Page 186 - The Evolution Impasse 2

184 RNA World Scenario, The

that these then com bined to geth er to ron men tal con di tions, this RNA
give rise to the cell. In the 1970s, it mol e cule sud den ly be gan pro duc ing
was re al ized that even Oparin's most pro teins. Later, when the need was
ba sic as sump tions, which he made felt to hide their in for ma tion in a sec -
in the 1930s were false: In the prim i - ond mol e cule, the DNA mol e cule
tive world at mos phere sce nar io, he had some how emerged.
in clud ed the gas ses meth ane and Instead of ac count ing for the be -
am mo nia that would per mit the gin ning of life, this sce nar io—ev ery
emer gence of or gan ic mol e cu les. Yet stage of which is dis tinct ly im pos si -
it was re al ized that the at mos phere ble and which is dif fi cult to even im -
at the time was not rich in meth ane ag ine—made the prob lem even
and am mo nia, but con tained high worse. It raised a num ber of in sol u -
lev els of ox y gen that would break ble ques tions:
down or gan ic mol e cu les. (See The 1- Not even one of the nu cle ot i -
Primitive Earth.) des that com prise RNA can be ac -
This dealt a se ri ous blow to the count ed for in terms of chance. Then
the o ry of mo lec u lar ev o lu tion. It how did nu cle ot i des come to geth er
meant that all the "prim i tive at mos - in the ap pro pri ate se quence to give
phere" ex per i ments, car ried by ev o - rise to DNA?
lu tion ists such as Miller, Fox and The ev o lu tion ist bi ol o gist John
Ponnamperuma, were in valid. For Horgan ad mits the im pos si bil i ty of
that rea son, oth er ev o lu tion ist quests RNA form ing by chance:
were launched in the 1980s, and the As re search ers con tin ue to ex am ine the
RNA World sce nar io was put for - RNA-World con cept close ly, more
ward. This sug gest ed that rath er prob lems emerge. How did RNA in i -
than pro teins, the RNA mol e cule tial ly arise? RNA and its com po nents
con tain ing pro tein in for ma tion are dif fi cult to syn the size in a lab o ra to -
emerged first. According to this sce - ry un der the best of con di tions, much
less un der re al ly plau si ble ones. 205
nar io—pro posed in 1986 by the
Harvard chem ist Walter Gilbert— 2- Even if we as sume that RNA,
bil lions of years ago, an RNA mol e - con sist ing sole ly of a chain of nu cle -
cule some how ca pa ble of cop y ing it - ot i des, did come in to be ing by
self came in to ex is tence by chance. chance, how did it de cide to copy it -
Later, un der the in flu ence of en vi - self? By what mech a nism did it suc -

The Evolution Impasse II