How a new genus is created?

Factual Questions
21

Your definition is incorrect. What you are defining is species, not genus. That’s why people keep talking about speciation.

Again, replace “genus” with “species” in all instances. Let’s talk about the Dobzhansky-Muller model of speciation, which is one of the simplest ways in which one species can become two. In this model, we focus on two genes: A and B. A and B need to interact as part of the process of making gametes, so if your A and B cannot interact properly, you are infertile.

Now, let’s take one big population of organisms. In the population, there will be some level of variation in both A and B, but stabilizing selection will ensure that over time, A and B will remain able to interact. Now, let’s split our big population into two little population - call them 1 and 2. A valley floods, or a forest is cut down, or a freeway is built in the middle of the range. Suddenly, the A and B pools are separate. While within 1 and within 2, A and B need to remain compatible, there is no constraint that means that 1’s A needs to be compatible with 2’s B. Genetic drift begins to happen. As it happens, in nearly every case where we’ve looked, genes involved in sexual reproduction are among the most rapidly evolving genes in the genome, being under sexual selection, so A and B are likely to change much sooner than other genes that control the liver, or bone structure, or coat color, or whatever. This is why reproductive isolation tends to occur faster than, say, massive size differences.

So in population 1, A begins to drift away from its ancestral structure, while in population 2, B begins to drift. Both 1A and 2B are still able to interact with their population’s partner molecules, but now, we bring the populations back together, and find that 1A is unable to interact with 2B. Congratulations. We now have an infertile hybrid, and speciation is achieved. Note that at no time during this process was any individual limited in their mating options - everyone was fully interfertile with everyone else in their population.

And this isn’t just a hypothetical. The individual gene pairs (A and B) have been identified in multiple pairs of closely related species, including in many fruit fly species pairs.

22

The species ring with California salamanders is probably the best example to answer the OP’s question. There are a whole chain of sub-species of these salamanders up the coast and down the mountains of CA (but not in the central part) like a big horseshoe. Each sub-species can reproduce with the species next to them… but the ones at the beginning of the horseshoe cannot reproduce with the ones at the end of it. Somewhere through all the gradual shifts in population, there has been enough speciation to prevent the two from interbreeding.

23

Not really. Ring species don’t have much, if anything, to do with Genera.

There is no good answer to the OP because the term “genus” is an entirely artificial categorization of living populations. It’s for our convenience of understanding, and doesn’t equate to anything that nature “cares” about.

24

Ok, to help this thread going to the right direction, here is the definition of species :

Biology A fundamental category of taxonomic classification, ranking below a genus or subgenus and consisting of related organisms capable of interbreeding. I didnt invent anything, it is found on Species - definition of species by The Free Dictionary . And a genus is a group of species. In taxonomy, we put the genus name followed by the spiecies name. Now back to the thread:

CurtC: I read you carefully, but you are also stuck with my question : if an individual from one group will no longer be able to mate with a member of the other group when that happens, this individual wont be mating with his own group, leading to extinction. But like I said initially, separating groups isnt answering the question. At one point, one individual wont be mating in his own group.

Innter Stickler yes, as you said we’re talking absolutely minute changes over extremely long periods of time,. 4 billions years of evolution of life to be more precise. But I am talking about that minute. What really occurs during this minute?

septimus Yes Darwin found different species of the same genus on the Galapagos islands. He even explained why food was the main factor birds needed to adapt to a new environnement. All those birds were different but still genetically compatible, therefore in the same species. With time, those birds could become new Genus, but…how?

Mangetout As you read above, I didnt invent my definition, I just put it to the simplest way so that everyone could understand.

And your definition doesn’t work, and you want us to tell you why? It doesn’t work because you’re making it up as you go along.
My definition works. As you read above, I didnt make it up. If you want, tell me why you disagree with my definition?

there is no particular reason why that tree should have any kind of categories of division; I agree, like I said, nature isnt here for man to categorise it.

