"As soon as he has been conceived, a man is a man" --Jerome Lejune
A French scientist, Etienne-Emile Baulieu, is the chief developer of a new drug called RU486. In a deadly twist of logic he claims that it could save thousands of lives, maintaining that he is acting in the best interests of women and that this drug has become the moral property of women: "My aim is to get rid of the word abortion because it is almost as traumatic as the fact itself". And he further says that "contemporary science has shown that 'conception' cannot be thought of as only fertilization". He considers gestation as a continuum from the beginning of the development of the gametes in the female embryo, until the time when this same female later conceives and brings a child to birth. From all of this he has invented a new term called "contragestion" and in this he includes the action of RU486. This coining of new terminology is done deliberately to cloud the understanding of the various processes involved in human reproduction.
It is therefore of great importance that when a human life begins should be clearly understood.
Other attempts have been made to confuse, and new terminologies have been invented and old ones altered. For example, a new term "pre-embryo" has been introduced in recent years. The definition of an embryo as given by Blakiston's Gould Medical Dictionary 1 is "a young organism in the early stages of development; in human embryology the product of conception from the moment of fertilization until about the end of the 8th week". The term fertilization in the same medical dictionary is defined as "the union of male and female gametes". The new term "pre-embryo" is supposed to refer to the time between the union of the sperm and ovum and the joining of the male and female pro-nuclei of the new cell. This implies therefore that the embryo does not come into existence until the union of the two pro-nuclei. It is a term of convenience to allow for the experimentation on new life after fertilization and before the union of the two pro-nuclei.
In recent years the term "syngamy" (from the Greek words together and marriage) has been altered in meaning from the union of gametes to the (later) union of the pro-nuclei. This supports the introduction of the term pre-embryo to de-emphasise the importance of the moment of conception.
Balinsky 2 defines fertilization as the fusion of two gametes (sex cells) a male and a female one followed by the joining together of the nuclei of the two gametes". Moore 3 (p.13) states: "Human development begins at fertilization, when a male gamete or sperm unites with a female gamete or ovum to form a single cell called a zygote". It was the illustrious Rudolf Ludwig Karl Virchow, a pathologist, who lived in the 19th century, who pronounced the famous aphorism "Omnis cellula e cellula" (every cell is from a cell). It was in the middle of the 19th century that it was established that reproduction of organisms was effected by the phenomenon of cell division.
When we are talking about the beginning of a human life we are talking about this cell -- the zygote (which means yolked together) and defined in the medical dictionary as an organism produced by the union of two gametes -- in other words, the earliest form of the embryo.
Nature prepares a long way ahead in reproducing the species. In the human female, as early as 19 days after conception, a number of cells is selected which will migrate to the developing ovary. When the fetus is 3 months old, they begin a long slow process of maturation during which the number of chromosomes is halved. This process of chromosomal reduction is completed at ovulation with the extrusion of the first polar body when the egg is then ready for fertilization. If it is not united to a sperm cell it will die within 24 hours.
The progenitors of the sperm cells are likewise set apart in the 19-day male embryo and eventually take their place in the developing testes. At puberty the immature germ cells multiply and mature, becoming sperm cells which have also undergone a process by which the number of chromosomes has been reduced by half. Fresh sperm cells mature daily until old age, which is quite different from the case of ovum production where only a certain number is present from the beginning and are gradually lost up until puberty and during ovulation until by middle age they have all disappeared.
The sperm cell must undergo further development and modification in the female reproductive tract before it is able to fertilize the ovum.
Of the 400 million sperm cells in a single ejaculate only 200 to 300 of the best and most suitable for fertilization are present in the outer fallopian tube at the time of fertilization. This is largely due to the selecting mechanism of the cervical mucus which the cervix produces under the influence of oestrogen prior to ovulation. The selection of the sperm which eventually fuses with the ovum, said to be merely random and chance, may be found to have another and more complex explanation.
After having passed through the selecting mechanism of the cervix the sperm cells must be capacitated. This is effected mainly in the uterine tubes by the removal of glycoproteins from the surface of the acrosome which lies over the nucleus in the sperm head (3, p.28).
The ovum is freely moving in the fallopian tubes due to the contractions of the muscles in the walls of the tubes and also partly due to the movement of fine hair-like processes (the cilia) of the cells of the tube which cause a current in the fluid. These movements are under the control of both ovarian hormones and neurophysiological hormones from the pituitary. The ovum is surrounded by an envelope of smaller cells called the "corona radiate" which accompanies it from the follicle in the ovary from which it was released. Sperm must work their way through this maze of cells, and they do this by digesting a pathway by the enzyme hyaluronidase which is released from the acrosome through small perforations in the cell membrane over the sperm head upon contact with the corona radiate -- "the acrosome reaction".
