Yes, another evolution question

Great Debates
1

Ok, I’ve read through a great deal of the talk.origins archive. There’s really no doubt in my mind that evolution occurs. But I am still confused about something, so feel free to educate. Go ahead and poke fun, too. Get it out of your system before the next drive-by gets a torn a new one.

Let me ask my question with an example, which you can tweak or massage as you wish (I’m kinky that way). Suppose every gecko is blue-eyed. One day, a random mutation leads to a brown-eyed gecko. It just so happens that the blue eyes stick out a helluva lot more than the brown eyes. As time progresses, the blue-eyed geckoes start to die out, and the brown-eyed geckoes start to dominate.

That being the case… how does a change in eye color lead to a new species? Or a change in skull thickness, or a change in skin color, or a change in [insert miniscule change here]? I could envision a mutation that affects genital size being a speciation event. A chihuahua hung like a St. Bernard wouldn’t be able to breed with the other chihuahuas. But what about all the non-genital mutations?

My suspicion is that it has something to do with the nucleotides not aligning properly. If the first brown-eyed gecko has a cytosine where there should have been an guanine, that could muck things up something fierce (or maybe not, it’s a crap shoot). If this is the case, though, how would the first brown-eyed gecko be able to have any offspring? Wouldn’t he be the first and only brown-eyed gecko?

So, yeah, that’s my question. I understand how a mutation can be subjected to directional pressure by the environment, and therefore come to dominate. What I don’t understand is how it leads to speciation.

Thanks in advance,
Quix

P.S. I’m a poster boy against the “Teach Creationism in School” people. I have a B.S. in Biochemistry, and I learned more from an hour at the talk.origins site than I ever did in Biology classes. But yeah, we need to crowd our science classes even more with World Lit studies. :rolleyes:

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It takes along time for a population to mutate enough to be considered a new species. One minor change does not constitute another species, and it takes many generations(hundreds and thousands) for a speication event. I doubt very much there is ever a single instant that say a gecko would evolve enough from one generation to the next to prevent reproduction. I am pretty sure that these things only happen over hundreds or thousands of generations.

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Furthermore, speciation events usually only occur when:

(A) A small population gets reproductively isolated from the main population, -OR-

(B) A dramatic change in claimate, local predators, food supply, or other environmental factor forces the population to adapt or face extinction.

In both of these situations, the rate of evolutionary change will be very rapid. It can easily take less than a thousand years – a mere blink of an eye in geological terms – for the population to have changed so radically that it is no longer capable of mating-and-producing-fertile-offspring with any extant members of the “old” population.

In between such dramatic speciation events, there are usually looooooooooong periods of little or no evolutionary change in the population as a whole. In other words, the general population has hit upon a genetic formula that is optimized for their current situation, and they exist in a kind of equilibrium for a long stretch of time (often over a million years).

This is what Gould and what’s-his-face mean when they talk about Punctuated Equilibrium.

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Hi Quixotic evolution really is a complex topic, huh? Let me say that the nucleotides line up regardless of which bases they contain. Mutations happen all the time. Pieces of chromosomes are even rearranged. And it’s ok (unless, of course, they mess up genes necessary for survival).

The previous posts were good descriptions, but I think I can add a little more. There is actually more to reproductive compatibility than physically fitting together. If you try to fertilize an egg with the sperm of most other species (getting around physical blocks, mating instinct blocks (different dances, displays, pheromones, etc.) or anything else) the egg will not be fertilized.

You are right that a single change in a superficial trait does not a new species make. As mentioned already, if a species is not split into seperate populations, each new mutation (if it’s not disadvantageous) will spread throughout the species. In your example, the species of gecko if discovered before the eye color change would be described as blue eyed, but after the change, the species would be (manily) brown eyed. Still one species.

So it is possible for a species to eventually become a new one without the “old” one being around for comparison. (You just can’t check if they can mate.)

I know this was a bit scattered, but hope it helps.

PC

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tracer: What’s-his-face = Niles Eldredge

To add to what others have said, especially regarding the pacing of evolution, small populations are virtually required for evolution to occur. In a large, interbreeding population, a minor change like brown eyes would quickly become muted. In a small population, however, even minor changes can become dominant fairly quickly.

Also, note that no one organism can be pointed at as being “the first” of a new species. Populations evolve, not individuals.

