וירד יהודה. דרשו רז"ל הורידוהו מגדולתו מפני המכירה. והקשה ר' אברהם בעז"ל כי לא תמצא מן המכירה עד שירדו למצרים כי אם כ"ב שנה שהרי יוסף במכירתו היה בן י"ז שנה ובן שלשים היה בעמדו לפני פרעה הרי מן המכירה עד כאן שלשה עשר שנים ושבעה דשובע ושנים דרעב הרי כ"ב שנה ובאותו שנה ירדו למצרים משנשא אותה יהודה בת איש כנעני עד שירדו למצרים תמצא יותר שהרי חשוב שנה ללידת ער ושנה ללידת אונן [ושנה ללידת שלה] הרי שלש שנים וכתיב כי ראתה כי גדל שלה משמע שהיה בן י"ג שנה הרי ט"ז שנה ללידת פרץ הרי י"ז ואפי' כי נאמר שלא היה פרץ כי אם בן שבעה שנים כשהוליד חצרון ושנה מלידת חמול שהוא היה מיורדי מצרים הרי מ"מ תמצא כ"ה שנים אלמא האי וירד קודם מכירה הוא. וי"ל דהאי כי גדל שלה לענין ביאה איתמר כי כבר היה בן ט' שנים. וכדתנן במס' נדרים בן תשעה ויום אחד שבא על יבמתו קנאה. ואמרינן בסנהדרין שהיו הראשונים מולידים בני ז' שנים: וירד יהודה, “Yehudah descended;” our sages explained that this choice of words by the Torah means that Yehudah’s brothers, who up until then had considered him as their leader and spokesman, demoted him on account of the sale of their brother Joseph and the anguish this had caused their father. (B’reshit Rabbah, 85,1) Ibn Ezra questioned this, seeing that only twenty two years elapsed between the sale of Joseph and the reunification of the brothers with him and the family’s moving to Egypt. We know that Joseph had been seventeen years old when he had been sold; we also know that he was thirty years old when he interpreted Pharaoh’s dream; we further know that the family descended to Egypt in the second year of the famine, i.e. nine years after Joseph had been appointed viceroy of Egypt. If you count the years from the time Yehudah got married to the daughter of the man described earlier until the descent of the whole family with Yehudah at their head more than twenty two years must have passed. If we count a year each for the time Yehudah’s wife was pregnant with each of her three sons, and add the years after Onan’s death during which Shelah grew to maturity, i.e. was old enough to get married, you already have accounted for 16 years. Add a year till Peretz could have been born and you have accounted for already 17 years. Even if you were to assume that Peretz was no more than 7 years old when he became the father of Chetzron and another year for the birth of his brother Chamul, all of whom are listed in Genesis chapter 46 as having come to Egypt with Yaakov and Yehudah, you already have accounted for 25 years not 22. One would have to say that when Shelah was described as having “grown” up, the Torah refers to his having become 9 years old, at which age it is possible to produce semen fit to sire a child. We can find support for this from the Talmud, tractate Niddah, folio 45, where the Mishnah discusses a nine year old who performed the levirate marriage ceremony on his sister-in-law whose husband had died without having had any children, that he cannot give such a sister-in-law a decree of divorce until he reaches the age of 13, as a minor cannot divorce his wife. Moreover, the original marriage of his deceased brother had been a marriage in the full sense of the word, and what he did was only to substitute for his deceased brother, so that any divorce cannot be less complete than that. According to an opinion quoted in the Talmud tractate Sanhedrin, folio 69, there were periods in former eras when seven year old males were able to impregnate females with their semen.