I was wondering how Darwin’s theory explains the apparition of new genus
since the definition of a new genus is to not being able to reproduce with its original kind, and Darwin’s theory is base on reproduction and natural selection.
Darwin's answer that a small group separated from the herd explain new species, but it doesnt explain the creation of new genus, on the contrary, in my opinion a group of lesser individuals will limit the probability of an individual to find a compatible mate.
Is that a hole in Darwin's origin of the species or is there something that I am missing?
All populations change over time. But the change is random. If nothing interferes with mating, incompatible changes are weeded out and the population shares roughly the same characteristics. If, however, part of a population gets split off from the rest of the group, the rest of the group can’t act as a sort of check on the changes. Now you have two groups of whatever animal randomly changing independently of each other. Eventually, enough changes happen that if you reintroduce a member of one of the groups to the other group, they can’t reproduce. And a new genus is born.
edit: I should add that I am not a biologist and I have not been trained in evolutionary theory. This is my understanding based on various books and discussions I’ve read.
Isolation of subgroups leads to seperate paths of evolution. The groups eventually have enough independent changes to become very different. I’m not sure where the ‘small group’ part comes in. If a small group becomes isolated, and does not flourish, it’s more likely to become extinct than to evolve.
You are missing two things. First, what a genus is, and second the time scales involved.
Genus are simply groups of related species. There is no hard definition of which species to include in a genus. They are just useful groupings agreed on by most biologists. Biological groupings are not based on hard tests. Even groups that we consider separate species have been known to inter-mate. There are very few hard boundaries. The only thing that needs to be true about a genus is that all member species of a genus should be more closely related to each other than to species outside their genus. You could include all foxes in the Cannis genus, but it would make no sense to only include some foxes and remove wolves.
As to scale, you need to remember that evolution does not stop once two populations have diverged enough to make two species. Take a proto-mammal living 65 million years ago. After a mass extinction of dinos, it spreads in both territory and niches due to less pressure from predators. Different populations become genetically isolated and speciate. Those species continue to spread and branch into more species. Given enough time, one population of proto-mammals will split up enough to give us all the mammals currently alive, from blue whales to shrews.
A new genus is created when taxonomists decide to create one. It’s really as simple as that - a genus is a completely artificial grouping, not a natural one.
It sounds, however, like you’re actually asking about species rather than genera, which, to be honest, Darwin really didn’t address in his On the Origin of Species, etc., despite the name.
New species arise, generally speaking, when a sub-population becomes separated from the parent population, and the two diverge genetically. When there is no further genetic cross-over between the two populations, it is generally said that the two are now separate species (the daughter population usually being considered the ‘new’ species).
Phylogeny is the study of how organisms are really related to one another.
Taxonomy is a system of classification imposed by humans, to categorise extant organisms into nested groups.
To a certain extent, these two disciplines agree - because organisms that share a recent common ancestor tend to be more similar than those that only share a distant common ancestor.
If we take the OP’s question in terms of phylogeny, it’s like saying that we know how the tips of the twigs on a tree can divide, but we don’t know how the main trunk of a tree can be forked.
In fact, it’s the same thing. The fork in the trunk of a tree is just a twig-branching event that happened a long time ago. Likewise, the divisions between species are happening now - the divisions between genera, families, phyla, etc (in terms of phylogeny, not just nomenclature) represent speciation-type divergences that happened in the past.
To illustrate the point on taxonomy, Linnaeus originally put all cats. large and small, into Felis.. Later scholars split out Lynx, Leo, Panthera, Leopardus, etc. Then there was a counter-movement to lump again, so that when I learned mammalian taxonomy there were only four genera:
[ul][li]Panthera, for the great cats.[/li][li]Neofelis, for the clouded leopard[/li][li]Felis, for the small cats up to and including the cougar[/li][li]Acinonyx, for the cheetah, considered truly aberrant from all other cats great or small[/li][li]Lynx, was recognized by a minority of respected mammalogists for the lynx, bobcat, caracal, etc., but most scholars included them within Felis. [/ul][/li]
Today, if you look at the more scholarly posts from the cougar thread or the Wikipedia article on Felidae, there are at least eight recognized and accepted genera, and quite possibly many more. This is based in large part on genetic analyses not available 30 or 40 years agho.
