` :The problem is that we don't know for certain.  If we knew the exact number of species alive on the planet today and could easily assess the status of those populations, then there would be no debate.  Generally speaking, among the scientific community, it is agreed that we are in the middle of a human-caused mass extinction since nearly every living system on this planet is in decline.  Animal and plant populations are falling as humans convert the biomass of this planet into human mass and/or destroy habitat to produce goods. :Aside from this, another reason why this argument stands despite a lack of definitive numbers is that tropical forests are being cleared before scientists can even determine what species exist within them, yet expeditions around the world have also shown that small patches of forest like these can contain dozens of new species of small vertebrates and hundreds of new species of insects (for example).  Therefore it is very likely that many species are going extinct even before we know that they exist.  Unfortunately we can't go back and see what existed before a forest was cleared, so we may never know what was lost or the exact extinction rate over the last few decades or centuries.  But then again, mass extinctions from the distant past are also based on estimates since not all species fossil, and fossil sites are not found ubiquitously around the globe. :Honestly, the only ``debate`` I have seen on this topic is within the entertainment circle (i.e. the news media), were controversy rules, regardless of merit.  I am all in favor of keeping articles (such as this one) in line with NPOV, and I have not looked for this debate within this article or related articles.  If such a debate is represented, here or elsewhere, only verifiable sources should be used.  Sadly, like any other political debate, there may be a lot of information out there on this topic, but very little of it may have any value. –  `