Flu strains appear to evolve faster in pigs than they do in humans, a study of over 600 viruses has shown.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/rapidly-evolving-swine-flu-viruses-could-infect-humans-and-cause-pandemic
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/international-business-times
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/health
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/swine-flu
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/animal-diseases
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/pigs
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/china
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/health-effects