後天 (kōten: not inborn) after + innate
Two suffixes change 後天 as follows:
後天的 (kōtenteki: acquired, cultivated)
The last kanji makes 後天 into an adjective.
後天性 (kōtensei: acquired trait)
The last kanji means “innate quality.”
If we chip the first character off this third compound, we find another word of intrigue and mystery lying inside: 天性. To learn what this word is all about, just follow the link.