Species in general are somewhat difficult to pin down. Thus, it becomes difficult to determine when speciation has occurred, since evolution (even during the relatively rapid periods of “punctuation”) is gradual within a population. We may be able to look at a given population at t = 0, then look at a similar population at t + 5 million years and see significant enough differences to declare them separate species. However, in between, we would likely see a gradient, with certain defining characteristics (those which define the “new” species) gradually becoming more prominent (and, again, by ‘gradual’, I do not mean ‘slow and steady’, but rather ‘occuring relatively slowly when compared to the lifespan of individuals, but still rapid in a geological sense’). We would probably not be able to pick any point between t = 0 and t + 5 million years and say, “Here is where the split occurred.”

In essence, ‘speciation’ is the ‘end’ result of accumulated variation. But, where you choose the ‘end’ can be rather subjective, making the determination of species in general somewhat subjective.

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Is it tacky to respond so quickly after the OP? Meh.

Ok, but that doesn’t really answer my question; it merely stretches out the timeline. What happens in that 100,000 years that makes blue-eyed geckoes genetically incompatible with brown-eyed geckoes?

Ok, let’s run with scenario B. So, because of some environmentally dramatic change, certain geckoes develop better eye color, thicker skin, sharper claws, more teeth, and stronger leg muscles. I still don’t understand why SuperGeckoes can’t mate with normal geckoes. 99.999etc% of their genes are still the same. What specifically changes in SuperGecko that makes them have sterile (if any) offspring with normal geckoes? BTW, I think Gould’s croney was Niles Eldridge, but don’t quote me on that… I’m too lazy to look it up (oh, the humanity of Ctrl-N and typing talkorigins.org :slight_smile: )

Well, yeah, that’s why I said it’s a crap shoot. Redundancy in the codon system is good, makes life a lot easier. A frameshift mutation is bad.

This does help a little bit, but I’m still confused (go figure). You said “a single change in a superficial trait does not a new species make.” Ok, I buy that. My return question is: Then what, specifically, DOES make a new species?

Thanks for the responses everyone, I really appreciate it.
Quix

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Think of it like this, Quix. You know the red and blue triangles that define the cold/hot settings for your air conditioning/heating unit in your car? How it starts out all blue then gradually turns all red? Think of a gecko as being near the blue end of the spectrum. Each mutation is a tiny, tiny bit closer to the red end. A difference between geckos of more than an arbitrary amount (let’s say an inch) on the spectrum means they can no longer interbreed. Speciation isn’t a set value, it’s an arbitrary but very real value of distance between points on the blue > red scale.

–Tim

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IMHO the idea of ‘species’ (as opposed to ‘genus’ and branches closer to the trunk) is an arbitrary construct which mankind has imposed on the natural world in order to categorise it; in reality (and particularly in the plant kingdom) there is a continuum of intermediate forms/hybrids/varieties all around at the same time; species emerge when parts of the continuum go extinct leaving gaps; the islands between the gaps are then distinct species, but only from the point of view of Man, nature doesn’t care one way or the other (except that the further apart that organisms are genetically (and sometimes morphologically) the less likelihood of a successful breeding.

The Genus Rubus (blackberries and raspberries) is a case in point - there are so many similar species, hybrids and varieties, nearly all of which can interbreed successfully and produce stable, fertile offspring, that (IMHO) many defined ‘species’ are have just been ‘picked’ from the general melange, maybe because locally distinct and apparently stable forms have arisen; in a couple of hundred years, there’s nothing to stop new forms taking over from them (if the conditions change to favour it).

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I originally posted this list on another message board where the level of intellectual rigor wasn’t quite as high as it is here. Nonetheless…

  1. Individuals don’t evolve, species and/or populations do.(Micro-evolution premise)

  2. One population from a species may evolve different traits than another population of the same species.(Micro-evolution premise)

  3. Every potential individual has a possibility space, which allows for limited variation from its parents. (Micro-evolution premise)

  4. Over the course of millions and millions of years populations may become separated either through geography, habitat preferences, etc.(Old earth premise)

  5. Once these populations diverge, one or both of them may change so much from what they both once were, that new species arise. (Macro-evolution conclusion)
    Perhaps the key word in all of the above is may. A population may or may not become a new species. Your illustration of brown-eyed geckos may very well never become a different species. Whether it does or does not will depend on any number of other factors: reproductive isolation, changes in habitat requirements, geographic displacement, etc. Blue versus brown-eyed seems to be, at most, a sub-species designation which is generally considered a somewhat arbitrary classification by taxonomists.