The latter two changes are within my lifetime – and I just became eligible for Social Security.
Taxonomy comes down to a matter of opinion because of evolution, I really wish people would stop trying to use the fuzzy lines as ‘evidence’ against it.
Working out where a species began can be like being given a colour spectrum, and having to decide exactly where the red ends, and the orange begins- red and orange are clearly different, but there’s no one point where it changes.
Species is the only level of classification that has any sort of biological reality, and even then, it’s really fuzzy at times. Genus on up are purely artificial labels of convenience to give scientists a shortcut to describe how closely related two species are.
So if you understand speciation, you understand, uh, genusiation? If you don’t, I don’t have time to spell it out for you. Google’s great for that kind of thing, as are the more patient members of the SDMB.
I agree that nature wasnt create for man to classify. It is difficult to separate species. Lots of discussions can be created just to classify one animal. But taxonomy isnt the question. Or is it? mmm
My definition of genus that I would like to keep in this forum is the innability to reproduce between two individuals at the level of the spermatozoid and the ovule. Even if we introduce a spermatozoid of a mouse with an ovule of an elephan, it wont work.
Inner Stickler said : " Eventually, enough changes happen that if you reintroduce a member of one of the groups to the other group, they can’t reproduce."
This is good for all genes, but is it for the (in)compatibility reproducing genes? Two groups separated will evolve in many ways, some might be physically (size) incompatible when they are reunited millions of years later. But they might still be geneticaly compatible.
Once a gene of sexual incompatibility appears in an individual, by definition, he wont be compatible with his group and will go extinct with no descendants to transmit his new incompatiblity gene. This looks logic, but I must be wrong somehow. If that phrase was right, there would be only one genus on Earth. So, tell me, how can a new genus be born?
That sounds like you’re talking about “species” and not “genus.”
It doesn’t happen with an individual, but gradually over many generations with two groups that were one species, then become separated. At any time, all the fertile members of either one of those groups can mate with any of his own group, but over many generations, an individual from one group will no longer be able to mate with a member of the other group.
Well, as others have pointed out, what you’re talking about is speciation. Genus has nothing to do with it.
As far as incompatibility goes, we’re talking absolutely minute changes over extremely long periods of time, not just thousands of years but tens of thousands, hundreds of thousands and thousands of thousands.
Replies focus on geographic separation. Perhaps cases like Darwin’s finches of the Galápagos should be mentioned, where a single isolated species developed into multiple species (indeed multiple genera) not based on further separation in space, but to exploit dietary niches.
If you’re talking about Genus, then you’re talking about taxonomy. Genus is a taxonomic term - it’s a synthetic grouping of similar species, formed on the notional basis that they have something in common that other species, outside of the Genus, do not. In many cases, this loosely correlates to recent common ancestry.
So you’ve invented your own definition of the term?
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.
Taxonomy is quite an ordered, nested, levelled structure. The reality of common ancestry is not. Speciation produces a branched phylogenetic tree, but there is no particular reason why that tree should have any kind of categories of division;
There are divergences that are happening now - speciation
There are divergences that happened at any point in the past - so we can theoretically group species by their recent common ancestors (which is kinda like genus, but not necessarily), but we can also group them (or group those groups) by their more distant common ancestors, which is kinda like other levels in taxonomy, but not necessarily.
English isn’t your first language, is it? That would explain your idiosyncratic phrasing. If you want to discuss almost anything, first you need to learn and use the commonly accepted terminology in the field, which will help those who do understand the discipline to explain the concepts.
If you start making up your own definitions and arguing from them, you will never learn anything. In this instance, once you learn what the standard terms are we can better discuss how your impressions may be inaccurate.
There is no such thing as “a gene of sexual incompatibility”.
You’re thinking that one species becoming incompatible with another is an abrupt on-time event – like someone throwing a switch. But rather it’s a gradual process. 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.
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.