There are divergences that happened at any point in the past Yes, but how? Everything is explained for divergences of species. Darwin is totally right on this.

DrFidelius You are correct, french is my first language. But I didnt create my own definition. I put it in my own workds.

The Hamster King:
There is no such thing as “a gene of sexual incompatibility”. I don’t know your background on genetics, but with all due respect, you are wrong. If you were right, then mice could fertilize flowers. Why? like you said, gene of incompatibility doesnt exist. In 4 billions of years, no evolution there.
You’re thinking that one species becoming incompatible with another is an abrupt on-time event – like someone throwing a switch. Yes! Unless you think that a group will get the same mutation among all its individuals at the same time. One has flip the switch first.
But rather it’s a gradual process. Yes, It has to be gradual. But how?

If two breeding groups are kept apart, gradually over time they will drift apart genetically. As little genetic differences pile up, they turn into medium genetic differences, and then large genetic differences, and then huge ones. It’s a smooth continuum. This explains speciation, but new genus. We cant talk about medium, large or huge incompatibility.
At any point, every member of each group is very similar to the rest of his group. He or she can breed just fine with other members of his group. But coupling with a member of the other group becomes less and less likely over time to produce a viable offspring. Eventually it becomes impossible. How can a group be less and less compatible after generations on genetic level, is such thing of a level of compatibility exists? If so, how many levels there is?

SmegHead I understood your example. I agree with the presence of genetic variety of the two genes A and B, but there must not be much because those genes are very important for reproduction. A small change and you are infertile. Also, there is a few flaws in this theory. First, there is no selection in both population that would prefer A or B. In both population, there is not a selective environment for sexual compatibility to favorise gene A or B. The process will be at random. At the separation, the mix was equal. And after many generations, the mix of both genes will still exists about population 1 or 2. I disagree that genes involved in sexual reproduction are among the most rapidly evolving genes in the genome. I believe it is the slowest. If you compare the development of embryos of fishes and humans, there is not much difference in the firs stages.
Also, I never heard of a laboratory that created a species of fly that couldnt reproduce with other flies. That would be an amazing discovery, we would have created a brand new genus that never existed before. If we could do that, eventually we could create a new genus of humans. Subhumans tu use as slaves for example, not good for the ethic tho.

Thank you for writing such a complex example SmegHead. Actually, I want to thanks all of you who responded to my thread trying to answer my question. If some of you have something to add, feel free. Your answers have made me think a lot.

25

::Has Grand Mal seizure::

26

No, that’s “genius.”

27

Yes, you did invent it. You looked up Species, then tried to extrapolate a definition of Genus from it, apparently on the assumption that they are the same sort of category. They’re not.

Species, as a modern biological concept, means a community of organisms, primarily characterised by the fact that they interbreed freely with one another.

Genus is a category within an arbitrary system of classification based on clues such as comparative morphology. They’re not the same kind of thing.

In cases where genus groupings happen to closely match phylogenetic ancestry, then a new genus is created when, in the past, a speciation event occurred, branching into two or more groups, which may or may not have speciated further into the modern collection of species within what we now call genera.

In cases where genus groupings don’t closely match phylogenetic ancestry, then a new genus is created when some learned fellows with beards decide it is a good idea to define a new genus and categorise some species within it.

28

You haven’t listed any reason here why the theory is flawed. You’ve just described the process of genetic drift.

Disagree all you want. There are decades of studies in evolutionary genetics that prove you wrong. Data trumps your belief. I’m done here if you’re just going to stick with your personal feelings over actual fact.

I didn’t say they were created in the lab. The studies were done on naturally occurring fly species, and, incidentally, those studies prove the D-M model does happen at least some of the time, making your objections irrelevant. Also, YOU’RE STILL COMPLETELY MISUSING THE WORDS GENUS AND SPECIES. KNOCK IT OFF.

29

Etrigan: (why do I keep expecting your posts to rhyme?)

