Ultimate Evolution Thread for CONTROLLED Debate

[PeteZaHut]

**For the sake of having something new, I am going to give this thread a bit more specific topic within the broader topic of evolution. Please don’t post on here just to argue for or against evolution.

I am going to first give my understanding of the theory of evolution. I acknowledge I don’t completely understand it, so please point out if I get anything wrong there. Then, I am going to give a few examples for specific discussion.

Part I:**

From what I have learned, evolution is based on natural selection. The technical definition I learned recently in a biology class was the “change in gene frequency of a population.” I don’t think that definition is really in question. What I am putting in question is that completely new species can develop (not just from one type of butterfly to another) but in the broadest sense, from unicellular organisms to humans. Anyway, natural selection is as follows: if you have a group of giraffes, some of them may have necks at X length, and some may have necks at Y length. Y length is longer than X length, so giraffes with the Y length necks can eat the food higher on the trees and have a better chance at reproducing. Over time, the giraffes with X length necks will die out and most of the giraffes will have Y length necks. But that doesn’t really change anything. Nothing is evolving. The long necks were there in the first place, and we are still dealing with the same type of giraffes. That’s where mutation comes in. Mutation is a RANDOM introduction of a new gene. So, lets say there is a group of rabbits with black fur that move to the polar region. One day, BY CHANCE, one rabbit has a mutation that gives him white fur. This is advantageous, so eventually, through natural selection, over many generations, the entire population has white fur. The idea is that over a long, long time this kind of change can produce new species.

Part II:

**Example 1: ** In the example of the rabbits, the rabbits lived there with black fur for a long time. This must be true because mutations are random. Nature cannot guess what kind of adaptation the rabbit needs and provide a mutation. The rabbits would have to wait many years before that mutation came a long. So, a lot of the rabbits probably would have gotten eaten, BUT they must have survived as a population because they were still around when the mutation took place. While the adaptation made the white furred rabbit better suited to the environment, the black furred rabbits were still capable of surviving and reproducing. So at least, shouldn’t there be a mix of black furred rabbits and white furred rabbits?

**Example 2: ** I apologize for the lack of details on this one. I was watching an episode of Planet Earth. I vaguely remember them going into some kind of cave, where a rare species of fish lived in some kind of pool or stream of water. These fish were unusual because the water had high levels of sulfur (I think). If not sulfur, it was some kind of chemical that would kill any regular kind of fish. My question to one of my biology teachers was how could these fish adapt to this water if any fish that was in there in the first place would die. The only explanation I could think of is that God put them there with the ability to survive in that water, or when the earth began, those fish were in that water and it just so happened that they could survive in it. The answer I got from my teacher was that the sulfur would have had to leak into the water very very slowly. Now, I am thinking that doesn’t make any sense. The main reason it doesn’t make sense is that mutation is random. I am just supposed to believe that out of all the fish in the world, one of these fish gained the mutation that allowed it to survive in sulfur-water? Not, only that, but it happened to gain this adaptation during the time span when the sulfur had started leaking in? It had to be during this time span because that is in the only stage where it would be advantageous (the rules of natural selection).

OKAY. SORRY, I DIDN’T MEAN FOR IT TO BE THAT LONG. PLEASE KEEP THE COMMENTS LIMITED TO AFFIRMATIONS OR CORRECTIONS OF MY ORIGINAL EXPLANATION OF EVOLUTION, COMMENTS ON MY EXAMPLES, OR INTRODUCTIONS OF SIMILAR EXAMPLES. OH, AND I UNDERSTAND THIS IS THE CATHOLIC ANSWERS FORUMS, BUT FOR SAKE OF THE ARGUMENT, PLEASE KEEP IT SCIENTIFIC; NO ANSWERS INVOLVING GOD.

 

[Touchstone]

**
Part I:**

From what I have learned, evolution is based on natural selection. The technical definition I learned recently in a biology class was the “change in gene frequency of a population.” I don’t think that definition is really in question.

