The scientific method applied to the theory of Evolution

[otseng]

The theory of evolution is the dominant theory to explain life that we see on Earth. This theory is the gold standard in which to compare all other theories of life since it is by far the most widely accepted theory in society in regards to life.

What I would like for us to explore is to apply the scientific method to the theory of evolution.

So, for discussion:
What are the relevant terms that must be defined in discussing biological evolution?
What is the hypothesis?
What are the predictions?
What are the evidences that correlate (or does not correlate) with the predictions?

If there are any other things you feel should be added to the list of questions, feel free to bring them up.

I anticipate this will become a lengthy thread. So, I would like to encourage people to spawn off new threads if an area is brought up that requires deeper discussion.

[Jose]

Good idea, otseng!

Before we start, though, I'd like to offer my current spiel about the Scientific Method, which will show up soon as an editorial in American Biology Teacher. The point is: few scientists actually use the so-called Scientific Method. I, for instance, was taught it in high school, but never saw it again throughout college, graduate school, postdoctoral research, or even the first 15 years of teaching in college. I had concluded that it was just one more aspect of science that had been replaced by something more current.

Then I discovered organismal biology and ecology. In these fields, the issues are so complex that it is really hard to do fully-controlled experiments. Rather, we do the best we can with the evidence available, then use the scientific method to test our understanding. If I want to know if my interpretation of the data is right, I make a formal statement of my interpretation (the hypothesis). Then, I ask what predictions my hypothesis makes. Then, I do experiments/make observations, and determine whether my predictions are borne out. If I can show that my predictions are wrong, I've learned something: my interpretation wasn't perfect. If I can't show my predictions are wrong, well...I'm closer to understanding, but I can't claim my interpretation is right because there might be something going on that I don't know about.

In my field, it doesn't work this way. The official rules are that we ask a question (not state an hypothesis), do the experiment and collect the data, and then use the data to figure out what must have happened during the experiment. A good experiment, or series of experiments, provides data that forces us to a particular conclusion. We then present that conclusion as an explanation, or a "model" of what is going on. It is possible (but rarely done in this field) to present the model as a formal hypothesis and use the scientific method, but since the data have already been gathered, and used to build the model, we just don't do this.

In general, it seems to me, the official Scientific Method is used in fields such as organismal biology and ecology, while the alternate that I've described is used in fields such as biochemistry and molecular biology.

Therefore, we can use the official Scientific Method to test our understanding of evolution, as you've suggested. We can also do it the other way, and ask specific questions, get the data, and then see what conclusions the data force upon us, and what explanations we can envision for what actually happened to give us those particular data.

It is good to keep this alternate scientific approach in mind as we do this. Evolutionary theory is exceptionally broad, and is composed of a great many other informational bits. Some of these other bits are, in my opinion, best approached by the alternate form of reasoning.

[rjw]

Gidday otseng,

I would agree in principle with what jose has written with respect to the “Scientific Method” (SM). There is probably no such thing. Put it this way, every time someone defines it, exceptions are found which disprove the definition.

Yet there are things which scientists do and which define a methodology of kinds, and so the first thing which must be defined is “Scientific Method”:-

Scientists construct theories. Theories serve several purposes and have several attributes:-

1) They provide an explanation for some aspect of nature.
2) They provide for their own verification / falsification by suggesting experiments that can be conducted to test themselves.
3) They rely on naturalistic metaphysics and axioms for their own foundation.
4) They use known laws, principles and ideas for their explanatory and experimental mechanisms.
5) Through the mechanism of 2) and using 3) and 4) theories can be modified, rejected or confirmed.
6) Because of the above points there can be (and generally is) several theories describing the one aspect of nature.

Perhaps the aspect of theory building by hypothesizing then testing and confirming, modifying or rejecting constitutes the SM.

As for the remainder of your post? The questions are hopelessly broad. Given that the Theory of Evolution (ToE) is so well established it is hard to sort out hypothesis, theory, explanation and prediction.

