Pt2 From Conception to Birth: Talmudic Perspectives on Fetal Development and Gender (Niddah 31a-b)

This is the second part of a two-part series. The first part is here.

The three partners in creating a person: God, the father, and the mother; and the corresponding body parts

The Talmud quotes a baraita that states that there are three partners in creating a person: God, the father, and the mother. 

1. The father “seeds the white (הלובן)”, forming the bones, sinews,¹ nails, brain,² and white of the eye (=sclera). 

2. The mother “seeds the red (אודם)”, forming the skin, flesh, hair, and “black of the eye” (=pupil). ³

3. God provides the spirit (רוח), soul (נשמה), appearance,⁴ eyesight, hearing, speech, ability to walk, understanding (בינה), and wisdom (השכל). 

תנו רבנן: 

שלשה שותפין יש באדם: 

1. הקב"ה 

2. ואביו 

3. ואמו 

1. אביו -- מזריע הלובן, שממנו 

   1. עצמות, 

   2. וגידים, 

   3. וצפרנים, 

   4. ומוח שבראשו, 

   5. ולובן שבעין 

2. אמו -- מזרעת אודם, שממנו 

   1. עור, 

   2. ובשר, 

   3. ושערות, 

   4. ושחור שבעין 

3. והקב"ה -- נותן בו 

   1. רוח, 

   2. ונשמה, 

   3. וקלסתר פנים, 

   4. וראיית העין, 

   5. ושמיעת האוזן, 

   6. ודבור פה, 

   7. והלוך רגלים 

   8. ובינה 

   9. והשכל

[...]

The Sages taught: 

There are three partners in the creation of a person: 

1. The Holy One, Blessed be He, 

2. and his father, 

3. and his mother. 

1. His father emits the white seed, from which the following body parts are formed:

   1. The bones,

   2. the sinews,

   3. the nails,

   4. the brain that is in its head,

   5. and the white of the eye. 

2. His mother emits red seed, from which are formed

   1. the skin,

   2. the flesh,

   3. the hair,

   4. and the black of the eye. 

3. And the Holy One, Blessed be He, inserts into him

   1. a spirit,

   2. a soul,

   3. his countenance [ukelaster],

   4. eyesight,

   5. hearing of the ear,

   6. the capability of speech of the mouth,

   7. the capability of walking with the legs,

   8. understanding,

   9. and wisdom.

[...]

The fetus is created from the clear part of the semen

דריש רבי חנינא בר פפא: 

מאי דכתיב: [...]

מלמד שלא נוצר אדם מן כל הטפה, אלא מן הברור שבה 

[...]

R' Ḥanina bar Pappa taught: 

What is the meaning of that which is written: [...]

This verse teaches that a person is not created from the entire drop of semen, but from its clear part. 

[...]

God counts the times that Jewish people have sex

דרש רבי אבהו: 

מאי דכתיב [...]

מלמד שהקב"ה יושב וסופר את רביעיותיהם של ישראל 

מתי תבא טיפה שהצדיק נוצר הימנה

[...]

R' Abbahu taught: What is the meaning of that which is written [...]

The verse teaches that the Holy One, Blessed be He, sits and counts the times that the Jewish people engage in intercourse [revi’iyyoteihem], 

anticipating the time when the drop from which the righteous person will be created will arrive.

[...]

Sexual methods for guaranteeing to have a baby boy, vs. girl

R' Yitzḥak quotes R' Ami, stating that the sex of a fetus is determined at the moment of conception. If the woman emits seed first, the child will be male, and if the man emits seed first, the child will be female.⁵

This idea is supported by a verse mentioning the sons and grandsons of Ulam, interpreted to mean that they were able to have many male offspring by delaying their own ejaculation,⁶ until their wives emitted seed first. This practice is said to influence the gender of their children, giving them the credit for having many sons. 

Similarly, Rav Ketina (רב קטינא) bragged that he could ensure all his children were male, by using the same method. 

Rava adds that having sex twice can also help ensure male offspring.

אמר רבי יצחק, אמר רבי אמי: 

אשה מזרעת תחילה -- יולדת זכר 

איש מזריע תחילה -- יולדת נקבה 

שנאמר [...]

(דברי הימים א ח, מ) "ויהיו בני אולם אנשים גבורי חיל, דורכי קשת, ומרבים בנים ובני בנים" 

וכי בידו של אדם להרבות בנים ובני בנים?! 