“change in gene frequency of a population” is the definition of biological evolution. That may be what you were getting at, but it sounds like you were thinking that “change in gene frequency of a population” was a definition of natural selection. Natural selection is an outcome of some of the processes that produce those changes in gene frequency, but it’s not the only one – genetic drift would be another example of a process that drives evolution, albeit in a random way (natural selection is not a random mechanism).

If that’s what you meant all along, sorry for the needless digression.

What I am putting in question is that completely new species can develop (not just from one type of butterfly to another) but in the broadest sense, from unicellular organisms to humans. Anyway, natural selection is as follows: if you have a group of giraffes, some of them may have necks at X length, and some may have necks at Y length. Y length is longer than X length, so giraffes with the Y length necks can eat the food higher on the trees and have a better chance at reproducing. Over time, the giraffes with X length necks will die out and most of the giraffes will have Y length necks. But that doesn’t really change anything. Nothing is evolving.

I guess you will have to lay down some markers then for what you mean by “evolving”, because that is very much what biologists would say “evolving” means. A famous example that comes to mind are “Darwin’s Finches” on the Galapagos Islands who are found to have sub-populations with different kinds of beaks as a result of adaptation to the environment/island where that group of finches live – longer, shorter, thicker, etc. depending on what is advantageous for feeding and survival in that location.

I can understand your reaction in saying “a longer neck does not a species make”, and if we are talking about a couple centimeters difference, I think that’s a solid objection. But if you think of a horse (which already has a long-ish neck) population evolving (say on a remote island like those finches) to a point where their necks were more than a meter longer than the average horse, you’d have quite a change, a change that biologists would consider “species worthy”, at least in terms of morphology (interbreeding is usually held out as the test for species borders, and that isn’t being addressed here).

There’s a lot more to say here, but maybe you will consider detailing what criterion you want to use to distinguish species. As I said, the general (though imperfect) rule of thumb is whether two populations can inter-breed and produce fertile offspring (a sterile mule from a donkey and a horse, for example, would not establish donkeys and horses as “interbreedable” and thus of the same species). It’s good to remember that “species” is really just a labeling and categorization system that is useful for humans how have an undying need to label and categorize; biology itself has no signs of anything that divides or groups populations into hard sets the way we use “species”. Every single individual is a “transition” to the next, and every time a population adds a new born or loses a member through death, the population necessarily has evolved and is not the same “kind” in the strict sense.

The long necks were there in the first place, and we are still dealing with the same type of giraffes.

I understand your saying “they were there in the first place” for the purposes of your example, but according to evolutionary theory, they weren’t there in the first place. The shorter necks had to come from somewhere, too. And if you wind it all the way back, you arrive at something like a bacterium, only much more rudimentary.

-TS

 

[Touchstone]

That’s where mutation comes in. Mutation is a RANDOM introduction of a new gene.

I believe you are looking for some precision here, so I’d like to suggest a revision to that: a mutation is not the introduction of a new gene – that would be the adding of new genetic material. Rather, a mutation is a change in a nucleotide sequence for a gene. I’m going to use an example that I think will work for you, but has a history of being terribly misunderstood and misapplied. If you think about the phrase “We the people”, a mutation would be something like changing one of the letters in that phrase – maybe the result of a “mutation” would be: “We tRe People”. We didn’t add any new letters, but changed one letter (the bolded ‘R’ was previously an ‘h’).

Necessary notice: nucleotides are not letters. Codons are not words. Genes are not sentences. DNA is not English, or any language at all. It’s useful pedagogically to approach these concepts through our understanding of English, but the analogy is actually very poor beyond the crudest connections.

So, lets say there is a group of rabbits with black fur that move to the polar region.

OK. Bummer for those rabbits. But OK.

One day, BY CHANCE, one rabbit has a mutation that gives him white fur. This is advantageous, so eventually, through natural selection, over many generations, the entire population has white fur. The idea is that over a long, long time this kind of change can produce new species.

