How do we know that Adam's Fall affects all of humanity?

The concept of original sin is foundational to Reformed theology, asserting that because Adam was our representative, his disobedience brought sin and death to all humanity. This is succinctly stated in Romans 5:18-19, where Paul explains, 'Therefore, as one trespass led to condemnation for all men, so one act of righteousness leads to justification and life for all men. For as by the one man's disobedience the many were made sinners, so by the one man's obedience the many will be made righteous.' Adam's choice in the Garden had repercussions that extended beyond his own life, fundamentally altering the human condition, thus demonstrating our need for a Savior.