Cain Was Not a Son of Adam

 Here's the evidence found in Scripture that Cain was not the son of Adam.

Jude 14 And Enoch, seventh from Adam, prophesied to these saying “Behold, the Prince has come with ten thousands of His saints 15 to execute judgment against all and to convict every soul for all of their impious deeds which they committed impiously and for all of the harsh things which the impious wrongdoers have spoken against Him!”

Jude seems to be referring to Enoch 1:9, which says in the Charles edition: “9. And behold! He cometh with ten thousands of His holy ones, to execute judgement upon all, and to destroy all the ungodly: and to convict all flesh of all the works of their ungodliness which they have ungodly committed, and of all the hard things which ungodly sinners have spoken against Him.”

Note that Jude calls Enoch “seventh from Adam”. In Charles' 1 Enoch, at chapter 60 verse 8 Enoch is also called the “seventh from Adam”. Adam himself does not count here, Enoch being seventh from Adam. Therefore, either Cain or Abel – but not both, must be included in this reckoning in order to arrive at 7 first-born males. There is no other way to reckon Enoch as “seventh from Adam” within the confines of Scripture. What can this refer to, except first-born males?

Seth, replacing the murdered Abel, therefore inherits the rights of the first-born from him. So we have: 1-Abel 2-Seth 3-Enos 4-Cainan 5-Mahalaleel 6-Jared 7-Enoch, and this also demonstrates the exclusion of Cain from his birth.

Thanks to Don Brown for writing this up - saved me the time.