Ram Samudrala (email@example.com) wrote: : James Foster (firstname.lastname@example.org) wrote:
: >Well, "evolution" does mean "change". But to biologists it really : >means "a change in the distribution of characters ocross : >generations".
: Well, I'm a biologist in a sense, and I just disagree with that : definition of evolution. In fact, this is the first time I've come : across it, even though I've discussed this topic with various : biologists.
I got it most explicitly from Grant, the guy who studied selection and evolution of Darwin's finches. Perhaps there isn't one single sense in which these terms are used, but some distinctions will help make it easier to discourse.
By the way, I'm only a biologist "in a sense". I'm a computer scientist by training, but I've been doing computational biology work for a few years.
: How do you differentiate between mutations that give rise to a new : function, and mutations that do not?
Why should you? mutations which lead to changes that increase in frequency due to selective pressure are "beneficial", while those that don't aren't. Of course, this classification can change overnight with the advent of a drought or an invasion of predators.
And what's a "new" function, anyway? Usually mutations only incrementally change some already-present characteristic, like sensativity to light, resistance to antibiotics, or length of beak.
: It could pass it on. What I'm saying is that at some point, for new : function to evolve, it must have happened in one organism (it could : happen simultaneously also), and subsenquently been selected to spread : to various generations. The evolution of function is an interesting : topic in and of itself, which not many people think about (though I do : know of published attempts to attempt to create function, it has not : been successful). This is what I've commonly heard (among : biologists/biophysicists) referred to as evolution.
Wouldn't resistance to an antibiotic, or ability to produce viable offspring, be new functions? These rarely spring into being de novo. They begin in a small degree, and then increase in degree. This is one of the (many) falacies in the anti-evolution reperatoir: the theory of evolution does NOT require functions and other characteristics to spring into existence in completly final form. Dawkins makes this point very forcefully in The Blind Watchmaker.
: How's that mutation different from a mutation that simply changes a : base pair, or an amino acid, without changing the function of the : protein?
Why should it be? I thought we had agreed that genetic drift, which is inherently neutral, is a source of evolution?
: I am not sure how you could observe new function evolve (I'm not : talking about observing functions being selected for, which I have : observed many times myself). So are you saying these people knew for
One day, people are alive. The next day, they die. Why? Because the bacteria in their bodies have developed the function of surviving massive doses of a common antibiotic. Isn't that what you're after?
: sure that the genes with the mutations that had these functions didn't : already exist in ALL the animals in their cattle, and that they : weren't just selected for?
I don't understand your objection. Being selected for changes the frequency of this character, and THAT is evolution. If you're trying to pin down the exact moment at which a trait enters an individual in the population, then you may be on a fools errand. Traits are often adapted and co-opted. For example, genes which code for one protein in hemoglobin may silently duplicate, and only over much time will that duplication develop some functionality. It's pointless to insist on isolating the original duplication event, because it was silent.
: What I'm saying is that to observe new function evolve, you would have : to make sure that the gene or genes that code for the function did NOT : exist in the population before. Otherwise, how would you separate : out natural selection and what I call evolution?
perhaps this is exactly why I'm objecting to your use of the word "evolution", eh? It sounds to me that you mean "mutation" by "evolution". The important point is that mutation without selection is not a particularly interesting concept, from an evolutionary perspective.
PS--I'm going to have to back out of this thread. I just don't have any more time. I have enjoyed the thoughtful, honest discussions (like the one I'm responding to). Ciao! -- James A. Foster email: email@example.com Laboratory for Applied Logic Dept. of Computer Science University of Idaho www: http://www.cs.uidaho.edu/~foster
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