Verse 1 is subordinate to verse 2 and contains two parts.

When men began to multiply opens this account very abruptly without any reference to what went before. Men is ʾadam as a collective noun, and so Good News Translation has “people.” The rendering “people” should be used in other languages also, if men refers only to adult males. Began to multiply means that human beings were starting to become numerous in relation to what they were at the beginning. In some languages it is quite natural to say “When people began to become numerous…”; in others a continuous tense or form of the verb can be used: “As people were increasing….”

On the face of the ground indicates that they were spreading out, expanding from the original place of creation. The sense of this expression is “all over the earth, everywhere.” New English Bible translates “to increase and spread all over the earth,” and Biblia Dios Habla Hoy “They began to populate the earth.” In some languages this is expressed simply as “Many people had come into the world and….”

The second observation and daughters were born to them does not mean that daughters had not been born before this time, but this is the narrator’s way of focusing his comments upon the beauty of the women in Gen 6.2. Daughters emphasizes the relation of these young women to their parents and ancestors. In some languages daughters were born to them may require rewording to say, for example, “When people began to increase and spread throughout the world, and they had daughters….”

Quoted with permission from Reyburn, William D. and Fry, Euan McG. A Handbook on Genesis. (UBS Helps for Translators). New York: UBS, 1997. For this and other handbooks for translators see here .