The most archetypical rat worldwide is the black rat, scientific name Radis Radis, followed closely by the brown rat, scientific name Rattus Rattus, followed closely by the brown rat,

scientific name Rattis Norvegicus. These two rats are sometimes referred to as old-world rats,

or true rats, in part to distinguish them from other small mammals that are rat-like, and which have rat in the name sometimes,

but which are nonetheless not technically rats,

like the North American pack rat or wood rat,

the broadly defined collection of species referred to as the kangaroo rat,

and the bandicoot rat,

which is a rodent most commonly found across Asia. Also superficially

similar to true rats, the brown and black rat, mice are what's called a sister group

to rats. A relationship we were only able to establish for certain after a 2009 study called

rodent philogony revised, analysis of six nuclear genes

from all major rodent clades. This sister grouping means that rats and mice are each other's

closest biological relative, and it's estimated that they evolutionarily separated from each other,

meaning they diverged into separate distinct species from a common ancestor

about 12 to 24 million years ago.

Which is interesting, considering that it's thought that the primate lineage

only separated from the rodent lineage, again we split from a common ancestor,

about 80 million years ago. One of the more visually distinctive traits of the rat,

its often longish, pinkish tail, is thought to serve three main purposes. First is that it allows

the rat to thermoregulate, to adjust its temperature,

by dissipating heat, by carrying blood from the rest of its body, especially the most active

and warm portions of the body, to the vein-dense tail, where the heat can then radiate outward from

...