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Fri 18 Jul, 2008 04:26 pm
Evolution is the ultimate pragmatist. It "cares" only about differential reproduction. So why is it that replicative molecules which must have started out small, evolved into larger replicative molecules with many more pieces and variations?
Is it simply the case that an increase in molecular size and variation results in an increased potential for reproduction?
The only known natural forces at work in evolution currently are Reproduction, Variation and Selection. But I'm wondering if there is an additional component working
within Natural Selection which links the increase in complexity to an increased probability of reproduction.
The article below gives a bit more information on the subject.
[URL=http://www.newscientist.com/channel/life/dn13617-evolution-myths-natural-selection-leads-to-ever-greater-complexity.html]An Article from NewScientist[/URL] wrote:Evolution myths: Natural selection leads to ever greater complexity
18:00 16 April 2008
NewScientist.com news service
Michael Le Page
In fact, natural selection often leads to ever greater simplicity. And, in many cases, complexity may initially arise when selection is weak or absent.
If you don't use it, you tend to lose it. Evolution often takes away rather than adding. For instance, cave fish lose their eyes, while parasites like tapeworms lose their guts.
Such simplification might be much more widespread than realised. Some apparently primitive creatures are turning out to be the descendants of more complex creatures rather than their ancestors. For instance, it appears the ancestor of brainless starfish and sea urchins had a brain.
Nevertheless, there is no doubt that evolution has produced more complex life-forms over the past four billion years. The tough question is: why? It is usually simply assumed to be the result of natural selection, but recently a few biologists studying our own bizarre and bloated genomes have challenged this idea.
Rather than being driven by selection, they propose that complexity initially arises when selection is weak or absent. How could this be? Suppose an animal has a gene that carries out two different functions. If mutation results in some offspring getting two copies of this gene, these offspring won't be any fitter as a result. In fact, they might be slightly less fit due to a double dose of the gene. In a large population where the selective pressure is strong, such mutations are likely to be eliminated. In smaller populations, where selective pressure is much weaker, these mutations could spread as a result of random genetic drift (see Natural selection is the only means of evolution) despite being slightly disadvantageous.
The more widely the duplicated genes spread in a population, the faster they will acquire mutations. A mutation in one copy might destroy its ability to carry out the first of the original gene's two functions. Then the other copy might lose the ability to perform the second of the two functions. As before, these mutations won't make the animals any fitter - such animals would still look and behave exactly the same - so they will not be selected for, but they could nevertheless spread by genetic drift.
Use your mutations
In this way, a species can go from having one gene with two functions to two genes that each carry out one function. This increase in complexity occurs not because of selection but despite it.
Once the genome is more complex, however, further mutations can make a creature's body or behaviour more complex. For instance, having two separate genes means each can be switched on or off at different time or in different tissues. As soon as any beneficial mutations arise, natural selection will favour its spread.
If this picture is correct, it means that there are opposing forces at the heart of evolution. Complex structures and behaviour such as eyes and language are undoubtedly the product of natural selection. But when selection is strong - as in large populations - it blocks the random genomic changes that throw up this greater complexity in the first place.
This idea might even explain why evolution appears to speed up after environmental catastrophes such as asteroid impacts. Such events would slash the population size of species that survive, weakening selection and increasing the chances of greater genomic complexity arising through non-adaptive processes, paving the way for greater physical or behavioural complexity to arise through adaptive processes.
And little dickies could shrivel up from under use I suppose.
No chance.
Quote:Rather than being driven by selection, they propose that complexity initially arises when selection is weak or absent.
Obviously. Otherwise I would look like Charton Heston in his prime and all the girls in the pub would look like (fill in name of your imaginary friend--Delia Smith in my case.)
First, there was only water...
That's interesting, Rosborne.
Complexity can be beautiful, but of course that is off subject.
I could conject that there is an (um...) predilection toward a system, or a reward that comes with a system. I speak from the old days, don't have much recent science ed. But I remember feedback/inhibition in biochem cycles, operon genes, very elegant. Ok, I don't remember that all that well, but that I thought it was elegant. The fluidity of these mechanisms which absorb/involve complex situations must have some kind of gain.. I suppose an energy gain. Or an improvement of some sort.
Out of my depth here, just talking.
ossobuco wrote:I could conject that there is an (um...) predilection toward a system, or a reward that comes with a system. I speak from the old days, don't have much recent science ed. But I remember feedback/inhibition in biochem cycles, operon genes, very elegant.
It's funny you mentioned "Feedback" because that's the same term that popped into my head when thinking about this stuff.
I was imagining replicative molecules floating around replicating, and getting bloated with neutral material simply due to random errors. Every time an error results in failure to replicate the line terminates. So the only direction the replicators can go is in the "bloat" direction. But bloating isn't necessarily complexity until selection comes along and culls the population in relation to some aspect of the local environment. In this way, complexity becomes defined as "effective relationship to environment".
