Evolution is a difficult subject for students, with well-documented confusion about natural selection, tree thinking, and genetic drift among other topics.
For Charles Darwin, eye evolution was a difficult problem to explain in terms of his evolutionary theory, and he devoted an entire chapter of "On the Origin of Species" to the discussion of the difficulties of his theory in which organs of extreme perfection like the eye figure prominently (Darwin 1872).
Evolution theory is a difficult concept to teach in a biology class because teachers fearing confrontation with students often avoid controversial concepts such as evolution (Nickels et al. 1996).
Modeling the evolution of porosity is a difficult task that requires knowing the value of the initial connected porosity and how it changes during the reaction.
Of course, this is not in itself a problem for linguistic nativists: formulating and testing hypotheses about human cognitive evolution is a massively difficult enterprise, due largely to the difficulty of finding evidence bearing on one's hypothesis.
Due to the complexity of the translation system, its origin and evolution is a notoriously difficult chicken-and-egg like problem.
For other airlines with long histories of rules-based approaches though, the evolution will be a more difficult--but still necessary--one.
The slogan will have to be matched with some substance on policy if Labour is to succeed in the difficult evolution from effective opposition to credible government-in-waiting.
As Zimmer noted in 2009 [ 88], predicting the outcome of evolution is difficult, especially human evolution where there are myriad factors influencing the selection of different traits.
For example, the application of international trading strategies of services is difficult because the evolution of service 'from a craftsmanship attitude to industrialisation of services' requires the development of new tools, approaches, and policies.