Your question is a bit like asking us to explore SM with respect to “the Theory of Gravity” (ToG) and asking:-

1) what must be defined,
2) what is the hypothesis,
3) what are the predictions,
4) what evidences correlate etc.

That evolution happened and happens is not a huge issue within the mainstream these days, anymore than the fact that gravity existed and exists. Like gravity though, the real question concerns one of mechanisms.

Just as we do not know what gravity really is, so we do not really know what the mechanisms of evolution really are. (Is there one or are there several? Is macro-evo just lots of micro-evo or do other mechanisms come into play? How does speciation occur? Is there one mechanism or are there several etc?)

So:-

1) What must be defined?

This is very hard to answer given that most things within ToE are well defined. “Evolution” is broadly defined as the change in morphology or allele frequency over time. “Gene” is defined. We sort of know what a “gene” is. “Mutation” is defined. “Selection” is defined. And so the list goes on.

Perhaps the one thing we cannot so easily define is the concept of “species”. Maybe that is the one thing that biologists agonize over to a large degree. But maybe it is hard to define simply because evolution can make the boundaries between species blurred. There are some good definitions – e.g. a species is a group that does not interbreed with other groups. This is a non-evolutionary definition. However, even with the good definitions there are always exceptions to the rule and, in this particular example, the rule breaks down hopelessly with respect to bacteria.

2) What are the hypotheses (and or theories)?

As with ToG, there are many hypotheses within ToE. One is that all living forms are related to each other through a process of common descent. Another is that evolution proceeds, in part, due to gene or chromosome duplication whereby a part of the genome duplicates allowing one of the duplicates to function normally while the other evolves. Another hypothesis is that some major evolutionary transitions occurred through the fusion of different bacterial systems. This list of hypotheses and sub-theories goes on and on and on.

3) What are the predictions (and explanations)?

Again, this depends. With respect to common descent, if geology has been faithful then one would expect to find fossils that are transitional in someway, illustrating a morphological change over time. One would expect to find similarities within the genome of certain life forms. With respect to duplications one would expect to find clusters of genes within animals and the more closely related the animals supposedly are, the more similar the clusters. One would expect to find these clusters in some animals but not in others. However, not only are these predictions of ToE, but the theory also explains these observations, when they have been made.

4) What are the evidences that correlate (or does not correlate) with the predictions?

Again, it is hard to make something of this question. Too vague. Point 3) above describes some predictions. The correlations? Mesonychid/artiodoctyle to whale transition (40-55 million years ago) documented in the fossil record; the reptile to mammal transition (200 million years ago) documented in the fossil record. These are a couple. With respect to gene duplication – that list is becoming enormous. Journals such as Genetics, Proceedings of the National Academy of Sciences, Trends in Ecology and Evolution, Science, Nature have numerous articles on this topic.

As for “non correlation”. If observations do not correlate then, as with all scientific theories, one of several things happens:-

a) the theory is rejected (does not happen often – unless the observation just cannot be accommodated, and its implications are too obvious)

b) the theory is modified (often happens)

c) the observation ends up being rejected because it cannot be repeated or was shown to be false (often happens)

d) the observation remains anomalous – people have no explanation for it and it does not appear fatal to the theory (often happens).

Like ToG, ToE has not had an a). Both certainly have had b), c) and d).

Certainly observations or evidence can be described that would be fatal to ToE as we currently understand it. Whether they would be fatal to ToE in total is another thing altogether.

Thus, solid evidence that Gen 1 is really the infallible word of God would be fatal to ToE altogether. We would really have good evidence that life was created in a couple of days, perhaps 6,000 years ago. Evidence that humans and dinosaurs co-existed would be fatal to current understandings of evolution but not necessarily fatal to evolution in general. Evidence that humans are as old as trilobites are as old as dinosaurs etc., would probably be fatal to ToE.

And so this list goes on.


So I have thrown something of a definition of SM into the ring and provided some guidelines as answers to your questions.

