As a matter of fact, in one of the early attempts to classify willows, Wichura (1865) found hybrids to be generally rare, although they could be extremely frequent locally, leading Darwin (1865) to express his bewilderment at the "extreme frequency of hybrid willows".
Whatever problems the samurai wasp may cause in the United States, the current alternative for stemming stinkbug damage is extremely frequent applications of a broad-spectrum pesticide.
Covenants have rarely been the actual instruments by which societies actually functioned for long, but they are extremely frequent as ideological foundations for sociopolitical legitimacy.
Osteoporosis is extremely frequent in post-menopausal women; nevertheless, osteoporosis in men is also a severe and frequently occurring but often underestimated disease.
As opposed to the previous two cases, face-to-face contacts are extremely frequent and appear to be the most important mode of co-ordination in close co-operation between producers and users.
These include not only HGT, which is extremely frequent in viruses, but also host shifts (the capacity to infect distant hosts) and convergence, which is relatively easy for simple structures such as icosahedral capsid proteins (Moreira and López-García 2009).
Colonisation of the upper airways is probably the main risk factor for VAP: it is extremely frequent and rapidly acquired in ICU but not all the colonised patients develop any clinical significant infection, neither all the tracheobronchitis (VAT) become VAP.
In recent years, it became apparent that these serious peri-implant biological complications are extremely frequent, and the incidence of mucositis has been reported to be around 80% and that of peri-implantitis between 28 and 56% (Lindhe et al. 2008).
