Natural Selection

[GutZ]

Can someone explain NS (in detail) to me? From what I read it seems to be missing a specific explaination...that being design. Is there a simulation that can explain how NS changes an organism over-time in relationship to enviroment/etc. To me as it stands, I gather that it "choses" a design (kinda) rather then naturally evolving, and that's frustrating.

[the tree]

I'm tempted just to say read the Blind Watchmaker but no, that'd be rude, Dawkins isn't that great a writer anyway, and I don't like the cut of his jib, or his smile, his smile really worries me.

 

Firstly consider these two axonims (if you have grounds to reject them, then go ahead and reject natural selection):

• For some reason (which doesn't really matter), progency resemble thier parents.
• But not exactly (the reason for this also, isn't the point).

Now let's think of some random organism, a snail maybe, and say that it has twenty offspring, each slightly different in thier own way. One of the offspring has a tendancy to be particurally good at producing more offspring and has twenty-five instead of the usual twenty. The tendancy to produce high amounts of offspring is then passed on to most of those twenty five and the third generation in our little story has a large quantity of those with tendancy to produce high amounts of offspring.

 

Back to the second generation again, let's say that another one of the snails couldn't digest food properly: she dies. Another one, only produces ten offspring for some reason, her grandchildren are a significantly smaller portion of the population than of the one that could reproduce lots but still higher than the dead one with no children.

 

All of the above is an example of natural selection, not a very exciting one, but one nonetheless.

 

There is no choice, there is no aim, there is no goal, there is no design, there's just the consequences of replication and variation.

[Dak]

i dont really get what you mean by 'choosing' a design...

 

contrived over-simplification alert!

 

basically, any of the random altereations to a species' design that increase that individuals ability to pass on it's genes (including: increased ability to survive to mating age -- increased fertility -- increased sexyness -- increased ability to look after it's young etc), will, obviously, increase that individuals ability to pass on it's genes.

 

therefore, advantageous mutations should spread throughout a population, till eventually all of the population have that advantageous trait, whilst bad ones should have trouble being passed on.

 

so... say the environment gets hotter. any individual that randomly has mutations that increase the effectivenes of it's heat loss (eg, increased ability to sweat, less hair etc) will be more effective in general and thus more likely to survive to mating age, and so more likely to pass on it's genes (including those that confur above advantages). any of it's offspring that inherit said genes will also have this increased ability to pass on their genes, thus continuing the above-average passing on of the genes for as long as it stays hot.

[MattC]

Natural Selection does not change an "organism" over time - rather, it changes a population, simply by merit of the fact that those organisms within the population that are more able to survive and reproduce will tend to have more babies who thrive.

 

Now, what I *think* you're asking is how the variation among individuals within a population comes about. That is, natural selection weeds out the bad ones - but how do we get so many different types of the same organism (ie taller or shorter, longer limbed, smarter, whatever) to begin with, for natural selection to work with?

 

If that is your question, than mutation is your answer. The DNA within every cell of an organism dictates (along with environmental factors) how an organism develops, from whether or not that organism is "smart" or good at something or not to how long the fingers and toes are, how much hair the organism has, and so on. Each time an organism reproduces sexually (as opposed to asexually), the DNA from two parents mix and produce a new set of DNA. During this process, and during the processes that make the eggs and sperm before hand, errors can occur. The code that determines how that organism develops (and ultimately, how it looks) can be changed into something completely new in this way.

 

Sometimes these changes are bad, and the organism dies, doesn't grow, lives a shorter-than-average life, or is just too ugly to mate. Other times the changes are beneficial.

 

That's where natural selection comes in.

 

If none of us have answered your question, try to rephrase it so as to be more specific, and I'm sure someone can help.

[Skye]

The basic assumption in regards to natural selection is that more offspring are born than can survive to produce offspring of their own. Natural selection is a concept that encapsulates how those that are to survive and reproduce are selected by nature.

[GutZ]

oh ok! In that case I guess I meant more of the biological mutations that cause a specific entity to produce...skin, feathers, teeth, etc. When it comes to those components what concludes which part is suitable for what enviroment and how? Is it just a random outcome from NS? For example, teeth: were there cases that didnt use the composition that makes up the teeth, animals or such that died off because it wasn't advantagous for that composition?

 

Is that clearer? I sure hope so.

 

I am trying to make sense that everything that has evolved to this point can be seen in terms of single interactions with it's enviroment. I wasn't sure if that was implied or not. I could see how the process works in my mind, it just didn't seem to work the way it was explained. I guess I wanted to know more about macro/micro mutation, not NS.

