Let’s say, many galaxies away, a long time ago, there was a planet exactly like ours. Same landscape, same distance from the sun, everything. When the very first peice of life came onto this planet, whether through creation, or accident, or aliens dropped it off, or whatever you believe, would it evolve in the same way our first life did? Would it keep evolving the same way and creating the same plants and animals in the exact same positions as our planet did? Would it create the dinosaurs? Would there be exact clones of us and me sitting here typing this exact same thread? I don’t understand why or how life would branch off into something completely different and there would be a whole new world unlike ours. If it would change, why?
a whole lot is based on “chance” here on this earth. from the very beginning. say some new mutated creature evolved that would’ve turned into you or me over the eons, but instead of it living a full life and reproducing, it got squished a few minutes after it was born, by some much larger creature chasing a fish.
now suppose the air pressure gradient was a little different, and instead of getting squished, the wind blew that little creature out of the way, and it went on to evolve into us.
very small details can make very big impacts over eons of magnification.
keeping that in mind, it seems highly unlikely that this planet that is like ours, but not ours, would be the same in exactly the right ways such that “chance” happened to take the course it did.
so, no, i don’t believe it would be like ours. there’s certainly a chance, but i think it’s a slim one.
There’s no reason to think it would. Evolution is not as “simple” as organisms adapting to their environment: first, a given mutation from which selection can build has to arise. Whether a given mutation actually arises is largely a result of chance, and there could well be multiple viable mutations in a given instance.
Even beyond the requirement that a mutation must first arise before selection can act upon it, the history of Earth is littered with cataclysms which have also had profound effects on the paths evolution has taken. If that asteroid hadn’t hit, in that particular place (there have been more than just “the big one”, at the end of the Cretaceous, by the way); if that sea hadn’t dried up; if that mountain range hadn’t formed…things would likely have turned out very different.
Are identical twins completely indistinguishable?
First, let’s assume that the imaginary planet is * exactly * like earth in every respect (tectonic plates shift at the same times, asteroids hit the earth in the same at the same place, etc. Which means this really boils down to…
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*Originally posted by Darwin’s Finch *
**Whether a given mutation actually arises is largely a result of chance, and there could well be multiple viable mutations in a given instance.
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Random chance. I guess you could say that I don’t believe that anything happens due to random chance. The mutation would either occur * for a reason , or not occur for a reason*. But I’m an ignorant teen, so you could probably persuade me rather easily.
What you are really asking, then, is if time were re-wound back to the beginning, would things still turn out the same? The answer is still, “most likely not”.
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Randomness does not imply lack of causation; it typically results from a complex interaction of causes which we cannot readily specify. Regardless of the cause, or causes, we still cannot necessarily guarantee the outcomes of such events. If I flip a coin 20 times and note the outcome, what guarantee do I have that if I reflip the same coin another 20 times, I will get an identical outcome, even if the parameters governing each flip are highly controlled?
Stephen J. Gould always said that if the film of all life on the earth were reversed and then rerun it wouldn’t be anything like the first run through. I’ll take his word for it. The number of possibilites at each decision “point” such as changes in habitat or new mutations are large and they all can survive. Which one, or ones would do so is a matter of chance. There is no reason that the absolutely perfect “best adaptation” would win out each time because its representatives are few in number and might be just plain unlucky. The habitat changes wouldn’t repeat exactly and the mutations are a matter of chance.
The human ejaculation contains between 300,000,000 and 400,000,000 sperm. If the timing of the ejaculation is off by a matter of mere seconds–a moment’s distraction perhaps–there is every reason to think that a different sperm cell will probably reach and fertilize the egg, in which case a different person will result. It might be a boy instead of a girl, or vice versa. Or, if the timing is off by mere seconds, perhaps no sperm will wind up fertilizing that egg. In which case, the woman may not conceive at all during that cycle, and even if she gets pregnant next month, both the father’s genetic contribution and the mother’s contribution to the new person will be different.
I put that in terms of human reproduction–every one of us is as improbable as winning the lottery, although, like the lottery, someone will win, some new person will be formed–but much the same applies to systems of reproduction that have been going on for hundreds and hundreds of millions of years–countless generations of individuals, each the product of variations in the most minute conditions on the molecular level which allow this gamete to win out over that one. If you built a time machine and went back a few decades ago and interrupted someone’s conception, the results on today’s world might be very small–some library assistant or copy editor or computer network technician would never have been born. Maybe a great leader or a monstrous tyrant would have never existed, and the new 2003 would look very different from the original one, or maybe just a message board would have a different moderator.
