There is apparently some question as to whether or not the fetus qualifies as a parasitical animal. I am just as surprised as you are at this notion but in the interest of fairness, I am willing to present my thoughts as to why the fetus does not qualify as a parasite.
The first step is to define the criteria for what classifies a parasite. One of the most important criteria for a parasite is that the parasite is always a different species from it's host. When I look up the definition for parasite I find the following.
These parasites spend only part of their lives as a parasite and another part as free-living organism. Examples are: Fasciola hepatica (Liver fluke (douve)) Schistosoma Ascaris Haemonchus http://www.icp.ucl.ac.be/~opperd/parasites%20/types2.htm
Here is a much clearer scientific description of parasitism in the Encyclopedia Britannica: (emphasis added)
Encyclopedia Britannica Article
Page 1 of 1 relationship between two species of plants or animals in which one benefits at the expense of the other, sometimes without killing it. Parasitism is differentiated from parasitoidism, a relationship in which the host is always killed by the parasite; parasitoidism occurs in some Hymenoptera (ants, wasps, and bees), Diptera (flies), and a few Lepidoptera (butterflies and moths): the female lays her eggs in or on the host, upon which the larvae feed on hatching. http://ehealthforum.com/health/jump_confirm.php?url=http://www.britannica.com/eb/article-9058426/parasitism (free temporary subscription required)
And here is a definition from Online Medical Dictionary: (emphasis added)
A type of symbiosis where two (or more) organisms from different species live in close proximity to one another, in which one member depends on another for its nutrients, protection, and/or other life functions. The dependent member (the parasite) benefits from the relationship while the other one (the host) is harmed by it. http://cancerweb.ncl.ac.uk/cgi-bin/omd?par
And here is another from the U of Penn Vet School: (emphasis added)
The term parasitism may be defined as a two-species association in which one species, the parasite, lives on or in a second species, the host, for a significant period of its life and obtains nourishment from it. This is a commonly accepted working definition of parasitism and using it we can emphasize several important features of the host-parasite relationship. Parasitism always involves two species, the parasite and the host. http://cal.vet.upenn.edu/projects/merial/i%20ntroduction/intro_1.htm
And here's another one from the U of MN (emphasis added)
A Parasite is by definition any organism which lives on or in the body of another organism of a different species (i.e., the host). This definition allows the name 'parasite' to be attached to many living species, including bacteria, fungi and viruses. http://www.cvm.umn.edu/academics/course_we%20b/current/CVM6201/stromberg_I.htm
And here is a definition from Aberystwyth University, Wales (emphasis added)
Parasitism is, like most other animal associations defined in terms of two different species, who form a regular association, although this seems sensible, and it does exclude consideration of the mammalian foetus as being parasitic upon its mother, there are some very interesting immunological parallels between the mechanisms the foetus uses to avoid being rejected by the immune response of its mother and the ways in which the parasites of mammals seek to avoid their hosts immune response. http:// http://www.aber.ac.uk/~mpgwww/Edu/Para_ism/PaIsmT%20xt.html
MedicineNet.com defines parasite as
Parasite: An organism that lives in or on and takes its nourishment from another organism. A parasite cannot live independently.
Notice that in that last definition there is an omission of the technicality that the organism is from a different species. Is this significant to you? When I discuss this topic with a pro-choicer they are quick to point out any definition that has this omission. The question though is whether or not this really is a factual omission or an editorial omission.
An editorial omission would be done for the sake of brevity. Certain elements of a definition may be glossed over when it is considered to either be common knowledge, or secondary to what the author considers important information.
Note this quote from a parasitology textbook:
A parasite is defined as an organism of one species living in or on an organism of another species (a hetero specific relationship) and deriving its nourishment from the host (is metabolically dependent on the host). (See Cheng, T.C., General Parasitology, p. 7, 1973.)
This comes from an authority in the field. With so many sources citing the criteria of differing species, it is disingenuous, at best, to take a generalized definition and submit it above all of the other highly credible sources as the only source that matters.
The fetus is the same species as the mother so biologically speaking, the fetus is not a parasite. Now it is acceptable if one wants to make the case that a fetus exhibits parasitic behavior. There are certainly limited similarities. The fetus also shares some similarities to a car but it would be scientifically inaccurate to say that a fetus IS a car.
Why is this even being brought up in serious debate? The answer is that pro-choicers object to the usage of terms like child, or baby, when describing the fetus. They accuse us of emotionalizing the debate needlessly. So they have brought their own term for the fetus into the discussion in their own attempt to emotionalize the debate. The parasite argument is nothing more than a strawman meant to distract from the real issues of abortion.
Let me clarify a few things about parasite just to make sure we can put this to rest.
A parasite is always from another kind of species.
A parasite is an invading organism -- coming to parasitize the host from an outside source.
A parasite makes direct contact with the host's tissues, often holding on by either mouth parts, hooks or suckers to the tissues involved (intestinal lining, lungs, connective tissue, etc.).
A parasite is an organism that, once it invades the definitive host, will usually remain with host for life (as long as it or the host survives).
also, with few exceptions, a parasite will remain a parasite for it's entire life. It cannot survive without a host.
It is not scientifically accurate to associate a human fetus with a parasite.
Let me go one step further, Is it accurate to associate a Zygote, Embryo, Fetus with a baby, or a child?
Let me give you a definition of baby.
n. pl. ba·bies
a. A very young child; an infant.
b. An unborn child; a fetus.
c. The youngest member of a family or group.
d. A very young animal
From the online free dictionary we see that the unborn are considered a proper application for the term "baby'. A Google search will reveal many sources that list the unborn as a proper definition.
Let's look at "child"
n. pl. chil·dren
1. A person between birth and puberty.
a. An unborn infant; a fetus.
b. An infant; a baby.
Again we see that the unborn are included among the proper applications for the word child.
So where does that leave the pro-choicer? Well, they have every right to use the term parasite metaphorically, but they have no grounds to use it scientifically. However, pro-lifers still seem to be on very good ground for referring to the fetus as a baby or a child.
I am all about accuracy when it comes to this debate. I seek truth no matter what the implications are for me. I am open to correction on this, or any other topic.
I will stand corrected:
If I can be shown an example of a parasite in nature that is the same species as it's host. I suppose one might bring up the Angler fish as an example. This is not a true parasitic relationship though because it is their reproductive method, which means that it is a symbiotic relationship.
or If I can be shown a credible source of parasitology that specifies gestating unborn as meeting the criteria for classification of parasite.