01:32
Building Blocks: Mass Extinctions
The ultimate example of an environmental change leading to the termination of a species is what's known as a mass extinction.
03:16
Building Blocks: Role of Evolution in Early Life
The ability to adapt to changing or difficult conditions is clearly necessary if an organism is to be biologically successful.
01:42
Disappearing Species and the Endocrine System
Zoologist and World Wildlife Fund senior scientist Theo Colborn talks about the impact of environmental toxins on the endocrine systems of exposed animals. Dr. Colborn observes that some of the species being affected have been in existence for milli...
02:28
Trees and Other Critical Resources
Former Sierra Club president David Brower talks about the value of critical resources, including trees, soil, water and rapidly disappearing species.