I know that there is already a similar thread to this one, however I like this one a bit better. Just want to say that Slevesques post was excellent unfortunatly perhaps somewhat misunderstood.
Hybridization: Note this is an
additive criteria
If an organism can hybridize with another organism -they are the same kind.
If that other organism can hybridize with yet another organism -they are all the same kind.
If that organism can...etc.
Note that if an organism can not hybridize with another organism this does not mean they are not from the same kind, this is because this ability may have been lost through mutations etc.
Both Mr jack's and greyseal's comments seem to show a common misconception that creationists don't believe that organisms change or that these changes can look quite big phenotypically. The point remains that genomes are degenerating (genetic entropy) and no new information arises.
Out of interest I came across this article
Molecular limits natural variation - creation.com yesterday as it was the featured article on the CMI website. It shows how large amounts of phenotypical variations can occur while maintaining the creation model. Kirschner and Gerhart’s facilitated variation theory is the main topic, which while being touted by evolutionists as strong evidence against ID it is actually the complete opposite. Note that the original authors believe that new "core processes" can arise naturally yet haven't been able to show how. Anyway, here is the abstract:
Darwin’s theory that species originate via the natural selection of natural variation is correct in principle but wrong in numerous aspects of application. Speciation is not the result of an unlimited naturalistic process but of an intelligently designed system of built-in variation that is limited in scope to switching ON and OFF permutations and combinations of the built-in components. Kirschner and Gerhart’s facilitated variation theory provides enormous potential for rearrangement of the built-in regulatory components but it cannot switch ON components that do not exist. When applied to the grass family, facilitated variation theory can account for the diversification of the whole family from a common ancestoras baraminologists had previously proposedbut this cannot be extended to include all the flowering plants. Vast amounts of rapid differentiation and dispersal must have occurred in the post-Flood era, and facilitated variation theory can explain this. In contrast, because of genome depletion by selection and degradation by mutation, the potential for diversification that we see in species around us today is trivial.
Sorry maybe a bit of a bare link, but if there is enough interest maybe we could open a new thread.
So in conclusion I think slevesques post showed that we are able to define a kind, however, have we carried out all the necessary research on every single organism to fully classify everything according to these criteria? No, not yet, but we are working on it, and what is wrong with that?