Frankly, early tribes of nomadic humans had little choice but to copulate and reproduce with their own offspring and close relatives bonobo-style, since the human population was sparse…as in the oft-asked questions by bible students, from where did Cain obtain his wife? What were Lot's daughters thinking? Clearly depicting that highly populated regions (such as China) have become so by reproducing with their own offspring in the past, as literal mother-fuckers, daughter-daters, father-rapers, close siblings, kissing cousins, and so on. Casting aspersion upon outsiders, whether deservedly or not, is simpler and easier, going with what one seemingly knows for sure (see 安). Sex with one's offspring is the paradigm of LUXURIANT REPRODUCTION since it requires minimal effort, generally does not require paying a fee, has the greatest chance of producing offspring due to repeated intercourse, and in some early cases with one's very young children assures that the parent will not catch the clap or the pox (syphilis)…but not saying anything for one's child, however.
「Emerging shafts with ability to distinguish and recognize the difference between clean emissions of semen and those with gonorrhea」and 「screwing in orifice」is the only way to safely REPRODUCE and PROLIFERATE.
「In traditional Chinese medicine, there has never been a mental disease called pedophilia (or an equivalent term), or homosexuality, or most of the other so-called sexual variations for that matter. …Children are usually described as natural sexual beings and erotic stimulation and sex-play are seen as beneficial to their healthy development.」
[ https://docx2.com/wp-content/uploads/Are-Any-of-the-Pharaphilias-in-DSM-Mental-Disorders_.pdf 2023-05-14 ]
Perhaps the source of the Chinese quip loosely translatable into English as「incest is best.」
「Historical accounts from the 18th century indicate that adult-child sex (particularly same-sex pairings) were an accepted practice in China, Japan, Africa, Turkey, Arabia, Egypt, and the Islamic areas of India (Trumbach, 1977). In 19th century London the going price for a virginal, 12-year-old girl, of good background, was reported to be 400 pounds (Bullough, 1964).」
[ https://www.ipce.info/library/journal-article/legal-social-and-biological-definitions-pedophilia 2012-01-01 ]

External source definitions …excluding politically incorrect concepts and other meanings deemed offensive today; may include extended definitions, euphemisms, and mnemonics)
Chinese: luxuriant; flourishing; to reproduce; to proliferate; see 吐蕃
Japanese EDRDG: grow luxuriously
Unihan extended: foreign things

Used within names (nanori)
しげ　･　しげる　･　ば