Why didn't mitochondria and chloroplasts cede all of their DNA to the nucleus, as did most hydrogenosomes and certain other organelles?
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I dont understand why we are to answer the question about invertebrates and innate immune systems under this question.
However, to generate immune cells is very wasteful--most of the T and B cells that are produced die--so there is likely an evolutionary advantage to undergo such a wasteful process. And that advantage is memory, we and other vertebrates tend to reach reproductive age after a relatively long adaptive, growing period and we need to remember what we have already dealt with. Invertebrates can live a long time--ie look at that lobster!, but to reach reproductive age is not likely to require as much time for defense against pathogens. The first evidence for DNA rearrangement is found as the cartilagenous fish change to the bony fishes, so that may be the time at which the benefits of memory responses for the host kicked it evolutionarily speaking.
Posted by: Dorothy Lewis | June 18, 2009 at 10:08 AM