Besides the common acceptation of this word, as signifying race, descent, lineage, it is used for the history and genealogy of a person, as in Genesis 5:1, "the book of the generations of Adam," that is, the history of Adam’s creation and of his posterity. So in Genesis 2:4, "The generations of the heavens and of the earth," that is, their genealogy, so to speak, the history of the creation of heaven and earth; also in Matthew 1:1, "The book of the generation of Jesus Christ," that is, the genealogy of Jesus Christ," that is, the genealogy of Jesus Christ, the history of his descent and life. "The present generation" comprises all those who are now alive; "This generation shall not pass till all be fulfilled," some now living shall witness the even foretold, Matthew 24:34. "Save yourselves from this untoward generation," form the punishment which awaits these perverse men, Acts 2:40.
The Hebrews, like other ancient nations, sometimes computed loosely by the fourth generation thy descendants shall come hither again." The duration of a generation is of course very uncertain; indeed, it is impossible to establish any precise limits. It is, however, generally admitted that a generation in the earliest periods is to be reckoned longer than one in later times. The Greeks regarded a generation as one-third of a century. It is now currently reckoned as thirty years.