How Can You Believe Life Arose From Random Chance?
Posted on Thursday, January 11, 2007 @ 08:11:58 PST by infidelguy
|
|
-- By JeremiahSmith
Short answer: I don't.
Long answer: I don't, and I'll tell you why.
This is one of the more common arguments against evolution that one will hear from the creationist camp. They insist that the random chances that must have been involved in the origin of life would be so massively improbable that it would be folly to insist on such nonsense to explain life on Earth; it would be like a tornado swirling through a junkyard and depositing a 747 airplane in its wake, they will tell you. However, this sort of argument has a flaw in it. In a nutshell, that flaw is "creationists don't know what they're talking about." In this FAQ, I will explain correctly how evolution works, illustrate the probabilities involved, and also point out flaws in the creationists' probability calculations.
First, we should probably understand what evolution means. In this FAQ, it will refer to two meanings of the word: the process of evolution and the theory of evolution.
The process of evolution is simply "change in the gene pool of a population over time", as stated here. (Remember, folks: Always cite quoted material!) The process of evolution has been observed in the lab and in the wild, in such animals as fruit flies, or elephants in Africa. (In Africa, the number of elephants with small or no tusks has greatly increased since the turn of the century; since tusk size is inherited, this is an example of evolution.) This evolution is a fact; it can be seen and observed.
The theory of evolution is the theory that all life on Earth and in the fossil record is descended from a common ancestor, and that the differences between life forms is due to genetically-inherited changes. Although the mainstream usage of "theory" indicates nothing more than a guess, "theory" in the scientific usage refers to something that has been supported by large amounts of evidence. When you hear a scientist talk about the theory of evolution, you can pretty much rest assured that he accepts evolution as truth. Note that evolution has nothing to do with the origins of the universe or of Earth. It technically does not include abiogenesis, either -- the origin of the first life. Evolution does not say how the first life came about; it merely says that after it got here, all life eventually came from it. However, I'll talk about abiogenesis anyway, since it's part of the origins of life too.
Those definitions should suffice for now, but if you want to know more, you can read up hither, as well as yon. Those links define evolution better than I have, and also clear up the usage of "theory".
Now to the fun stuff. Creationists will assume that evolution relies simply on mutations. (There are many different kinds of mutations; some involve single genes, some involve larger parts of chromosomes, some involve entire chromosomes. We'll lump anything that affects the genes of an individual and the inheritance of those genes under the term mutation.) While mutations are a very important part of evolution, they're only half the story. The other half is natural selection. Mutations are quite random; they're unpredictable. (Some sorts of mutations will be more common than others, though, but they're still pretty random.) But. The other half of evolution is natural selection, and that is certainly not random. Harmful mutations will end up removed from the gene pool, while beneficial mutations will become more common; that is the essence of natural selection. The genes that end up going on to the next generation are not chosen at random, but rather based on how they affect the organism's ability to live and reproduce.
Let's say I have a big cardboard box with a small hole in the bottom, throw in a bunch of balls of random sizes, and then shake it thoroughly. Some of the balls will fall out the hole and others will stay in. Even though the balls themselves and their sizes were chosen randomly, the ones that will stay in the box are not random; they are the balls that were too big to fit through the hole. The balls represent genes, the balls that in the box are genes that are passed on, and the hole represents natural selection; in this case, the selection pressure is towards balls that are large.
A small ball might remain in the box after one shake (i.e., after one generation), but after a few more shakes, it will be gone and the "small ball" gene will have been removed from the population. This is a very simplified version of natural selection: readers should note that it does not, nor is it intended to, represent evolution in its entirety. The main reason is that the balls do not reproduce. If they could, though, we could make a very simple model of evolution. Start with a population of balls. "Mutate" some of them at random by making them a little bit bigger or a little bit smaller. Then, run them through the Box O' Natural Selection. Take the ones that remain in the box, make copies of them, and make another population of balls based on the ball sizes that got passed on. Repeat natural selection.
Eventually, we'd end up with a population of balls suited to the task of not falling through the hole. Natural selection has done it again! Changes in the selection pressures will influence the development of a species in different ways; what was once a beneficial mutation could become a neutral mutation (i.e., it doesn't harm or hurt the organism in any appreciable way) or even a harmful mutation. For instance, if a machine was added that removed balls that were approximately twice the radius of the hole, the formerly-beneficial mutation of being twice the hole size would turn into a harmful mutation. If a machine chose balls based on color, a neutral mutation that changed a ball from white to light gray -- which would have had no effect with regards to size-related pressures -- would suddenly turn into a life-or-death situation.
Natural selection is the non-random complement to the randomness of mutations. Without it, there would be no evolution; any mutation that came along could get passed on. Our box of balls would never turn into a population of large balls; it would stay random. A few balls might hop out due to zealous overshaking (unless, of course, balls could mutate to become heavier or to stick to the cardboard box, but let's not complicate things) but there would be no selection. In the absence of selection, sometimes a population will end up changing its gene pool at random. Sometimes, a natural disaster will happen, or something else that happens at random, and drastically change the proportions of genes in a population just by chance; this is known as genetic drift. For instance, say the balls are evenly divided between 5 sizes of ball. If some accident ends up randomly "killing" 90% of the largest balls, but only 10% of each of the other sizes there would be genetic drift. Genetic drift is actually a very large part of evolution. That said, though, natural selection will still step in and keep things non-random
These are simply the basics of the effects of randomness in evolution. Further reading: Evolution and Chance, by John Wilkins, which is more technical than what I've written. Random Genetic Drift, by Laurence Moran, which points out more on genetic drift. Where d'you get those peepers?, by Richard Dawkins, which has a nice example of how something complex -- in this case, the eye -- can arise using simply mutation and natural selection. There is, of course, much more information on evolution than is linked here: anyone who has any other good links explaining this, send 'em over.