[lucaspa]

oh ok! In that case I guess I meant more of the biological mutations that cause a specific entity to produce...skin, feathers, teeth, etc. When it comes to those components what concludes which part is suitable for what enviroment and how? Is it just a random outcome from NS? For example, teeth: were there cases that didnt use the composition that makes up the teeth, animals or such that died off because it wasn't advantagous for that composition?

 

Yes. The competition for scarce resources is what "concludes" that a trait is suitable for that environment.

 

Look at natural selection as a design competition. The environment sets the design problem. Such as: what design will allow a water predator to move thru water fast enough to catch and eat prey?

 

Each individual is a possible design for that problem. BUT, there are far more design entries than the environment can support. So the individuals/designs have to compete for the scarce resources: in this case, prey. Those designs that are better win and those designs that are worse lose.

 

Now, the key is that the winners reproduce and their offspring inherit their designs. But the offspring also modifiy the designs due to variation. So now you have a competition between the modified design in the next generation. Again, not every design can win. The better designs win and the poorer designs lose.

 

And so it goes generation after generation after generation. An accumulation of design modifications.

 

In the example I gave above, physics and the necessity to bite and hold prey means that there is one general design for a water-borne predator. This is why sharks, ichthyosaurs, and dolphins look very similar. BUT, the particular starting point of design (land animal for dolphins) and chance in the types of variations thrown up, means that there are differences. For instance, since dolphins have a modified running motion for swimming (since they started out as runners), their tail fin is horizontal. And dolphins born with a tail fin not horizontal would not go as fast as those born with a horizontal tail fin.

 

I am trying to make sense that everything that has evolved to this point can be seen in terms of single interactions with it's enviroment. I wasn't sure if that was implied or not. I could see how the process works in my mind, it just didn't seem to work the way it was explained. I guess I wanted to know more about macro/micro mutation, not NS.

 

1. There is not a SINGLE interaction with the environment. There are multiple and simultaneous interactions. We tend to look at the few simple interactions because they are easier to understand. But most of the time there are contradictory interactions and natural selection must find the best compromise design. Also, there is always a cost-benefit analysis.

 

2. What do you think is "micro" and "macro" mutation? Some mutations are in Hox developmental genes and can have a huge effect. For instance, change one base in the Ubx gene and you go from multiple legs to six legs or the reverse. Or change the Manx gene and either get or lose a complete tail. But whether such radical changes between two generations happen during evolution is doubtful.

[lucaspa]

Can someone explain NS (in detail) to me? From what I read it seems to be missing a specific explaination...that being design. Is there a simulation that can explain how NS changes an organism over-time in relationship to enviroment/etc. To me as it stands, I gather that it "choses" a design (kinda) rather then naturally evolving, and that's frustrating.

 

Better to read Dennett. Natural selection is an unintelligent process to give design. It is an algorithm to get design. That is, follow the steps and design is a guaranteed outcome.

 

So, yes, plants and animals are designed. But designed by natural selection.

[GutZ]

 

1. There is not a SINGLE interaction with the environment. There are multiple and simultaneous interactions. We tend to look at the few simple interactions because they are easier to understand. But most of the time there are contradictory interactions and natural selection must find the best compromise design. Also' date=' there is always a cost-benefit analysis.

 

2. What do you think is "micro" and "macro" mutation? Some mutations are in Hox developmental genes and can have a huge effect. For instance, change one base in the Ubx gene and you go from multiple legs to six legs or the reverse. Or change the Manx gene and either get or lose a complete tail. But whether such radical changes between two generations happen during evolution is doubtful.[/quote']

 

1. Like from the DNA to the production. How basically the DNA describes the chemical procedures and "materials" to construct..."whatever". That process seemed oddly explained for me. I think I need more information or education on biology as a whole.

 

2. I have no idea, I just assumed. I know....nothing about gentics, genome, all that.

 

So Yeah, I guess I need some suggestions for reading. Damn there never is that simple answer is there?

[the tree]

I would suggest that if you wanted to understand Natural Selection, you should forget about genetics for a while. Natural Selection is something that happens because of inheritance and variation. Genetics is how inheritance and variation happen in the first place. You could have Natural Selection without genes if you found another way of getting the whole varying replication thing.

 

But as you say, you wanted to learn about mutation and well, that is genetics. I don't know that much about it but hopefully Skye (or another expert) can fill us in on what DNA actually does and how it changes from time to time.

