Why Intelligence Matters
Human intelligence varies from person to person — and that variation matters, because smarter people generally earn more money, enjoy better health, and live longer as well. But where does intelligence come from, and how is it built? Intelligence is the ability to understand the world, think with rationality, and use resources effectively to deal with the challenges of life.
Meaning of Intelligence
Intelligence is the ability to learn about, learn from, understand, and interact with one’s environment. It includes several specific abilities:
- Adaptability to a new environment.
- Capacity for reason and abstract thought.
- Ability to comprehend relationships.
- Capacity for original and productive thought.
- Ability to evaluate and judge.
Intelligence is cognition comprising sensory, perceptual, associative, and relational knowledge — the sum total of all cognitive processes including the coding of information, planning, attention, and arousal.
Formal Definitions of Intelligence
| Definition | Proposed By |
| “The essence of intelligence is to judge well, to comprehend well, and to reason well.” | Binet and Simon (1905) |
| “A person is intelligent in proportion as he is able to carry on abstract thinking.” | M.L. Terman (1921) |
| “Intelligence is a global capacity of an individual to think rationally, to act purposefully, and to cope effectively with the environment.” | Wechsler |
| “Capacity to utilize past experiences to solve new problems.” | Anstey (1966) |
A Multi-Factor Picture
Intelligence isn’t determined by any single cause — a combination of biological and environmental factors together shape how a person’s intelligence develops and expresses itself.
Heredity and Environment
Heredity provides the physical body with certain inherent capabilities, while environment provides for the maturation and training of the organism. In 1940, Newman concluded that variations in IQ were determined about 68% by heredity and 32% by environment. Since heredity can’t change over an individual’s lifetime, any variation in IQ during that lifetime is attributable to environment — improved nutrition, health, and stimulating situations can all account for such change. The environment of children aged 2 to 4 appears especially critical, since this is normally when a child learns language; better homes, schools, medical facilities, and less economic discrimination all provide the means for achieving a mentally able population.
Age
A person who is bright or dull in childhood tends to remain bright or dull throughout life. Growth in intelligence can continue through the early twenties — a person achieves maximum IQ at about 20 years, remains stable for roughly ten years, and then IQ tends to decrease. Some abilities remain constant while others decline, tied to declining physical efficiency. It’s also observed that more intelligent people show more rapid mental growth and continue developing longer than those who are mentally less able.
Race and Nationality
There is no prominent evidence to show that race is a factor in determining intellectual level. Differences that exist between families are due to environment, and differences observed between races are also mostly due to differing opportunities for training in early years. All the evidence indicates little or no difference in inherited intellectual capacity due to race — the idea of inherently ‘inferior races’ is simply not true.
Culture
Culture determines the degree of a person’s attitudes and abilities, which in turn shapes intelligence.
Health and Physical Development
Physical and mental health is closely related to one’s ability to achieve desired outcomes. A person with delicate health may not possess enough energy to engage in mental activity to the extent needed for success. Physical defects — such as incomplete maturation of brain cells, sensory impairments, and physical handicaps — can interfere with observable intelligent behaviour. Diseases also affect intelligence, and unfavourable health more broadly affects an individual’s mental status.
Sex
It’s a popular belief that boys are supposed to be more intelligent than girls — but research studies have shown no significant difference between the sexes on average. Girls tend to show slight superiority in language, memory, and appreciation. Where differences in intelligence do appear, they’re caused partly by environmental conditions rather than sex itself.
Social and Economic Conditions
Home plays a significant role in a child’s early developmental years, and home conditions influence behavioural attitudes. The financial status of parents, neighbourhood, and broader environmental conditions also affect intelligence — but through the mechanism of socioeconomic status, not through any direct biological pathway.
Seven Factors at a Glance
| Factor | Key Takeaway |
| Heredity & Environment | IQ variation ≈ 68% heredity, 32% environment (Newman, 1940); environment drives lifetime change since heredity can’t. |
| Age | IQ rises until ~20, plateaus for ~10 years, then declines; more intelligent people show longer, more sustained mental growth. |
| Race & Nationality | No credible evidence race affects inherited intellectual capacity; differences trace to environment and training opportunity. |
| Culture | Shapes the attitudes and abilities that feed into intelligence. |
| Health & Physical Development | Poor health, physical defects, and disease can all interfere with intelligent behaviour. |
| Sex | No significant overall difference; girls show slight superiority in language/memory/appreciation, attributable to environment. |
| Social & Economic Conditions | Home environment and socioeconomic status shape intelligence development, especially in early years. |
