How large is a cat's brain?
Cat intelligence
The brain of the domesticated cat is about five centimetres (2.0in) long, and weighs 25–30g (0.88–1.06oz).[1][2] If a typical cat is taken to be 60cm (24in) long with a weight of 3.3kg (7.3lb), then the brain would be at 0.91%[3] of its total body mass, compared to 2.33%[3] of total body mass in the average human. Within the encephalization quotient proposed by Jerison in 1973,[3][4] values above 1 are classified big brained, while values lower than 1 are small brained.[5] The domestic cat is attributed a value of between 1–1.71 relative to human value that is 7.44–7.8.[1][3] The largest brains in the Felidae family are those of the tigers in Java and Bali, of which the largest relative brain size within the panthera is the tigris.[6] It is debated whether there exists a causal relationship between brain size and intelligence in vertebrates. Correlations have been shown between these factors in a number of experiments. However, correlation does not imply causation. Most experiments involving the relevance of brain size to intelligence hinge on the assumption that complex behavior requires a complex (and therefore intelligent) brain; however, this connection has not been consistently demonstrated.[7][8][9][10][11]
Adaptation
The conflict between the size of the human foetal brain at birth, (which cannot be larger than about 400 cm, else it will not get through the mother's pelvis) and the size needed for an adult brain (about 1400 cm), means the brain of a newborn child is quite immature. The most vital things in human life (locomotion, speech) just have to wait while the brain grows and matures. That is the result of the birth compromise. Much of the problem comes from our upright bipedal stance, without which our pelvis could be shaped more suitably for birth. Neanderthals had a similar problem.