The doctrine of worthier title, like the Rule in Shelley's Case, had its origin in attempts by royal courts to defeat various devices contrived by lawyers during the era of feudalism to retain lands in their families while avoiding feudal duties, and to secure its free alienability.
The creation of family settlements designed to preserve land within the family, transfer it without feudal duties due to the lords of the fee upon transfer at death, and preserve it from claims of creditors, occupied the ingenuity of many common lawyers during the late Middle Ages.
These concerns underlie the explanation given in Coke on Littleton: But if a man makes a gift in tail, or a lease of life, the remainder to his right heirs, this remainder is void, and he hath the revision in him; for the ancestor during his life beareth in his body in judgment of law all his heirs, and therefore it is truly said that haeres est pars antecessoris.
This interpretation draws strength by analogy from the common words of a conveyance in fee simple, "to N. and his heirs."
Adam's intent in these words of conveyance would appear to be to grant Beulah a life estate, and then create a vested remainder interest in his apparent heirs Caleb and Dinah.
By the operation of the instrument, Edward would have a life estate in the land, while Fran would inherit the rest of the estate immediately; then "Adam's heirs" – i.e., Dinah – would have a vested remainder interest in the land, and expect to inherit it upon Edward's death.
Instead of a life estate in Edward, followed by a vested remainder in Dinah, the doctrine of worthier title operates to disinherit Dinah completely, treats the interest of the heirs as a mere reversion, and upon Edward's death gives the land, as well, to Fran.