What don't we know? The 125 biggest questions facing science

To celebrate its 125th anniversary the July 1 issue of Science magazine focused on the 125 biggest quandaries so far not understood by scientists.

The journal surveyed more than 100 leading researchers in myriad disciplines and asked them to focus on questions that have a chance of being answered within the next 25 years.

It took 17 drafts to whittle the list down to 125.

Here are the top 25:

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?