TF: Pan Pan Jiang
THE O RIGIN OF THE SPECIES :CHAPTER 5(L AWS OF VARIATION )
The effects of “use” and “disuse”seem topuzzleDarwin.What arethe observationsthathe istrying to
explainandwhat arethe competing hypotheses?
Darwin is unsure whether change is a result of disuse leading to atrophy or rather, change results from
natural selection reducing the structure. He notes that in cases of artificial selection, it is easy to
conclude that use in domestic animals enhances certain parts, while disuse diminishes them, but it is
more difficult to observe natural organisms. Darwin, in examining different examples, comes to
differing conclusions as to what causes change. For example, when talking about blind animals in
caves, he attributes loss of eyes to disuse, because he thinks that the useless eyes could not
negatively impact the organisms and thus, not be acted upon by selection. Other modifications, such
as the reduction of wing size in some birds, are said to have been acted upon by selection, such as
progenitors of the ostrich using its leg more and wings less, resulting in the modern day form.