According to both a 2016 article and a 2011 article in Deseret News, eight of twelve children that Joseph Smith, Jr. allegedly fathered by plural wives have been proven by DNA not to be his children. This is too substantial of a number (two-thirds) to be ignored and has great implications in proving that Joseph didn't practice polygamy. It is interesting, though, that Web sites promoting Joseph Smith as a polygamist either ignore these findings or state they only prove that he didn't have children by these plural wives--not that he didn't have plural wives. However, the fact of the matter is that presently these findings strongly suggest that Joseph Smith did not practice polygamy.
So, how will not having any children by alleged plural wives prove that Joseph didn't practice polygamy? To answer this question, we must first understand one of the basic purposes of practicing polygamy in the early LDS Church. According to the article on Women and Polygamy at the Mormon Polygamy Web site, "...one of the stated purposes of polygamy was to 'raise up seed unto the Lord....'" In addition Todd Compton, a noted author regarding Joseph Smith and polygamy, in an article for the Signature Books Library, The Four Major Periods of Mormon Polygamy, states "There [in Nauvoo] he [Joseph Smith, Jr.] combined restorationist biblical polygamy with the idea that one gained a higher status in the next life based on the quantity of wives and offspring in this life. This gave the religious rationale for large plural families in later Mormonism." Also, "with very few exceptions ... polygamy was oriented toward childbearing." It would appear, then, that having children was an objective of plural marriage. Further evidence supporting this purpose of polygamy is found in the Utah LDS interpretation of Book of Mormon scripture. The Utah LDS Book of Mormon, Jacob 2:30, states: "For if I will, saith the Lord of Hosts, raise up seed unto me, I will command my people; otherwise they shall hearken unto these things." The Utah LDS Church interprets this scripture to mean that if the Lord is going to raise up a people unto Him, then He will command them to practice polygamy. Again, the implication is that the purpose of polygamy is to procreate so that the Lord can have a righteous people. However, the most important evidence supporting this position is Utah LDS Church law about celestial marriage (polygamy). According to the Utah LDS Church, a revelation on celestial marriage (Section 132 of the Utah LDS Doctrine and Covenants) was written by Joseph in 1843, but God had revealed to him the principles and doctrines of this revelation as early as 1831. In part this document states, "for they [plural wives] are given unto him [the husband] to multiply and replenish the earth, according to my commandment..." (Utah LDS Doctrine and Covenants 132:63). Thus from the above references, including the law upon which celestial marriage was based in the Utah LDS Church, it is clear that a basic purpose of plural marriage was to procreate.
As stated above, the Utah LDS Church alleges that Joseph was the one through whom God gave the celestial marriage law. If this is true, Joseph would have known from the revelation that procreation was a part of that law. And as the prophet and leader of the Church, he would have been obliged to obey that law of God to the fullest extent. If he didn't, he would lead his people away from God's promise that in eternity they would "be gods, because they have no end; therefore shall they be from everlasting to everlasting, because they continue; then shall they be above all, because all things are subject unto them. Then shall they be gods, because they have all power, and the angels are subject unto them" (Utah LDS Doctrine and Covenants 132:20).
Therefore, if the Utah LDS Church and Community of Christ Church and most historians are correct that Joseph taught and practiced polygamy, he would have necessarily tried to father children by polygamous wives. This is true because, as shown above, procreation was a purpose of celestial marriage. And Joseph, as prophet and leader of the Church, knew the law and would have tried to obey it. In addition, the number of children he fathered with Emma (9 children born from 1828 to 1844) shows he had the ability to procreate during the time period that the Utah LDS Church alleges he knew about the doctrine of celestial marriage. Thus, if Joseph practiced polygamy, because of the law of celestial marriage, he would have fathered children by his polygamous wives. Half of the children alleged to have been fathered by Joseph and polygamous wives were proven by DNA not to be his children. Considering that procreation was a purpose of celestial marriage, these DNA results are strong evidence that Joseph didn't practice polygamy. And one day, when DNA evidence proves Joseph didn't father any children outside of his union with Emma, Joseph will be proven innocent of practicing polygamy.