BLA: The Role of Hormones in Human Behavior

Arnold Berthold (1849)

An experiment demonstrating the role of hormones in animals. 

Hormone tested: testosterone

Animal tested: roosters

Prior Knowledge: Testosterone is a hormone that is responsible for:  

1. Development of male sex organs in an human embryo 

2. Secondary development of sex characteristics in males during puberty 

3. Sex drive throughout a male's life 

Arnold Berthold was the curator of a local zoo in Gottingen. He performed one of the first endocrine / hormone experiments in history.

Aim: Berthold aimed to identify the effects of testosterone in behavior through the castration of roosters

Subjects: six castrated roosters

Method:

- Quasi-experiment: a quasi-experiment is a study that has most of the characteristics of a normal study, but is unable to control some potential factors (such as age or sex of the subjects)

Berthold surgically castrated six healthy roosters. Castration refers to when the testicles are removed, which consequentially stops the subject's production of the hormone testosterone. Then, Berthold divided the roosters into three groups of two roosters.

• Group 1: control group - the roosters were kept capons 
• Group 2: the roosters were transplanted the testicles of another rooster
• Group 3: the roosters were re-implanted with their own testicles

Hypothesis: unknown

Although the hypothesis is unknown, because Berthold was trying to identify the roles of testosterone in male behavior, it is likely that he predicted that testosterone was involved in the male-specific behavior of roosters.

Results:

It was observed that the castrated roosters were less aggressive, less masculine, and had lost their interest towards hens. Berthold observed the castrated roosters to have a lesser tendency to crow, fight and mate.

The roosters that had reacquired testicles (group 2 & group 3) behaved normally, as any other uncastrated rooster.

Autopsies of the roosters in groups 2 and 3 revealed that the re-implanted testicles did not re-establish nerve connections with the rest of the body.

Conclusion:

Testicles release a hormone (testosterone) that influences aggression and dominant male behaviors.

Connection to the topic: hormones in human behavior:

- Berthold was able to identify that a biochemical released by the testes (i.e. testicles) was largely the cause of male characteristics and male behavior. This is because the roosters that were kept castrated (group 1) did not show any male specific behaviors and also had lost physical characteristics of male roosters - see image below. 

Group 1 / Group 2 / Group 3

Evaluation:

- Berthold only tested animals: validity of this experiment is only relative to the tested species

- ^ However, human males also have testicles and their endocrine systems also secrete testosterone, so the results may be highly relevant to the human male population

- Animals were harmed in this experiment

- No humans were harmed in this experiment

- The experiment was performed in the mid 19th century: outdated

- This study encourages the study of the endocrine system and hormones in relation to human behavior.