Original sentence: Others say that these features are arbitrary, and point to the the internal construction of the double bass, which is proportionately identical to the violin's, as a more weighty piece of evidence than the external features.While the violin, viola and cello are true members of the ancestral violin family, the double bass's origins are disputed It is sometimes taken to be part of the viol family, due to its sloping shoulders, its tuning, and its sometimes flat back
Edited sentence: While the violin, viola and cello are true members of the ancestral violin family, the double bass's origins are disputed--commonly mistaken to be of the viol family, due to its sloping shoulders, its tuning, and its sometimes flat back, but these features are arbitrary,  the internal construction of the double bass is proportionately identical to the violin's