In a study of whether phonological inventories have become more or less complex over time, Marsico (1999) shows that languages dating back as far as 10,000 years are equally-complex in terms of their number of segments, consonant/vowel ratio, average number of consonants and vowels, and frequency hierarchy of the segments.
marsico (1999) also notes that modern languages tend to have slightly more consonants today than their ancestors did in the past.