1) what term did lamarck use to explain how new species emerge

2) what term did Darwin use to explain how new species emerge

Jean-Baptiste Lamrack had a theory known as "Theory of Inheritance of Acquired Traits". In this, an organism's physical traits would be modified by continuous usage and these changed traits would be passed down to the offspring.

Charles Darwin had the theory of evolution, or "Survival of the Fittest". He believed that all organisms possessed their own set of natural traits, and the environment would put pressures that would allow organisms with a certain trait to survive while the others would die out.