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Of all species that have existed on Earth, 99.9 percent are now extinct. Many of them perished in five cataclysmic events.

According to a recent poll, seven out of ten biologists think we are currently in the throes of a sixth mass extinction. Some say it could wipe out as many as 90 percent of all species living today. Yet other scientists dispute such dire projections.

As our panelists debate the issue, they also consider how one species -- Homo sapiens -- may be triggering a modern mass extinction.

are we in the midst of a mass extinction
  Question submittal is now closed. Please go to the forums to read our panelists' answers to the user questions.
Ariel E. Lugo (a man)Ariel E. Lugo is director of the USDA Forest Service International Institute of Tropical Forestry in Río Piedras, Puerto Rico. An ecologist, his research has focused on tropical ecosystems, particularly rain and dry forests and forested wetlands.

Predictions about the level of species extinctions on Earth have all overestimated the process. There are many reasons why scientists are failing with these predictions. For example, we don't know how many species there are in the world, we don't have a sound method for estimating extinction rates, and we don't understand how species respond to human and natural disturbances. Subjectivity dominates the dialogue when facts are hard to come by.

I believe that we are not in the throes of mass extinction. Our approach to the problem is not balanced.
  • Rates of species extinction are overestimated because natural resilience is underestimated.
  • We list the reasons why natural ecosystems are fragile, but we don't list the reasons why they are resilient.
  • Attention is given to the factors that might play against species survival, while little attention is given to the mechanisms that allow species survival in a human-dominated world.
  • Attention is given to deforestation, but not as much to forest recovery.
  • The negative effects of alien species (those that are relatively new to a habitat) are highlighted, but their positive roles are ignored.
  • Data that show increasing number of species per area after disturbances are ignored, because we tend to value species by their rarity or date of arrival to a particular location.
  • We focus on destructive human activities but ignore the positive contributions that humans make through ecosystem management.
The quality of the debate will improve when we adopt a holistic approach to evaluating the turnover of species on Earth, incorporate all relevant factors into the equation of extinction and survival, and shed our biases against those species that somehow are held in low regard.
(Boldface added.)
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