 In response to Ariew’s proposal, however, Griffiths and Machery (2008) argue that canalization is actually a multi-dimensional phenomenon. There is no such thing as “the” degree to which a trait is buffered against “the” environment. Rather, for each trait there are many different environmental factors capable of influencing its development, each to varying degrees. Ariew’s example with the songbirds seems to work only because it is oversimplified. With examples of real birds it proves unworkable. For example, the songs of the much-studied Brown-headed Cowbird are relatively insensitive to the songs of other male cowbirds. This is in contrast to the equally well-studied Song Sparrow, whose songs are highly sensitive to conspecific male songs. So, when we focus on just this factor – male conspecific song – the cowbirds seem relatively canalized or “innate” compared to the sparrows. However, other researchers focus on the ways that courtship interactions (with females) influence song development. When it comes to this environmental factor, the song of male cowbirds is much more sensitive (less canalized) than most sparrows. Hence, song development will appear more or less canalized or “innate” in these taxa depending on which environmental factor we focus. Hence, Griffiths and Machery conclude: