Final answer:
The "crabs" commonly transferred between people refers to the crab louse or pubic louse (Pthirus pubis), which is a parasitic insect that lives in pubic hair and feeds on blood.
Step-by-step explanation:
The organism commonly known as "crabs," which move from the hair of one person to that of another, is the crab louse or pubic louse, scientifically named Pthirus pubis. The crab louse is one of three types of lice associated with humans, alongside the head louse (Pediculus humanus capitis) and the body louse (Pediculus humanus corporis). These tiny parasites live in human hair, with the crab louse specifically found in pubic hair where it feeds on blood, leading to itching and irritation. As a common sexually transmitted parasite, the crab louse is a subject of health education and biology. Research on lice has provided insights into human evolution, such as dating our divergence from chimpanzees and supporting the 'Out of Africa' model of human migration through the study of genetic diversity in lice populations.