Final answer:
Anthropologists E. B. Tylor and Lewis H. Morgan were the first to develop the notion of unilineal evolution in the 19th century, suggesting a linear progression of societies. Their ideas were eventually challenged by Franz Boas who proposed that cultures evolve along unique paths.
Step-by-step explanation:
The concept of unilineal evolution was developed by the anthropologists E. B. Tylor and Lewis H. Morgan in the 19th century. Unilineal evolution is a theory that proposed societies progress linearly from a state of 'savagery' through 'barbarism' to the highest stage of 'civilization'. This perspective was characteristic of the evolutionary thought of the period and positioned Western societies at the pinnacle, justifying colonialism and social hierarchies.
The idea of unilineal evolution was later critiqued by Franz Boas, who argued that each culture develops according to its unique historical trajectory and in interaction with others, thus rejecting the idea of a single linear path of cultural development.