There have been many attempts over time to explain the mechanism behind the evolution of living organisms. two of the better known theorists include charles darwin and jean baptist lamarck. how would lamarck's explanation of the evolution of long necked giraffes differ from darwin's explanation?

Lamarckism is the idea that an organism can pass on characteristics that it has acquired during its lifetime to its offspring while Darwin believed that the desires of animals have nothing to do with how they evolve, and that changes in an organism during its life do not affect the evolution of the species.

Lamarck believed that giraffes originally had short necks, and when they couldn't reach the leaves in the high tree tops they stretched their necks and acquired longer ones which then they passed on to their offspring. 

Darwin believed that originally some giraffes has short necks while others had long. And when the short-necked giraffes could no longer reach their food they would starve. Resulting in only the long-necked giraffes to live and continue on the cycle of reproducing long-necked giraffe. Thus being called natural selection.