Actually they don't, since they are a remnant of the pre-Darwin Linnean taxonomy which was based solely on morphological traits. So, for example, two of the defining traits of a mammal are hair as a skin covering during at least part of its life and milk glands for nourishing the newborn. Since, I possess those traits, it is correct to define me as a mammal.
Darwin introduced the idea that shared morphology could be explained as an effect of common ancestry. So the categories work in an evolutionary context too, though not as well. As more emphasis has been placed on genetic clues to actual inheritance, and taxonomy has been becoming more cladistic, the old categories are not as important. Some strict cladists advocate doing away with them altogether as they give a false sense of hierarchy. The terrestrial vertebrates, for example, are all given class status, even though some are descendants of others--which ought to put them in a lesser ranking in the Linnean system.
Exactly, along with 6 billion+ other individual creatures. So the species is a collectivity. There is no species of 'gluadys' because 'gluadys' is not a collectivity or even potentially a collectivity.
Sure, if the human species dwindles in number until only one is left, that individual will still be human, but that is hardly relevant to the issue. That individual, qua individual, will still not be "species x" but simply the last remaining exemplar of what was once a population of similar individual creatures inter-related by procreation and inheritance.
Sure, and in doing so, I am naming the collection of individual creatures to which it is related and which it resembles because of that relatedness. If someone, seeing one of my cats, asked "who is that?" I would say "Makheer" or "Louis" or "Lacroix" and these are not species.
Right, but they are certainly not assuming that the living dinosaur of which this is a remnant was the only creature of its kind. They give it a species name because the existence of one fossil implies the former existence of a group of individuals of the same species.
In short, none of these examples removes the idea that a species is, by definition, not an individual qua individual, but a category of individuals grouped together through reproductive affinities which assure a commonality of morphological character traits.
No, the definition of species doesn't imply the origin of species.
I am not certain what you mean by "genetic changes in groups". Genetic changes can only occur in individuals. But, because they are genetic, they can be inherited. Of course, it follows they can only be inherited by descendants of the individual in which they occurred. So, right away, in the next generation, there will be two groups within the species: a small one consisting of those who inherited the genetic change from one of their parents, and a larger group which did not.
If, at some point, these groups are separated from each other, the group with this change (and others which are also never passed on to the other group due to the separation) could become reproductively isolated from the other group and so become a new species.
You are partially right. Unless and until the separation involves reproductive isolation, it is not the same thing as the generation of a new species. If the barrier keeping the groups apart is geophysical the division is of one species into two groups--not the first appearance of a new species. However, the geophysical separation permits different traits to appear and spread in each group without affecting the other. And if members of the two groups are brought together again, they may be unwilling or unable to successfully mate with each other. This has been verified experimentally several times. And it appears to happen in nature as well, as in ring species or rapid radiations such as observed in chichlid fish.
So while separation of some sort is essential to speciation, depending on the nature of the barrier, it is not identical to speciation. What non-reproductive separation does is provide an incubator for the development of reproductive isolation. Speciation is the development of reproductive barriers between two groups that were originally one species.
Of course, sometimes it happens that the form of separation involves a barrier to reproduction right from the beginning. So then, separation and speciation occur concurrently.
Possibly, but this creature still has to be of the same kind as its parents and siblings.
Actually, it is the reverse. What one needs to be certain of is that the process of evolution is taking place, that the mechanisms which permit a species to diversify and change form over time really do that.
If evolutionary change doesn't happen, there is no historical narrative possible, no matter how tempting it may be to invent one.
But since evolutionary change does happen, the historical narrative is an inevitable consequence. Of course, we often don't know the details of the narrative. That is a matter of ongoing research. But it is the process of evolution that tells us there is a historical narrative of evolution that is potentially traceable all the way back to the last universal common ancestor. The history doesn't prove evolution happened. Evolution proves the history happened.
Sure, as long as he is by-passing the normal modes of reproduction. But that is not the scenario you have been presenting till now. You have been uniting the reproductive process and God's creation of individuals as simultaneously an act of nature and an act of God.
Yes, but that one individual (a bacterium, for example) is still potentially part of the group that will be its descendants or the remnant of the group that was its ancestors. It is not a species qua individual.
If it is still reproductively compatible with the group it came from, then it is likely still the same species, or a close enough species to still hybridize from time to time. This is why speciation is gradual. The development of reproductive barriers doesn't happen all at once with one individual. The two groups separate (reproductively) over a period of several (sometimes hundreds) of generations.
But the distinct individual creation which is the ancestor of a new species is not yet a different species than the other individuals of its own generation. The differentiation of its descendants (or those of them that carry its unique species traits) from the descendants of its siblings and neighbours happens gradually as for one reason or another, they cease to mate (or even to be able to mate) with each other.
Right. That's why it takes time for a new species to emerge from another. There is seldom a key moment where you can pinpoint when two sub-species become two species.
Ah, so we have a classic Platonic realist here. Of course, many in the church have taken that stand. And many, like myself, prefer Aristotelian nominalism (a la Thomas Aquinas). The realist/nominalist controversy over the nature of form was one of the most intense debates of the High Middle Ages. And I doubt it was ever resolved, though few would take the realist stand today.
Upvote
0
