I just tripped and fell down another rabbit hole. I was going to skip this week, but I would love input on this issue, so here it is. Earlier I argued that the organism was a multispecies entity. This makes perfect sense if we consider mitochondria to be symbiotic bacteria in a host cell, and we talk about the microbiome. Now here is the question: If you catch the flu, or get a bacterial infection (to keep it cellular), is that disease part of you as an organism?
Dang another rabbit hole.
There are two important points to remember. First, in the phenotypic view I am advocating considering the phenotype to be a vector through time, with every trait (a measured aspect of the phenotype) having a time element. Thus, it is not my weight, but my weight when I am 19001055824 seconds old (that is approximately how old I am while writing this). This means that even very temporary things such as whether you are inhaling or exhaling is technically a valid trait. Thus, if you have a fever of 104 degrees on a Saturday morning, that is the value of the trait “body temperature” at that particular moment. The question is, do we make a distinction because that temperature is “caused” by a flu virus? The truth is I am beginning to believe we cannot make that distinction.
Taking a clearer example. Consider a person who chooses to dye their hair purple. This color comes out of a bottle, and it is no sense genetic or otherwise heritable (well, maybe in some odd cultural sense). That said, it is part of the phenotype. If you were to categorize people by the trait “hair color”. this person would go into the “purple”. Thus, it is a valid trait, and a valid part of their phenotype. How do we deal with this? I would argue that the best way would to consider the bottle of hair color to be a non-heritable or environmental influence on the phenotype. By analogy, I think it is perfectly reasonable to suggest your 104-degree fever is also part of your phenotype.
This woman has a purple hair. It is certainly part of her phenotype, but probably not heritable. (from http://darkuro.tumblr.com/)
So, your fever is part of your phenotype, but is the virus part of you as an organism? Certainly, we would not consider the bottle of hair color to be part of an organism. It is an external aspect of the environment that changes your hair color. Cold air temperatures may cause you to put on a coat (the coat wearing trait?), but it is certainly not part of your body. However, the virus differs here. It is IN your body, and in fact it is in your cells.
Consider our microbiome. There certainly are aspects of the microbiome that are acquired from our parents, either at birth, or because we live next to them as infants, and many of these we will pass on to our children. Thus, they are heritable from the phenotypic perspective. However, others are picked up late in life, perhaps when we temporarily change our diet, and then lost again, perhaps when we revert to our old diet, and are not heritable. I think a strong argument can be made that this microbiome should be considered part of the multispecies organism: Selection acts on the whole organism; outside of perhaps prokaryotes, single species organisms don’t exist; as far as I know, animals cannot survive without their symbionts. From an experimental perspective, it is difficult or impossible to separate symbionts that are heritable from those that are non-heritable, and perhaps more important both can have significant effects on our phenotypes in ways that can affect our fitness. Thus, I think it can be argued that all aspects of the microbiome, whether heritable or not, should be considered part of the organism. Nor does it makes sense to me to argue that there is a minimum residence time before a symbiont or disease should be considered part of the organism. Such a waiting time is necessarily arbitrary, and as a result there will always be situations that are ambiguous.
Now comes the question: Should we make the distinction between the bacteria that we picked up on vacation that makes it easier to digest shrimp from another bacteria that gives us diarrhea? I cannot think of a criterion that does not require special pleading that incorporates the former, but not the latter into the organism.
One final caveat is that it is important to remember that the most appropriate unit to assign fitness depends on the trait being investigated. Thus, the colony might be the appropriate unit if we are examining colony defense, the organism if we are examining foraging behavior, and the cell if we are examining cancer. Perhaps the organism is best thought of as being equally fluid. A flu infection is an assault on our bodies, thus if our trait is immune response, maybe the organism is everything but the flu virus, whereas if we are looking at body temperature the organism is everything including the flu virus. This is a bit of a conundrum for me, and I am happy to get any feedback that anybody else may have.