In reading Samuel Butler's Deadlock in Darwinism, we see that one of Butler's arguments is that Mr. Charles Darwin devotes entirely too much attention to random variation in a species and not enough to use and disuse. With regard to the example of the giraffe stretching its neck that Butler presents in his piece, Lamarckians and those who favor use and disuse against random variation would protest that the giraffe acquired its long neck by desiring to reach foliage at a greater height, and by consistently stretching it's neck for the purpose of reaching this foliage, were able to do so.
The key word in this perspective is desire. In lecture we discussed that this characteristic of desire could be passed down from generation to generation, ensuring that the giraffe's who desired to stretch their necks would survive. The problem with this is that while the desire may be passed down in some regard because of observed behavior and imitation of this behavior by the next generation, the gradual stretching of the neck throughout a giraffe's lifetime does not alter their genetic makeup for physical characteristics and thus, the elongated neck never becomes a permanent feature of the next generation of giraffe.
What can alter the genetic makeup of any species is random variation. A random variation means that there has been a slight alteration in the genetic makeup of a being that has produced a slightly altered characteristic, such as an elongated neck in the case of a giraffe. Now that this random variation has entered the gene pool, it has a chance of reoccuring in the next generation. This chance is increased through use and disuse, as favorable variations may help certain animals to succeed in their environment and have a better chance of reproduction. As these animals with favorable variations breed and become more prominent, we see an evolution of that species that has been based on random variation and supplemented by use and disuse, which is exactly how Mr. Charles Darwin explained the process of evolution in the Origin.