Once through, the sperm now confront the zone pellucida which is a clear coat which encapsulates the ovum. By the action of trypsin-like enzymes (acrosin and neuraminidase) from the acrosome the sperm set about digesting a path through the zone pellucida which is receptive to them. However, as soon as one sperm cell has passed through the zone pellucida the receptors to all the other sperm cells are blocked and consequently they are shut out or stuck within the substance of the zone pellucida. The favored sperm travels on, like the Prince in "The Sleeping Beauty".
All sperm cells and the ovum will die within hours unless this sperm contacts the cell membranes of the ovum, but when this contact occurs the cell membranes of both sperm and ovum fuse and at this point the metabolic activity of this new combined cell (the zygote) is set in motion. A life begins with this syngamy (joining of gametes) which may last 70 years or longer unless thwarted.
To prevent the union of gametes is contraception. To prevent the continuing development of the cell (zygote) formed by joining of egg and sperm (syngamy) and to terminate the ensuing development is to terminate this human life. It is abortion.
Immediately upon the fusion of the sperm membranes with the cell membrane of the ovum, the cytoplasm of the ovum enfolds and gathers in the sperm head and tail, and releases granules which are in the outer part of the cell. This further contributes to the prohibition of the chance entry of other sperm cells by altering the receptivity of the ovum membrane to sperm.
The constitution of this cell is unique within the human species to which it belongs. It contains organelles or microscopic "machinery" which initiates and directs the development of the zygotes, by synthesizing the necessary proteins from elements within the substance of the cell (amino acids).
As part of this activity, the second polar body is extruded. This contains a small amount of cytoplasm, together with a haploid number of chromosomes (23). This extrusion will occur only after sperm and ovum have joined. Now, the pro-nucleus from the sperm head and the pro-nucleus from the ovum meet in the centre of the zygote. A fine skein-like structure (the spindle) is formed from the centrosome of the sperm head. The DNA replicates in both pro-nuclei and the chromosomes line up along the centre of the spindle and mingle. This event is called by the geneticists amphimixis which is defined as a "combination of both kinds". The zygote contains 46 chromosomes, 23 from the mother and 23 from the father of the embryo. It is the father's sperm which determines the sex of the embryo at fertilization by contributing either an X or a Y chromosome. Sexual characteristics although determined immediately will be expressed later on.
Soon the cell prepares to divide for the first time in the billions of cell divisions that will subsequently occur during the process of growth and development of organs, limbs and senses of this particular human individual.
The phenomenon of twinning has posed a problem for some people due to the fact that many widely differing opinions and estimates have been advanced as to when division of the organism takes place and therefore when it can be said that the individual twins have come into existence.
The discussion centres around twins arising from the division of one zygote, which is called monozygotic twinning. When this occurs has only been speculative, but important recent work in the field of genetics by Jeffries and Surani in the last 3 years tells us a lot about the behavior of the genome. It is now known that the genes in the male pro-nucleus are programmed differently from those of the female pro-nucleus, making this totipotent cell the most specialized cell in the life of the new organism. There is a specialization of information carried by the male and female pro-nucleui. The male chromosomes are primarily responsible for the organization of the formation of the placenta, and the female chromosomes for the organization of the formation of the organs of the individual.
As soon as this cell splits the cells pass information to and from each other. Some differentiation between the cells has occurred. One of these cells now divides. In the three-cell embryo, the differentiation has progressed to the point where the communication between the cells has defined the whole as an individual, and each cell is committed to development along a specific pathway. This is quite different from a tissue culture colony of independent cells, that will continue to be unspecialized no matter how many times they divide.
No longer is each cell totipotent or capable of developing into an individual. Twinning must occur very soon after fertilization, in the human very probably not beyond the 4-cell stage (J. Lejeune, personal communication).
In the totipotent cell, the genome (all of the genetic material contained in the chromosomes) is specifically programmed to develop into an individual. The genome is organized to perform as required by activation of some genes and suppression of others. The two cells which come next are programmed differently. Other parts of the genome are made available for specific duties, and other parts are silenced and rendered inactive. Thus progressively differentiation takes place and eventually cells become committed to producing specific tissues, for example, skin or bone or liver which under some circumstances can replace and repair tissue in adult life. Others which are most highly differentiated and specialized cannot replace themselves once they have been damaged or lost; this applies to the cells of the nervous system.
Even though these events are not yet completely understood, the fact remains that in the initial cell (the zygote) formed by the joining of the gametes (syngamy) from the first moment of fusion of the sperm and egg, one or more unique lives have begun.
To prevent the destiny of the totipotent cell at its inception, is to destroy one life or the two or more lives determined from the beginning.
1 Blakiston's Gould Medical Dictionary, 4th Edition, 1979. (McGraw Hill: New York.) [Back]
1 Balinsky, B.I. (1970). An Introduction to Embryology. 3rd Edition. Ch. 6. p. 107. (W. B. Saunders Company: Philadelphia.) [Back]
1 Moore, K.L. (1988). The Developing Human. 4th Edition. (W. B. Saunders Company: Philadelphia.) [Back]