Im not surprised at your statement ros, since much popular literature in the subject of evolution seems to insist on that paradigm. Several authors, including Gould , have always held us up short to remind us that there is, from the fossil record, a whole number of examples of " cladistic neotony" where simpler body forms are retained into successive clades and these get further refined into simpler and simpler forms. Trilobites are an example. In the early to mid Paleozoic, these critters were leaving tests that indicated an evolution to extreme spinosity and eye structures , Then, as environmental conditions varied, they resettled into simpler torpedo shapes until many species , in the Permian, were just like "pill bugs" of the sea.
There are whole groups of applied folks (in the oil patch) who make their livings doing cladograms of specific species of foraminiferans , because , by looking at the rapid changes these things undergo, they adapt to more organic condition that are suitable for oil formation and trapping.Forams, because they reproduce so quikly, evolve quickly also. There are many examples f daughter forams much simpler in body style than their parent forms.
Sean Carrols book "The MAking of the Fittest" has a good chapter on the rise of Apparent complexity from the basic toolkit of the genomic structure. He stated that The measurable effect of evolution is diversity, not necessarily complexity. Certain lifestyles that are impressed by environmental conditions or genetic drift, or even normal Hardy Weinberg distribution make for many derived species that are simplified and , in manyspecies of marine invertebrates, sexual diversity itself has resulted in the evolution of entire male members of the species to have become actual parasitic lifeformes attached to the females. They used to be free living but, in a time that post dates the formation of a substrate(like a coral reef or an ocean vent), they gradually evolved into true parasites on the female, and evolved into extreme simple forms.
Also, the whale is an example of a simpling up of an early "bauplan", . How about ratite birds, or insects that have lost entire body sections over time.
Although the apparent rise of complexity is seen in the fossil record, we are often not attuned to a search for the opposite effect in the same rocks.
Sadly, in the science of academic paleontology,careers are mostly made by finding pituitary giants, or distinct "missing links" in the fossil record. WHile there are hundreds of otherpaleo guys and lately, paleogeneticists who make their livelihoods in the quest of the very things that headline your thread, most of these guys are employed by oil companies or in some other applied area.
One of my early grad students did a dissertation on a new species of trilobite which displayed an apparent retained paedomorphism ( "larval" features seemed to be retained through successive time and this gave an apparent simplified body style). The diisertation wound up being a statistical analysis of the sedimentology of fossilization rather than evolution.
An evolved form, simpler in morphology than its predecessors is usually highly adapted to a specific niche and , by definition, will disappear when that niche disappears. Paedomorphic forms are even more finely tuned to their environments and (as the man said) are trapped by the same environment.
Like dumbing down is supposed to be a feature of regulatory bureaucracies such as Media and creativity diminishes in an environment of correctness which is an axiomatic feature of scientific "facts" and disguised by smokescreens of excluding esoteric language formulations which are relieved by the occasional colloquialism such as "critter".
Creativity become something to talk about and the talking becomes a substitute for it.
What time do you get out of bed fm?
Sorry spendi, Im straight. I really am flattered by your advances but Im not interested.
Why does evolution seem to produce complexity?
Because evolution is a very complexed product?
farmerman wrote:Sean Carrols book "The MAking of the Fittest" has a good chapter on the rise of Apparent complexity from the basic toolkit of the genomic structure. He stated that The measurable effect of evolution is diversity, not necessarily complexity.
This is what I was getting at in my previous post. Except that diversity without any improvement in replicative capacity is really just "Bloat".
One of the key questions with "Complexity" as related to evolution has always been "what's the definition of Complexity?"
In the original post, one of the reasons I tried to avoid the term complexity and instead phrased it as "numbers of parts in the replicator (or diversity)" was because I was trying to approach the problem from a simplistic state before the label of complexity came into play.
But it's pretty clear from following that line of reasoning that it's not the number of parts (or diversity) which makes something complex, it's the ability of those parts to accomplish replication within an environment which makes them complex.
If we decide that the definition of biological complexity is "maximized reproductive efficiency within an environment", then we really
can say that evolution produces complexity, because it does produce "reproductive efficiency within an environment" even if that efficiency comes from reducing the number of genes in an organism (as noted in your previous post).
Even though evolution is directionless with regard to any particular design, it is not directionless with regard to reproductive efficiency. In addition, it appears that the best way to achieve this efficiency is to accumulate more genes in the genome, or more molecules in the replicator.
dont be hung up on reproduction alone. PAssing "through" of traits that economize or "Complexify" things like respiration, circulation, or assimilation are all able to be tracked through the various phyla.
Once a trait becomes manifest and then is imprinted on the genome by sexual congress or by mutations, then the "career options" of the subsequent trait carrying organisms are fairly limited. Its like limiting successive generations to operate within a specific circle of possible traits. Usually big changes from organisms that are continually eveolving, dont happen. (Thats why the common ancestor approach must be kept in mind). If an organism, nicely evolved to live in a desert environment is immersed in water, it will , no doubt, go extinct. If 10 different species of the organism are all immersed, maybe one will have some organisms with webbing between their toes. Done over and over, weve taken a Pachycetus to a full whale status.
