Why are various categories of animals, and then man, encouraged to “be fruitful, and multiply” (Gen 1:22, and in the case of man, at 1:28)?

What is the significance of this injunction? Reproducing and flourishing as a group seems to be both specially valued by God and is presented as a blessing (“God blessed them, saying”; 1:22). Othernatural processes are not similarly blessed; probably, there is some special meaning behind an emphasis on reproduction, particularly because it is repeated several times as a blessing, promise, or injunction (especially at Genesis 9:7, after the Flood: “be ye fruitful, and multiply; bring forth abundantly in the earth, and multiply therein”). In short, life as such is specially prized by God: sacrificing the life of the most valuable animals atoned for sin; the most serious sins concerned unjust killing as well as improper reproduction; and the very most horrible pagan heresies involved sacrificing human life, especially a child’s life. Accordingly, the greatest reward of the Hebrews was to “multiply thy seed as the stars of the heaven, and as the sand which is upon the sea shore.” (Gen 22:17) Moreover, one of the saddest and desperate conditions of a young woman in the Bible was the inability to bear children. Life, in the Bible, is repeatedly shown to be among the greatest of blessings and holiest of things we can value.