Is it permissible to bury males and females in a single grave?

There is a scholarly consensus on the impermissibility of burying more than one individual in a single grave unless [absolutely] necessary, as when there is insufficient space [in the graveyard], the absence of someone capable of digging a grave, or when another one is not available. The Messenger of Allah and his Companions were accustomed to burying each individual separately except out of a necessity.

When a necessity exists, the most meritorious is buried first facing the qibla [En. direction of prayer] followed by the next in the degree of merit and according to the order of preference concerning the imamate [En. leading others in prayer]. This is because of the hadith narrated by Jabir who said:

We complained to the Messenger of Allah on the day of Uhud and said: "O Messenger of Allah! It is a hardship upon us to dig a grave for every [dead] person!" So the Messenger of Allah said: "Dig deep, dig well, and bury two or three persons in a single grave".
They said: "O Messenger of Allah! Whom should we bury first?"
He replied: "Bury the one who memorized Qur`an the most".
Jabir said: "My father was the third of three to be buried in the same grave" [Bukhari and others].
A wall of earth is made as a barrier between two individuals buried in the same grave. A father is buried before his son out of respect, even if the son were more meritorious; a mother is buried before her daughter; women must not be buried in the same grave with men unless this is confirmed to be a necessity and on the condition of making a barrier of earth between them; a male is buried before a female, even if he were her son, and a male is placed at the head of the grave and the female at the foot.
Allah the Almighty knows best.