Stasis and Evolution

Hi Bluejay,Interesting topic, and I hope you get some creationist responses.Another interesting part of the "missing fossil" equation is how fast can the punctuation occur. For some idea of that, see Differential Dispersal Of Introduced Species - An Aspect of Punctuated Equilibrium where certain introduced species serve as surrogates for the founder populations.In each case the founding population was small.In each case the species spread was determined by how well it was pre-adapted to the ecology.In each case there are similar species in the ecology that are being displaced in different degrees by the invaders, but existing populations are not necessarily wiped out.This shows that a pocket population that evolves independently of a parent population does not have to be large to initiate a punctuation event, it just needs the right conditions of adaptation and reasonable fitness to the ecology that it is spreading into.So if anyone wants to discuss the punctuation aspect instead of the stasis aspect, then you can direct them to the Differential Dispersal Of Introduced Species - An Aspect of Punctuated Equilibrium thread. Except (as has already been pointed out to him) that evolution selects for adaptation to the ecology - it's a response mechanism, with feedback for fitness. Thus if the ecology does not change, then natural selection operates to cause stasis, as all mutations that would alter the fitness to a lower level are selected against rather than allowed. To change away from a fit phenotype would be contrary to evolution.Enjoy.

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Hi Perdition & Bluejay,For some off the cuff measurements of the differences in living animals and in skeletons see Dogs will be Dogs will be ???Notice that measurements of bones and establishing their proportions is one of those things that paleontologists actually due to determine species and changes.Enjoy.

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Hi CosmicChimp I don't follow. If you have a population in ecology {A}, natural selection will select for fitness to ecology {A}. If the ecology changes to {B}, then natural selection will select for fitness to ecology {B}, rejecting mutations that move the population away from fitness for ecology {B}. However, if ecology doesn't change, then natural selection will continue to select for fitness to ecology {A}, rejecting mutations that move the population away from fitness for ecology {A}.Enjoy.

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Hi CosmicChimp, let's see if we can clear this up. Evolution in general, and natural selection in specific, is a response mechanism, it doesn't cause anything, but it reacts to everything that affects survival and breeding.The cause of the change or the stasis is the ecology -- how the population fits in with the rest of the biology around it. If it changes then the population will adapt or perish, but if it stays the same then the population will stay the same or perish.Mutations still occur, and natural selection still benefits the more fit over the less fit, whether the ecology changes or the ecology is in stasis. Whether a mutation is beneficial or deleterious is related to how it affects the fitness of individuals in the population, it isn't inherent in a mutation to be one or the other. So yes, the probability of a new mutation increasing fitness decreases as the population nears "absolute fitness" when the ecology is static, but it is still measured for fitness to that ecology by natural selection. Which is why you have population explosions and rapid speciation after extinction events.Enjoy.

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Hi Arphy, There is no dictum that organisms must change, evolution is a response feedback system. When there are changes in the ecology the population is under pressure to adapt to the changes or perish, when there are no changes there is no pressure to change.First, let's look at what constitutes a level of change to move out of stasis. You seem to have a picture in your mind of a certain amount of change, but are having some trouble with categorizing it, developing a metric to determine it. I have tried to develop a discussion on the topic of how large a difference is large enough on the Dogs will be Dogs will be ??? thread. Note that biologists don't care how big (or small) the change is once speciation has occurred. Competition for resources yes - more so when the resources are limited, but not so much when opportunities to use new resources are available, as this changes the competition matrix. When one variety can make better use of a new resource/s than another variety, then it will be more successful in that new ecology leaving the old version behind in the previous ecology to which it is well adapted.Rather than survival of the fittest, one should consider the survival of those able to survive, as any organism barely able to survive and reproduce has met the minimal requirements of evolution to proceed.Here's an example of a speciation event in the fossil record:Pelycodus: gradulastic

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Here you can see the general evolution of this population of organisms increasing in size from bottom (oldest) to top (youngest) and three attempts to branch off, the first two becoming extinct as there is apparently not enough ecological difference between parent population and the daughter population to support both populations. The third population, however, succeeds, with sufficient ecological difference to support the smaller daughter branch on the right side and the larger main population branch on the left side. The large sized organisms move into new ecological opportunities that the smaller branch is not as able to take advantage of, while leaving the opportunities of the old ecology to the smaller population that the larger ones are not as able to take advantage of.When we look at the main branch we could call that stasis, as the organisms are morphologically similar, albeit of different overall size. This is the same kind of difference between modern Coelacanths and ancient ones. But when we compare it to the other branch we see that change in size is important to the whole picture of adaptation to the ecology, and does not really qualify as stasis. Neither of these branches demonstrate stasis in the fossil record.Both are fit for their new ecologies, but it is the ecological opportunities that are different and that drive the changes seen The branching diagram above covers about 5 million years.Personally I would agree that competition between daughter species in nearby, overlapping, or especially in the same areas (as appears to be the case here) would drive any sexually isolated daughter populations to move away from the parent, or another daughter, population ecology into separated ecologies as fast as possible to enhance their survival options. In this case one population continues to get bigger - to concentrate on opportunities their larger size affords - while the other rapidly gets smaller, reverting to the more distant ancestral size - to concentrate on the opportunities their smaller size affords. Think treetop versus forest floor.This is one of the reasons that the rates of evolution will almost inevitably vary when new species first evolve, compared to the rate of evolution once they have become well established in a stable ecology. Now consider that where we have a static ecology, and therefore no pressure to change nor any opportunity to take advantage of new ecologies, that the competition will be to remain as well adapted as the ancestral population were: the small changes that tend to diverge from the parent population are not as successful at surviving and reproducing, so stasis is selected to match the static ecology. By definition "neutral" mutations are ones that do not effect the selection process. This could involve fur patterns, eye color, size, etc etc around the normal values, and would show up as gradual change over even longer periods of time due to genetic drift and chance factors (killed by natural cause, tree falling etc) that are not selection factors.Enjoy.Edited by RAZD, : clrty

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Hi caffeine, I've been thinking about this for a while. I think that would have to be a very stable ecology. Ultimately I think that genetic drift would change any species that is that adapted to so many ecologies that it can survive equally well in many of them.I think of 50 Starlings, intentionally introduced in 1890 and now universal pests across america as an example.See Differential Dispersal Of Introduced Species - An Aspect of Punctuated Equilibrium for more.Enjoy.

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Hi caffeine, it's just some thoughts I had, not a complete answer. I just figured they were a good example of what you were describing. It would be interesting to see if they still mate with european birds with the same degree of success as is normal in each subpopulation (neutral drift).One of the problems with a highly adaptable species with a large range of possible habitats would be confining it to a stasis ecology.To study the idea you'd probably need to set up a lab experiment, first to select for multiple ecology adaptation, then to isolate parts in each sub-ecology.I'd bet on some traits being lost by drift if they are not selected against.Enjoy.

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