"Well, that's all well and good, Mr. Smith, but how did the original life get there? Even if evolution is random, the origin of the first life that things evolved from must certainly have been random!" And to that I say, "My last name's not Smith; this is a pseudonym." I'd also say "Abiogenesis wasn't random either."
Abiogenesis, for the uninitiated, means life originating from non-life. This is NOT the same as the spontaneous generation that Pasteur disproved, by the way: he showed that larger life forms like mice and stuff did not spontaneously arise fully formed. There is nothing saying that very primitive life can not form from increasingly complex molecules. (Always remember to cite your sources and also brush your teeth.) Abiogenesis says that a self-replicating molecule happened to form, and that once it was able to replicate, evolution took over and started modifying it by natural selection, genetic drift, and mutation.
So, how could such a molecule form? Such molecules are known to exist; for example, here's a nice link. Given the short lengths of these replicating molecules, and the fact that molecules would be coming together all over the planet, the time for a self-replicating molecule to come together from amino acids would not be long at all. (Because I haven't studied biochemistry as much as I have other subjects related to this discussion, I would like to direct readers to Lies, Damned Lies, Statistics, and Probability of Abiogenesis Calculations, by Ian Musgrave, which explains this better than I could. The Wikipedia also has some stuff
Sometimes, a creationist will choose a protein sequence that's known to be part of life, calculate the probability of it forming at random, and loudly proclaim that it would be impossible for any life to form. However, they make errors in their calculations which greatly inflate the numbers. First, some of the arguments I've seen choose a sequence much larger than what abiogenesis theorists claim was the first life: they make calculations based on 300 subunits instead of the 30 or so subunits in some known self-replicators. (Subunits refers to smaller molecules that build up larger ones; DNA and RNA are made of nucleotides, proteins are made of amino acids, etc.) The second is that they calculate probabilities after the fact: they start with a given molecule that's needed in life, and then see what the probability is of getting that specific molecule. The problem with this is that there are conceivably trillions of molecules that could serve the same function as the given molecule, which aren't taken into account at all.
For example, grab an ordinary deck of playing cards. A usual deck will contain 52 playing cards. A lot of decks come with 2 jokers (call them A and B), and some even come with a little card listing the probabilities of poker hands and a card with an order form for a book on poker. We'll throw those cards in too, just to make the numbers bigger, giving us 56 cards in our deck. Let's take 12 decks of cards, and label each card in each deck so we can tell which deck each card came from. We now have 672 distinct cards. Shuffle them really well, and then deal them out one by one. Those with a statistics background will know there are 672! different orders you could draw the cards. (672!, read 672-factorial, is 672 times 671 times 670 times... ...times 3 times 2 times 1.) 672! is a number so huge my graphing calculator can't handle it; the largest factorial it can find is 449!, which has 997 or so digits. 672!, by my calculations, has at least 1500 digits. One could say that the probability of any given combination coming up would be 1 in 672!, which is nearly impossible. But wait! If you deal out the cards, you're going to get some combination. But the chances of getting that combination are 1 in 672!. What gives? Did we just do the impossible? No. The distinction here is that we didn't specify or predict a combination ahead of time. If we had, we'd more than likely never guess the combination to be deal.
Now, we have to take into consideration that a lot of the combinations would be considered acceptable. There are a ton of proteins that could serve a given function; if we calculate the probability of getting any of them, rather than a specific one, the odds get better. For instance, if any sequence starting with the Ace, 2, and 3 of Spades from Deck 3 (in that order), is considered acceptable, then the chances of getting an acceptable card deal rockets up to 1 in 302,111,040. A large number, but massively smaller than 672.
Now, we also have to take into consideration that these sorts of reactions aren't limited to a small area. If it was just one trial, one molecule being formed at once, even the probabilities we'd reasonably expect for abiogenesis would be prohibitive. We wouldn't be here debating how we got here; we'd still be hydrocarbons. But, there was not one molecule being formed at once; there were billions of them in our oceans, continually forming at random. According to Ian Musgrave's sources, a 55-amino-acid protein can form in one to two weeks. That, my friends, is a lot of random trials going on. It's highly likely that we'd end up with useful proteins after just a year; after a million years -- an eyeblink in geological time -- we'd almost certainly end up with some chemicals that could get life started. They might not necessarily be the same molecules that gave rise to us -- actually, they almost certainly wouldn't, if we were to start the whole thing over -- but they would give rise to something that we'd call life.
So, to answer the question:
Evolution isn't random at all. Natural selection plays a role in "picking out" beneficial mutations and weeding out harmful ones. Abiogenesis, on the other hand, is rather random, but the probabilities involved are in no way prohibitive to life forming in the time frame that we'd expect.
More linkies:
More on abiogenesis probabilities.
More on evolution in general.
A lot of stuff on evolution.
Or you could browse the whole site; it's all goo.
Note: I am not an expert in the fields of biology or biochemistry, merely someone with a lot of free time and a lot of intellectual curiosity to use for killing that time. There may be errors in the above FAQ; if you see any, let me know. If you can provide any other information, such as links, corrections, or simply more details, feel free. Just don't be an ass.
(c) 2003 Jeremiah Smith, except for all the stuff that was quoted, which is (c) respective authors.
about abiogenesis in general. Any other links regarding processes of abiogenesis would be helpful, though.
|
| How Can You Believe Life Arose From Random Chance? | Login/Create an Account | 0 comments | | The comments are owned by the poster. We aren't responsible for their content. |
|
|
|
No Comments Allowed for Anonymous, please register |
|
| |
|
* You can syndicate our news and blog using the file