Right, this kind of change. Changing fur color alone is not going to affect interbreeding, and so long as that is the diving line for species, fur color changes by themselves won’t produce a new species. But the elongation of necks example you gave would be more representative of the kinds of changes that trend in the right direction for a new species. Longer necks don’t prevent interbreeding either, on their own, but necks that are 1 meter longer than the “ancestor” population are a significant enough change to the basic body shape, that we can imagine that this new “long necked horse” would have other structural changes that wen along with longer necks to support those longer necks – the “long necked horse” may have taller, stronger front shoulders, and maybe a more sloped back and shorter rear hips, like a giraffe does, so as to support the effective use of that longer neck.

Those are changes right there that mean something, but what those changes have the potential to do is discourage interbreeeding between “long necks” and “short necks”. There’s lots of other reasons why the “long necks” might be sexually isolated from “short necks” (e.g. physical separation), but even in cases where “long necks” and “short necks” live in the same areas, the body differences can reduce interbreeding rates. As interbreeding diminishes, the two populations necessarily become genetically divergent. If mutations occur later on in the “long neck” population that become fixed, and are such that interbreeding becomes problematic no matter how motivated a “long neck” and a “short neck” may be, you have the cleft of species in place. The “long necks” and “short necks” are genetically diverged at that point, and it won’t matter if the inhabit the same areas, as they cannot interbreed anymore. The changes that happen to “long neck” populations are thus isolated form any changes that happen to “short neck” populations, and vice versa.

More tomorrow.

-Touchstone

 

[Leela]

Hi Pete,

I suspect that your emphasis of CHANCE and RANDOM are meaningful to you. Why have you emphasized them. I don’t think that these are scientifically meaningful terms. How is saying that a phenomenon is random diferent from saying “I don’t know”? Mutations must occur for natural selection to work in creating changes big enough to result in new species, but it doesn’t add any information to say that mutations occur “randomly”. It just means we can’t predict when they will occur, but we know that they do (I’m not expert, but Ithink such transcripition errors have actually been observed). To explain evolution through natural selection, it is not nessary to be able to predict mutations. It is enough to know that ther occur.

Best,
Leela

 

[Sair]

I’m afraid I can’t pretend to Touchstone’s level of detailed knowledge regarding evolutionary processes, but I do have a few thoughts that I think are relevant to this discussion.

I understand that many people find it difficult to comprehend the workings of evolution, especially when concepts such as ‘chance’ and ‘mutation’ tend to get misapplied somewhat in the popular perception. But here’s my understanding, anyway. Firstly, when it comes to chance, I think that we tend to forget just how much time we’re dealing with here. Geological time is unimaginably vast, and when scientists talk about species emerging ‘suddenly’ or ‘rapidly’, what they’re talking about is hundreds of thousands, perhaps a few million years. That is rapid, for time that is counted in the hundreds of millions of years. The action of chance across that time scale is quite a different concept from the action of chance in, say, playing a hand of poker. Secondly, if one thinks only of genetic mutation as a force for evolutionary change, it further skews the picture. As I understand it, most genetic mutations actually produce disadvantageous changes, and it’s only in fairly extreme or highly changeable environments where mutations may confer some advantage over the unmutated form.

Anyway, that aside, my next thoughts I shall endeavour to link to your fish example.

These thoughts concern normal genetic variation within a species. Consider the differences that exist between humans. We are all the same species, but we differ widely in terms of our physical features and capabilities - skin colour, height, strength, build, flexibility, etc etc. Some people’s capabilities suit them to particular activities - or, to put it another way, suit them to life in certain environments or situations. The same would be true of fish. If we take as given that the sulfur content of a certain body of water increased gradually (and by ‘gradually’, I mean in relation to the time scale mentioned above) then there would have been certain fish whose genetically varied characteristics allowed them to tolerate the initially minimal levels of sulfur in the water. If we also suppose that there was some advantage to living in that particular body of water - perhaps predators would be less eager to enter sulfurous water? - then there would be additional survival benefits to being able to tolerate sulfur in the water. Over the generations, those fish whose genetic characteristics enabled them to survive to reproduce in the increasingly sulfurous water would eventually result in fish who were specifically adapted to live in water with high sulfur content. Here we have an example, then, where a changing environment and genetic variation work in concert to drive the process of evolution. This is natural selection at work.

