There are no “good” genes or “bad” genes. There are genes that survive into the next generation and those that don’t.
Differences between the combination of the parent’s genetic make-up and their offspring that are not explained by this combination are called “mutations”.
These mutations are random.
If these mutations are advantageous (they usually aren’t) then the organism has a better chance to pass these new “mutated” genes on to the next generation. Those organisms that do not have this new advantageous mutation are less likely to pass on their regular old “unmutated” gene.
Give or take a couple of thousand generations, these “mutated” genes are now the norm and, voila a new species had evolved.
I am now going to assume these assumptions are true. If they are not, please explain where I went wrong. Here are a few things I need straightened out.
Why do organisms devolve? Man no longer has a tail because it was not needed. But just because an organ is not needed doesn’t mean the organ’s genes just disappear. There has to be selection against the unneeded organ, right?
Are all new species the product of incest? I mean, if these mutations are random, what are the chances of the same mutation happening at about the same time to different “families” of animals? Is there something about the expression of recessive genes that I’m not understanding (this is probably the case since my understanding of recessive and dominate genes does not go beyond 2nd term biology)?
It is my understanding the human genome project has found a whole mess of “junk” DNA. What is this stuff? Is it DNA that has been proven to have no use, or is it DNA for which a use has not been uncovered? Is it the remnants of past un-advantageous or no longer useful mutations? Why do humans go through the trouble and energy of reproducing it if it truly is junk?
As you can see, a little knowledge is a dangerous thing.
Regarding the tail - from what I understand, evolution works on a sort of minimalism philosophy. If something is not needed, it gets edged out by things that are. For example - the case of the tail. For an organism to produce a tail takes resources. A tail can also get stuck (e.g. when a predator is chasing the animal), making that animal disadvantaged for survival. A tail can be more of a hindrance when not climbing trees etc. (depending on the animal’s lifestyle). An animal has a finite amount of resources available to it, and they will get diverted to something more useful (e.g. ‘being able to run fast’). Check out Richard Dawkins’ books - e.g. “The Blind Watchmaker” - very interesting treatises on evolution.
Not necessarily. Remember that if something is “not needed” it is a disadvantage to have it in the first place. It takes all sorts of extra energy and maintenence to deal with a tail. The tail itself is useless, so it is more advantagous not to have one. Another example is the human apendix; it’s dormant in modern man because it is not needed any more. It would probably be more advantagous to do away with it altogether; again, we’d be saving energy (and doing away with apendicitis) but it’s such a minor thing that it doesn’t make much of a difference. We have far more serious things to worry about.
Remember that a gene need not be posessed by both parents for the child to have it. Half the offspring’s genes come from the mother, and half from the father.
With a dominent gene, you need only one gene from either parent in order for it to be expressed. For a recessive gene to be expressed, the offspring must have it from both the father and mother. Thus, recessive genes can be “carried” several generations without expressing themselves. If two carriers of the same mutated, recessive gene happen to meet by chance and have offspring, there is a 1/4 chance that the offspring will express the gene.
Good question.
Some “junk” DNA is just genetic material left over from millions and millions of years worth of evolution. Some may be useful, but nobody is quite sure.
You’re right that it takes a lot of energy to reproduce all the “junk” but it would take a lot more energy to do a big DNA cleanup project!
Much of the “junk” DNA is not junk. There have been at least two threads on that in recent months, and I am not going to do your work for you. I will say, briefly, that what was once thought junk, have been found to have useful purposes: stop DNA, etc. The extent of the usefulness of this “junk” has probably not been exhausted. There is still much we don’t know about the DNA sequences.
I think Lemer explained pretty well what I thought about expression of mutant gene. It’s a good think to keep in mind that evolution doesn’t give a hoot about what’s good for you.
I guess my question is: How do these new genes come to express themselves if they appear randomly if not through some sort of incest? Are these mutations brought on by environmental pressures so that it is possible that more than one organism can experience the same mutation? If this is true then these mutations are not so random.
