact of our position and where we view it from. A dispassionate observer would count species and number of individuals and conclude, as Gould suggests, that it was, is and always will be the age of bacteria. The apparent complexity is a tiny blip on the really big picture.

NosyNed responds to me: That's still saying that there has been an overall net increase in complexity. How typical of Gould to find fault with a concept because of its consistency with the facts. Given Gould's generally uncharitable view of natural selection, I'm not surprised that he only marvels at the apparently universal ecological niche it provides the smallest, simplest organisms. I prefer to consider its other achievements such as the human brain at least marginally more praiseworthy, considering both are the product of the same cumulative series of drunkard's walks. Call me biased.------------------
I would not let the chickens cross the antidote road because I was already hospitlized for trying to say this!-Brad McFall

Emotionally I agree with you. And, in one sense, intellectually in that the human brain seems more interesting (more valuable in some way). However, "praiseworthy" isn't a survival trait. In the context that we are having this discussion it is exactly the filling of niches, the diversity that counts. Bacteria win that and are therefore more "praiseworthy".I don't see him (in "Full House" ) as saying anything more than we see this progression only because we have a very biased viewpoint. It isn't a big deal but it is a useful way to step back an look at things. When we are extinct will there be a follow on sentient species? I don't think that is assured at all. Given the time it took us to arise I don't see that there is a strong pressure to select for "smarts".The apparent increase in "aveage complexity" is only there because we don't take a real mathematical average. My guess is that Gould may well be right, the mathematical increase is very very tiny.The average living thing is still a bacteria. Or actuall that might be the median. The average is possibly much less complex. I recently read an article that says bacteriophages are 10 times more prevalent and based on that I suggst that they may represent the most common (and average ) form of life on the planet.

I just want to try and explain a possibility for YEC. The reason some of the animals were so big is the same reason noah lived to be 900+ years old. Now is it not true that reptiles don't stop growing until their death? That would give them a lot time to get quite large. Also if say the reason why noah lived to be 900+ was because of a lack or solar radiation before the flood, then that radiation that came after the flood could cause mutations in DNA which would not let animals live as long, and maybe even not grow as fast.so ya theres 2 cents, umm ya thats all off the top of my head and im no scientist.

I think I follow some guy in all this, why not have both brains and bacteria? Is thinking from fungi hydrophobin facial self-assembly on contact with a waterlipid interface back to bacteria and as forward as our brains DO think too much to ask?? for the dinos death due to no warm blooded thermal contact metabolics that bacteria without a digetive system will never enter?;i!)`

Gould...the guy never had it right.The problem with most evolutionists is that they do not understand the niche. A niche is a role in an ecosystem as well as a physical space within that system.If an organism will produce more offspring than another of the same species by moving into a new niche, then it will. It is a simple matter of stochastics. If an species moves into a niche already occupied by another, then it will not only have to out-reproduce it's neighbors, it will have to preserve that niche that is now under greater pressure. Gaussian exclusion is a difficult proposition at best and species tend to move into unoccupied niches.The reason we see organisms getting larger is that these are the most often unoccupied niches. The reason they are so often unoccupied is that organisms that are large also tend to be slow reproducing K-type species rather than fast reproducing R-types. Since this mode of reproduction produces fewer individuals, the variation within that species is limited and the species is less able to cope with environmental changes.Thus, large animals are more prone to extinction than small ones and the available niches for larger animals are more plentiful because of this. There is almost always an unoccupied niche for large animals in an ecosystem, we just don't see them until the animal occupies it.

Could you explain this some more?If there are more available niches for large animals why do they go extinct more? If there are more niches for large animals why are the smaller animals more numerous and with more diversity?

One of the central tenets of Darwin was that variation existed within a species and thus selection would act upon this to select which individuals would leave behind the most offspring.The carrying capacity of a biome is limited and you can see that a large animal will have fewer individuals in their population than small animals and yet these large animals will generally take longer to reach sexual maturity. Fewer individuals give rise to less variation within that population and this in turn gives selection less chance to act on differential reproductive success. This differential reproductive success is the bottom line with evolution. It doesn't matter if an organism is more complex or larger. What matters is whether the offspring of one type survive at a greater rate than another.Thoughts to ponder: Why did the mammoths on Wrangel Island have such small stature? What was the influence of predation on size?http://packrat.aml.arizona.edu/Journal/v37n1/vartanyan.htmlThere is a good explanation of these extictions and it was published shortly after Martin published his thought on the matter.