1. Introduction

Human reproductive behavior is studied by specialists of many disciplines. Until now, however, there has been no convincing explanation of the fall in birth-rate in developed countries. Demographic investigations show that many modern couples are limiting themselves to one child, even as men and women express in opinion surveys the desire for larger families. This discrepancy has been explained by the fact that more than 50% of respondents said they would prefer a family with two children, one boy and one girl. That is to say that spouses would be more willing to have a second child, on condition that they could be assured of having either a son or a daughter. The impossibility of determining the sex of a future baby has thus proved a negative influence, decreasing the likelihood that couples will decide to have a second child.

preferable family structure

used questionnaire

So, if we provide parents with the opportunity to realize their reproductive rights, there will not be any great change in the ratio of the sexes within the population. The population itself, however, may well be affected, increasing in countries where couples had previously limited themselves to one child, and decreasing in those where people usually have more than two.

Investigations in various branches of science have provided data on the planning of a child's gender, and methods for gender planning have been proposed. None of these theories or methods, however, gives a convincing explanation of why the process of pre-zygotic sex determination should exist in nature ... prezygotic more info >>>

2. Pre-zygotic selection

Immunological factors doubtlessly have a great effect on conception. We have evidence of this fact from the investigation of rabbits, immunized with spermatozoid antigens. The effect of the antigens drastically altered the gender-ratio among descendents along the female line. When mating took place after the introduction of X-sperm antigens, more males were born, and when Y-sperm antigens were introduced, more females ... more info - prezygotic selection >>>

3. Meiotic Drift

It is well established in cyto-genetics, that there is an active process which leads to genetic drift within a population. This happens during meiosis as a result of crossing-over, when during the exchange of chromosomes, factors distribute themselves in ratios different from those postulated by Mendel's laws. Experiments on fruit-flies have shown how meiotic drift can be induced (for example, by spirochaeta infection, and by certain mutagens), and to what extent it can lead to a change in the ratio of genders (in some cases, the percentage of female descendents along the male line can be as high as 95%) ... meiotic drift more info >>>

4. The Cytogenetic Basis of pre-zygotic sex determination

In accordance with the above, the cyto-genetic basis of pre-zygotic gender determination can be seen as a testosterone dependant process - crossing-over during the course of meiosis. During this process, the distribution and exchange of sex-chromosomes occurs according to Mendel's laws, but the determination of the functional characteristics of X- and Y-carrying spermatozoids does not. As a result of meiotic drift, the surface membranes of X- and Y-carrying sperm acquire special characteristics which are realized during immunological reactions after the sperm enter the woman's genital tract ... sex determination more info >>>

5. Sexual dimorphism of spermogenesis and ovogenesis

The two sexes differ fundamentally in gametogenesis. The basic difference is that spermatogenesis is a dynamic, strictly ordered process of forming new cells, whereas in a woman an already formed cell is induced to develop further. The male organism, therefore, can be influenced by outside forces, and the female can transfer these influences to successive generations ... sexual dimorphism more info >>>

6. Population functions of gender

Differences in gametogenesis are necessary in nature to ensure the realization of the population functions of the sexes. According to our current understanding, the female sex represents 'long-term memory' and the male 'operating memory' (25, c.108). This idea helps to understand the phenomenon by which the level of stress in a population influences the rate of male births ... populatory functions more info >>>

7. The Mechanism of negative reverse connection of sex ratio regulation

More than 30 years ago, specialists postulated that intensity of sexual activity is a mechanism of negative reverse linking between the secondary and tertiary ratios of a population. This is easy to explain. When there are more males than females in a population, then the rate of male sexual activity decreases, and conversely, when there are more females then males, it rises ... negative feed-bacc connect more info >>>

8. Variations in the rhythm of sexual activity

We must turn our attention to the condition of the human organism at various levels of sexual activity. It has been established that with frequent ejaculations, several of a man's sperm indexes change. The fertilizing abilities of the sperm are not, however, reduced ... sexual activity var more info >>>

9. The importance of the frequency of male ejaculation

It is well known that periods of sexual abstinence encourage the conception of female children, and that frequent sexual activity leads to the conception of more males ...ejaculation fr more info >>>

10. Ideas about the relationship of the level of sexual desire to the rate of sexual activity

We assume that there exists a 'basic,' genetically determined level of sexual desire, and that this level can change under the influence of personal factors, sexual partners, and the micro- and macro-social environment. The various levels of a subject's sexual activity can therefore be classified as belonging to one of three states ... sexual activity more info >>>

11. Genealogical Trees ... genealogical tree more info >>>