But one person may be an ancestor only to one or two children, but a half dozen grandchildren, a score of great-grandchildren, a hundred great-great-grandchildern. The changes will spread out and grow from generation to generation. Go back far enough and remove one person and multitudes will have never existed, and will be replaced by other people, maybe a lot like the ones from the original timeline, but maybe a lot different. Go back far enough, interrupt the conception of a pre-human hominid, and whole species may be replaced by new ones–maybe Neandertals never exist, maybe something a little smarter than Neandertals exists which out-competes Homo sapiens sapiens. Go back far enough, remove one organism, and whole classes or phylums never exist. There are no echinoderms. Or insects. Or vertebrates. There are other forms of life which take their place, and fill their ecological niches, but they’re no more insects or echinoderms or vertebrates than the people who might have existed had my parents both married other people would be me. Those other hypothetical half-brothers or half-sisters of myself might have some things in common with me, but would they be moderating the Great Debates forum of the Straight Dope Message Board in January of 2003? Those non-insects might be like insects in some ways, but would they have exactly three body segments and six legs? Would the non-insects be butterflies or bumblebees or praying mantises? And go back far enough, kill off (or mutate) one bacterium with a stray photon of ultraviolet light, and every multicelllular organism that exists, from people to octopuses to redwoods, might be replaced with something else, not better or worse, but different. There might be things that swim in the ocean and things that photosynthesize and maybe even things that think, but we wouldn’t recognize them.
Maybe there is a God or cosmic order which preordains the fall of every sparrow or the fertilization of every egg–and if this is the case, then of course there is no free will, for whatever that argument is worth–but I don’t see any reason to think so, and every reason to think not.
Chance is an illusion generated by lack of facts. Given the exact same circumstances, the exact same thing must happen. An event occurs only if there is sufficient cause, and if there is sufficient cause the event must occur. We don’t always know all the pertinent facts, and perhaps cannot know them, but that’s merely an epistemic difficulty. Causality doesn’t care what we know or don’t know.
There is an argument for the (slightly Star-Trekkian) idea that humans are humanoid in shape because the environment favours bipedal intelligent life with bilateral symmetry, opposable thumbs, sense cluster situated at the top etc… - if there were any weight to this idea, then we might be able to expect aliens to be generally humanoid, but the idea is a bit ‘out there’.
That’s all a bit anthropomorphic. There is nothing to prevent an arthropod-like creature (maybe modified to improve blood and oxygen circulation) developing size, intelligence and machines (look at the mouthparts of a crab and you’ll see just how easily they could adapt to tool use). We humans like to think our humanoid shape is optimal but that is just prejudice. The theory that everything will be our shape is, IMHO, vanity. In Star Trek it’s to keep the FX costs down.
I agree, although it’s quite likely that the humanoid form is not unique to Earth. - it’s difficult to imagine the unimaginable - indeed the term ‘arthropod-like’ may in fact be Terramorphic…
Well, I’d say the bipedal shape isn’t a bad way to go. I would expect aliens to likely share some characteristics with us, namely:
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Symmetry. On a solid landscape, this would be left/right symmetry, and perhaps multifaceted symmetry. In a gaseous environment (getting a bit weird here, think aliens flying about Jupiter) it might well be top/bottom symmetry. Symmtry offers certain advantages that are difficult to compensate for. I can imagine some creatures without it, but not many.
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Central neural cluster in any intelligent species: It appears that a tightly wound mass of thinking tissue is needed to effectively think.
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Centralization of sensory apparatus: This is the most speculative, but there is a good chance the location of our ears and eyes and moth and nose is no accident.
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Types of sensory devices: Aliens may well be able to pick up “colors” and things we don’t, and will be likely unable to understand some of our sensory information. However, I suspect things like eyes and ears and the sens of touch will be present in some way. These senses are so darned useful, its difficult to imagine a higher species evolving without them. One works at effectively infinite range, hearing works all the time (even closable ear ports won’t totally block it out, hence useful to avoid those nasty alien Monsterbeasts hungry for your blood!
), and the last functions all around you body at once.
