Answer by Oliver Starr:
I'm not sure it's possible to answer this question with any degree of accuracy since we haven't even reliably identified all terrestrial vertebrates and have only limited knowledge of the numbers of many. There's even great controversy about how many wolves there are in just a few states, for example. Even though that number is a trivial component of total weight, every little bit adds up.
The one thing we can be sure of is that the ratio gets worse every year. Humans have virtually no selective pressure put upon them while wild animals have more every year.
Making matters worse, poaching, mining, deforestation, competition for range with domestic livestock and the ever increasing demand we humans have for land are all reducing the numbers and thus weight of the wild denizens of our planet.
It wouldn't surprise me at all if we were close to 99% vs 1%. This is a sad statistic considering that as recently as 700,000 years ago, humanity was nearly wiped out:
Thus, in just a blink of the evolutionary eye, we went from an inconsequential component of the terrestrial vertebrate population to one that is not only dominant buy massively so.