 

[Touchstone]

Part II:

**Example 1: ** In the example of the rabbits, the rabbits lived there with black fur for a long time. This must be true because mutations are random. Nature cannot guess what kind of adaptation the rabbit needs and provide a mutation. The rabbits would have to wait many years before that mutation came a long. So, a lot of the rabbits probably would have gotten eaten, BUT they must have survived as a population because they were still around when the mutation took place. While the adaptation made the white furred rabbit better suited to the environment, the black furred rabbits were still capable of surviving and reproducing. So at least, shouldn’t there be a mix of black furred rabbits and white furred rabbits?

Given that you’ve said here that the black rabbits were able to survive well enough to keep reproducing until such time as this white fur mutation happened, then we would expect there to be quite some time involved in a “crossover” to a white-furred population. And for any size population, it would take many generations for the selection pressures to work themselves out statistically, and even then, the complete disappearance of dark fur may take a long time, or may never happen. This is because white fur may be a recessive allele. If it is, then even there are extraordinary adaptational advantages to white fur, when one of the parents has dark far and the offspring receives a dark allele, it will be dominant over the white allele from the other parent, producing dark fur as the phenotype.

All of which to say that yes, there would be mix, and for a large number of generations most likely, in the example you have here.

**Example 2: ** I apologize for the lack of details on this one. I was watching an episode of Planet Earth. I vaguely remember them going into some kind of cave, where a rare species of fish lived in some kind of pool or stream of water. These fish were unusual because the water had high levels of sulfur (I think). If not sulfur, it was some kind of chemical that would kill any regular kind of fish.

I think this is the tonguefish, no?

My question to one of my biology teachers was how could these fish adapt to this water if any fish that was in there in the first place would die. The only explanation I could think of is that God put them there with the ability to survive in that water, or when the earth began, those fish were in that water and it just so happened that they could survive in it.

Just getting dropped into sulfuric, low pH water does sound like it would need a miraculous bit of help for it to survive. But in the case of the tonguefish, what you have is an environment where the fish don’t get “dropped in”, but rather a set of thermal vents that generate lots of heat and spew sulfur and acid elements into the water, but both the heat and the sulfur become diffuse as you get farther away from these vents. So imagine that you are a “non-sulfur” fish in that area, competing for the scarce resources that exist in your environment. Getting too close to the sulfur source kills you, but it also kills other fish. If some of your buddies develop just a little more tolerance for sulfur over many generations, eventually they will be able to get closer to the vents without dying from the exposure. Not much closer, but just a little.

Now, that small amount of increased tolerance gives the tonguefish an advantage, if a modest one. The tonguefish, now just a little bit more durable in dealing with sulfur in the water than it used to be (we’re talking about populations here), and more durable than other competitors for resources in the area, can now exploit any food sources available in the slightly more sulfuric areas. This can be a big boon for the tonguefish, just as a result of a small development in sulfur tolerance. Other fish and non-sulfur-tolerant animals have to keep out, but the food sources in that zone would be “easy hunting” for the adapted tonguefish.

If there are food sources for the tonguefish in these vents (and it appears there are – small worms in the sediments, maybe hydrothermal bacteria on which to feed), you have the first steps toward the evolution of an extremophile species, which the tonguefish appears to be, amazing for its ability to swim around in these very hot, highly acidic environments, “living with molten lava for a home”.

But the point I’m trying to make is that the adaptation to these extreme environments happens like everything else in evolution – in step-wise, gradual fashing, with fits and starts and lots of trial and error. The tonguefish, for instance, in that first set of adaptations, would be only just slightly more tolerant of sulfur. That makes food sources available for them that weren’t previously, and aren’t available to other species in the area that aren’t similarly adapted. But they aren’t swimming directly over the vents at that point, they are still far off, to survive. Over long periods of time, the population “pushes the envelope” to creep closer and closer to the extreme conditions, as it slowly adapts to those extremes, and thus can exploit the food sources and survival advantages there.

