Six categories summarize the main possible explanations: mismatch with the modern environment, pathogens coevolving with hosts, constraints on what selection can do, unavoidable trade-offs, reproduction at the expense of health, and defenses such as pain and fever that are useful despite causing suffering and complications (Nesse 2005b).
We propose that the common patterns of nucleotide motif usage observed in hosts and viruses coding sequences are caused by host-induced and host-specific constraints, and are key factors in understanding the genomic evolution of Flaviviridae family and its hosts.
The host model constraints include mass, momentum, energy, vorticity and enstrophy conservation.
Recently, Desneux et al. (2012) suggested that host range constraints among parasitoids could be strongly influenced by host phylogeny (phylogeny specialization).
Pollinator host preference constraints permit reproduction on closely related Ficus species, but uncertainty of the frequency and duration of these associations requires better resolution.
Previous work on TEs suggests that that these elements are not under host selective constraints (Silva and Kidwell 2000; Pace et al. 2008), and instead, TEs evolve neutrally upon inactivation of their transposition in the host genomes.
Virtually all teaching hospitals are subject to a host of economic constraints -- increasingly tight limits on Medicare spending, the policies of managed care companies, labor shortages and rising pharmaceutical and malpractice insurance costs.
In addition, new technologies, more complex procedures, and a host of external constraints have changed where and how we teach technical and procedural skills.
