Definition of Species
Offline One of the more reasonable (or less unreasonable) creationist arguments I've heard is that evolution creates changes within species but cannot split species into others. While I do not believe this to be the case, it seems to me that this argument deserves more attention than those which deny micro-evolution as well, since denying that evolution can produce changes within a species can be dismantled by simply pointing towards the nearest dog.
In any case, it seems to me that the first step towards proving macro-evolution would be to provide a non-controversial working definition of "species". The only such definition I have heard (and I may be seriously out of the loop) is that two animals are of different species if they are unable to produce viable offspring. While this definition works well enough for species whose reproduction works by meiosis, it simply does not apply to single-celled organisms who reproduce through mitosis or binary fission.
Since the easiest form of speciation to directly demonstrate is most likely that of single-celled organisms, my instinct is to next provide a definition of "species" which clearly applies there. Can someone more knowledgeable in these subjects help me in this endeavour?
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Species are sets of organisms which can breed amongst themselves. In evolutionary theory, speciation is defined as cumulative genetic mutation to the point where the gametes of the new organism will not fuse with the gamete of the prototype, thus interbreeding is prohibited and a new lineage develops.
This line of argument is the same as the argument, “if humans evolved from chimps, why are they still here”. A foolish argument. We can apply the previous axioms to this. Evolution by gene drift works on individuals, not species. If the new combination is successful, the individual will have a greater survival chance and reproduce more, passing the new gene to his children. As long as a gene exists in the pool, the individual and his offspring have the chance for further advantageous mutations to occur (and occur they will, for mutation happens during every single undergoing of mitosis, which happens millions of time per day). The survival of an organism matters little so long as s/he had reproduced, is the gene that matters. An old species does not “disappear” if a new one arises. It might disappear only if the new species is superior and destroys its predecessors (early humans most certainly undertook genocide against the Neanderthals).
The trick to macroevolution or speciation is a probability function called cumulative mutation. A prototype organism is bestowed with an advantageous mutation. He has increased survival probability and passes it on to his children. He reproduces more than the other organisms of the same species because of this advantage. So do his children, and the gene becomes more and more prominent in the pool. Since there are more of this mutated version of the organism of the sample, the probability function states that there is a higher likelihood that one of the mutated children will chance upon an advantage mutation, and then...the cycle continues. Go through this 200 times, and the organism will be unrecognizable. This is macroevolution.
Typically, speciation between two absolutely most closely related occurs after one million base pair mutations. That is probably enough to prevent fusion. This seems like alot but it is not when one considers that mitosis happens millions of times per day.
Typically, evolution works with dupicative error. This is a form of genetic mutation where an extra piece of the genome is accidently copied twice, leaving one part free to mutate. When this happens, whole families of related genes arise. These genes are called paralogs. throughout evolution, 200 paralogs have been conserved for three billion years. These, unsuprisingly, control the basic and critical functions of life, RNA synthesis, metabolic pathways, inorganic ion transport, transcription etc
"Physical reality” isn’t some arbitrary demarcation. It is defined in terms of what we can systematically investigate, directly or not, by means of our senses. It is preposterous to assert that the process of systematic scientific reasoning arbitrarily excludes “non-physical explanations” because the very notion of “non-physical explanation” is contradictory.
-Me
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Right, I understand all of that, but none of what you just said applies at all to organisms which do not undergo any form of meiosis.
In a single-celled meiotic species, calling the organism its own gamete is stretching things a bit, but I'll let that slide because we all know what it means there. On the other hand, in a single-celled mitotic species there is no cellular fusion at all so how can two mitotic species be distinguished?
Prokaryotes that do not undergo meisosis but instead duplicate by binary fission have a different method of evolution by genetic mutation.
First of all, meisos is irrelevant to the process. Mitosis or binary fission both produce duplicative errors which are passed on. Meisosis is usually not as important a player in evolution by genetic mutation. Prokaryotes do not undergo mitosis, but they undergo an almost identical procedure called binary fission.
Furthermore, prokaryotes have a remarkable ability to exchange genetic material by a different process which is critical to bacterial evolution. This is called horizontal transfer. Horizontal transfer is an ability eukaryotes do not have because their DNA is enclosed in an intercellular packaged membrane (hence the name eukaroyote). Horizontal transfer occurs when bacteria simply exchange genes by passing them through the cell membrane to each other. This can occur either by direct junction fusing or literally uptaking of the new material. Prokaryotes can take any peice of nucleic acid string and simply incorporate it immediately because their DNA is not kept in an intercellular membrane.
Thus one can imagine how easily a helpful mutation is passed from bacteria to bacteria and prokarytic evolution continues.
Furthermore, the distinguishing for different species of bacteria is different. They are classed on
a) structure, hence the different domains
b) genetics, doesnt matter if there is no gamete (as bacteria are haploid)
c) fatty acids and antigen structure
I'm not a bacteriologist, but it seems to me that your creationist is just sniping about classification systems.
"Physical reality” isn’t some arbitrary demarcation. It is defined in terms of what we can systematically investigate, directly or not, by means of our senses. It is preposterous to assert that the process of systematic scientific reasoning arbitrarily excludes “non-physical explanations” because the very notion of “non-physical explanation” is contradictory.
-Me
Books about atheism
Yeah, that's why I included the term in my original question.
Yup, not a problem. I'm not even asking about how binarily fissile organisms evolve, but this could be helpful anyway, thanks.
So... we don't have a uniform definition of "species" which can be applied to all unicellular and multicellular organisms?
