Lucretius, De Rerum Natura
William Ellery Leonard, Ed.

     And when perchance, in mingling seed with his,
The female hath o'erpowered the force of male
And by a sudden fling hath seized it fast,
Then are the offspring, more from mothers' seed,
More like their mothers; as, from fathers' seed,
They're like to fathers. But whom seest to be
Partakers of each shape, one equal blend
Of parents' features, these are generate
From fathers' body and from mothers' blood,
When mutual and harmonious heat hath dashed
Together seeds, aroused along their frames
By Venus' goads, and neither of the twain
Mastereth or is mastered. Happens too
That sometimes offspring can to being come
In likeness of their grandsires, and bring back
Often the shapes of grandsires' sires, because
Their parents in their bodies oft retain
Concealed many primal germs, commixed
In many modes, which, starting with the stock,
Sire handeth down to son, himself a sire;
Whence Venus by a variable chance
Engenders shapes, and diversely brings back
Ancestral features, voices too, and hair.
A female generation rises forth
From seed paternal, and from mother's body
Exist created males: since sex proceeds
No more from singleness of seed than faces
Or bodies or limbs of ours: for every birth
Is from a twofold seed; and what's created
Hath, of that parent which it is more like,
More than its equal share; as thou canst mark,-
Whether the breed be male or female stock.