The Mirror test of Self-Recognition (MSR) has been the gold standard in the quest to find the self-aware. Unfortunately, only a handful of species have ever passed it. Some scientists have been surprised that the subject of their research fail, as their intuition informs them their animals must be close to that level of consciousness. Some, such as the pig don’t even have the excuse of failing to understand the nature of mirrors, since many of them can use mirrors to locate otherwise hidden objects. As such they are particularly interesting MSR failures, and worthy examples of why this test is so revered.
All mammals that actually do pass MSR, have shown greater cognitive talent, at almost every other task put to them, than any animal who has failed it. Furthermore, the tested intelligence of those species that do pass is in line with the proportion subjects in the species that pass the MSR. The gorilla looks to be near the baseline of this group, with only a few, fairly disputed. individuals ever passing. Based on other tests, pigs are about 150 IQ points, on my scale, below this level. Macaques, however, are only 40 points off.
Recently, it has been claimed that Macaques can be trained into passing MSR. If confirmed, it implies that self-awareness may reach slightly beyond the great ape group in primates.
Similarly, a minority of elephants pass MSR, but a new test suggest that at least 90% of elephants are self-aware.
Both of the above studies provide valuable extensions to this test. Unfortunately, for the cetaceans, the problem with MSR is the greater difficulty in testing limbless animals an aquatic setting. To my knowledge, the two genera that have passed it are the only two to be tested so far, though publishing bias may be a factor here.
Despite the suggestions of some, neither of the above-linked new tests provides a substantial reason to believe the MSR invalid.