Literature Notes Octopus is invertebrates. They should not have spinal cords, but they have eight! And they have protocadherins three times more than humans.
Literature Notes encephalization quotient (EQ) is superior to brain-to-body mass ratio because there are parts of the brain that do not correlate with cognitive function. Human brain is superior to other mammals because of the neuron packing density (NPD) and the gyrification of the cortex (making the cortex high in volume).
Literature Notes Suzana Herculano-Houzel debunked the beliefs that our brains were special because we have more neurons and expend more energy than would be expected for our size. Turns out, the neurons in our cortex was just 20% of all our brain's neurons despite having 80% of the total brain mass.