Final answer:
The concept least applicable to the origin of new species is the inheritance of acquired characters, as it is not supported by modern evolutionary science unlike factors like variations, genetic drift, and isolation.
Step-by-step explanation:
The origin of new species, a core concept in evolutionary biology, can be attributed to various mechanisms. Within these, variations, genetic drift, and isolation are all recognized factors that contribute to the formation of new species. However, the inheritance of acquired characters, a concept that suggests that traits acquired during one's lifetime could be passed to offspring, is largely discounted by modern evolutionary science. This idea, often associated with Jean-Baptiste Lamarck, has been superseded by the understanding of genetics and the process of natural selection.
For example, genetic drift can dramatically alter the genetic makeup of a small population through events like the bottleneck effect or the founder effect. Isolation, such as in allopatric speciation, can lead to species divergence. Variations are essential for natural selection to act upon, allowing the most adapted individuals to survive and reproduce. Therefore, the correct option that is least applicable for the origin of new species would be the inheritance of acquired character.