Lamarck believed that the stretching elongated the giraffe's neck, which became a useful characteristic and was passed onto future generations. This resulted in the length of the giraffe's neck increasing over time. It is now commonly accepted that Lamarck's ideas were wrong.
Lamark suggested that organisms can acquire traits which benefit them without any genetic means. He suggested that a change was gradually introduced into organisms of a species during their lifetime and this change could then be seen in the offsprings.
This idea was wrong because an organisms characteristics cannot change in his lifetime.
The theory of Lamarck's inheritance can be disregarded by our knowledge about hereditary genetics.
