Confirmation bias in science

“…if the only tool you have is a hammer, everything begins to look like a nail” (Maslow, 1969)

Confirmation bias is the tendency to search for, interpret, or recall information in a way that confirms one’s beliefs or hypotheses (wikipedia).

The History of science is replete with examples of confirmation bias. The earth was thought to be flat for thousands of years until sailors not falling off the edge and the advent of astronomy showed the theory to be false. Philosophers of antiquity thought the Sun revolved around the earth (Geocentricism) until Galileo’s telescope showed the theory was false and the opposite true (Heliocentrism).

The process of showing and attempting to show theories to be false by experiment was invented by philosopher Sir Karl Popper and is detailed in his landmark text ‘The Logic of Scientific Discovery’. It is the cornerstone of good science. If theory and experiment disagree, the theory is falsified; if theory and experiment agree, the theory survives. Theories that have survived years of experiment without falsification are called laws. Examples include the laws of physics, the laws of chemistry and the biological laws of evolution through natural selection and Wolfe’s law that form follows function.

Laws act as trustworthy filters through which information and new theories can be judged. If theories violate natural laws, they are false.

natural laws

Modern running-related examples of confirmation bias include the belief that cushioned, structured shoes are necessary for running; that running injuries can be treated with yoga-type stretching; and that high-intensity-intermittent exercise like Cross Fit is the best way to health and fitness for humans.

  • Physics and evolutionary biology show the shoe theory to be false. The forces of running do not simply go away and we know that natural selection shaped the human body to specialise at distance running without added equipment.
  • The theory that stretching helps running injury is also falsified by both the physics and evolutionary biology laws. Stretching alters the stiffness of tissues affecting their ability to withstand and control forces. Evolution selected soft-tissue properties that stabilised joints (ligaments) and stored elastic energy (tendons), stretching adversely affects both properties.
  • The recent suggestion that high-intensity-intermittent exercise is the best way to achieve health and fitness is falsified by fundamental principles of biological chemistry and evolutionary biology. Humans are endurance (aerobic) animals that evolved in a calorie-deficient environment with low-level but prolonged daily activity. Anaerobic metabolism is inefficient, quickly depletes energy stores, produces damaging and inflammatory by-products and is a mismatch with our evolutionary heritage.

Stick to the laws

In the sea of information of confirmation bias, trust only that which agrees with the fundamental laws of physics, chemistry and evolutionary biology. By the most rigorous application of science, they have never been falsified so are the only principles we can trust.


Maslow, A (1969). The Psychology of Science: A Reconnaissance. Boston: Gateway

Popper, K (1980). The Logic of Scientific Discovery (10th Ed). London: Hutchinson