Contrary to traditional interpretations according to which eating from the tree of knowledge of good and evil was some “original” sin that brought all kinds of evils in the world, Genesis is quite explicit that the very first sin was not committed by Adam and Eve but by their first son, Cain, when he killed his own brother Abel for no reason. Although God made clear that he intended humans to multiply and populate the whole earth when he had planned their creation in the first chapter of Genesis, Adam and Eve had their first children only after they ate from the tree of knowledge of good and evil and were expelled from the garden of Eden. While all languages use euphemisms for sexual intercourse, what is interesting – and probably unique – about the Bible is that it uses the word “to know,” implying that sexual intercourse with the purpose and the awareness of having children is also the result of eating from the tree of knowledge. As a result of knowledge, humans not only have children, but the children develop skills so that Cain learns how to cultivate fields and Abel learns how to raise animals so that humans no longer depend for their food on what grows naturally as all other animals do, but are able to provide their own needs. Humans not only are able to provide their own needs, but they can provide way beyond their needs, and this ability is powerfully conveyed through a practice that humans adopted and is without any parallel in the animal world, that is, to offer sacrifices to a deity by which they basically destroy through fire some of the best that they produce. While in paganism gods always demand sacrifices and never reject any, what is again unique about the Bible is that God rejects Cain’s sacrifice. Although no reason is provided as to why God was displeased with Cain’s sacrifice, taking into account that sacrifices in the Bible are family meals in which the firstborn acts as an officiant, it would have been reasonable for Cain to conclude that God expected the two brothers not only to bring sacrifices together, but also to share what they produced since an abundant diet for humans includes both vegetable as well as dairy products. That is precisely the purpose of reasoned reality, that is, to enable humans to cooperate and therefore to vastly improve their productivity and enrich their lives. Instead of using his rationality to understand what God tried to teach him, Cain decides to kill his brother. In order to prevent the murder, God confronted Cain and explained to him that murder is a sin that for the first time would enter the word, and after Cain still went ahead and killed his brother and God confronted him again about what he had done, Cain could not provide any rational justification for this first sin, implying that sin is whatever humans do and cannot be justified rationally. Therefore, Cain and his descendants are credited with creating the violent societies that humanity has always known, with weapons, city walls for defenses, and violence that have no rational justification in human societies.