Final answer:
Jean-Baptiste Lamarck's idea that traits acquired or lost by an organism during its life due to use or disuse could be passed to offspring is known as the inheritance of acquired characteristics or Lamarckian inheritance, and is a part of Lamarck's theory of evolution.
Step-by-step explanation:
One of Lamarck's key ideas, which suggested that parts of organisms used frequently would become bigger and stronger and those not used would disappear, is known as the inheritance of acquired characteristics or Lamarckian inheritance. This concept is a component of Lamarck's theory of evolution, which proposed evolutionary change results from the abilities of organisms to adapt to their environment through the use or disuse of different traits. For example, Lamarck used the giraffe's long neck as evidence, theorizing that it developed over generations as a result of the ancestors stretching their necks to reach higher leaves and then passing the trait on to their offspring.
Although Lamarck's idea about the inheritance of acquired traits was an attempt to explain how evolution could occur, modern genetic research and Darwinian natural selection do not support this aspect of Lamarck's theory. Lamarck's contributions, however, were pivotal in the early discussions of evolutionary biology, fostering the development of the field. Scientists now understand that, while direct inheritance of acquired traits as Lamarck described isn't accurate, epigenetic changes can influence how genes are expressed, which aligns somewhat with the concept of organisms responding to their environment.