[Skye]

How basically the DNA describes the chemical procedures and "materials" to construct..."whatever".

I think this is a question which would take alot of answering to do it in any detail. Basically though, DNA codes for the production of RNA, many of which then code for the production of protein. These processes are carried out, and controlled, by proteins. These proteins bind to specific sites on the DNA and RNA, and this in itself is another 'code'. The proteins that bind to DNA often do so because of signals that come from within the cell or from outside the cell. These signals may be in the form of simple molecules or ions, or as other proteins. These molecules, ions and proteins form signalling 'pathways', and the pathways form a kind of circuitry that is interlinked and often circling back on itself to produce feedback. This circuitry is how much of the 'decisions' are made within a cell controlling gene expression. Part of that is the release of signals from the cell, which in multi-cellular organisms is how much of the co-odination in development of an organism is achieved.

[GutZ]

I would suggest that if you wanted to understand Natural Selection' date=' you should forget about genetics for a while. Natural Selection is something that happens because of inheritance and variation. Genetics is how inheritance and variation happen in the first place. You could have Natural Selection without genes if you found another way of getting the whole varying replication thing.

 

But as you say, you wanted to learn about mutation and well, that is genetics. I don't know [i']that[/i] much about it but hopefully Skye (or another expert) can fill us in on what DNA actually does and how it changes from time to time.

 

I guess I arbitrarily put the two together. I often do that. I think I get the basic concept of Natural Selection though. I will try to find some books on it, in the future I hope to slowly gather a nice private collection of beautiful science books from all fields *dreams*.

 

and...

 

Thanks Skye, I will have to read that over...a few hundred times to get it.

 

*btw* my multi-colour flag is a parady of another thread, it means I am a highly confused individual (not the other meaning lol, I take chances..) , so in the future you guys know I am not going to make much sense. I've been trying though, I know it must be frustrating to read my posts.

 

Also thanks to everyone who helped out!

[Skye]

NCBI has a few good books online, but reading them is a pain because you have to search for things within them.

 

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=Books

 

These books from there are pretty good, standard textbooks for alot of biology subjects.

 

Biochemistry

Berg, Jeremy M.; Tymoczko, John L.; and Stryer, Lubert.

New York: W. H. Freeman and Co.; c2002

 

Molecular Biology of the Cell

Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter

New York and London: Garland Science; c2002

 

Developmental Biology

Gilbert, Scott F.

Sunderland (MA): Sinauer Associates, Inc.; c2000

[GutZ]

That's ok, I plan to live for atleast 50 years more, I'll get bored eventually and read alot of books (when I become 25 maybe).

[lucaspa]

1. Like from the DNA to the production. How basically the DNA describes the chemical procedures and "materials" to construct..."whatever". That process seemed oddly explained for me. I think I need more information or education on biology as a whole.

 

2. I have no idea' date=' I just assumed. I know....nothing about gentics, genome, all that.

 

So Yeah, I guess I need some suggestions for reading. Damn there never is that simple answer is there?[/quote']

 

There are simple examples, but no, things are not usually simple. However, the concept of natural selection as a design competition does, I think, make the concept simpler. OK, reading suggestions:

 

1.Evolutionary Biology by Douglas Futuyma.

2. Li, W-H. Molecular Evolution. Sinauer, Sunderland MA,1997.

 

Also a quote from someone who uses natural selection to design computer chips (who then doesn't understand how the chips work ):

 

"I'm really exploring what evolution can do that humans can't," he [Thompson] explains. "There are properties that humans have great trouble designing into a system, like being very efficient, using small amounts of power, or being fault tolerant. Evolution can cope with them all." Evolving A Conscious Machine BY Gary Taubes Discover 19: 72-79, July 1998

[lucaspa]

I think I get the basic concept of Natural Selection though.

 

For everyone, let's try Darwin's summary of natural selection:

 

"If, during the long course of ages and under varying conditions of life, organic beings vary at all in the several parts of their organization, and I think this cannot be disputed; if there be, owing to the high geometric powers of increase of each species, at some age, season, or year, a severe struggle for life, and this certainly cannot be disputed; then, considering the infinite complexity of the relations of all organic beings to each other and to their conditions of existence, causing an infinite diversity in structure, constitution, and habits, to be advantageous to them, I think it would be a most extraordinary fact if no variation ever had occurred useful to each beings welfare, in the same way as so many variations have occured useful to man. But if variations useful to any organic being do occur, assuredly individuals thus characterized will have the best chance of being preserved in the struggle for life; and from the strong principle of inheritance they will will tend to produce offspring similarly characterized. This principle of preservation, I have called, for the sake of brevity, Natural Selection." [Origin, p 127 6th ed.]