That sort of determinism breaks down at the quantum level. Can you set things up so that a particular uranium nucleus will fission, and emit radiation that alters the DNA in a particular cell at a critical instant? No.
Smiling Bandit, all your criteria are met by a crab, or pretty much any arthropod.
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They have bilateral symmetry.
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They have brains.
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They have sensory apparatus at the front, near the brain for rapid data transfer. It is no accident that your sense organs are grouped on your head. When you were a fish, having your detectors at the front end was an advantage over having them at the back – you detected things sooner and having your brain close to them meant you could react to them sooner.
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There are only three types of external enviromental changes detected by biological sensors: electromagnetic radiation (eyes for long range detection of light & UV wavelengths, skin for short range detection of infra red); pressure changes (ears for long range, skin for short range); chemical concentration gradients (tongue for short range, nose for long range).
None of the above favours a biped over any other bilateral, limbed body form. One thing you missed is the requirement to manipulate tools, which can met by arthropods’ infinitely adaptable mouth parts (and are themselves highly evolved legs).
What is more interesting is how arthropods, some of which were huge, metre long sea dwellers in the Cambrian Age, were out-competed by chordates in the “be a big beast” ecological niche. What “edge” does a chordate have over a similarly sized arthropod?
The exoskeleton of the arthropod becomes less of an advantage and more of a burden as size (and the demand for agility) increases.
Well, in this case of the planet, where the parameters are * extremely * controlled, the coin flipped 20 times will come out with the same outcome. The parameters controlled are the position of your hand and the amount of effort you put into flipping the coin with your thumb.
Actually, even if you hypothetically went back in time with your time machine you couldn’t change what happened in the past. In trying, you would either be the cause of what you were trying to change or have no effect on it whatsoever. So, if you destroyed millions of bacterium eons ago, you would be preventing the crazy six eyed reptil flying creatures that would have appeared on earth, and instead would create something like bats. I hope that made a little sense
That is, if you don’t believe in the theory of multiple universes. With the randomness of particles at the quantum level, it seems as if every single thing that could possibly happen happened in alternate universes. So there would exist a universe in which 2 billion years ago a human suddenly appeared and killed a bunch of bacteria and made way for another species, or effectively killed off any chance of life altogether. In 2003 of that universe, life may be radically different or not exist. The multiple universe theory helps when dealing with all those nasty time travel paradoxes.
That level of control is impossible to achieve, of course. With each flip, air currents change; muscle contractions differ slightly; electrons may be scraped off the coin. Even if you let a computer do it, fluctuations in the power may cause a nanosecond delay on the flip, etc. And how can you be certain that the flipping force is applied to the exact same point, each time, down to the exact same atoms being struck? No matter how much you try to control each and every aspect precisely, you will ultimately fail. If for no other reason, the time coordinate of that flip is different, so you can’t exactly duplicate any given flip, therefore you cannot be absolutely certain of the outcome.
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A claim which you have absolutely no evidence for, and no way to verify, so it’s quite irrelevent. MEBuckner’s example was simply demonstrating that minor changes can have profound effects later on (See: chaos theory), and had nothing to do with any real or imagined limitations on time travel.
If you wish to claim that “if we rewound time back to the beginning, and everything happened exactly as it did the last time, we would get exactly what we have now”, there’s not much to debate. Except maybe whether determinism is a valid philosophy.
Outside of absolute determinism, however, if you rewind time and let it unfold without outside constraint, you simply cannot guarantee future outcomes. Just as we cannot guarantee future outcomes based on present conditions.
Of course, if you took this in a lab, a myriad of microscopic mistakes would occur and probably at some time change the results of the experiment. I’m speaking of a * hypothetical * situation here, in which every aspect of the first experiment would be the same as the second. Would it not produce the same results? I don’t understand why you think it wouldn’t.
As with the time travel thing, I guess the statement I made was rather irrelevant to this topic, but I was just trying to correct MEBuckner in what I thought was true.
I’m familiar with chaos theory, thank you. If a butterfly flaps its wings, it might intensify and eventually create a tornado halfway across the world. You would believe that if that butterfly flew east instead of west for 30 seconds, the tornado would be prevented, and thousands of lives would be saved. I ask: What would cause the butterfly to head east? It must have some purpose in heading west, and therefore, if the same conditions were present, it would head west every time and would have no reason in heading east. Unless of course you believe in random chance, which I don’t think * ever* really occurs.