Many scientists agree that the only taxonomic category that is real is species. Species are a collection of populations that can and do interbreed with one another. All other taxonomic categories are artificial human constructs. That means organisms do not sort themselves into the same genus, family, order, class,...
Best answer: Many scientists agree that the only taxonomic category that is real is species. Species are a collection of populations that can and do interbreed with one another. All other taxonomic categories are artificial human constructs. That means organisms do not sort themselves into the same genus, family, order, class, phylum or kingdom in nature. Because these taxonomic categories are artificial, they can change from one person to another.
That means person A can consider 2 different animals to be the same genus, but person B may consider them to belong to 2 different genus, or even 2 different family or order. The categories of kingdom phylum etc. were invented by Linnaeus, who was a creationist. Since Darwin proposed evolution, evolutionary biologists find that they can keep the Linnaean system and apply it to evolutionary relationships. Linneaus group organisms into the same genus if they are very similar but are different species. He separates 2 species into 2 different genus if he finds them a bit more different. Exactly how different is not defined. In general of course, 2 different families should be more different from each other than 2 different genera. That means organisms of different kingdoms are the most different from one another. Evolutionary biologists realize that sometimes similarities are due to convergent evolution, meaning organisms that are not closely related to each other often evolved to be very similar because of similar adaptations to a similar environment. OTOH, two close relatives can be very different if they have evolved a lot of differences over a short period of time.
The job of the taxonomists is therefore to figure out which similarities are due to common ancestry and which are due to convergent evolution. Only animals that are close relatives are grouped into the same category, or taxon. For example, the chimpanzee and the bonobo are close relatives that are very similar to each other, so they are grouped into the same genus. In contrast, the gorilla, although a close relative to the chimp, is classified as a different genus than the chimp because of morphological differences, but they are both placed in the same family because they are more similar and closely related to each other than they are to species in a different family, such as the Old World monkeys. The lesser apes such as the gibbons are also placed in a different family than the great apes for the same reasons.
Even though the thylacine is very similar to the wolf, they are not placed in the same genus, family, or even the same order because scientists find that they are not close relatives, despite their similarities. They classify the thylacine in the same order as marsupials but in a different order than the wolf. As Darwins put it, organisms that share the same ancestor are first grouped into a particular taxon, for example Class Mammalia is the taxon for all mammals because they share a common ancestor. After that, Mammalia can then be split into different subcategories based on ancestry and differences. Ancestry comes first of course. Therefore thylacines and wolves are separated into different orders because thylacines share a more recent common ancestor with other marsupials than they do with the wolf. Orders are then split into different families based on ancestry and morphological differences. Although wolves share a common ancestor with bears, seals, weasels, skunks, and raccoons, wolves are placed in a different family than bears, seals, weasels, skunks and raccoons because they are very different morphologically. Each family however, can only include organisms that share a common ancestor.
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