At some point you find that “logic” and arm-chair speculation needs to be compared against what is actually observed in the real world or what can be done inthe controlled environment of a lab. This is why Darwin spent so many pages in “The Origin of Species” writing about pigeon breeding.

When your ideas are in conflict with what has been observed (either directly observed or by reasonable inference from direct observation) it indicates that something is wrong.

I cannot claim to be an expert on all the biological literature published over the past 150 years, but I can assure you that you are not the first to ask these questions and they have been answered to the satisfaction of people who work in the field for decades.

30

They need to get rid instain ancestors who kill thier geniuses. It was in the news this mroing. A moth in Ar who had coll her three geniunses with light wings. They are taking the three moths back to New York to lady to rest in the sooty factory. I am truley sorry for thier lots.

31

It’s pretty difficult to “put it to the simplest way so that everyone could understand” when you don’t understand the definitions of either species or genus yourself. You are essentially just making stuff up.

32

The Linnaean system was designed in the 18th century, and the definition of a species has changed since then. As already noted, it is only the “species” that biologists officially recognize. The other taxa (subspecies, genus, family, etc) are conventions, but there is no official organization to approve how they are applied. Biologist also use DNA rather than morphology when they are trying to classify populations, so if they tend to clump together in clusters, that makes it easier, but that is often not the case in the real world.

We can talk about speciation because it is determined by whether the populations breed in the wild. But there is no “event” or defining characteristic like that to determine what Genus a particular group of species belongs to.

33

You’ve answered your own question: With time. Time can do so much!

But the reason I’m responding is that I’m annoyed. I’d rather you ignore my post altogether than to read it and dismiss parts, without comment, as though they were wrong. In mentioning Darwin’s finches I wrote “indeed multiple genera”. Since, as others point out, classification into genera is arbitrary you can find references to 3, 4, or 6 genera of Darwin’s finches, but they all derive from a single species less than 6 million years ago, and no source (except, now, you) describes them as a single genus. Here’s a pdf where you can learn more:
http://www.eebweb.arizona.edu/courses/galapagos/handouts%202009/articles%202009%20for%20web/phylogenetic%20relationships.pdf

Hope this helps.

34

Everyone here agrees with that definition, but you keep using the criteria of interbreeding to apply to genus. You’re repeatedly using the word genus to apply to the definition of species that you yourself are quoting.

I’m assuming, since you describe your question as how two groups can develop that are incapable of interbreeding, that you’re really talking about species, not genus.

I thought we had explained this in detail. I’ll try again.

Let’s say you have a population of cats. Some of them move into a new area, because their prey have begun living there as well. The cats in the new area don’t typically mix with the cats in the original area, just because they’re in physically separate locations. Maybe some climate change has caused the land between the two habitats to become inhospitable to them.

Now right after they have separated, you could mate a cat from area A with a cat from area B, right?

But what about after 10,000 years? There have been gradual changes in the populations, so that they’re not exactly the same anymore. Most likely, after this short time period, they’ll still be able to interbreed.

What about after 100,000 years? Now the two populations of cats have diverged more - you can easily identify which group an individual comes from by sight, but they’re still very similar. Maybe at this point they can be bred, but their offspring will be sterile. This happens a lot in nature.

What about after 1,000,000 years? The two populations have accumulated so many changes that the can no longer interbreed at all. They are two separate species.

Now, do you understand that at any time in this scenario, any individual is fully capable of interbreeding within his own population? It’s just that the populations over time have drifted far enough apart that the two groups can’t interbreed.

Your thinking is wrong. It’s not that there is one mutation that suddenly happens, making an individual too different to breed within his population. Sure, that can happen, but that individual will produce no offspring.

The way speciation works is that there will be very small changes to the populations’s genome, and these changes will accumulate to make interbreeding less likely. It’s common that before interbreeding becomes impossible, there will be a time during which they can produce offspring but the offspring will be sterile - think of horses and donkeys here. But by this time they’ve become separate species.

