When did Yitzchak live in Geror

The Torah does not explicitly state when exactly the famine erupted and caused Yitzchok and Rivkah to move to G'ror. The Torah does put the story after the incident of Eisav selling his birthright, which occured when Avraham died (at 175) when the twins were 15 years old.

Logically it could not have occurred while they were growing up, because it would have been too hard to hide the children and keep their identity (as children of Yizchak and Rivkah) secret. Thus, it could only have occurred during the twenty years before they were born or after Avraham had died.

This depends on and argument as to whether or not the Torah tells things in chronological order or not. If the Torah does not necessarilyput things in chronological order (Ain mukdam u'meuchar baTorah) as Rashi says, then we cannot know when the incident occured. We can make a logical argument that Avraham was still alive during those twenty years and a famine that chased Yitzchak away and forced him to resettle would have affected Avraham as well. If he had been around, his reputation would probably have affected thecourse of events. THe memory of what occurred when he was in Gror would have protected Yitzchak.

On the other hand, if the Torah does list events in chronological order (Yaish mukdam u'meuchar batorah), then the events had to have occurred after the sale of the birthright. The question does arise, where were Yaakov and Eisav? This seems to imply that they were older and had already been on their own.

It would seem that Eisav had not yet married as the news of his marriage would have spread and made the ruse impossible. We know that Eisav married at the age of 40, in order to emulate his father. Professor Nechama Leibowitz brings up the point that Eisav actually led a band of fighters and used them to defend the family. She states that this can explain why the shepherds of G'ror used "lawfare" to harass Yitzchak rather than attacking him and attempting to take the wells away.

The Torah says that they caused problems and disputed the ownership of the wells. Professor Leibowitz says that this is because they did not dare to attack directly.

This seems to limit the priod of time in which the famine occured and Yitzchak was able to claim that Rivkah was his sister. After that he settled in B'er Shevah for the rest of his life.

Evidence that Avrohom had a daughter

When the Torah tells us that Avrohom was "blessed in everything" (Bakol), there is a dispute as to what that means exactly.

1. Avrohom and Sarah had a daughter as well as Yitzchak
2. Yitzchak was Sarah's only child and Avrohom did not have a daughter.
3. Avrohom had a "magic healing gem" with healing properties
3a. He was blessed with all manner of riches.

Option 1 is because a person is considered to have fulfilled "be fruitful an multiply" only when he has both a son and a daughter. The small kaf in Chayei Sarah in the word "U'Livkosah" (and to weep for her) shows  and indication of "UL'vitah" (and for her daughter. That is it implies that their daughter died at the same time as Sarah. This explanation states that Avraham could not find anyone for her to marry as the entire world was made of of idol worshippers. Unlike Yitzchak, she would have had to go to her husband's family and would have beeen lost.

The second explanation states that for the reason given above, it was actually a blessing for Avraham not to have a daughter.

When Yitzchak went to Geror, he told everyon that Rivkah was his sister. Avraham by this time was well known and therefore, it would have been well known who his family was and whether or not he had a daughter. For the claim to be believed, the fact of a daughter had to be known.
 

An honest judge doomed S'dom

Rabbi Sorotzkin asks why does the Torah emphasize that Lot was "at the gate of the city". Rashi says that this means that he had been appointed a judge. Rabbi Sorotzkin states that Lot was an "honest" judge and could not be bribed. He enforced the law impartially without fear or favor. Until then, the judges could be bribed and would let people off. That meant that people who had committed the "crime" of having guests would be allowed to go free. This postponed the doom of S'dom. Once Lot became the judge and could not be bribed, there was no longer a source of merit in the city and it's fate was sealed.

Hashem gives us a chance to get it right

Adam had three sons one of whom died.

The line of Kayin ended with Lemech who had three sons, one of whom created weapons that were used for death.

The line of Sheth ened with Noach (son of Lemech) who had three sons. The curse of Kena'an can be attributed to his father Cham and can be considered "like" death.

The line of Shem ended with Terach who had three sons, one of whom died.

It can be considered that he finally "got it right" and produced progeny that were able to resist the idol worship that had taken ove the world. Of his two surviving sons, Nachor had twelve sons, eight by his wife and four by his concubines. Avraham had Yishmael and Yitzchak.

Yishmael's line is given at the end of Parshas Chayei Sarah and shows twelve sons. Nothing further needs to said about them.

Yitzchak had Yaakov, who had the twelve shevatim, 8 by his wives and four by the "servants" of his wives. While he considered them wives as well, they seem to have considered themselves more like concubines.

It should be pointed out that "concubine" was a legal status and is not the way we would consider it nowadays.

This brings to mind the medrash that Hashem offered the Torah to all the nations in the world before giving it to us at Har Sinai. It appears from the history of the worls, that every lineage had the chance to reach the level of Avraham, but failed. Once someone finally "got it right", the Torah follows that group to see if they can manage to continue on the right path.