Transferability of animal test results to humans

3. When there aren’t enough volunteers

In addition to basic ethical considerations, one of the reasons researchers use animals for experiments is because humans are not always ideal subjects for investigating biomedical issues. Organisms that reproduce quickly, such as zebrafish or mice, are more suitable, particularly for researching hereditary diseases.
There are often insufficient human volunteers for scientists to be able to research the genetic, physiological or anatomical causes of many rare diseases. This means that animal experiments are needed to gain an understanding of the disease or to develop APIs to treat it. But why are experiments involving animals even suitable in the first place?