How did Lamarckism explain the effects of not using an organ?

In the context of Lamarckism, the theory posits that environmental changes create new needs for an animal, leading to shifts in behavior and the use of specific organs.12

According to this doctrine, the consistent disuse of an organ or body part leads to its decline, weakening, or eventual atrophy. Lamarck argued that these material alterations—whether they were the strengthening of frequently used parts or the weakening of those left unused—were acquired during the organism's lifetime. He further proposed that these acquired characteristics could be transmitted to the organism's offspring, provided both parents underwent the same changes.12

It is important to note that this theory has been scientifically discredited, as there is no evidence that such physical changes resulting from use or disuse are inherited by subsequent generations. Modern biology relies on genetics to explain the transmission of traits, rather than the inheritance of acquired characteristics.312