The solution of the riddle in Text 4 in the Geraardsbergen Manuscript is: Cain
Cain is Adam and Eve’s first born child. Since Adam was never born, but made of clay by God, Cain was born before Adam was born. Eve as well was never born, but she was made from one of Adam’s ribs.
Cain is also known to be the first crop farmer. Adam’s ‘mother’ was the clay he was made from, so Cain’s grandmother is Mother Earth. By planting and growing crops he took the earth’s virginity.
Adam and Eve’s second child was Abel, who became shepherd. When both he and Cain offered God some of their produce, God was very grateful for Abel’s offerings, but hardly payed any attention to Cain’s. This made Cain so angry that he killed his younger brother. The earth’s population thereby was reduced from 4 to 3, a quarter of all mankind was slain by Cain.
See also: Genesis 4,1-8.
Read more about riddles in the Middle Ages.