What do you think?

I suspect you think that ToE is not scientific? If so, then perhaps you need to set up your own definitions and propose something you think illustrates your point. That would narrow the topic considerably and allow us to concentrate on something particular. If you can argue your case well, then we would have something to think about. If we can argue our case well then you would have something to think about.

Importantly we would have something particular to discuss. At the moment your questions appear far too broad (IMHO) – particularly for someone who has just awoken on a Saturday morning after a farewell party the night before.


Regards, Roland

[Jose]

Thank you, rjw. Your insights help us. Maybe what we should do is choose one aspect of ToE, and explore that one in the manner suggested by otseng. While it may be redundant, given that there is already a common descent thread, I wonder if common descent might be the place to focus. The reason is simply that this is one of the biggest issues for creationists, and thus it deserves serious exploration. The common descent thread asks "what is the evidence," which is not entirely the same as asking "what are the predictions of the model, and are they met?" If this is too similar, though, we can move the discussion to that thread, and consider a different aspect of ToE here (whaddyathink, moderators?)

I'll take a stab at stating the hypothesis, and making a few predictions.

hypothesis
All organisms on earth are related. The first living thing diversified into several different varieties, which eventually became sufficiently different that we call them different species. Each of these species diversified into different varieties, which eventually became sufficiently different that we call them different species. This pattern of diversification and speciation recurred repeatedly. As various environmental catastrophes occurred, some species survived, while others succumbed. Therefore, the life that exists at this time represents the descendents of some, but not all, lineages.

predictions

1. Hierarchical relationships Among existing organisms, some should be much more similar than others, depending on the time that they have had to diversify since their last common ancestor. That is, there should be groups of very similar organisms within each local population, with greater diversity between populations or varieties of the same species. There should be groups of similar species (for which we would need a name, such as genus). There should be groups of similar genera (families). Etc.

2. DNA sequence similarities The pattern of similarities described in (1) should occur at the level of the genes (because the hypothesis species genetic relationships).

3. Morphological similarities The pattern of similarities described in (2) should also occur at the level of morphology, to the extent that morphological characteristics are genetically coded.

4. Ancestral fossils Ancestral species that are now extinct should be represented by fossils, at some probability that depends on the ecological conditions in which the organisms lived, the numbers of individuals, the presence of easily-fossilized hard structures, the types of sediments that buried individual specimens, the geological events that those sediments have undergone since the burial of the individual specimen, the particular characteristics of those rocks at the present time, and whether a fossil-hunter happens upon the fossil in the brief window in time when it has become exposed, but not weathered beyond recognition.

5. Non-ancestral fossils Fossils should also represent species that are related to the direct ancestors of existing organisms, but are not themselves direct ancestors. (That is, species that were among the diversity of life at the time, but whose lineage terminated in extinction).

6. Ages of fossils Rocks of younger ages should contain fossils that are more similar to existing species than do rocks of older ages. [This phrasing is important: younger rocks can also contain fossils that are quite different from existing organisms, if the lineage represented by those fossils has since gone extinct. The similarity prediction applies to the lineage of existing organisms, and the diversity associated with that lineage.]

7. Transitions Transitions between species, as represented in the fossil record, should be consistent with existing genetic mechanisms. [This is a prediction because the hypothesis has the inherent assumption that genetic inheritance has followed the same basic mechanism that it does now: DNA is the genetic material, and is passed from parents to offspring; mutations in DNA sequences can occur, creating new "versions" of genes when they do; meiotic recombination (for those species that have meiosis) can increase genetic diversity by "reshuffling" the different "versions" of genes that exist in populations.] Obviously, this prediction breaks down for the earliest life forms that may have existed prior to the advent of DNA as the genetic material; it is valid only for evolution since the DNA-using common ancestor.

OK...there's a short list. There are probably other predictions and better phrasing for both predictions and hypothesis. Take pot-shots at will.

