Final answer:
Head lice originated before body lice, corresponding to the divergence of the human lineage from chimpanzees six million years ago. Body lice are more dangerous as they transmit diseases and adapted to live on clothing, reflecting a significant evolution after humans began wearing clothes around 170,000 to 190,000 years ago.
Step-by-step explanation:
The evolutionary history of lice associated with humans is intricate and reflects the changes in human habits and habitats. The common ancestor of head lice and body lice diverged in line with the human lineage's separation from chimpanzees approximately six million years ago. However, head lice came before body lice.
Body lice are considered more dangerous than head lice because they have adapted to live and lay eggs on clothing, which can lead to more significant health risks. They can spread diseases such as typhus, trench fever, and relapsing fever. In contrast, head lice do not transmit diseases but can cause itching and discomfort.
Research indicates that humans lost body hair about a million years ago but did not start wearing clothes until around 170,000 to 190,000 years ago. This delay allowed for the adaptation of head lice into body lice, which then evolved structures to cling onto clothing instead of hair. This change has necessitated the study of clothing practices and the implications for disease transmission amongst humans.