 

Notice how this is a syllogism.

 

Premises:

1. Individuals vary between themselves. Darwin documents the truth of this premise exhaustively in Origin.

 

2. Struggle for life based on geometric increase in the number of individuals. That is basically: more individuals are born than the environment can sustain. Darwin also exhaustively documents the truth of this premise.

 

Conclusions:

1. Individuals with variations useful in the struggle will survive the struggle.

2. If the variation is inheritable, then the offspring will also have the variation.

 

Notice that, like all valid syllogisms, if the premises are true, then the conclusions must also be true. Well, the premises are documented to be true. Therefore, the conclusions are true.

 

Gutz, you don't need genetics. All you really need to know is that:

1. Individuals vary.

2. The variations are inheritable. The mechanism of that inheritance, as someone pointed out, is irrelevant. It can be saving program lines in a computer or it can be DNA.

 

There is a simulation of natural selection and evolution somewhere on the web. You can watch the evolution of virtual organisms.

[bombus]

That's ok, I plan to live for atleast 50 years more, I'll get bored eventually and read alot of books (when I become 25 maybe).

 

Natural Selection is easy to explain.

 

Imagine if you put a population of goats on an island that has only one food source - apples on trees.

 

The apples that are low down get eaten first and all the goats can reach them.

 

Eventually only the higher up apples remain, and only those goats that are slightly taller (by "chance" due to continual variation caused by tiny differences in genetic makeup caused by random mutation - due to background radiation) are able to reach them.

 

In a year when food is scarce (e.g there has been a drought) only the taller goats survive - or at least more of them survive than shorter goats.

 

The survivors breed and their offspring have (obviously) more of the the 'taller' genes.

 

If this carries on, eventually the average height of the goats will increase and eventally the goats could be classed as a different species.

 

That's evolution by natural selection.

 

Obviously in the real world things are far more complex, but the principle remains the same.

[Xerxes]

I would suggest that if you wanted to understand Natural Selection' date=' you should forget about genetics for a while. Natural Selection is something that happens because of inheritance and variation. Genetics is how inheritance and variation happen in the first place.

 

[/quote']There is a host of non-sequiturs in here. "Forget about genetics....natural selection....happens because of inheritence and variation...genetics is how (sic) inheritence and variation happen in the first place."

 

Sorry, but this makes no sense. Oh, and why do you think that natural selection is "something that happens" because of inheritence and variation? Cart before horse here, I think.

 

As I tried repeatedly to explain on the WiSci (I was Ben there, by the way), genetics, as the study of variation and its inheritence, its spread through populations etc, does not, in any way, require a knowledge of the molecular mechanisms underlying. It is still genetics in the classical sense - the study of inherited variation.

[lucaspa]

There is a host of non-sequiturs in here. "Forget about genetics....natural selection....happens because of inheritence and variation...genetics is how (sic) inheritence and variation happen in the first place."

 

Sorry, but this makes no sense. Oh, and why do you think that natural selection is "something that happens" because of inheritence and variation? Cart before horse here, I think.

 

Xerxes, go to my post where I post Darwin's summary of natural selection. All you need to know is that traits are inherited. You don't need to know why inheritance happens. And Darwin didn't know why. He didn't have modern genetics when he discovered natural selection.

 

As I tried repeatedly to explain on the WiSci (I was Ben there, by the way), genetics, as the study of variation and its inheritence, its spread through populations etc, does not, in any way, require a knowledge of the molecular mechanisms underlying. It is still genetics in the classical sense - the study of inherited variation.

 

And like genetics doesn't require the molecular mechanisms underlying it, so understanding natural selection doesn't require knowledge of the source of variation and inheritance. Variation and inheritance are the premises of Darwin's syllogism of natural selection. He demonstrates that these premises are true, but not the underlying mechanisms for them.

 

That is why we have Neo-Darwinism (also called the Modern Synthesis). That was the integration of classical genetics with evolution.

[Xerxes]

luca I agree with almost everything you said. I am an evolutionary geneticist by training (ain't I grand!), so why wouldn't I? I have, however, constantly to take issue with students who think that a gene "is" DNA, and that genetics is somehow the study of DNA. You have shown that you don't think so - bravo!

