Picture a circle that has been closed for a long time. Whatever is inside it came from inside it, and nothing has arrived from outside for generations. The same features keep coming round, the same weaknesses too, and after a while nobody in the circle can see what is missing, because there is nothing there to compare with. That closed circle is the one picture behind all three uses — the only thing that changes is what is being kept inside it.
The packet gives the make-up directly: inbred is the past participle of inbreed, which is in- plus bred. So the word literally says bred within, and the source's own first gloss for the character sense is 'bred within; innate'.
來源把組成寫得很清楚：inbred 是動詞 inbreed 的過去分詞，也就是 in-（在裡面）加上 bred（繁殖、長出來的）。字面上就是「在裡面長出來的」。來源在講性格那個意思時，第一句解釋正好也是 bred within（在裡面長出來的），所以兩個用法的關係在字典裡就看得到，不用另外推測。
Wiktionary (kaikki) entry for inbred, source_ref kaikki:3f6f69a190036ae4:647858166:11227, etymology_text 'From the past participle of inbreed, equivalent to in- + bred', with sense gloss 'Bred within; innate'.
Three branches
血緣：圈子裡生出來的
字面意思，核心畫面本身：關著的圈子裡關的是血緣。
adjective · C1
Bred from parents that are close relatives, often over several generations, so that the animals, plants or people in that line share most of the same family background and very little new comes in.
近親繁殖的
性格：從小長在身上的
圈子還是關著的，但裡面關的不是血緣，而是一個人從小長出來的傾向：沒有人教，也拿不掉。
adjective · C1
Used about a quality, feeling or habit that has grown in someone from very early on and now seems part of who they are, rather than something they were taught or decided later.
天生的、根深蒂固的
群體：只跟自己人往來
圈子關著的是一群同事。沒有人是親戚，但人、想法和肯定都只在內部流動，效果跟血緣封閉一樣。
adjective · C1
Used about a group, organisation or profession that mostly draws its members, its ideas and its praise from inside itself, so that little comes in from outside.
封閉近親化的