The most common and most likely answer to this crossword clue is the 8 letter word ATAVISMS
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Buddy explains!

The straight part
We know that "resemblances to ancestors" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case resemblances to ancestors = atavisms.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ATAVISMS mean?
ATAVISMS noun- The reappearance of an ancestral characteristic in an organism after several generations of absence.
- The recurrence or reversion to a past behaviour, method, characteristic or style after a long period of absence.
- Reversion to past primitive behavior, especially violence.