If one allows theirself to get wrapped up in terms like "sinful nature" which the Liberal NIV translators used for the Greek word that actually means 'flesh' (sarx), then one will have a difficult time understanding about the idea of sin, and how sin began. And I'm not talking about Adam and Eve either.
Apostle John said that the devil sinned from the beginning (1 John 3:8). John was pointing to the time 'of old' when Satan first rebelled in coveting GOD's throne. That happened in a previous world earth age that God ended prior to bringing this second one with Adam and Eve. So sin entered in first by Satan's acts, for in the parable of Ezekiel 28, God showed that He originally created Satan good, and that Satan was originally perfect in his ways with following God, until Satan rebelled (see also Isaiah 14 and Ezekiel 31).
Apostle John also defined sin. He said sin is the transgression of the law (1 John 3:4). For Satan to have been the first one to sin, it means God's law was established even back in that previous world earth age when Satan was perfect and followed God.
Understanding that old world then, and why God ended that old world because of Satan's overthrow, then one is ready to put God's creation of today beginning at Genesis 1:2 into perspective, including His creating Adam in the flesh, and the imperfection of flesh with its lusts and wants affecting Eve to cave into sin when tempted by Satan ("that old serpent") in God's Garden of Eden.
Our flesh, which God created for this present world time, and is to be destroyed, is never meant to be perfect. Nor can it ever be made perfect. It is a body of corruption, doomed to destruction back to the elements where it came from, either at flesh death, or at the change on the "last trump" (1 Corinthians 15:50-54).
So just who... are those who try to make us believe that flesh can ever... become perfect? The Occultists, because that is the very idea they teach. Even with the eastern religion of Buddhism, they believe that once you get everything right in your living in this world, you will then have no need to be reborn, and are loosed from the supposed 'wheel of Karma', and become perfect, having achieved Nirvana. Those occult ideas are actually the same old temptation that Satan did upon Eve in God's Garden, the idea of one born in the flesh becoming their own god.
Few understand what their theory of evolution is actually about involving this matter. Darwinism is actually allied with the Occultists. The occultists centuries ago (long before Darwin), proposed that life evolved from water, and then evolved to mineral and plant life, and then to animal life, and then to a man. But the occultists don't stop there. Their final theory of evolution is from a flesh man to a... god! And that is actually where the idea that our flesh can be made perfect originates. It's not from The Bible, because God's Word shows that our flesh is going to be destroyed along with this 2nd world earth age (1 Corinthians 6:13).
In the future world to come, our flesh will be cast off, not needed any more. This is the change that Apostle Paul was talking about in 1 Corinthians 15. We instead will put on the "spiritual body", which is the body type of the world to come.
