Intelligence is a prominent topic of discourse today by scholars and the general population alike. Although, one of the most studied concepts and behaviors in humans, animals, plants, single-celled organisms, and technology, there is no singular definition of intelligence. The English word “intelligence” itself is derived from a Latin verb meaning to discern.

Although the evolution of human intelligence is thought to arise only in the last 2 million years, where Paleolithic traits of intelligence such as empathy, theory of mind, mourning, ritual, and the use of symbols of tools, great apes also began showing ability for cognition and empathy during this time. These ideas posed the question of what sets humans apart, in which philosophers have attempted to answer this by theorizing and creating instruments for measurement.

Many texts credit Francis Galton and Alfred Binet as the first to theorize and measure intelligence, but Herbert Spencer (1820-1903) was the first to create a substantive theory of intelligence. Spencer determined intelligence by the quality and quantity of adaptive associations made of an individual within their environment by making continuous external and internal adjustments. Spencer’s definition says that humans differ only in the complexity of their adaptive associations.

Since then, numerous other influential psychologists in the field of intelligence have attempted defined the term, but common elements discussed include planning, observation, attention, problem solving, learning, imagination, judgement, experience, abstract thinking, goal directed adaptive behavior, memory, creation, and assimilation.

It is often thought today that the measure of intelligence in higher organisms is derived from the complexity of neural connections within the cerebral cortex, which is distinctly large and complex in mammalian brains. Because of physical constraints, such as energy and processing constraints, the human brain is also limited in ways that other organisms, such as plants, single-celled organisms, and artificial intelligence is not. Therefore, perhaps the attempt of humans to define intelligence is limited by our own capacity.

Sources:

Princiotta, D., & Goldstein, S. (2015). Intelligence as a conceptual construct: The philosophy of Plato and Pascal. Handbook of intelligence: Evolutionary theory, historical perspective, and current concepts.