Lucrecio en el Libro I “Sobre la naturaleza
de las cosas” (Rerum Natura)
“Nada ha emanado de nada por voluntad divina”
Your serpent of the Nile is bred now of your mud by the operation of your sun:
so is your ....
Antony and Cleopatra, Act II, Scene VII
For if the sun breed maggots in a dead dog, being a god-kissing carrion,—
Have you a daughter?
Hamlet, Act II, Scene II
William Shakespeare (1564-1616)
How, in short, did life begin?
• When the earth formed some 4.6 billion years ago, it was
a lifeless, inhospitable place.
• A billion years later it was teeming with organisms
resembling blue-green algae.
• How did they get there?
• … in the mid-19th century two important scientific advances
• set the stage for modern discussions of the origin of life.
discredited the concept of spontaneous generation.
He offered proof that even bacteria and other microorganisms arise from parents
The second advance, the theory of natural selection, suggested an
answer. According to this proposal, set forth by Charles Darwin and
Alfred Russell Wallace.
• Protobionts are abiotically created molecules surrounded
by a membrane.
– They can engage in simple reproduction and metabolism
– The can maintain an internal environment different than the
• Liposomes can spontaneously organize in water from
lipids and organic molecules
• Oparin-Haldane hypothesis—Early earth was a reducing
atmosphere that led to synthesis
• Miller and Urey tested the hypothesis which yielded amino
– Demonstrated that abiotic synthesis was possible
– Analysis of meteorites show presence of AAs
• Synthesis of macromolecules may have been initiated by
formation of AA polymers
• In the 1920s Oparin and Haldane proposed that the energy to produce the organic
compounds could come from lightning or intense UV radiation.
• In 1953 Stanley Miller and Harold Urey of U of Chicago tested the Oparin-Haldane
hypothesis. Others have tested it as well with different recipes for the atmosphere.
The major part of the hypothesis may not be correct in that the atmosphere of earth
may not have been reducing nor oxidizing. IT is thought that pockets near volcanic
openings were reducing and that first organic compounds formed near underwater
• The abiotic synthesis of macromolecules may have occurred through the dripping of
amino acid solutions on hot sand, rock or clay. This forms a AA polymer that could
act as a weak catalyst for other reactions.
What was first: chicken or egg? That is: DNA or proteins?
Surprising answer emerged recently: none of the above.
It was probably RNA! Whole life could have started with RNA (and proteins), which evolved
into DNA. This idea is called an “RNA world” hypothesis.