35

And different populations can become reproductively isolated even while being genetically compatible. If the cats in one area have some environmental pressure to become larger (say that there are few mice there and many rabbits) then the larger individuals in that population will survive a little better than the smaller individuals.
Over a relatively short time, one population of the cats is significantly larger than the other (who live where there are plenty of mice) and then they might not recognise the tiny cats as potential mates if they ever encounter them.

Species tend to split off from the main population at the edges of their natural range. A natural range is pretty much where the organisms are most comfortable, given temperature, food availabilty, and al that jazz.
The edges of a natural range are exposing the groups living there with slightly different conditions. You don’t need mutations to get thicker coats, you just need the naturally hairier individuals to survive better at the cold end of their range. Given time, the average hairness of the sub-groups there becomes greater than the core population’s hairiness.
These little changes build up until members of one group can or will no longer interbreed with the central population.

36

Analogy: Picture a road that splits in two, with one of the branches going down a ramp (like, say, a highway exit ramp). Let’s say that we define it as being “one road” for as long as it’s possible for a person to jump from one ramp to the other, and “two roads” after that point. It clearly starts as one road, and anyone going down one way or the other has a smooth, continuous path. But eventually (and precisely where is a bit vague), it becomes impossible to smoothly go from one road to the other, and you have two roads.

37

Maybe it’s a reading error. Look again at the definition you cite:

That is the definition of species. Why are you using that definition of species for your thread about genus?

Note that the part you underline, capable of interbreeding, defines a species which is a grouping ranking below a genus in that very definition?

38

Etrigan, since English is not your first language, I wonder if you know that “species” is both singular and plural. One species. Two species. The definition you gave is for a single species. It’s used as a singular noun, not a plural. The “capable of interbreeding” refers to organisms within a single species. It does not mean that multiple species are capable of interbreeding with each other.

39

I read all your posts. I understand your points of view. Some have valid points and made me think a lot. I agree with most of what you said. In this post, I want to add something that was missed since the beginning.

An ovule is surrounded by all kind of proteins. Some of them help the spermatozoid enter into it. While some others blocks spermatozoids that arent compatible. Please, tell me if I am wrong here, because this is the base of my hypothesis on this thread.

If a mutation occurs in one of the genes that create those proteins, it can do those things.

  1. Make the individual sterile.
  2. Make the individual incompatible sexually with its group. Implicating no descendants.
  3. Make the individual more sexualy compatible with its group
  4. no effect.
  5. something that I didnt think about. Again, please help.

Could the addition of mutations causing effect #3 cause, with time, by inadvertance an incompatibility with others from the same kind? You should note that those mutations causing effect #3 would be highly transmissible to other generations and very selective by nature.

What do you think?
Notice that I didnt use Genus or Species in this Reply or include a definition into my own words. I hope my english is good this time. And I am sorry if I offended anyone. I write here to find knowledge, not to insult people.

40

Could it? Yes

Must it? No.

There’s no particular reason why any kind of mechanism that has one kind of effect in one sort of organism need have a similar (or any) effect in a different sort of organism - there can’t possibly be any hard and fast rules for the question you’re asking, because the precise mechanisms by which fertilisation actually takes place aren’t the same across all of nature.

It seems like you’re searching for some kind of grand (or simple) unifying cause for speciation. I don’t believe there is one - in fact, I think it’s pretty plain that there can’t be one.

Speciation may be driven by any number of factors - including those that, initially, don’t alter the organism at all - for example, geographic separation can be the driving event - after which, the two divided populations are free to change in two different directions - and there’s no reason why these changes need affect the biological capability to cross-fertilise first - the next mutation that drives the two populations apart could be a mutation effecting a change in mating behaviour, dietary preference, etc - and you can end up with two species that, even if reintroduced to one another, don’t interbreed, even though they technically could.