DarrenS and freido, perhaps the tail was not a good example since a tail can be disadantageous. How about eyesight? If you live in the dark you might not need to see, but you wouldn’t be selected against if you could see. Yet moles are blind. Did the genes that gave mole sight just atrophy from non-use?
I do read all the genetics and evolution threads(with and without the creationism thrown in) as they come up barbitu, I did miss Ben’s though. But I have to tell you, the biology that I took in high school and college did not prepare me for the SDMB! When the conversation starts drifting into mtDNA patterns in the Sub-Sahara as compared to Switzerland and the functional significance of LTRs, things soon begin flying over my head.
Any body part or organ that is unnecessary is, from an evolutionary point of view, “excess baggage” and will eventually be evolved out. (As to why we still have our spleen…hmmm…and tonsils…wait - isn’t current thinking that tonsils are actually useful?)
I really encourage you to read Richard Dawkins’ books, they cleared up a lot of things for me (especially “The Blind Watchmaker”)
In the case of the mole: eyes are prone to damage and infection…they are a potential vulnerability for predators to attack. All in all, moles are better off (given their underground lifestyle) with rudimentary eyes that can just distinguish light from dark (moles are not totally blind).
First, don’t get squemish at the word. The incest taboo is not instinctive–many animals will hump there mothers and sisters if given half the chance, and plants, of course, are indicriminate. (Although many species demonstrate behavior that encourages breeding further out on the family tree-males or females wandering off when they reach sexual maturity, that sort of thing.)
Two, remember that for the vast majority of animals a “generation” is fairly short-1-5 years to sexual maturity. So 15 years after an advantagous, recesive mutation occurs you could have hundreds of fourth cousins who all carry it.
Three, genes that are neutral can hang out for hundreds of thousands of years. There are many minor variations between humans that are totally neutral. (think earlobe shapes). So what happens is that a neutral mutation occurs and spreads, almost at random, through the population. Then, the enviroment changes and that neutral mutation becomes either useful or dangerous. And everyone with it either replaces all the other people or die out. The important thing to remember is that mutations occur before they are useful, not when they are needed.
Another thing to keep in mind about “devolving” (as was already brought up) is how biologically expensive an organ or trait is to keep or maintain. For the mole question, eyes take a lot of energy, nerve cells, and maintenance to keep, and are delicate organs as well. They’d be one of the first things to go if not being used. I saw years ago where they sent a person down into a cave to live for several months to see what happens. When she came up she had to wear big sunglasses for a long time, perhaps months or years as her eyes had adjusted to low light levels; that’s not really an evolution thing, but it shows what happens to important traits with a changing environment. Given several generations of living in the dark, you’d probly suffer eye damage if you came up in the sun, although the shape of your nose probly wouldn’t change nearly as quickly.
Random mutations are happening constantly, and are quite common. Don’t think of the word “mutation” in a nucular accident sense such as growing a third arm out of your neck; more like subtle differences between you and your next door neibor… things you might not even be able to dectect. Human beings are full of mutations in relation to each other since for the most part times are good and every type of gene gets passed on - tall, short, fat, skinny, pretty, ugly, athletic, sluggish, strong, weak, aggressive, passive, diabetic, near-sighted, cancer-prone, smart, dumb, clumsy, mean, and nice people of every color under the rainbow are being born faster than we can put up housing for them all. In a more natural setting, most of these variations would be eliminated regionaly depending on the pressures that be. Also don’t overlook immigration and emmigration of new people/organisms into the population to give even more mutations for nature to work on.
Evolution doesn’t always make scientific sense; remember we are trying to make up rules and devellop theories for a process that has been up and running for a long time before we showed up… and we’re nowhere’s near figuring it all out yet. One quick example of this… Here in N.America we (people being the organism here) like having a nice tan; the “tall dark man” is generally attractive, just look at all the beach bums and tanning beds around. When I was in Thailand, none of the locals sun tanned… in fact they wear lots of long sleeves and try not to get darker because to them a fair complexion is more attractive. This doesn’t make much evolutionary sense, but could be a driving factor in mate selection none the less.
