Per capita income and human population levels in a country have direct influences on its environmental outcomes. Countries with same level of income may have different rate of income growth and vice versa, suggesting that the influence of the rate of income growth on environmental outcomes could be different than that of income level. Similarly, the rate of population growth might have different impact in addition to the impacts of sheer number of population. We explore this empirical question using country-level data on threatened species published by IUCN for the year 2007. Controlling for other factors, our model estimates the influences of the rate of population and income growth on threatened mammals and birds across 113 continental countries. The results suggest that, among other factors, the rate of population growth has significant influences on number of threatened mammals and birds.