“Biological Limits to Information Processing in the Human Brain”, 1995 (; backlinks; similar):
The human brain is a product of Darwinian evolution and as such it has evolved from a set of underlying structures that constrain its ultimate potential. A combination of the physical size of the dendrites, axons and the associated blood vessels, and therefore their related signal space, limit the amount of information the brain can effectively store and process.
By analysing the inter-relationship of the key constraints we have shown that:
The maximum effective diameter of the human brain is around 10–20cm.
The interconnectivity of neurons is dictated by thermal, volumetric, signal processing and transmission constraints, and is not, a priori, a key system parameter for intelligence.
Intelligent signal processing inflicts an order of magnitude time constraint on an optimized structure.
Thus we contend that the human brain is at, or near, the capability limits that a neuron-based system allows. This implies that our future evolutionary potential is limited and that, as a species, Homo Sapiens may be near the pinnacle of achievable intelligence using current cellular carbon technology.