Rat

Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most important of which to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus. Many members of other rodent genera and families are also referred to as rats, and share many characteristics with true rats.

Rats are typically distinguished from mice by their size; rats are generally large muroid rodents, while mice are generally small muroid rodents. The muroid family is very large and complex, and the common terms rat and mouse are not taxonomically specific. Generally, when someone discovers a large muroid, its common name includes the term rat, while if it is small, the name includes the term mouse. Scientifically, the terms are not confined to members of the Rattus and Mus genera, for example, the pack rat and cotton mouse.

Intelligence

Because of the ability to learn, rats were early on investigated to see whether they may exhibit general intelligence like larger or more complex animals. A 1929 study did not find a g factor,^[9] nor did a 1990 work;^[10] a 1935 study^[11] did:

Robert Thorndike, for example, provided strong evidence for g in rats by the use of a variety of tests such as mazes, problem-solving tasks, and simple avoidance conditioning (Thorndike 1935). Performances tended to correlate across tasks, with stronger associations found between mazes and problem-solving than with simple avoidance tasks. Thorndike (1935) also reviewed a dozen earlier studies which also suggested that the highest correlations are found between more complex problem-solving tasks. However, it should be noted that there were other contemporary studies that found split or near zero-order correlation matrices for other populations of rats across cognitive batteries (see Royce 1950).

—^[12]

In 1993, Anderson measured rat performance and factor analysis produced a g, and also correlations with rat brain size^[13] (like inhumans and primates). Locurto & Scanlon 1998,^[14] Matzel et al. 2003,^[15] Matzel et al. 2004,^[16] Kolata et al. 2009^[17] and Matzel et al.2011^[18] replicated the factor (but did not investigate brain size); 2003 Locurto et al., 2006 Locurto et al. in contrast found their factor analysis giving 4 factors rather than 1.