"Speak to the Children of Israel, saying: When a woman conceives and gives birth to a male, she shall be contaminated for a seven-day period as during the days of her separation infirmity shall she be contaminated."(12:2)
The first question that arises is why is there any type of Tumah (contamination) at all in one of the most miraculous and beautiful events in Life-Childbirth? The second question is why the Tumah period for a male child is a total of 40 days and the Tumah period for a female child is twice as long at 80 days? The third question is why a Chatat (sin-offering) must be brought at all by the mother?
What did she do wrong? The Shem Mishmuel (Rabbi Shmuel Bornstein, the Rebbe of Sachaczev, Poland) quotes his grandfather the Kotzker Rebbe (R' Menachem Mendel of Kotzk 1787-1859) who says the birthing process is "an Act of G-d". Anyone who has experienced childbirth knows fully well that this may be the Greatest Miracle that they will ever witness on earth in their Lifetimes. The Shem Mishmuel asked his grandfather if this is so how does Tumah enter into this incredible miracle?
The Kotzker Rebbe answered that Tumah only enters the picture after the whole Miraculous and Holy birthing process is over. The Kli Yakar brings down a Zohar that evil spirits always attach themselves to a Holy Place. Evil is Parasitic. It always looks for the Holy to degrade it. Evil gains energy when Holy Man slips. Evil is empowered by Man's sins. G-d departs after the Birth occurs. Evil then tries to fill the void. The Tumah does not strike the newborn. It strikes only the Holy Mother. R' Tzaddok HaCohen(1823-1900)also tries to answer why the Mother alone is Tamei. No one is Perfect in this world. The Yetzer HaRa (evil impulse) strikes everyone. This is what the Nachash(Snake) did to Man. He brought the Yetzer HaRa and Evil into Man. He started with the woman. He infused the Yetzer HaRa into Chava first.
The Yetzer HaRa of idolatry has been for the most part abolished by our Spiritual growth. However, the Yetzer HaRa of Arayot ( illicit relations) was attempted to be abolished too. If it had been, then the woman would not become Tamei after birth. When the attempt at abolishing Arayot was made even the chickens stopped laying eggs. The Yetzer HaRa brings about Man and Woman coming together and their attraction for one another. This is how a child is brought about. The Yetzer HaRa also brings Tumah. This is how R' Tzaddok HaCohen frames it.
The Woman brings a Chatat(sin-offering) after birth to rid herself of the Yetzer HaRa which created the Tumah state. This is regardless of the fact that the whole process produced a Holy child through a spectacular Miracle by the hand of G-d, Almighty. The Chatat(sin-offering) is brought to atone for the sin of Chava which brought labor, and the birthing process as we know it into being in the first place. "To the woman he said, I will greatly increase your suffering and your childbearing; in pain shall you bear your children. Yet your craving shall be for your husband, and he shall rule over you."(Bereishit 3:16). It is G-d's infinite Mercy and direct intervention that allows for the Miracle of Birth at all. The forces of Tumah try to prevent this "act of G-d". These forces go after the male birth with a special vengeance. Males apparently according to the above have stronger counteracting forces than the Females. It may be because males have many more Mitzvot to perform than the Females including a Brit Milah (remember Adam HaRishon was born without an Orlah in Gan Eden-Brit Milah was only necessary once Man was banished from Gan Eden).
These forces are able to shorten the mother's Tumah period from 80 days for Females to only 40 days for males. The Ramban tries to answer the question of why males produce Tumah in the mother for only 40 days and females produce Tumah in the mother for 80 days in a different way. This situation has unfortunately been raised by 'feminists" to discredit our Religion. These critics do not understand or don't know what I have already said above. It is possible they just don't know the depths of the Torah. The Torah has many levels and it is unfortunate that many only look at it superficially. The whole Torah fits beautifully when one digs deep enough. I will try to answer these critics and also explain the Ramban in Medical and Scientific terms.
The Ramban says "both the male embryo and the female embryo are "completed" in forty one days (after conception). The reason for the distinction (80 days vs. 40 days) is because the nature of the female is cold and moist…as it is known that it takes longer time to become cleansed from cold illnesses than from warm ones."(12:4) My understanding of the Ramban is that because the female fetus is both closer genetically (XX-No "Y" Chromosome) and Hormonally (producing Estrogen rather than Testosterone) the female fetus essentially is more attached to the mother than the male fetus.
The "rejection" phenomenon which occurs to any "foreign body" whether a Kidney Transplant or a fetus is less so for a female fetus because of the closer Genetic and Hormonal matchups. Therefore, the male child and its attachments to the Mother only require 40 days of Tumah for the Mother. The female fetus which has much less of a "rejection" phenomenon (the Ramban uses the word "cold") produces a longer Tumah period in the Mother. In simple terms, the daughter is more attached to the Mother than the son.
The Torah is a Living source of Science. All the pieces of the puzzle fit when you delve deeply into the Torah. It is up to each and everyone of us to do so. Shabbat Shalom. In memory to Moshe Ben Zalman Yehuda Z'L