Final answer:
The Bactrian camel evolved two humps to store fat as an energy source, an adaptation to the cold desert environments where it lives. In contrast, the dromedary camel, adapted to the Arabian Peninsula's climate, has one hump. These differences are the result of the separate evolutionary paths taken after camels migrated from North America.
Step-by-step explanation:
The Bactrian camel evolved to have two humps as an adaptation to its environment, which was different from that of the dromedary camel. Early North American camels migrated to various parts of the world, some reaching East Asia and others South America. Through evolution and natural selection in these new environments, descendants of the original camel ancestors developed diverse adaptations.
The two humps of the Bactrian camel are reservoirs of fat, which can be utilized by the animal as an energy source during long periods without food. This feature is particularly useful in the harsh, cold desert environments where food can be scarce. In contrast, the dromedary camel, with a single hump, evolved in the Arabian Peninsula, which has a different climate and ecological niche.
Therefore, the number of humps on a camel relates to the specific survival strategies that emerged through natural selection based on the differing ecosystems each camel species inhabited after they migrated from their North American origin.