One way of avoiding the problem of determining which features are original and which are inherited is to use a computational methodology such as lexicostatistics, with one of the earliest attempts being Fleming 1983.
wˈʌn wˈeɪ ʌv ɐvˈɔɪdɪŋ ðə pɹˈɑːbləm ʌv dɪtˈɜːmɪnɪŋ wˌɪtʃ fˈiːtʃɚz ɑːɹ ɚɹˈɪdʒɪnəl ænd wˌɪtʃ ɑːɹ ɪnhˈɛɹɪɾᵻd ɪz tə jˈuːz ɐ kˌɑːmpjuːtˈeɪʃənəl mˌɛθədˈɑːlədʒi sˈʌtʃ ɐz lˌɛksɪkˌɔstɐtˈɪstɪks, wɪð wˈʌn ʌvðɪ ˈɜːlɪɪst ɐtˈɛmpts bˌiːɪŋ flˈɛmɪŋ nˈaɪntiːnhˈʌndɹɪd ˈeɪɾi θɹˈiː.