According to Shi'a Islam, there was no incest.
Here's a brief summary from Hayat-al-Qulub Volume 1, Section 2 (Merits of Adam and Hawwa’ (Eve), Reasons behind naming them so, the beginning of creation).
Adam had 70 twins. Every twin consisted of a boy and a girl. Thereafter, Allah gave him 2 sons, one after another, called Shith and Yaafith. When both grew up and Allah wanted to multiply human beings and as the Qalam had made the sisters unlawful for their brothers, Allah sent a huri, Nazala and ordered Adam to marry Shith to her.
Next day another huri, Mauzela was sent and Allah ordered that Yafith be married to her. Adam did as was told. Shith got a son and Yafith a daughter. When both attained maturity Allah ordered Adam to marry them and Adam obeyed.
Since Shith (or Hibtullah), was the first successor to whom a will was made, the lineage of Prophets and Messengers of Allah began from him.
For the beginning of the lineage of common men,
When Haibatullah was born and attained maturity, Adam asked Allah to provide a wife for his son. Allah sent a huri and Adam married her to his son. Through her, four sons were born. Then Adam had another son. When he grew up he was married to a Jinn woman and she gave birth to four girls. Later Shith’s sons were married to the daughters of the Jinn woman. Therefore beauty from the huri and forbearance is from Adam, while every bad quality, ugliness and stupidity is due to the Jinn woman. After giving birth to sons, the huri returned to the heavens.