I would particularly like to hear from creationists as to whether these predictions seem valid, and whether there are others that are commonly presented in creationist circles, but that evolutionists don't know about. These could be points of divergence in our views of what the hypothesis really is--something for which we should have a consensus at the outset.[/i]

[otseng]

I suspect you think that ToE is not scientific?

I've never stated such and I hope I've not implied that.

At the moment your questions appear far too broad (IMHO)

Perhaps, and as Jose suggests, the thread can focus on one aspect it, such as common descent.

I bring up this thread for several reasons:
1. If we are going to debate CvE, everything is fair game to debate, including evolution.
2. ToE is by far the dominant theory on life. It should be the standard in which to compare all other competing theories. It would provide the model for what constitutes a scientific argument for a theory.
3. This will provide an opportunity to define exactly what is the ToE.
4. This will provide an opportunity to argue for and against the ToE.

As for the SM, if there are alterations to the SM that I mentioned, those can also be used.

As for discussing common descent, I'm torn between discussing here or in the common descent thread. I feel that the existing common descent thread is perhaps one of the best threads in the CvE subforum. Yet, I don't feel like that thread is complete and that there could be much more to discuss there.

But, I leave this thread open to how evolutionists would like to approach the question. If common descent is the core issue of the ToE, then I'm open to having it discussed here.

One suggestion before we dive too deeply in - perhaps it would be prudent to first define what exactly the ToE states. What exactly is the theory of evolution?

[Jose]

Just what is the Theory of Evolution? Well....I'll throw out some things, and perhaps others can modify what I say until we get a coherent statement that we all agree upon.

The Theory of Evolution

Life on earth changes with time, and has done so since life began.

Hmmm...As I look for more to write, I wonder if this might actually be the entire statement of the theory. The rest is either aspects of the mechanism of how life changes, or the results of changes that have occurred. I'll expand below with separate statements on these two issues.

Mechanisms

1. Change occurs through a combination of three essential features of life:

heritability of traits
variation of traits
differential reproduction

2. Now that we know about genetics, we can simply the first two of these to say genetically-coded traits. The nature of DNA is that from time to time, mutations happen; coupled with the reassortment that occurs at meiosis, this generates genetic diversity, or variation of heritable traits.

3. "Differential reproduction" is merely the idea that some individuals have more offspring than others.

--Natural selection achieves this by virtue of the fact that the individuals that are best "fit" for their environment have more offspring, and the ones that are less "fit" have fewer. In fact, "fitness" is defined as "how many offspring you have."

--Breeding programs by humans also achieve this by virtue of the fact that humans choose which individuals will be the parents of the next generation. Humans have guided dog evolution from the wolf ancestor to the many breeds of dogs we now have. Humans have guided chicken evolution from the red jungle fowl to the many breeds we now have.

--Genetic drift achieves this by having random events result in some individuals having more offspring than others. As an example, maybe a flood kills all of the individuals in a (small) population that happen to have a particular genetic variation, so the others are the ones that reproduce.

4. Because the issue comes up often, but is often misunderstood, I will make a separate statement about mutation. Mutation is no more, and no less than a change in DNA sequence--possibly caused by an error in DNA replication, or by cosmic rays or background radioactivity. If an individual organism inherits DNA that carries a newly-induced mutation, and lives to pass on that newly-induced mutation, then that mutation simply becomes part of the genetic diversity of the population. A mutation is not a change of an individual into something else (like a turtle changing into a ninja warrior). That is: individuals do not change. Change occurs at the level of how many individuals of any particular type are in a population at any particular time.

Results of Change

1. One result of evolutionary change is that the individuals in any direct lineage (grandparent to parent to child to grandchild, etc. over the course of eons) may have very different characteristics when examined at any point in time. This is illustrated in the classic cartoon of the ocean blob next to a fish next to a fish walking out of the ocean next to an amphibian next to a reptile next to a mammal-like thing next to a monkey-like thing next to a human. This is a funny cartoon because it conjures up the image of one individual changing through all of these different forms.