S.J. Gould wrote a piece for Discover Magazine in 1992 called, What Is a Species?. In it, Gould suggests that species are, in fact, real things in the world. “Species are not arbitrary units, constructed for human convenience, in dividing continua. Species are the real and objective items of nature’s morphology. They are ‘out there’ in the world as historically distinct and functionally separate populations ‘with their own historical role and tendency’…”

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What you describe in Rubus, with respect to numerous species, probably has more to do with the individuals doing the classification than whether the species concept is valid. Some taxonomists prefer to split a group based on relatively minor differences, others prefer to lump populations together as a single species, and chalk up the differences to mere localized variation. Which, of course, simple adds to the confusion as to what is, or is not, a species.

I do, however, agree with what jharding said about the reality of species - they are discrete, natural entities. I feel that anything above the species level is largely arbitrary, but convenient nonetheless.

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jharding and Darwin’s Finch:

[quote]
I do, however, agree with what jharding said about the reality of species - they are discrete, natural entities.**

Well, now…Are you suuuure :smiley: ? Still a debatable issue, I think. Just to play Devil’s Advocate, I’ll raise the following points/questions.

1.) What do you make of the multiplicity of species concepts? Which one/s do you adhere too? If a species is a species under one concept, but not another, where does that leave the “discrete, natural entity”?

2.) Tell me where you would place the unisexual populations of Cnemidophorus laredoensis ( or any other unisexual species ) that arose from multiple hybridization events but is grouped in the same “species”? Howabout gynogenetic Ambystoma platneum that are clonal triploids that must mate with one of the unisexual parent species ( that contributes no genetic material ) to reproduce.

3.) What do you do with actively evolving populations that are not quite on the end of the continuum where they are separate species? Where is the dividing line where they are part of one “discrete, natural unit”, and not the other?

Nope. I don’t think I buy it. It may sound like heresy :smiley: , but Gould is more likely wrong on this one, IMHO.

  • Tamerlane
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I think that you’re missing his question. It’s not “how does something become a new species” but “how do new species become incompatible with old species?” My understanding is that for the most part, random mutations are responsible for speciation. Occasionally a favorable mutation may indirectly cause speciation, and even more rarely speciation may be directly beneficial, but for the most part the beneficial mutations and the speciation mutations are separate. Suppose that there is another group of geckos that keeps the blue eyes, but has a bunch of other random mutations that cause the two groups to no longer be compatible. Now, while the blue-eye geckos can’t mate with the brown eyed ones, that is not to say that blue eyes cause the geckos to not be able to mate with the brown eyed ones; that’s just a visible characteristic that identifies individuals that have other invisible characteristics.
As an analogy, suppose we get a group of people and split them into two groups. One we stick on a tropical island, the other we put in the arctic. The first group will develop an extensive vocubulary dealing with heat, the sun, and sunburns. The latter will develop an extensive vocabulary dealing with cold, snow, and freezing. Furthermore, the basic words of the language will drift, with slang becoming standard and standard words becoming slang. Eventually, the two groups will be mutually unintelligle. You might be tempted to ask “How did one group creating a bunch of new words dealing with heat, and the other creating a set dealing with cold, cause them to be mutually unitelligle?” But that’s not what caused them to be unintellible; the two are correlated, but there isn’t a causual relationship.

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The Ryan: Small nitpick - Random mutation isn’t teribly common and actually tends to account for very little genetic variety, at least in terms of expressed phenotype. The bulk of novel genetic features arise out of “cross-over” in meiosis, i.e. during sexual reproduction.

Which is why sex is so common. Sex is enormously costly in terms of energy involved - Far easier to be a parthenogen. For one thing you have a tremendous reproductive advantage in that every individual can produce young, not just half ( or whatever proportion is female ).

The cost of parthenogenesis though, is genetic stagnation. Evolution ( barring those incredibly rare instantaneously adaptive mutations ) works very, very slowly on unisexual populations. Sexually reproducing populations therefore are much more flexible to changes in the environment and whatnot in terms of Natural Selection because they generate far more genetic novelties to work with.

So parthenogenetic “species” of lizards in the American Southwest have a reproductive advantage ( all female population ) and possibly a “vigor” advantage ( as clonal products of hybridization they may preserve the benefits of heterosis or “hybrid vigor” ). But they are likely evolutionary dead-ends, as they cannot adjust nearly as quickly, evolutionarily speaking, as their unisexual congeners to changes in environment ( or disease, or whatever ). Of course it has been theorized that they can conceivably backcross with a bisexual species to form a new ( possibly tetraploid ) unisexual species. There have been a couple cases of male individuals found that may be exactly that. But that discussion can start getting complex :smiley: .

