In class we spoke of how gene transfer has occurred across species and how natural selection has not selected against the incorporation of this foreign DNA. The example Dr. Johnson gave in class was of how the human endometrium, which develops into the placenta, originated from the DNA of a virus.
Chapter 4 of Natural Security compares the human immune system to our national security system and, during the development of the argument, explains how viral DNA managed to incorporate itself into the human genome and become a necessity for survival. Apparently, parasites employ addiction modules to attain stability within the host cell. Addiction modules are sets of functions that require both toxic (T) responses to non-group members and anti-toxic (A), responses to in group members. Bacteria have immune systems that are both self sustaining and self destructive and the immune system of prokaryotes are considered examples of T/A gene pairs. Interestingly, many of these systems have developed through virus like agents that employed the T/A system to integrate themselves and infect the host cell. So although the host self is suffering because it has been infected by the virus, the host cell cannot afford to undergo self destruction kr create defenses to eliminate the virus cell because the incorporation of the virus into the cell has provided the cell with adaptations essential to its survival.
Now, a few questions for the class:
1) Would you define this process as adaptive?
2) Am I using the word "adaptation" correctly if I say that it is an adaptation on behalf of the viruses to develop a T/A gene that behaves like an addiction module and provides the effects expected from an addiction module?
3) Do you think that it was an adaptation on behalf of early host systems to not select against the vulnerability some of its cells had to certain viruses?
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