 

Where I slightly disagree with you, though it's not a point I would want to press, is that Darwinian theory is syllologistic in the usual sense of the term. I don't know if philosophers would recognize the word "antisyllogism", but that's really what it is: we see the survivors, we know there's a stuggle, we assume the survors are the fittest.

 

The mistake, in my opnion, is that made by people like Des Morris, who went that one step too far: if it exists today, it must have been selected for, which we now know to be false in general

[Edtharan]

Xerxes, go to my post where I post Darwin's summary of natural selection. All you need to know is that traits are inherited. You don't need to know why inheritance happens. And Darwin didn't know why. He didn't have modern genetics when he discovered natural selection.

I agree here. One does not need DNA to have inheritance of traits. It can easily be reproduced with computer code, or even in the lengths of a straw. The person doing the experiment provides the replication (cutting another straw to the correct size) and variation (cutting the new straw at a slightly different lengths from the base).

 

As for Genes, the straw has no "genes" (nor DNA) and so it shows that you can have inheritance without "genes too.

 

Note: If you are wondering about what I mean by the "Straw", I posted a thought experiemnt (but you could do it in real life - and I have done so myself) that used cut straws to demonstrate how selection works. You can find it in this forum with a search (or If you want I can repost it here).

[john5746]

I wonder if there is ANY process that doesn't have variation?

[lucaspa]

I wonder if there is ANY process that doesn't have variation?

 

Human manufacture. We turn out hammers, screws, etc that are identical. The degree of how identical depends on the precision of the machine tools.

 

You can quibble that there is variation at the molecular level, but at the level of "trait", each hammer or screw is identical.

[lucaspa]

Where I slightly disagree with you, though it's not a point I would want to press, is that Darwinian theory is syllologistic in the usual sense of the term. I don't know if philosophers would recognize the word "antisyllogism", but that's really what it is: we see the survivors, we know there's a stuggle, we assume the survors are the fittest.

 

A syllogism is a form of argument. Two premises and a conclusion. Darwin has those premises. You can find them in the "ifs":

 

1. Variation.

2. Struggle for existence (deriving from geometric increase in population)

 

Conclusion: variations beneficial to the organism will be selected.

 

It's not an "assumption" that the survivors are the fittest. Population genetics demonstrated that by looking at traits/designs and the environment. It was easy to reverse engineer the environment to show that the designs selected did work better in the environment. The peppered moth in England is one example.

 

One recent study where the "fittest" were predicted ahead of time is here:

Evaluation of the rate of evolution in natural populations of guppies (Poecilia reticulata). Reznick, DN, Shaw, FH, Rodd, FH, and Shaw, RG. Science 275:1934-1937, 1997. The lay article is Predatory-free guppies take an evolutionary leap forward, pg 1880.

 

The mistake, in my opnion, is that made by people like Des Morris, who went that one step too far: if it exists today, it must have been selected for, which we now know to be false in general

 

This is the idea that EVERY trait is under natural selection. It is also Dawkins' position. Gould, Lewontin, and others argued against it. I would agree that it is false, but that is my conclusion from the data. However, Dawkins and others have not reached the same conclusion and the argument continues. So I'm not at the point where I can say we "know to be false in general". I can point to examples and say "selection doesn't account for that particular trait" but I certainly can't say that "in general" traits that are in existence were not selected for.

[Xerxes]

A syllogism is a form of argument. Two premises and a conclusion.

No shit!!

 

1. Variation.

2. Struggle for existence (deriving from geometric increase in population)

 

Conclusion: variations beneficial to the organism will be selected.

 

Look, I'm not going to argue philosophy, but the major premise is observed, the minor is assumed; it is not logically self-evident that this is true, unless one looks at the "conclusion first. Anyway, drop it, it's not important.

 

This is the idea that EVERY trait is under natural selection. It is also Dawkins' position. Gould, Lewontin, and others argued against it. I would agree that it is false, but that is my conclusion from the data. However, Dawkins and others have not reached the same conclusion and the argument continues. So I'm not at the point where I can say we "know to be false in general".

Then you were confused by my slightly mathematical terminology. One says that x is false in general if one can't find a proof that rigourously exludes not-x. And proofs do not, in general, come from data, these are merely probabilities. But, if you conclude from the data that there are exceptions to x, you are entitled to say "not true (i.e. false) in general" (As it happens, Lewontin is my hero, so I would agree with him, wouldn't I?)