It is unclear where Rabbi Yochanan got this medical fact from. Was it "daat Torah?' I would assume otherwise -- that it was contemporary ancient science. Indeed, as I mentioned in Beitza, Greek science discussed that hens require excitement (stimulation) to lay eggs, and could get rubbed/excited from the ground. And perhaps this -- what we would call hormonal -- connection extended to other species as well. Or they might envision it arising from psychosomatic causes - thus, Rav Nachman elaborated that if she intended to marry someone, her body would not have had that reaction.
When Rabin came he stated in the name of R. Johanan: A woman who waited ten years after [separation from] her husband, and then remarried, would bear children no more. Said R. Nahman: This was stated only in respect of one who had no Intention of remarrying: if, however, one's intention was to marry again she may conceive.
Raba said to R. Hisda's daughter: The Rabbis are talking about you. She answered him: I had my mind on you.A woman once appeared before R. Joseph, and said to him: Master, I remained unmarried after [the death of] my husband for ten years and now I gave birth to a child — He said to her: My daughter, do not discredit the words of the Sages. She thereupon confessed, 'l had intercourse with a heathen'.
Yet, this pronouncement is challenged by empirical evidence. Thus, Rava's wife was originally married to Rami bar Chama. She married Rava more than 10 years after Rami's death.
Raba said to R. Hisda's daughter: The Rabbis are talking about you. She answered him: I had my mind on you.Thus, the Rabbis were talking about her, either as a counterexample, or as someone who's conduct in the intervening time required explanation. She answered him based on Rav Nachman's elaboration. Depending on your reading, they were either wondering about the truth of Rabbi Yochanan's statement, or else never doubted it.
The woman who appeared before Rav Yosef seems to be challenging Rabbi Yochanan's statement with empirical evidence. Rav Yosef did not believe her, and asked her not to be motzi laaz on the words of the Sages. At which point she confessed.
This particular gemara does show concern for empirical evidence. On the previous Amud, the assumption was made that a woman cannot conceive from the first intercourse, and at the top of this amud, Rava points out that Tamar conceived from her first intercourse. But it is something to be resolved and harmonized, such that Rav Nachman answers what she did so as to be able to so conceive.
By the way, Rav Yosef's exchange with this woman reminded me of an earlier Biblical exchange, with a bit of midrashic elaboration. From Yehoshua 7:
According to midrash, Achan disputed this. He had, after all, been singled out by lot. To cite the midrashic account:
Joshua inquired of God, why trouble had befallen Israel, but God refused to reply. He was no tale-bearer; the evil-doer who had caused the disaster would have to be singled out by lot. Joshua first of all summoned the high priest from the assembly of the people. It appeared that, while the other jewels in his breastplate gleamed bright, the stone representing the tribe of Judah was dim. By lot Achan was set apart from the members of his tribe. Achan, however, refused to submit to the decision by lot. He said to Joshua: "Among all living men thou and Phinehas are the most pious. Yet, if lots were cast concerning you two, one or other of you would be declared guilty. Thy teacher Moses has been dead scarcely one month, and thou has already begun to go astray, for thou hast forgotten that a man's guilt can be proved only through two witnesses."
Endued with the holy spirit, Joshua divined that the land was to be assigned to the tribes and families of Israel by lot, and he realized that nothing ought to be done to bring this method of deciding into disrepute. He, therefore, tried to persuade Achan to make a clean breast of his transgression. Meantime, the Judeans, the tribesmen of Achan, rallied about him, and throwing themselves upon the other tribes, they wrought fearful havoc and bloodshed. This determined Achan to confess his sins. The confession cost him his life, but it saved him from losing his share in the world to come.
The midrashic elaboration is based on Yehoshua saying
|יט וַיֹּאמֶר יְהוֹשֻׁעַ אֶל-עָכָן, בְּנִי שִׂים-נָא כָבוֹד לַיהוָה אֱלֹהֵי יִשְׂרָאֵל--וְתֶן-לוֹ תוֹדָה; וְהַגֶּד-נָא לִי מֶה עָשִׂיתָ, אַל-תְּכַחֵד מִמֶּנִּי.|
The midrash explains this was in response to Achan's denial of the efficacy of the lot, since he had been chosen in the previous verse by lot. Achan agrees, confessing, saying:
וַיַּעַן עָכָן אֶת-יְהוֹשֻׁעַ, וַיֹּאמַר: אָמְנָה, אָנֹכִי חָטָאתִי לַיהוָה אֱלֹהֵי יִשְׂרָאֵל, וְכָזֹאת וְכָזֹאת, עָשִׂיתִי.
And Achan answered Joshua, and said: 'Of a truth I have sinned against the LORD, the God of Israel, and thus and thus have I done.
Why did Yehoshua ask him to confess? Because
Endued with the holy spirit, Joshua divined that the land was to be assigned to the tribes and families of Israel by lot, and he realized that nothing ought to be done to bring this method of deciding into disrepute.Similarly, Rav Yosef did not wish the words of Chazal to be brought into disrepute, and knowing that the woman must have withheld something, asked her to confess, which she did.
I don't know of any modern medical studies that would confirm this observation or the reverse, but must confess I would not be surprised if it were not the case.
I did see a recent article about how having intercourse actually can have an effect on a woman's body (hormonally), so that I can see the possibility that continuing to have intercourse or not could affect her ability to have children or prompt menopause.