PS, by definition of decreased complexity, the very locomotion systems of whales are much less complex than their ancestors Pachycetus
farmerman wrote: PS, by definition of decreased complexity, the very locomotion systems of whales are much less complex than their ancestors Pachycetus
But I might argue that there has been no decrease in complexity because the genome of the whale is probably virtually identical to Pachycetus. The genes for the missing limbs are probably still there. And the genes for blowholes, baleen and blubber were probably there in Pachycetus as well, they just weren't expressed yet.
I think it all depends on how we define complexity.
When someone says, "evolution leads to complexity", and another person says, "no it doesn't". What definition are each of them using for complexity?
fm wrote-
Quote:Sorry spendi, Im straight. I really am flattered by your advances but Im not interested.
I asked you what time you got out of bed not what time you got up.
You do have a tendency I have noticed of looking at matters from the particular angle you do. There are one or two in the pub like that. The interpretations seem to leap forth so rapidly that it is almost as if they are waiting to be sprung from the traps.
I'm like that myself but in the opposite direction.
I know spendi won't accept any information that shows biological transition, but there was an interesting segment on TV yesterday that shows a fish that has the making of human limbs, and the Smithsonian in Washington DC has them.
Sorry, but I don't remember the name of the fish that they showed.
ros, your topic was about evolution PRODUCING complexity. You werent discussing the genome , otherwise I have no ideas where you wish to go in this. AS I said about Sean Carrolls book, his entire topic is on "fossil genes" that remain on the genome even though the organism has "devolved" into a simpler form. Its a f(environmnetal pressures).
Theres no doubt that a whales flipper is much simpler an appendage than is a fully srticulated brachial process.
MAybe you should articulate your point, Im talking about morphological evolution, not the resultant genomic expression. I could turn this about and ask,'Which comes first, the genomic changes or the actual morphological evolution"? We went through this once before in someones topic (may have been yours) about "Evolution without genetic change"
My feelings have always been mostly leaning toward the "bookkeeping function that genes play" not necessarily the causitive factor in evolution becasue a gene is just a gene.
farmerman wrote:ros, your topic was about evolution PRODUCING complexity.
Actually the topic is, why does evolution SEEM to produce complexity?
I wanted to avoid saying that it does or doesn't, because that's what I'm trying to figure out.
There are really two questions in my mind:
1. What is the definition of complexity in relation to biology?
2. Does evolution actually lead to complexity?
Does that help clarify things a bit?
farmerman wrote:Theres no doubt that a whales flipper is much simpler an appendage than is a fully srticulated brachial process.
I'm not so sure about that. A flipper is simpler in that it has fewer bones, but it also has hydrodynamic qualities/shapes that are extremely well adapted to the environment, and which arms/legs don't have at all.
farmerman wrote:Maybe you should articulate your point
I'm trying.
ros wrote-
Quote:I wanted to avoid saying that it does or doesn't, because that's what I'm trying to figure out.
Besides the fact that you won't ever figure it out while you have a hole in you eggcup there is the problem of what you would achieve if you ever came to believe you had done.
rosQuote: A flipper is simpler in that it has fewer bones, but it also has hydrodynamic qualities/shapes that are extremely well adapted to the environment
EXACATIKALLY!! Mods that run to the simpler (substitute evolutionarily economic) are derived by successive trials and errors (and the errors are recorded in the fossil record , an example of that is the Basilosaurus- a final precursor to the Zeuglates or eo whales) Tha BAsilosaurus was, not a dinosaur despite its name. It was a mid point of whale evolution that still had the whale like ancestors with "swivelling heads" and articulating brachia. The final steps occured with the compression and "simplification" of the structures that were ever so adapted to a deep water environment (remember whales evolved in the Asian subcontinent as that part of the SOuthern Ocean was separateing chunks off Africa and slamming into Asia. The subcontinent was a "trailing edge " tectonic env ironment, sorta like the CApe. SO the first "Cetii" were actually hoofed animals who plowed into shallow lagoons and strayed out into deeper waters. SOrt of like tapirs and capybaras.
Quote:Actually the topic is, why does evolution SEEM to produce complexity?
. My take on that is that it only seems to be because thats what many are looking for and few are spending equal time on the neotony preserving species or ones that have actually become less complex.
To define complexity, one has to look at overall morpjology and make a full list. (complexer circulatory system eg without an open ystem like insects. Or a respiratory system that doesnt use spiracles and an open flow of oxygenated fluids) How about plants, think about the complexity of seeds and their dispersal by symbionts , etc as opposed to vegetative or budding or naked seed plants )
Quote:Now these men, even in the company of artists, playwrights, poets, and beautiful concubines, suddenly shone forth. Their words, more or less literally, became golden. Their audience listened not with the casual heed of people who are collecting quotable epigrams, but with the truly rapt attention of those who expect to make money by what they hear.
J.K. Galbraith.
It was all bullshit when JK was talking about investment trusts and it's all bullshit now they've all moved on to a simpler subject: investment trusts being beyond their wits 70 years on.
anybody invite sir drinksalot?
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