The main 2 observation which Lamarck made is:
1. Use and Disuse of Organ
2. Inheritance of Acquired Characters.
The Use and Disuse of Organ states that, only those character will last longer or pass on to next generation which are getting in use day by day. And, the organ will vanish if it not in use. Like, Tail in Human.
Inheritance of Acquired Characters, a theory that suggests physiological changes that an organism acquires throughout the course of its existence might be passed on to children. It's often referred to as the theory of adaptation or Lamarckism, after French biologist Jean-Baptiste Lamarck's theory of evolution.
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