2. Another result is the hierarchical relationships that are seen in comparison of different life forms. It is the pattern of the hierarchical relationships that have led to the theory of common descent from a single common ancestor; evolution per se doesn't require a single common ancestor. There could have been many, but the relationships suggest otherwise.

3. Another result, which is possible because of the way geology works, is that there are fossils of some of the individuals from times past, and they don't look like existing organisms.

4. Another result is that changes are occurring now. That is, we can demonstrate "microevolution." This gives us the ability to determine the mechanistic details of how it works.

Please feel free to criticize and suggest changes to what I have said here.

[rjw]

Hello otseng,

My apologies for the assumption that you believed ToE to be unscientific. By far most YECs I have debated/discussed/argued with, claim that ToE is “unscientific” or that it is a “religion”. (see Ken Ham The Lie: Evolution).

I think jose has narrowed the field very well and the issue of common descent is a key one for ToE. As a result I am happy to run with that one.

What exactly is the Theory of Evolution?

Another of those “ouch” questions. Potentially too broad – a bit like “What is the theory of Gravity?”. Hopefully something can be said that is kind of accurate, which will provide a vehicle for discussion, and will satisfy you and anyone else who may join in.

I used the words “kind of” above, because to describe the theory requires a book. A good descriptive book is “What Evolution Is” by Ernst Mayr. Here I am, attempting to describe the theory in a paragraph!

ToE is the theory that all extant life forms are related through a lineage of common descent, that began with a replicating molecule some billions of years ago and through a series of changes (mutations?), life adapted in various ways (was selected) to a multitude of environments. In the process a series of related genetic systems (and hence morphologies) developed, leading to the patterns we see in life today.

ToE encompasses many aspects:

1) Abiogenesis (this is traditionally left out of ToE. I have included it here.)
2) the mechanisms of change,
3) the mechanisms of adaptation,
4) speciation,
5) rates of change – gradual or punctuated,
6) the fossil record and its interpretation; the genetic record and its interpretation,
7) geology – the changing of environments and habitats over time etc.,
8) notions of competition and cooperation etc.,
9) etc.

Hope this helps to get something going.

Regards, Roland

[otseng]

ToE is the theory that all extant life forms are related through a lineage of common descent, that began with a replicating molecule some billions of years ago and through a series of changes (mutations?), life adapted in various ways (was selected) to a multitude of environments. In the process a series of related genetic systems (and hence morphologies) developed, leading to the patterns we see in life today.

I think this is a good one paragraph summary of the theory. If nobody else has any modifications to this, I think this should suffice for our statement of the ToE.

1) Abiogenesis (this is traditionally left out of ToE. I have included it here.)

If you would like to include abiogenesis in the ToE, I am fine with that.

Are there any other terms that should be defined at the onset of this discussion?

[rjw]

Gidday otseng,

There is nothing extra from me. I guess definitions and clarifications will come as time goes by.

Regards

[nikolayevich]

So, for discussion:
What are the relevant terms that must be defined in discussing biological evolution?
What is the hypothesis?
What are the predictions?
What are the evidences that correlate (or does not correlate) with the predictions?

I agree this sounds great. I've summarized some of the assertions made so far. I stripped some descriptions of enumerated predictions and such (attempting brevity), though of course they are in the original posts above for anyone to read.

hypothesis
All organisms on earth are related. The first living thing diversified into several different varieties, which eventually became sufficiently different that we call them different species. Each of these species diversified into different varieties, which eventually became sufficiently different that we call them different species. This pattern of diversification and speciation recurred repeatedly. As various environmental catastrophes occurred, some species survived, while others succumbed. Therefore, the life that exists at this time represents the descendents of some, but not all, lineages.

predictions

1. Hierarchical relationships
2. DNA sequence similarities
3. Morphological similarities
4. Ancestral fossils
5. Non-ancestral fossils
6. Ages of fossils
7. Transitions
OK...there's a short list. There are probably other predictions and better phrasing for both predictions and hypothesis. Take pot-shots at will.

