Final answer:
Darwin rejected the 'type' concept of species because it contradicted his observations of species variability and the evolution of species over time due to natural selection and geographical separation.
Step-by-step explanation:
Charles Darwin rejected the "type" concept of species because it did not accommodate the variability and adaptability within species that he observed in nature. In his seminal work, On the Origin of Species, Darwin proposed that species are capable of evolving over time due to natural selection, where random changes in their physical and mental structure might confer advantages or disadvantages to their survival. This view clashed with the then-prevalent belief in unchanging 'types' of species. Furthermore, Darwin's idea of allopatric speciation highlights that species separated geographically over time can evolve into distinct species, which contradicts the static 'type' concept.
It is also notable that Darwin disagreed with Lamarck's notion that acquired traits could be inherited, and with the absence of knowledge on genetics during his time, he was unable to explain the mechanics of how traits were passed from one generation to the next. Instead, Darwin focused on the evidence of evolution through natural selection and adaptation, deducing his theories from his observations during his voyage on the HMS Beagle, especially his studies on the Galapagos Islands.