A viable strategy, very common in fungi for example ( and aphids, and plenty of other things ), is to have both clonal AND sexual reproduction at different life stages. Hedging the bet as it were.

  • Tamerlane
14

yes, many ‘species’ that we see ‘out there’ are indeed functionally separate, but as Tamerlane says, that may have happened as a gradual process; for example, if we were lucky enough to visit, say, the Galapagos islands in our time machine and fast-forward through the centuries, we would see populations of a common ancestor for Darwin’s Finch(es) :wink: gradually diversifying into different niches and eventually becoming separate species.

There is logically therefore, a ‘grey’ area when they are neither separate species or identical anymore; were we to try and classify them into various species at this point, we’d reach quite different conclusions from those we make today.

My point is that this process is still going on today and in the case of Rubus, we may very well be in that ‘grey’ area, where there are very diverse populations, but there is doubt as to whether they constitute separate species or not.

Taxonomy would be a much simpler thing to apply to a static system, but the whole point is that evolution hasn’t stopped and the organisms we see around us are in a variety of stages of transition.

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Oops - I mean it has been theorized that a unisexual species could backcross with a bisexual parent species to produce a novel bisexual species.

  • Tamerlane
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In reference to whether or not species are real, discrete, entities.

Evolutionary science to me is akin to an in-ground backyard swimming pool. You generally have a pretty small area in which to put said pool. And if you want a diving area you will need to slope the bottom of the pool fairly sharply to get enough depth. Well, it doesn’t take much before I find myself taking that one step too far into the deep end and suddenly I’m in over my head. (Is it wrong to mix a tennis metaphor with a swimming one in the same post?)

In a brief answer to your specific questions. Question number one: I’d go along with reproductive compatibility, although I recognize there are exceptions, but I don’t think exceptions would preclude any definition. But I’m treading water now in the deep end here.

Question two–I just don’t know (still fighting my own ignorance here). Deep end of the pool again.

In response to your third point, I’d respond that when and where species first start to diverge is indeed a grey area and one that taxonimists might find troubling. However, I’d also say that this does not indicate that species are not discrete things in general. In the aforementioned article by Gould, he talks about the evolutionary bush, with each branch representing a discrete species…

**… you might still grasp the principle of bushes and branching bu still say: Yes, the ultimate product of a branch become objectively separate, but early on, while the branch is still forming, no clear division can be made, and the precursors of the two species that will emerge must blend indefinably. And if evolution is gradual and continuous, and if most of a species’ duration is spent in this state of incepient formation, then species will not be objectively definable during most of their geologic lifetimes.

Fair enough as an argument, but the premise is wrong. New species do (and must) have this period of initial ambiguity. But species emerge relatively quickly, compared with their period of later stability, and then live for long periods–oftem millions of years–with minimal change.**

I know, I know you kind of have to buy into punctuated equilibrium to go a long with this, but I think it does at least illustrate, in part, why that indefinite period is not that much of a big deal.

Please be gentle on the return… :slight_smile:

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The indefinite period is only going to be short if the conditions make it so; what if (back to Rubus again, sorry) the prevailing conditions [sup]1[/sup] happen to favour diversity within a population? - the indefinite period might go on, well, indefinitely if nothing happens (like isolation of a small subset or a change in conditions)

[sup]1[/sup] Go on, challenge me to give an example of this scenario.

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Well, I’d say that the length of time isn’t necessarily the measure of concern, but rather the degree of change from the ‘original’ species. So, whether that change happens relatively quickly or rather slowly doesn’t matter–what matters is that enough change (to produce another species) did occur. When that ‘indefinite period’ lasts indefinitely, then our evolutionary bush might just show a nub–rather than a fully formed branch.

19

No, you’re right, length of time isn’t an issue; what I’m trying to say though is that the concept of species is, to a degree at least, arbitrary as it tries to compartmentalise a collection of things that may not actually be discrete at all.

If we are to admit that evolution is still an ongoing process (as indeed we must), then it’s likely that right now there are examples of diversity that have not quite yet differentiated into separate species, but are also too diverse to be classified as a single species either (I suppose that’s why we have subspecies and varieties in the mix too really)

My point was (I think) that we can too easily think of the ‘branches’ as all being of equal length and spacing, when in fact nature isn’t concerned with how and whether things fit into an organisational chart.

Besides, hybrids between distinct species within the same genus can and will often (not always) produce viable offspring, even without the interference of man, so this isn’t a reliable yardstick for what constitutes a distinct species.

20

No mention of Protein Homology yet?