Was an 18th century thinker who believed that living forms changed in response to the environment yet still rejected the idea that one species could give rise to another.?

Yes, the 18th-century thinker you are referring to is Jean-Baptiste Lamarck. He proposed a theory of inheritance of acquired characteristics, suggesting that organisms adapt to their environments over time, but he did not accept the idea of one species evolving into another. Lamarck's ideas laid the groundwork for later evolutionary theories, despite his rejection of speciation. His concepts were eventually overshadowed by Darwin's theory of natural selection.