Heh, I don't have a specific creationist I'm dealing with yet, I'm just preparing myself for a project I'll be undergoing soon. To reiterate, it seems to me the simplest way to prove macro-evolution to a creationist is to show it to them by experiment. In order definitively demonstrate that macro-evolution has occurred in a given experiment, we need an applicable, non-controversial definition of what constitutes a species (if it's at all controversial you can bet the creationist will try and weasel out of it that way). It sounds to me like you're saying there isn't one I can use which functions for all organisms?
SPECIES:
IN ANIMALS THAT UNDERGO VERTICAL TRANSFER OF GENETIC INFORMATION (fancy way of saying SEX): Two diploid organisms whose genomes match closely enough that their gametes can fuse
IN ANIMALS THAT DO NOT (haploid organisms): Species are classed based on genotype, external structure and antigen tissue
*Certian haploid organisms like the yeast Saccharoma Cervecias have the ability to reproduce sexually and asexually (haploid fusion and meiosis and binary fission)
"Physical reality” isn’t some arbitrary demarcation. It is defined in terms of what we can systematically investigate, directly or not, by means of our senses. It is preposterous to assert that the process of systematic scientific reasoning arbitrarily excludes “non-physical explanations” because the very notion of “non-physical explanation” is contradictory.
-Me
Books about atheism
Why? Evolutionarytheory predicts that defining 'species' will be difficult, because 'species' is a categorization, and evolutionary theory is one of the reasons why we reject Aristotelean cateogirzation in lieu of Galileo's continuum....
We create categories to understand the world, it's part of our 'divide and conquer' mentality of breaking things down into easily understandable parts.... but evolutionary theory itself demonstrates that the concept of stolid, unchanging 'categories' is itself wrong... every type of life exist along a continuum.. from ancestor to decendent, and along different 'species'... there are no easy, clear, 'pure' demarcation lines...
The reality is that we have to choose a category that fits a specific need. So whatever definition of 'species' you come up with will exist to fit those needs, but life is under no obligation to accept your categories as 'objectively true'!
Anyway, whatever scientific definition you come up with, speciation has been observed in real time, so the entire point is moot.
"Hitler burned people like Anne Frank, for that we call him evil.
"God" burns Anne Frank eternally. For that, theists call him 'good.'
todangst: I agree and I'm quite aware that categories like "species" are things that we invent in order to understand the world around us and that evolution involves specifically blurring lines between our categories, but when trying to point out that red and orange are different colours in a rainbow there is no clear delineator but there are places in each colour that you can look at and say that the colours are different.
Since I know that species are another mostly arbitrary classification system, I have been asking for a working definition which is non-controversial, both of which are conditions put on the practical applications of the classification system, rather than on some elusive "truth" of the matter. Once again I realize that borderline cases are not going to convince creationists, but with an agreement on the definition of species beforehand clear cases must be acknowledged or ignored completely.
The vagueness inherent (and necessary) in classification systems is one of the ways that creationists attack evolution in the public mind and while a universal, strict definition would probably do more harm than good, I can't see the use in leaving the vagueness of definitions exploitable in a particular conversation.
Yes, but it would be an error to hold that red and orange represent an objectively true, mind independent 'category' out in platonic space... the reality is, as we both know, that light itself is a spectrum
I'm not saying you don't know this, so put your guard down, my point is simply this: the fact that life IS a continuum is a refutation of creationism, and a support for evolution, so why try to mask this as an embarrassment when it's a strong point for evolution? The embarrassment is solely on the shoulders of the creationist who MUST be able to give us iron clad, never fail, categories, or concede the failure of creationism.
There's nothing wrong with conceding that every definition of 'species' is created inter-relationally, and with the goal of 'solving a problem' or 'answering a specific' question.
The only 'agreement' we need it whatever agreement is necessary to solve whatever particular problem we have... there is no one good definition for this reason alone.
I'd again explain the truth: that vagueness is precisely what we'd expect... there's vagueness by necessity, all along the continuum. To try and wipe away the vagueness only masks the truth.
For example: Is virus "alive"? By some definitions, yes. By others: no. Where is the clear, obvious demarcation line between 'life' and "non life" There ISN'T any, and this is precisely what we'd expect. Should we 'solve this problem' by saying "virus is alive, period, now shut up?" or should we actually embrace the truth by highlighting the vagueness itself?
Think how valuable this is to abiogenesis... abiogensis looks at where non life crosses over into life... portraying the vagueness in defining virus as life only helps justify the basis of abiogenesis... It's an utter embarrassment for creationists that there are no clear demarcation lines between life and non life, between species... They are the ones who need to be put into the hot seat: "Give us YOUR obejective, non arbitraty, never fail definition of life, for species"
They will fail, because it's impossible, because as we both know, existence is a continuum, and is under no obliglation to follow along with our neat little cubby holes...
"Hitler burned people like Anne Frank, for that we call him evil.
"God" burns Anne Frank eternally. For that, theists call him 'good.'
That's a very good point. For some reason I hadn't thought of it like that, despite that fact that I've thought about the life/non-life thing you mention later every time I read an abiogenesis post. For some reason I just never thought of applying it here - thanks!
You're very welcome. It's obvious that you already had all the pieces of the puzzle from your post.
Creationists project out their flaws onto others, this is their first, and main defense. If a creationst claims that a naturalist has problem X, you can be sure that in most cases the truth is that the creationist is the one with the problem. This is the case here. In fact, this is almost always the case with creationist claims: that naturalist are dishonest, that they collude with other naturalists, that they silence criticism, and so on... every one of these complaints about naturalists is a projection of a real problem for creationists...
"Hitler burned people like Anne Frank, for that we call him evil.
"God" burns Anne Frank eternally. For that, theists call him 'good.'