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Author | Topic: Evolution and complexity | |||||||||||||||||||||||||||||
JIM Inactive Member |
I'm currently reading "Evolution and Analysis by Freemon and Herron" and I came upon a statement which peaked my interest.
quote: Assuming the validity of the Big Bang theory, it seems self-evident that the universe has been increasing in complexity since its genesis. Biological life has been a major leap in this drive towards complexity and for the moment, human beings epitomize the height of this process. The emergence of cognition, consciousness, and imagination in the primate brain seem like a small miracle, and the consequences enormous in the context of earth's history and destiny. If there is no "inexorable trend toward more advanced forms of life" why did more advanced forms of life evolve with increasing velocity ever since the appearance of life some 3-3.6 billion years ago? Simpler forms of life are highly versatile and successful. What is the impetus for this increase in complexity? Is it merely a rule of natural selection that increasing complexity and organization are favaoured under certain environmental conditions because these are exactly the attributes of life that confer it improved fitness? If this is the case, there indeed is a trend towards complexity. Increase in complexity seem to me an observational fact. What I really would like to know is why. More importantly, why did life first emerge? I do not think this is an insignificant question. Was it simply a fortuitous accident? But then how do you define 'accident' in the context of the natural universe? Can the universe as a whole be also under the control of an evolutionary mechanism of some sort, in which biological evolution may be integrated? Thanks,JIM Faith may be defined briefly as an illogical belief in the occurrence of the improbable. . . . A man full of faith is simply one who has lost (or never had) the capacity for clear and realistic thought. He is not a mere ass: he is actually ill." ---H. L. Mencken [This message has been edited by JIM, 01-28-2004]
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crashfrog Member (Idle past 1467 days) Posts: 19762 From: Silver Spring, MD Joined: |
If there is no "inexorable trend toward more advanced forms of life" why did more advanced forms of life evolve with increasing velocity ever since the appearance of life some 3-3.6 billion years ago? Firstly, the vast majority of the Earth's biomass continues to be relatively simple organisms. It's just that you don't tend to think about them. (Just stop and ponder, for a moment, how many individual bacteria there are on planet Earth. Whew!) And think about it this way. Imagine the first living thing. It's literally the simplest organism that could possibly still be considered alive. Actually, imagine a population of them. Now, imagine that one thing changes about a few of them. If that change was for the simpler, they all die, because they're no longer complex enough to be alive. If the change was for the complex, they live, and have advanced capabilities or something. When you're at the bottom of the barrel, there's no place to go but up. If you see a "trend" in evolution towards complexity, you're looking at it the wrong way. Complex, multicellular life is like a blip on the evolutionary radar. Most living things continue to be very simple indeed. It's just that it's easy for humans to forget about them.
Increase in complexity seem to me an observational fact. Then you need to look a little harder. I'd reccommend reading Gould's "Full House". It's a great explanation of thise very phenomenon.
More importantly, why did life first emerge? Why not? It's just a kind of chemistry. I'm inclined to think that it's inevitable, given enough time.
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Loudmouth Inactive Member |
Crashfrog has hit it on the nose. Humans tend to overlook the microscopic life on earth when considering "life on earth." We tend to look at cuddly and cute macroscopic species, such as mammals. For comparison, there is probably more bacteria in your colon than there are humans in the world. Nematodes (roundworms) species outnumber mammal species by a magnitude of at least 10. The same could be said for arthropods.
Subjectively and qualitatively, life could be considered to be increasing in complexity as an overall trend. Of course there are exceptions to this rule, such as obligate intracellular parasites, namely chlamydia. These bacteria like organisms require a host in order to multiply, they have lost the ability to do this on there own. I consider this a loss of complexity, but it is a very subjective judgement. Until complexity can be measured quantitatively, we will be stuck with subjective judgements and general trends. I wonder what the units would be (eg, evolution caused an increase of 23 complexicons in E. coli, )
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hitchy Member (Idle past 5118 days) Posts: 215 From: Southern Maryland via Pittsburgh Joined: |
thank you both for simply stating the problem with irreduscible complexity--we look at it from the wrong end. same goes with ID people who play with probability. anyway, i like the obligate intrecellular parasite thing. one more example, "more complex" parasites such as the twisted-wing parasite (Strepsiptera). the males are free living and look like tiny flies, but the female is an obligate endoparasite in other insects. she has lost most of what would make her a fly-like insect. some families of this order have free living stages, but that in no way disputes how "more complex" organisms can become "simpler" as they evolve.
