Several instances exist in the Doctrine and Covenants where Joseph Smith, the LDS Prophet during the time when most of the D&C revelations were received, was chastised for mistakes he had made while as prophet. From the outset, then, it has been clearly demonstrated that LDS leaders are fallible.
One of the major hangups people have with the LDS Church is a misinterpretation of LDS President Ezra Taft Benson's speech, "14 Fundamentals in Following the Prophet" which includes the statement that the prophet will never lead the Church astray. Those who misunderstand Benson's words think that thereby the LDS Church teaches that prophets are infallible. It does no such thing. It is true that the prophet will never lead the Church astray, but that is in large part because the same Holy Spirit that animates and teaches prophets should animate and teach members of the Church as well, helping us to see when he when a prophet is speaking as a prophet and when he is speaking his own opinion.
Unfortunately, there is some celebrity that follows being an LDS Prophet or Apostle or some other general leader of the Church. This should not be. With that celebrity comes the mistake of treating as infallible truth not only everything such leaders say, but especially what is published in books under their authorship This also should not be. Joseph Fielding Smith warned about such shortsightedness:
You cannot accept the books written by the authorities of the Church as standards in doctrine... Every man who writes is responsible, not the Church, for what he writes. If Joseph Fielding Smith writes something which is out of harmony with the revelations, then every member of the Church is duty-bound to reject it.It is important for members of the Church--and especially missionaries--to not allow anti-Mormons to dictate to them what the Church supposedly teaches. Perhaps the most prominent of such foistings by detractors whose goal is really to destroy the Church rather than to be truthful, is "The Adam/God Theory" that Brigham Young may or may not have taught. Regardless of what Brigham Young said, this theory is not and never has been LDS Church doctrine. If it were a doctrine of the Church, we'd be teaching it from time to time in Sunday School and hearing about it every now and then in LDS General Conference. That doesn't happen.
Does the LDS Church have an official position on the Theory of Evolution? No, it does not. It leaves research on such scientific issues to the scientists. However, does the LDS Church have a position on the origin of man? Yes, it does. That much has been revealed. The LDS First presidency issued a statement in 1909 that clarified that humanity is the offspring of divine parents and not part of the same evolutionary process as the animals.