I would particularly like to hear from creationists as to whether these predictions seem valid, and whether there are others that are commonly presented in creationist circles, but that evolutionists don't know about. These could be points of divergence in our views of what the hypothesis really is--something for which we should have a consensus at the outset.[/i]

If we can agree that this thread will be most useful in determining "what" ToE is by looking at the mainstream and well accepted predictions of the same, it seems reasonable to me that so long as the above (and predictions suggested by rjw and other evolutionists on the forum) are generally relevant to the current understanding of ToE, we shall all benefit (no pot shots yet needed). We should of course also make room for evolutionists here to differ according to personal experience and learning, as scientists all do. This will not likely affect ToE itself, but rather show plausible explanations at different angles to be fair.

Mechanisms

1. Change occurs through a combination of three essential features of life:
heritability of traits
variation of traits
differential reproduction

2. Now that we know about genetics, we can simply the first two of these to say genetically-coded traits. The nature of DNA is that from time to time, mutations happen; coupled with the reassortment that occurs at meiosis, this generates genetic diversity, or variation of heritable traits.

3. "Differential reproduction" is merely the idea that some individuals have more offspring than others.

--Natural selection achieves this by virtue of the fact that the individuals that are best "fit" for their environment have more offspring, and the ones that are less "fit" have fewer. In fact, "fitness" is defined as "how many offspring you have."

--Breeding programs by humans also achieve this by virtue of the fact that humans choose which individuals will be the parents of the next generation. Humans have guided dog evolution from the wolf ancestor to the many breeds of dogs we now have. Humans have guided chicken evolution from the red jungle fowl to the many breeds we now have.

--Genetic drift achieves this by having random events result in some individuals having more offspring than others. As an example, maybe a flood kills all of the individuals in a (small) population that happen to have a particular genetic variation, so the others are the ones that reproduce.

4. Because the issue comes up often, but is often misunderstood, I will make a separate statement about mutation. Mutation is no more, and no less than a change in DNA sequence--possibly caused by an error in DNA replication, or by cosmic rays or background radioactivity. If an individual organism inherits DNA that carries a newly-induced mutation, and lives to pass on that newly-induced mutation, then that mutation simply becomes part of the genetic diversity of the population. A mutation is not a change of an individual into something else (like a turtle changing into a ninja warrior). That is: individuals do not change. Change occurs at the level of how many individuals of any particular type are in a population at any particular time.

Perhaps we can look at Mendel's work on heredity and assess the limitations and loopholes, if you will, in genetic diversity and adaptation. How has our understanding been enhanced since his time (by Morgan et al) and what does it all mean for ToE?

Results of Change

1. One result of evolutionary change is that the individuals in any direct lineage (grandparent to parent to child to grandchild, etc. over the course of eons) may have very different characteristics when examined at any point in time.

2. Another result is the hierarchical relationships that are seen in comparison of different life forms. It is the pattern of the hierarchical relationships that have led to the theory of common descent from a single common ancestor; evolution per se doesn't require a single common ancestor. There could have been many, but the relationships suggest otherwise.

I think that I gather what you are saying, but would rather not assume. If you could clarify what you mean by "...could have been many, but the relationships suggest otherwise"...

3. Another result, which is possible because of the way geology works, is that there are fossils of some of the individuals from times past, and they don't look like existing organisms.

4. Another result is that changes are occurring now. That is, we can demonstrate "microevolution." This gives us the ability to determine the mechanistic details of how it works.

We can look at the possibilities within microevolution as well as the inherent limitations. For instance, how much of ToE is based on microevolution over time, what are the exceptions, and what are the concrete observable types. I use the term 'observable types' to refer to what can be seen in the lab or in nature.