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Loudmouth Inactive Member |
Sorry for the double post.
quote: This is an interesting question in that basic chemistry and physics govern both processes. However, the scale on which these things happen is quite different (eg, mutation of a gene compared to supernovae). But it isn't the scale that separates the two but rather natural selection. I can't think of an example where matter or the massing of matter is affected by a selection process (Eta may correct me on this). The closest thing that I can come up with is the creation of heavier elements in supernovae which then results in more "complex" arrangments of bodies, be they solar systems or space dust. So the only way I see of integrating both types of evolution (universe vs life) is in looking at how things are passed on to the next "generation". That is, supernovae pass on heavier elements to the next generation of celestial bodies in a similar way that DNA is passed on to subsequent generations. However, celestial bodies are not changing so that they better fit their environments but rather trying to balance themselves within physical laws. In the long run, I can't see a way to infer a common mechanism between the evolution of the universe and the evolution of species. I don't see biological evolution as a subset of universal evolution, but I can see them as being independent of each other.
quote: It might be as simple as "why did the rock fall to the ground when I let go of it?" If certain conditions are met life may just be a simple effect of chemistry just as a falling rock is a consequence of gravity. The origin of life, however, is still very speculative (the Big Bang probably has better models at this point). In my opinion, huge amounts of progress could be made in this arena if life were found on another planet/moon/asteroid. It would be interesting to see if other life forms use different strategies for self-replication which could then give us clues as to the mechanisms and reactions that can lead to life. This is why scientists have high hopes for upcoming missions to Europa (a moon of Jupiter). If Europa does have liquid water and as a consequence it has life this could be one of the biggest discoveries of the last century, if not last millenia. I'm sure there are a few scientists who have wet dreams about Europa, hopefully they can make those dreams a reality.
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:æ:  Suspended Member (Idle past 7185 days) Posts: 423 Joined: |
Loudmouth writes:
Actually there are a few methods of quantitatively analyzing completxity, though I'm not too familiar with their finer intricacies. One method is the Shannon Theory of complexity that basically says that the information contained in a signal is inversely proportional to its probability. In other words and in simlpe terms, a low-probability signal has a high information content. If a signal were binary i.e. on/off, then the probability of the signal is 1/2, so -log2(1/2) = 1 bit of information. Until complexity can be measured quantitatively, we will be stuck with subjective judgements and general trends. Another is the Kolmogorov-Chaitin Theory of complexity that says the measure of complexity is directly related to the length of the shortest program it would take to output a specific string. That is, the string A x A x A x A x A x A x A x A x A x A x A could be expressed algorithmically as A10, whereas the string A x B x C x D x E x F x G x H x I x J x K" cannot be compressed in the same manner. Last there is the Bennett Theory of complexity that says the complexity of a system is directly proportional to the time the system has been in existence. For example, as a computer continuously spits out the unending decimals of pi, the system gets more and more complex. I'm not real clear as the metric which measures the rate of increase, though. I found most of my information at this site here: http://www.geocities.com/...orest/Andes/9063/complexity.html
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Loudmouth Inactive Member |
quote: Actually, couldn't you compress "A x B x C x D x E x F x G x H x I x J x K" into K! (factorial)? Just a minor point, but I do get the gist of what you were talking about.
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:æ:  Suspended Member (Idle past 7185 days) Posts: 423 Joined: |
Not really because in this case the letters are variables, or unknowns. If we knew that A = 1, B = 2, C = 3, etc... THEN we could compress it into a factorial.
I forgot to mention that I'm not real clear as to how (or IF) biological changes can be accurately modeled within the context of any of these theories.
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NosyNed Member Posts: 8996 From: Canada Joined: |
What you have described is "information" not complexity.
Information is very high in a completely random string and very low in a monotonous repetition. However, a random string has something missing. It is not as "interesting" as the bits of a computer program which may have high information content and even look random. But it is not random, it has some meaning in the right context. The word "complexity" is an attempt to capture this extra idea which is different from the Shannon information. I don't know a lot more than that but it is, apparently, hard to get a good definition of "complexity" so that it may be quantified. I'll let you know if I find something. Common sense isn't
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MarkAustin Member (Idle past 3815 days) Posts: 122 From: London., UK Joined: |
quote:quote: To extend crashfrog's pont, once the first organism has evolved, any other must be more complex. This has the effect of evolution filling in the ecological niches for increasingly complex organisms. As long as all the "simple" niches are filled, the only way evolution can proceed is towards greater complexity,since an existing "simple" organism, would almost certainly be better suited to the ecological niche than a new mutant. However, if these simple niches do exist, there is nothing to prevent species losing functionality to fill them. The classic examples are cave or underground dwelling animals, who tend to lose eyes and body colour, and parasites, who lose the ability for independent existance.
