Taboo and Genetics | Page 8

she
be free from diseases which may be communicated to the child either before or at the
time of birth. This applies particularly to gonorrhoea, one of the most widely prevalent as
well as most ancient of maladies, and syphilis, another disastrous and very common
plague which is directly communicable. As to "birthmarks" and the like being directly
caused by things the mother has seen or thought about, such beliefs seem to be founded
on a few remarkable pure coincidences and a great deal of folk-lore.
Reproduction in its simplest form is, then, simply the division of one cell into two parts,
each of which develops into a replica of the original. Division is also the first stage in
reproduction in the most complicated animal bodies. To get an idea of what takes place in
such a division we must remember that a cell consists of three distinct parts: (a) the
protoplasm or cytoplasm, (b) the nucleus, and (c) a small body known as the centrosome
which need not be discussed here.
When a cell division takes place, the nucleus breaks up into a number of thread-like
portions which are known as chromosomes. There are supposed to be 24 pairs, or 48, in

the human cell. All the evidence indicates that these chromosomes carry the "factors" in
inheritance which produces the characters or characteristics of the individual body.
In mitosis or ordinary cell division, these chromosomes split lengthwise, so that the new
cells always have the same number as the original one. When the germ-cells of the male
and female make the division which marks the first step in reproduction, however, the
process is different. Half the chromatin material passes into each of the two cells formed.
This is called maturation, or the maturation division, and the new cells have only half the
original number of chromosomes. Each of these divides again by mitosis (the
chromosomes splitting lengthwise), the half or haploid number remaining. The result is
the gametes (literally "marrying cells"--from the Greek gamé, signifying marriage).
Those from the male are called sperms or spermatozoa and those from the female eggs or
ova. (The divisions to form ova present certain complications which need not be taken up
in detail here.) Of the 24 chromosomes in each sperm or egg we are here concerned with
only one, known as the sex chromosome because, in addition to transmitting other
characteristics, it determines the sex of the new individual.
Neither the ovum nor the spermatozoon (the human race is referred to) is capable alone
of developing into a new individual. They must join in the process known as fertilization.
The sperm penetrates the egg (within the body of the female) and the 24 chromosomes
from each source, male and female, are re-grouped in a new nucleus with 48
chromosomes--the full number.
The chances are half and half that the new individual thus begun will be of a given sex,
for the following reason: There is a structural difference, supposed to be fundamentally
chemical, between the cells of a female body and those of a male. The result is that the
gametes (sperm and eggs) they respectively produce in maturation are not exactly alike as
to chromosome composition. All the eggs contain what is known as the "X" type of sex
chromosome. But only half the male sperm have this type--in the other half is found one
of somewhat different type, known as "Y." (This, again, is for the human species--in
some animals the mechanism and arrangement is somewhat different.) If a sperm and egg
both carrying the X-type of chromosome unite in fertilization, the resulting embryo is a
female. If an X unites with a Y, the result is a male. Since each combination happens in
about half the cases, the race is about half male and half female.
Thus sex is inherited, like other characters, by the action of the chromatin material of the
cell nucleus. As Goldschmidt[1] remarks, this theory of the visible mechanism of sex
distribution "is to-day so far proven that the demonstration stands on the level of an
experimental proof in physics or chemistry." But why and how does this nuclear material
determine sex? In other words, what is the nature of the process of differentiation into
male and female which it sets in motion?
To begin with, we must give some account of the difference between the cells of male
and female origin, an unlikeness capable of producing the two distinct types of gametes,
not only in external appearance, but in chromosome makeup as well. It is due to the
presence in the bodies of higher animals of a considerable number of glands, such as the
thyroid in the throat and the suprarenals just over the kidneys. These pour secretions into

the blood stream, determining its chemical quality