ToE is the theory that all extant life forms are related through a lineage of common descent, that began with a replicating molecule some billions of years ago and through a series of changes (mutations?), life adapted in various ways (was selected) to a multitude of environments. In the process a series of related genetic systems (and hence morphologies) developed, leading to the patterns we see in life today.

ToE encompasses many aspects:

1) Abiogenesis (this is traditionally left out of ToE. I have included it here.)
2) the mechanisms of change,
3) the mechanisms of adaptation,
4) speciation,
5) rates of change – gradual or punctuated,
6) the fossil record and its interpretation; the genetic record and its interpretation,
7) geology – the changing of environments and habitats over time etc.,
8 ) notions of competition and cooperation etc.,
9) etc.

Hope this helps to get something going.

I believe between the various aspects of ToE mentioned so far, we can go quite far. Perhaps we could limit this list to 2 through 9 at the moment or simply for our discussion of common descent, since Abiogenesis rightly deserves its own thread, though I would accept as Otseng has done that this can be included in our discussion of ToE overall.

I used the words “kind of” above, because to describe the theory requires a book. A good descriptive book is “What Evolution Is” by Ernst Mayr.

We can explore the following definitions to help us along, especially with regards to speciation:

The biological species concept

Ernst Mayr 's Biological Species Concept, the most widely accepted definition for species, defines species as "groups of interbreeding natural populations that are reproductively isolated from other such groups" .

Most discussion of speciation has been based on this species concept. Most hypotheses about speciation concern mechanisms which establish reproductive isolation.

In the Biological Species Concept, species are unified by gene flow within a common gene pool ; gene flow involves migration and interbreeding.*

The phenetic species concept.

Phenetic species are defined as as populations distinguished by discrete clusters of phenotypic characters.

The phenetic species concept resembles the practical criteria commonly used to describe species.  A population can be defined as a species by a group of phenetic characters sufficient to distinguish it from other populations.

The phenetic species concept has no theoretical basis.  Its source is our common intuitive sense that species are, in fact, discernable in nature prior to any theoretical justification.

Note the relation of the phenetic species concept to the typological species concept , in which a species is defined by resemblance of its members to some ideal type or to a specific type specimen .

Note also that a phenetic (or typological) species will require a new or modified definition if it undergoes significant evolutionary change without speciation.  This is also true for ecological species but not for reproductive or cladistic species.*

The recognition species concept.

The recognition species concept places emphasis not on reproductive isolation per se but on mechanisms for recognizing suitable mates.

In this concept, a species is defined by mutual recognition of suitable mates among the members of a population.

"Specific mate recognition system " is the term given to a method of recognizing mates that is shared by all the members of a population.

In this concept, mate recognition is causal for the origin of species, while reproductive isolation is a secondary consequence of mate recognition.

The "recognition species concept" is thus associated with a more specific hypothesis concerning speciation than is the more general "biological species concept".*

The cladistic species concept

Cladistic species are segments on a cladogram, joining branch-points on the phylogenetic tree.

In many situations, this is not only intuitively sensible but coincides with other species concepts.

This concept begs the several questions addressed by the nontemporal concepts, regarding how such segments are to be recognized and why (or whether) they even exist) in the first place.

Species formed by hybridization (common among higher plants) do not fit easily into the cladistic species concept, although they present no special difficulty for other concepts.

The cladistic species concept also introduces awkward nomenclature involving pseudoextinction .  When a new population splits off and diverges from its source, the original population becomes a new species and must be given a new name even if it remains unchanged.*

*A zoology 304 "Concept of Species" outline found here.
Feel free to alter (add or edit) the above. It seems a fairly simple summary of the concept of species which Mayr contributed to. When discussing speciation these terms should help us to hone in on the predictions, observations and determining factors of "common descent". What is the realm of possibility? What are the limitations? What are things which have not yet been seen but should be true? (I think it is important to narrow in on "current" limitations of ToE to distinguish what it can and cannot describe).

I very much enjoy hearing each of your views on these things. I wonder what common ground we can find on this thread, since I think there are necessarily some intersecting points which we will find.