Why are we saying that the product of fertilization is human? From http://www.terravista.pt/enseada/1881/lifebegi.html
"2) Fertilization
Now that we have looked at the formation of the mature haploid sex gametes, the next important process to consider is fertilization. O’Rahilly defines fertilization as:
"… the procession of events that begins when a spermatozoon makes contact with a secondary oocyte or its investments, and ends with the intermingling of maternal and paternal chromosomes at metaphase of the first mitotic division of the zygote. The zygote is characteristic of the last phase of fertilization and is identified by the first cleavage spindle. It is a unicellular embryo."9 (Emphasis added.)
The fusion of the sperm (with 23 chromosomes) and the oocyte (with 23 chromosomes) at fertilization results in a live human being, a single-cell human zygote, with 46 chromosomes—the number of chromosomes characteristic of an individual member of the human species. Quoting Moore:
"Zygote: This cell results from the union of an oocyte and a sperm. A zygote is the beginning of a new human being (i.e., an embryo). The expression fertilized ovum refers to a secondary oocyte that is impregnated by a sperm; when fertilization is complete, the oocyte becomes a zygote."10 (Emphasis added.)
This new single-cell human being immediately produces specifically human proteins and enzymes11 (not carrot or frog enzymes and proteins), and genetically directs his/her own growth and development. (In fact, this genetic growth and development has been proven not to be directed by the mother.)12 Finally, this new human being—the single-cell human zygote—is biologically an individual, a living organism—an individual member of the human species. Quoting Larsen:
"… [W]e begin our description of the developing human with the formation and differentiation of the male and female sex cells or gametes, which will unite at fertilization to initiate the embryonic development of a new individual."13 (Emphasis added.)
In sum, a mature human sperm and a mature human oocyte are products of gametogenesis—each has only 23 chromosomes. They each have only half of the required number of chromosomes for a human being. They cannot singly develop further into human beings. They produce only “gamete” proteins and enzymes. They do not direct their own growth and development. And they are not individuals, i.e., members of the human species. They are only parts—each one a part of a human being. On the other hand, a human being is the immediate product of fertilization. As such he/she is a single-cell embryonic zygote, an organism with 46 chromosomes, the number required of a member of the human species. This human being immediately produces specifically human proteins and enzymes, directs his/her own further growth and development as human, and is a new, genetically unique, newly existing, live human individual.
After fertilization the single-cell human embryo doesn’t become another kind of thing. It simply divides and grows bigger and bigger, developing through several stages as an embryo over an 8-week period. Several of these developmental stages of the growing embryo are given special names, e.g., a morula (about 4 days), a blastocyst (5-7 days), a bilaminar (two layer) embryo (during the second week), and a trilaminar (3-layer) embryo (during the third week).14
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