Proving hypotheses is difficult in natural history (pace the philosophical reality that no significant statement in empirical science can ever be said to be "proven").
Discerning between natural and human-mediated dispersals can be difficult in the Mediterranean ([ 91], and references herein).
However, identifying and quantifying the causative factors underlying the initiation of dispersal is difficult in uncontrolled natural settings.
Difficult students are difficult in detention too.
Furthermore, they concluded that the presence of aldehydes should normally be difficult to detect in natural systems if metastable equilibrium is reached between aldehydes and carboxylic acids at expected redox conditions.
In our view, one might interpret these results as showing that selection is such a powerful mechanism that whenever there is a large selection pressure, it does adapt the population rapidly and it will therefore be difficult to demonstrate in natural populations.
These 3 routes are not mutually exclusive and, as noted above, may be difficult to disentangle in natural infections.
An important insight from the work presented here is that polyploid states are intrinsically unstable, may exist only transiently, and thus may be difficult to detect in natural populations.
Many of the parameters defined here may be difficult to determine in natural populations [ 25], but our results demonstrate the importance of understanding the role of life history parameters and their interactions, despite the difficulties.
The highly intensive and controlled nature of these types of studies enables the longitudinal tracking of a disease process from a defined point of exposure through to infection, diagnosis, and treatment, allowing observations and measurements to be made that would be difficult to obtain in natural infection.
