Jorge Andrea reminds us that the approaching process between the mother and the future child will occur according to several conditions, such as vibrating affinities, tuning, true hypnosis, and mutual influences between the mother and the reincarnating being, as well as a mechanism originated from previous lives.

Andre Luiz stated:

Children and parents, even when they consider themselves distant from one another, they always maintain from a moral point of view the magnetic affinity. [i]

Eventually, Spirits who are not linked to certain families may be referred to them, with the purpose of improving their progress. Kardec comments on this matter:

God allows that, in some families, unpleasant Spirits or Spirits of strangers reincarnate with the dual objective of providing progress to both sides. Thus, the bad improve little by little through the contact with the good, and their care for them contributes strongly for this. Their character softens and all dislikes vanish. This is the way the merging of the different levels of Spirits occurs. [ii]

5 - How do we reincarnate?

The general law of evolution establishes basic principles that guide the reincarnation process: a biological-spiritual automatism presiding over the process.

Andre Luiz reminds us that:

[...] Reincarnations and disembodiments, in general, simply follow the law. There are biogenetic principles guiding the world of living forms on the occasion of physical rebirth, and transforming principles, which govern the phenomena of death, in all manifestation areas.

These "biogenetic principles", mentioned by the Spiritual author, follow in the human species, a line more or less defined, individualized in the following cases: 

1 - Numbness and general weakening of the entity during the process of reincarnation with miniaturization of his spiritual body. 

One of the items that constitute the physiology of reincarnation is the miniaturization of the spiritual body of the Spirit, who is in the process of reincarnating. Leon Denis clarifies us: 

The incarnation begins by a gradual approach, through the absorption of the material molecules to the perispirit, which decreases and condensates [...] [iii] The condition of numbness and weakness of the Spirit in the process of reincarnation and the urgent need to link up again with heavy fluids on the planet are accompanied by a reduction of the volume of the spiritual body, which, according to Andre Luiz, occurs because of a decrease in the intermolecular spaces. [iv]

Andre Luiz refers to the restraining of the perispirit by saying:

Candidates to reincarnation, without sufficient spiritual development to supervise reincarnation at their own discretion, and far from the primitive inferiority, which would make them absolute slaves of the physical heritage, are accepted at institutions-hospitals where disembodied magnetizers, very competent due to their  noble and developed Spirit, apply on them balsamic fluids, which makes them fall asleep for different periods, according to their spiritual development, so that the psychosomatic principles adapt themselves to the appropriate restraining, by means of sleep therapy. 

2 - Psychic linking to a woman, who is in reproduction conditions, and with whom the reincarnating Spirit has affinity; absorption of the miniaturized entity through the mother's genesic center. 

After the restraining of the spiritual body, and being the individuality near the magnetic field of the future mother, the fluid exchange between them will intensify. The psychic energy of the reincarnating Spirit is gradually guided funneling towards the female genital organs.

Andre Luiz explains:

Reincarnation, as well as disembodiment, is a biological shock. Attached to the maternal reproduction matrix, in search of new forms, the perispirit is influenced by strong electromagnetic currents, which require that it immediately decreases its volume. Consisting of chemical principles similar, in its properties, to hydrogen, expressing through molecules significantly spaced apart from each other, when it is linked to the female genesic center it experiments an expressive contraction, in the same manner our body reacts to a strong electric charge. Then, the reduction of the volume of the subtle spiritual vehicle occurs and the intermolecular spaces decrease. All useless matter, which is not essential to the main work of recasting the form, is returned to the ethereal plane, and thus the perispirit offers us an aspect of wear or of greater fluidity. [v] 

3 - Generation of a magnetic field by the reincarnating Spirit with magnetic selection of gametes, connection with the ovule cell, and management of fetal formation. 

The reincarnating individuality, with its miniaturized spiritual body, attached to the mother's genesic center, generates a magnetic field, of fundamental importance in the selection of gametes that will form his future body, in fertilization and embryo/fetal development. The psyche of the Spirit that returns to the planetary world - showing his evolutionary status, his personal identity, tastes and trends, virtues and vices, and his need to progress - projects himself in the space where the reproduction phenomena will happen, actively participating of the reincarnation physiology. 

How does the Spirit operate then? The initial binding of the reincarnating entity with its miniaturized spiritual body will be to the maternal ovule (female gamete). Woman's ovaries have about 400,000 ovules during their first period. Each month, an ovule (the ovaries alternate cyclically), influenced by hormones released by the pituitary gland, undergoes maturation process and is released from the ovary, being collected by the fallopian tube. Scientists admit, so far, that ovulation is a random process, i.e. the factors that are not known determine which ovule, over others, will undergo the process of maturing and will be released. This process, however, is not random. The reincarnating psyche, via its magnetic field, tunes up with the female gamete, whose set of genes identifies itself with the personal characteristics, i.e. its spiritual identity, where its changing requirements are reflected. The energies of the reincarnating entity projected on the "selected" ovule will magnetize this cell, triggering the physiological mechanism known by the biology of reproduction as "ovulation".

A similar process will occur when the "selection" of the male gamete takes place. During ejaculation million sperm dispute the privilege of joining the female gamete at the end of a close race, through the female genital tract. Which sperm will win the race? The fittest, the researchers say! In fact, the one who wins the race is the one who carries in its twenty-three chromosomes the genes that are in tune with the reincarnating psyche. 

End of the process 

At the end of the race, which takes place, as a rule, in the posterior third of the fallopian tube, sperm (carrying 23 chromosomes) and ovule (also with its 23 chromosomes) merge their cores, originating the ovule cell with 46 chromosomes from human species. At that moment, the reincarnating Spirit concentrates its energies in the cell that has just been formed, connecting then, in a more ostensive manner, to the material dimension.

At the end of the fertilization, with the formation of the ovule cell, begins the cell multiplication process, which will result in the formation of the embryo and later the fetus. According to the official science, the development of the ovule cell, the cell differentiation, and the migration of cells to specific organs occur due to an intricate interaction of a complex set of genes, the mechanism of which is very little understood. What is true, however, is that the magnetic field generated by the psyche reincarnating actively participates in the formation of the embryo and fetus, acting in the differentiation of cells and structural organization of tissues and organs of the developing human being. Obviously, there are genes that account for the process of formation of fetal organs, but these genes, like all others, would be under the influence of the powerful irradiation of the reincarnating psyche. 

Kardec, examining the process of reincarnation, comments:

To be more accurate, we have to say that it is the Spirit itself that shapes its wrapping, and fits it to his new requirements; improves, develops and completes the body, as he experiences the need to express new faculties; in a word, it models it according to his intelligence. God gives him the materials; it is up to him to use them properly.[vi]  

According to Emmanuel, in the book "Thought and Life":

  [...] Stem cells, through live seeds, reproduce our cliches of consciousness in the intangible work of formation of a new body. In the uterine chamber, the dominant reflection of our individuality impresses the fetal plate or the set of germinal principles, which form the foundations of the new physical instrument, confirming our purpose to accomplish our tasks, for which we are called to perform in this world during a certain period of time.

And Andre Luiz:

In the mind lies the command. Consciousness traces the fate, the body reflects the soul. All aggregation of matter obeys the spirit impulses. Our thoughts produce the forms that we use in life. [vii]