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Darwin's Terrier Inactive Member |
Firstly, the vast majority of the Earth's biomass continues to be relatively simple organisms. It's just that you don't tend to think about them. (Just stop and ponder, for a moment, how many individual bacteria there are on planet Earth. Whew!) No need to try to get your head around that level of incomprehensibility. There is a mind-boggling statistic closer to home. It is that the bacteria in and on your body outnumber your own body cells ten to one. Mirroring the point that to the first approximation, all species are extinct (99.9% of all there’s ever been), we can also say that to the first, and probably the second and third, approximation, all organisms on earth are microscopic. Cheers, DT
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Darwin's Terrier Inactive Member |
It’s also worth noting that, where it offers a survival advantage, simplicity is just as merrily adopted. The obvious example is Sacculina barnacles. Barnacles are arthropods -- fairly ‘advanced’ critters with a hard exoskeleton. Yet Sacculina adults are little more than jelly-like blobby endoparasites of crabs, resembling with their root system that spreads through the crab some sort of simple plant. See eg here. Only in their larval stage is their arthropod affinity apparent. Compared to ‘normal’ barnacles, they are very simplified.
Is a two-legged creature ‘simpler’ than a four-legged one? I’d have thought so -- it’s got fewer parts. Yet cetaceans have lost their back legs through evolution, and snakes, caecilians, amphisbaeneans and so on have lost all four limbs. Evolution will go for simplicity too: there’s no inevitable climb to greater complexity. Cheers, DT
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Dr Jack Member Posts: 3514 From: Immigrant in the land of Deutsch Joined: Member Rating: 8.7 |
I thought of an analogy that might be useful:
Imagine flipping coins for all eternity, and counting runs of heads. Over time the longest run of heads will increase, but the average run of heads over any fixed length of time will remain constant.
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FliesOnly Member (Idle past 4145 days) Posts: 797 From: Michigan Joined: |
Just thought I'd pipe in with my 2 cents worth:
I guess the best place for me to start would be by explaining how I have come to understand the word "complexity". First, I think it's important to keep it in a biological context. With that in mind, I think of complex organisms as those with the most "parts". But then we have to decide on what constitutes a "part"? Well, in terms of animals, I have viewed parts as organs and organ systems. I'm not a botanist or a mycologist, but I would guess that there are tissues in these groups that could be used to distinguish between complex and simple. I'm sure there are other, more precise definitions out there, but when we are talking about living things, IMHO the definition of complexity should focus on measurable characteristics, otherwise it becomes meaningless. A few people have correctly pointed out that simple life forms far outnumber complex life forms, but that was not really the question. We need to understand that natural selection does not "choose" more complex organsims, it merely selects those that are best adapted to their current environment. So why should we think that evolution leads to more and more complex organisms? The answer is: "we should not". I just think that it's a natural bias on our part (humans) to want to view complex organisms as inevitable, because without such a drive, we would not have evolved. But does such a drive exist? Now, in answer to the question at hand, I think crashfrog stated it quite nicely very early on. There really is no observable evolutionary trend towards increased complexity. I think we all agree that in terms of complex versus simple, things can only get so simple and still be considered "living". If we accept this (and how can we not?), then early on in evolutionary history, life would have had no "choice" but to become more complex. The real test comes later (now?), when we can look at middle lines of descent (the first mammal, the first arthropod, the first tree, etc.) and then look at the evolutionary trends. When we do this, we see that it goes both ways. Some things become more complex, while others become less complex. Importantly, there is no significant difference between the two "directions". Gould's "Full House" does a wonderful job of explaining this, as crashforg (and I must pat myself on the back here too, for I have mentioned this on a few occasions as well) mentioned. I recommend it to anyone that thinks evolution leads to more complex organisms. Anyway, just my contribution to the discussion.
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NosyNed Member Posts: 8996 From: Canada Joined: |
Nice analogy, Mr Jack. I think it might help some understand the message.
Common sense isn't
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