The Creationist Challenge - Can You Identify Kinds?

None of this is of any relevance, though. Domain, class, family and all the other taxanomic levels are purely arbitrary human inventions. They have no existence in the external world. They are far less clearly defined than the concept of 'kind'.Imagine that some geneticists sit down somewhere and do a detailed analysis of Canid genomes. They conclude that Canids share a common ancestor 6 million years ago.Would it make sense from this to conclude that Felids all share a common ancestor 6 million years ago, as do Ursids, as do Discoglossid frogs? After all, Canids are a family, and if it's true of one family, mustn't it be true of all families?No, of course it mustn't. This reasoning is obviously nonsense. Determining that one particular x is y doesn't determine that all x's are y. This is even more so when 'x' is a vague and wishy-washy invented concept. If there really were such a thing as biblical kinds, and Canidae was equivalent to a kind, there's absolutely no reason to expect that 'kind' should therefore correspond to the invented category 'family'.

Sorry for my slow reply - been very busy in work. Others have mostly answered this, but a quick couple of thoughts.If you look at the ranks assigned to different groups, it's clear that they're not consistent. There are amphibian genera that have been around since the Palaeocene, about 60 million years ago, while many mammal genera are less than 10 million years old - Gorilla, Pongo and Homo probably all diverged from each other within the last ten million years.Now, it's possible of course that this is because these groups haven't undergone evolutionary change at the same rates. Maybe the great apes have had a burst of sudden diversity, while mudpuppies haven't changed much for the last 60 million years. If this were true, though, it creates a clear problem for the idea of objective ranks, though, if we're trying to fit it into a framework that shows relationships.Imagine we have one genus, with four species: A, B, C and D. A and B are sister species; C is the sister to the clade A+B, and D is sister to the claide C+(A+B). Over a few million years, B experiences intensive selection pressure and undergoes rapid morphological change, while the remaining three species are relatively static.At the end of this process, B is now sufficiently divergent from A to justify its own genus, in order to be consistent with how we classify genus. But, if classifications are supposed to represent relationships, C and D must also be given different genera to A, otherwise the genus becomes paraphyletic with respect to B. So, we wind up with four monspecific genera, three of which (A, C and D) are all more similar to each other than the objective standard of difference we've agreed upon to define the idea of 'genus'.

Species is also pretty arbitrary, since there is no single definition of 'species'. The most commonly mentioned one, the Biological Species Definition, is inconsistently applied where it can be applied and, for the majority of species, cannot be applied at all. Most species reproduce asexually.In a specific context, you can define 'species' and say you're using it non-arbitrarily. When we're making grand comparisons across the whole tree of life, though, species often doesn't mean the same thing and is not an objective classification.