For example, there are all types of dogs in terms of size, coloration, and shape. There are also dogs breeds who have particular skills such as scent dogs, hunting dogs, bird dogs, watch dogs, herding dogs, fighter dogs, etc., But these are not considered separate species, inspire of wider differences than those birds. Why are these not considered separate species of dogs? Is cataloging a subjective thing?
There is no clear, simple, universally accepted definition of a "species." But in general you won't get into too much trouble if you call a species:
"A population of organisms sharing a gene pool, which under normal circumstances do not interbreed with members of other populations, even if they have the opportunity, the physical ability and the genetic compatibility."
Thus:
- Lions and tigers are separate species. Hybrids (called ligers or tigons depending on which parent was the male) have been produced in captivity, but never in a natural environment.
- Wolves and coyotes are separate species. Lately they have been cross-breeding in Canada, but this is because there are so few wolves that they can't always find a mate, and probably also because some coyotes doubtless reason that if their offspring are larger than those of their pack-mates they might have a survival advantage.
- Wolves and dogs are a single species. While a wolf might regard a small dog as food, they often mate with dogs of their own size.
In fact, wolves and dogs are different enough to be called
subspecies. Dogs have smaller brains to accommodate the lower-protein diet of a scavenger, they have teeth that are more suited to an omnivorous diet than to ripping apart a wildebeest, and they are much more gregarious, even with "pack-mates" of other species. This is because of the changes in dog DNA since we have taken control of their breeding.
The various dog breeds regard each other as fellows and have no reservations about mating, even to the extent of finding creative ways to overcome a colossal size difference. People are astounded to find their Rottweiler, who they didn't even know was pregnant, whelping a litter of tiny half-Chihuahua pups, who have to be hand-fed because their mouths aren't big enough to hold the nipples. The other extreme is more dire, a Shih-Tzu bitch with a single half-Labrador puppy that must be delivered by Caesarean section, and also has to be hand-fed because she can't produce enough milk for him.
Although we can breed dogs and get all shapes, sizes and colors, and behaviors, we never get a cat or buffalo. We call everything we get a dog, period. Today, different color toe nails on a wild animal would be a new species based on the more detailed method of cataloging.
This is not true. You need to take a few more biology classes to expand your knowledge of genetics.
The ancient would still call that a cat.
The ancients knew virtually no science. They had no microscopes or computers so not only could they not analyze DNA, they didn't even know it existed. Today we classify animals, plants, fungi, algae, bacteria and archaea (the six Kingdoms of living organisms) according to their DNA.
Based on the ancient cataloging method, have we even witnessed an entirely new critter come from another species, all ready to start it own lineage?
There are two forces that drive evolution: mutation, which creates new genes, and environmental change, which alters natural selection to favor new genetic combinations. There was more radiation four billion years ago when the earth was young, so mutations occurred more often, but today the rate is much slower. The same can be said for environmental change, since the planet is more stable that it used to be and about the only major force to alter natural selection is the global warming and cooling cycle, which waxes and wanes a few times in the course of one million years.
I'm not a biologist and the only group of organisms I can claim any scientific knowledge of is animals. For the larger animals that generally breed on an annual cycle, it usually takes several tens of thousands of years for a new species to arise. The only mammal I'm aware of that evolved recently is the polar bear. Its speciation form the black bear began about 100KYA (KYA = "thousands of years ago") and completed somewhere around 10KYA when its teeth reached their current configuration. The only bird I know of in this category is the bald eagle. I don't know when it began to speciate from the white-tailed eagle but this speciation was also complete around 10KYA.
I sure it has happened during evolution but I am not sure if human witness records of live animals will show this. The ancient catalog was assumed to have been created because of that.
The technology of writing was invented during the Bronze Age around 5KYA. Before that there were no records except a few paintings, which were hardly detailed enough to distinguish two closely related species from each other.
Other phyla of animals reproduce more quickly and may go through several generations in a year. Perhaps new species of worms have arisen on our watch, but I've never heard of them being mentioned in the writings of the ancient Egyptians, Mesopotamians, Indians or Chinese.
Bacteria of course can reproduce several times in one day so perhaps they spin off new species all the time. But nobody even knew they existed until the microscope was invented.
The bottom line is that species (as well as all the higher taxonomic groups: genera, families, orders, classes, phyla and kingdoms) are classified by their member organisms' DNA and by whether or not they routinely breed with a group with only slightly different DNA--not by the color of their toenails. Pomeranians and St. Bernards are one species; their DNA is almost indentical and they will try valiantly to interbreed if you leave them alone together. Donkeys and zebras are two species; their DNA is considerably different and they will only interbreed with human encouragement--including not having any available mates of their own species around.
Obviously we don't have DNA from organisms more than a few thousand years old, so when paleontologists find a fossil they just have to do the best they can to classify it and decide whether it's a new species. We do a much better job of it with living organisms, or ones that haven't been dead for so long that the DNA in their bones has been replaced by minerals.