אלא מתוך שמשהין עצמן בבטן 

כדי שיזריעו נשותיהן תחלה 

שיהו בניהם זכרים 

מעלה עליהן הכתוב כאילו הם מרבים בנים ובני בנים 

והיינו דאמר רב קטינא: יכולני לעשות כל בני זכרים 

אמר רבא: הרוצה לעשות כל בניו זכרים, יבעול וישנה

R' Yitzḥak says that R' Ami says: 

The sex of a fetus is determined at the moment of conception. If the woman emits seed first, she gives birth to a male, 

and if the man emits seed first, she gives birth to a female, 

as it is stated: [...]

This statement is also derived from the following verse: “And the sons of Ulam were mighty men of valor, archers, and had many sons and sons’ sons” (I Chronicles 8:40). 

Is it in a person’s power to have many sons and sons’ sons?!

Rather, because they delay while in their wives’ abdomen, initially refraining from emitting semen 

so that their wives will emit seed first, 

in order that their children will be male, 

the verse ascribes them credit as though they have many sons and sons’ sons. 

And this statement is the same as that which Rav Ketina said: I could have made all of my children males, by refraining from emitting seed until my wife emitted seed first. 

Rava says another method through which one can cause his children to be males: One who wishes to make all of his children males should engage in intercourse with his wife and repeat the act.

Times in her menstural cycle when a woman can become pregnant

R' Yitzḥak citing R' Ami says that a woman becomes pregnant only by having sex close to the onset of her menstrual cycle.⁷

Meanwhile, R' Yoḥanan says that a woman becomes pregnant only by engaging in intercourse near the time of her immersion in a ritual bath, which purifies her from her menstruating status. ⁸

Both statements are supported by scriptural references.

ואמר רבי יצחק אמר רבי אמי: 

אין אשה מתעברת אלא סמוך לוסתה 

שנאמר [...]

ורבי יוחנן אמר: סמוך לטבילה 

שנאמר [...]

And R' Yitzḥak says that R' Ami says: 

A woman becomes pregnant only by engaging in intercourse close to the onset of her menstrual cycle, 

as it is stated: [...]

And R' Yoḥanan says: 

A woman becomes pregnant only by engaging in intercourse near the time of her immersion in a ritual bath, through which she is purified from her status as a menstruating woman, 

as it is stated [...]

1. גידים  - this is a general common term that includes both tendons (in Modern Hebrew, gid refers exclusively to tendons) as well as nerves (in Modern Hebrew: עצב - atzav), see, for example, Gid hanasheh - Wikipedia.

The Talmud states elsewhere that a person has 365 sinews (גידים), see Hebrew Wikipedia, “רמ"ח איברים“.

2. מוח שבראשו - literally: “the marrow that is in his head”. Usage of word moakh alone to mean brain is a later development.

3. The logic of the pattern in the grouping between father and mother seems to be based on color, as explicitly stated (white vs red), as well as structure vs appearance:

Father's Contribution (“white seed”): This includes the bones, sinews, nails, brain, and the white of the eye. These elements are generally more structural or supportive components of the body, suggesting a focus on the strong/hard and foundational/ supporting roles typically associated with masculinity.

Mother's Contribution (“red seed”): This covers the skin, flesh, hair, and the black of the eye. These aspects are more related to the soft/delicate and general external appearance of the body, typically associated with femininity.

4. קלסתר פנים - Jastrow says this word comes from Greek krústallos, Latin crystallum, meaning “crystal”, and therefore “brightness”, i.e. “beauty of features, countenance”.

5. The Talmudic sages believed that women also ejaculated semen, just like men, and that it plays a role in conception; this was a common belief in the classical world.

See some discussion here: Niddah 28a ~ Gender Determination — Talmudology.

6. משהין עצמן בבטן - literally: “waiting on [her] belly”.

7. סמוך לוסתה. The assertion that a woman becomes pregnant only by having sex close to the onset of her menstrual cycle is not supported by scientific evidence. Fertility is highest around the time of ovulation, which typically occurs about 14 days before menstruation begins.

See Wikipedia, “Fertility“ > “Menstrual cycle“:

Peak fertility occurs during just a few days of the cycle: usually two days before and two days after the ovulation date.

8. The assertion that a woman becomes pregnant only by engaging in intercourse near the time of her immersion in a ritual bath aligns more closely with scientific understanding (as compared to the previous statement of R' Yitzḥak citing R' Ami, as noted). This period indeed coincides with the time around ovulation when a woman is most fertile.

To break it down: women who keep nidah can generally resume intercourse around 12-14 days after the start of their menstrual period.

Peak fertility is around day 14 of a 28-day cycle, with the fertile window extending from approximately day 10 to day 16.