http://www.facebook.com/ScienceReason ... Complexity (Chapter 4): The Origin Of Life: Chemistry + Biology = Abiogenesis
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Stars like our own Sun form from gas clouds that have about every kind of element there is as well as some pretty complicated molecules. Stuff leftover after the sun forms usually turns into a system of planets. Some of these planets have solid surfaces, perhaps liquid seas and a gaseous atmosphere; a rich environment for atoms and molecules to come together in complex chemical reactions.
Carbon atoms in particular, link together to form complex organic molecules and amino acids. Chemical catalysts speed reactions along. The products of one chemical reaction become the raw material for new reactions. At some level of complexity a catalyst became an enzyme, an amino acid chain became a protein, a loop of chemical reactions became a metabolism, and chemistry became ... biology.
On our own planet, and perhaps countless others - life arose. The DNA molecule, which is the basis of all organic life on Earth, is more intricate by far than any spiral galaxy - because the structure of DNA contains something new - something that was missing from inanimate matter before the origin of life - it contains information. The DNA molecule encodes not only the information necessary to make copies of itself, but the information necessary to construct an entire organism.
The blueprints for an ant or a dolphin or a bullfrog or a person ... all of this information is somehow built into the structure of an organism's DNA in a molecular code billions of letters long. This information wasn't always there. The first DNA molecules could probably do little more than make copies of themselves from the surrounding molecules.
This self-reproduction is a fundamental aspect of what we call "life". And once there was life, a new set of rules took over - the laws of natural selection.
Life became matter that evolved as a result of environmental pressures ... matter that changed randomly ... but those changes endured if they improved a lifeforms chances of survival in each environment ... Change with a purpose.
While species evolution is determined by the interaction of random changes and environmental pressures, changes in an individual life form can be the result of that organism reacting and adapting within its own sphere of influence - it can push back at its environment.
The better a system was at making copies of itself, the more copies there were in the next generation. As the first living organisms adapted to ever-changing environments, a great diversity of living things arose. A side effect of this increased diversity was increased complexity.
Single-cells soon joined together to form multi-cellular colonies. And cells in these new colonies - once functionally interchangeable - became increasingly specialized, some cells did the digesting, others became responsible for movement.
Specialized cells led to specialized tissues and organs. And, most importantly, cells that could respond to light or electricity or chemical disturbances evolved into full-fledged nervous systems.
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