THE QUESTIONS ：The Top 25 (what we don't know?)

  Essays by our news staff on 25 big questions facing science over the next quarter-century.

> What Is the Universe Made Of?

> What is the Biological Basis of Consciousness?

> Why Do Humans Have So Few Genes?

> To What Extent Are Genetic Variation and Personal Health Linked?

> Can the Laws of Physics Be Unified?

> How Much Can Human Life Span Be Extended?

> What Controls Organ Regeneration?

> How Can a Skin Cell Become a Nerve Cell?

> How Does a Single Somatic Cell Become a Whole Plant?

> How Does Earth's Interior Work?

> Are We Alone in the Universe?

> How and Where Did Life on Earth Arise?

> What Determines Species Diversity?

> What Genetic Changes Made Us Uniquely Human?

> How Are Memories Stored and Retrieved?

> How Did Cooperative Behavior Evolve?

> How Will Big Pictures Emerge from a Sea of Biological Data?

> How Far Can We Push Chemical Self-Assembly?

> What Are the Limits of Conventional Computing?

> Can We Selectively Shut Off Immune Responses?

> Do Deeper Principles Underlie Quantum Uncertainty and Nonlocality?

> Is an Effective HIV Vaccine Feasible?

> How Hot Will the Greenhouse World Be?

> What Can Replace Cheap Oil -- and When?

> Will Malthus Continue to Be Wrong?