Why Lamarck's theory about the inheritance of acquired characteristics is incorrect?

Question

anonymous · Answer

Lamarack believed that if an animal needs a particular trait (eg. a long neck) in order to survive, it is able to "will it" into existence. For example, a giraffe may want a longer neck so it stretches and stretches it till it becomes longer to eat the leaves on the tops of trees. This is called the law of use and disuse. This is incorrect as changes in a species occurs due to mutations and variations for which is selected by the environment. This is called natural selection (developed by Charles Darwin).

anonymous · Answer

Of course if you use your muscles, they become stronger in power and bigger in size!
what Lamarck said was that these acquired characteristics are being transferred to the offsprings, while we (now) know that most of the acquired characteristics don't have any influence in DNA sequence and hence they are not hereditary.

anonymous · Answer

Because acquired characteristics are NOT INHERITED. Your children will not have only one arm if you lose an arm before you have them.