Pearl was a prolific writer of academic books, papers and articles, as well as a committed populariser and communicator of science.

Pearl's interest in statistical methods in biology began at the University of London, where he worked alongside Karl Pearson.

[6][7][8] In 1929, Pearl's friend William Morton Wheeler was about to retire as the Dean of the Bussey Institution at Harvard University.

However, Edwin Bidwell Wilson, a Harvard mathematician, was a critic of Pearl and did not believe he was fit for this position.

Pearl stated that he discovered the law of population that represented an S-shaped curve of growth, but Wilson thought that his data was insufficient and did not support this assertion.

This research had mistakes in its data analysis, so Wilson saw this study as an opportunity to attack Pearl and prevent him from becoming the new dean.

He wanted to use eugenics and biometry in medicine and public health in order to gain knowledge of human heredity.

He later became the director of a new Institute of Biological Research at Johns Hopkins in 1925 that was aimed at examining the genetics and environmental factors of disease.

This research institute combined biometry, genetics, and medicine to investigate the hereditary predisposition of tuberculosis and hypertension.

When conducting his research of these diseases, Pearl recorded the height, weight, handedness, measurements of different body parts, and physical descriptions.

[18] From 1927 to 1932, Pearl and his colleague Alan Meyer were important figures of one of the first birth control clinics in the United States called Baltimore's Bureau for Contraceptive Advice.

Pearl was a supporter of birth control, but had a more conservative and scientific approach when compared to the ideologies of Margaret Sanger.

He published works on animal behavior, population growth, food and prices, Jewish and Christian marriages, and vegetarianism.

Controversy continued when Pearl conducted a study on tobacco in which he demonstrated that smoking decreases longevity while drinking does not.

In 1908 Max Rubner observed that mammals of different size and longevity had equal mass specific metabolic output.

Pearl speculated that lifespan was limited by vital cell components that were depleted or damaged more rapidly in animals with faster metabolisms.

[21] Denham Harman's free-radical theory of aging later provided a plausible causal mechanism for Pearl's hypothesis.

His work demonstrating longer lifespans for flies with lower metabolic rates, also, raised the question of whether or not a similar phenomenon might be found in other species, including humans.

Thus, he became a mentor to John B. Calhoun, famous for his ecological studies of rodent populations and their possible importance for modern humans.