-TS

 

[Touchstone]

The answer I got from my teacher was that the sulfur would have had to leak into the water very very slowly. Now, I am thinking that doesn’t make any sense. The main reason it doesn’t make sense is that mutation is random.

Right, but instead of thinking about the “sulfur getting turned on”, think about the sulfur (and heat) being fixtures of a marine environment that the tonguefish population appraches gradually with increasing buildup of tolerance to those extremes.

I am just supposed to believe that out of all the fish in the world, one of these fish gained the mutation that allowed it to survive in sulfur-water?

Yes and no. The mutation occurred, but one needn’t think that just that one fish got a once-in-forever mutation that made him (and thus his offspring) “sulfur-tolerant”. Maybe this mutation is a quite common one, as mutations, go, and involves an allelic change that happens to fish (and other animals) all over the world. For example, if we call this mutation X, and *X *is a slight change in the way hemoglobin is produced (and I’m making this part up – I know nothing about the biology of sulfur tolerance in fish!) and that change has the effect of making any recipients of that change more tolerant of sulfur, then what would be happening is that X occurs here and there all over the environment, and the recipients have slightly improved sulfur-tolerance (among other things). But that doesn’t matter for all the other cases, because they are not living in an environment where sulfur-tolerance helps or even matters.

But the tonguefish, of all the recipients of change X, it can make good use of that change, and proceeds to exploit that slight tweak to its constitution to pursue food sources in places other tonguefish and other animals cannot. This just makes it a matter of statistics, then. X happens with some small probability, and even when it happens, there’s some very small probability that that the “sulfur-tolerance” feature will be a factor. In most cases, the mutation of *X *doesn’t do anything, survival-in-sulfur wise.

Not, only that, but it happened to gain this adaptation during the time span when the sulfur had started leaking in? It had to be during this time span because that is in the only stage where it would be advantageous (the rules of natural selection).

That would certainly make the odds much tougher. But I think you will find, in looking at the environment in that example (whether it’s the tonguefish or some other species) that the process works slowly and in the reverse direction of what you are think. Mutations and other means of variation lead to phenotypes that have increased capabilities with respect to some part of the local environment. The ‘hot sulfur’ part of the ocean there for that population has always been there, but the food sources have always been accessible. So when some individuals acquire an above average tolerance to sulfur, they can go closer than the others, and get easily meals. Now the “perimeter” is closer to the sulfur vents, just by a little. Maybe half a million years later, another mutation takes hold that lets the holders of that mutation go closer stil. If you think about acid spewing into the ocean from a vent, you can understand how this encroachment can be very gradual. Rather than sulfur just “dumped into their tank”, where the fish must adapt on the fly or die, the sulfur gets more and more dilute as you get farther from the source. So you can “creep up on it”, gradually, over millions of years, until you have such highly developed tolerances that the tonguefish can swim and eat and live in what looks like a cloud of molten lava (or right above it).

-Touchstone

 

[PeteZaHut]

Hi Pete,

I suspect that your emphasis of CHANCE and RANDOM are meaningful to you. Why have you emphasized them. I don’t think that these are scientifically meaningful terms. How is saying that a phenomenon is random diferent from saying “I don’t know”? Mutations must occur for natural selection to work in creating changes big enough to result in new species, but it doesn’t add any information to say that mutations occur “randomly”. It just means we can’t predict when they will occur, but we know that they do (I’m not expert, but Ithink such transcripition errors have actually been observed). To explain evolution through natural selection, it is not nessary to be able to predict mutations. It is enough to know that ther occur.

Best,
Leela

The reason I emphasized “chance” and “random” is because I wanted to make the point that nature does not notice that an organism would benefit from a certain mutation, then give it that mutation. A bunch of mutations might occur, then after a while, there might be an advantageous one, which natural selection acts upon.