It is related in this work: "Humans and their collective microbiota are segmented into many local communities, each comprising an individual human with his or her symbionts. This ecological pattern, characterized by strong interactions within distinct local communities and limited interactions or migration between them, is described as a metacommunity." (Dethlefsen, McFall-Ngai and Relman, 2007) a second level of metacommunity organization is in existence because "individual humans belong to social groups that tend to share a similar microbiota." (Dethlefsen, McFall-Ngai and Relman, 2007) at each of these levels the structure of the metacommunity "allows selection to occur between the local units (or between individuals and social groups), which promotes mutualism...such selection occurs when a local symbiotic community succeeds or fails together, with more successful communities increasing in abundance or prevalence relative to less successful communities." (Dethlefsen, McFall-Ngai and Relman, 2007) II. COMMUNITY-BASED CO-EVOLUTION FACTORS

Dethlefsen, McFall-Ngai and Relman (2007) identify three factors affecting co-evolution in human beings that have typically be the focus of study, which include the community's effects of: (1) lifestyles; (2) diets; and (3) diseases. These three factors have been traditionally believed to be the cultural factors most affecting the human survival and the resulting evolutionary process however; it is now being acknowledged by science that genetic factors in combination with lifestyles, diets, and disease both have an impact on the evolutionary process of all living things. One such example is provided in the work entitled: "The Co-Evolved Helicobacter Pylori and Gastric Cancer: Trinity of Bacterial Virulence, Host Susceptibility and Lifestyle" which relates the fact that the "Helicobacter pylori is an important yet unproven etiological agent of gastric cancer." (Akhter, et al., 2007) This infection is more prevalent in countries such as India and other developing Asian countries...

This is a prime example of co-evolutionary processes in which the parasitic organism and the host which in this case is the human being and their gastric system have developed in cohesion wherein the parasite does not kill the host but in fact produces a resiliency to that infection within the host.
SUMMARY and CONCLUSION

Much is yet to be understood concerning evolutionary processes and most specifically co-evolution however, scientists and researchers alike are beginning to understand that the process is one that may cross boundaries of species and that co-evolution across these boundaries does occur and at a much higher rate that previously deemed possible.

Bibliography

Jones, Richard H. (2000) Reductionism: Analysis and the Fullness of Reality. Bucknell University Press. Online available at http://books.google.com/books?id=sUgnio874NUC&dq=human+coevolution

Wheelis, Mark, et al. (1998) Manual for Assessing Ecological and Human Health Effects of Genetically Engineered Organisms. Scientists Working Group on Biosafety. Online available at http://www.edmonds-institute.org/manp1os.pdf

Akhter, Yusuf, et al. (2007) the Co-Evolved Helicobacter Pylori and Gastric Cancer: Trinity of Bacterial Virulence, Host Susceptibility and Lifestyle. Infectious agents and Cancer, 29 Nov 2007. 2:2 Online available at http://www.infectagentscancer.com/content/2/1/2

Dethlesfsen, Les; McFall-Ngai, Margaret, and Relman, David a. (2007) an Ecological and Evolutionary Perspective on Human-Microbe Mutualism and Disease. Nature 449 18 Oct 2007. Online available at http://www.nature.com/nature/journal/v449/n7164/full/nature06245.html

Co-Evolution