Thursday, September 18, 2008

The origin of evolution

I found this rather neat paper in PNAS on how natural selection and evolution actually predate the origin of life. If you assume that to be alive you must require the conditions of being able to replicate and evolve, than you have to wonder which came first. According tho their model, not only did abiotic information systems undergo natural selection but evolution favored the emergence of replication. It's a short read if you understand mathspeak (which I don't), but here's the gist of it from the concluding paragraph....

Traditionally, one thinks of natural selection as choosing
between different replicators. Natural selection arises if one type
reproduces faster than another type, thereby changing the
relative abundances of these two types in the population. Natural
selection can lead to competitive exclusion or coexistence. In the
present theory, however, we encounter natural selection before
replication. Different information carriers compete for resources
and thereby gain different abundances in the population.
Natural selection occurs within prelife and between life and
prelife. In our theory, natural selection is not a consequence of
replication, but instead natural selection leads to replication.
There is ‘‘selection for replication’’ if replicating sequences have
a higher abundance than nonreplicating sequences of similar
length. We observe that prelife selection is blunt: Typically small
differences in growth rates result in small differences in abundance.
Replication sharpens selection: Small differences in
replication rates can lead to large differences in abundance


4 comments:

Anonymous said...

"If you assume that to be alive you must require the conditions of being able to replicate and evolve, than you have to wonder which came first."

Is a virus alive?

Anonymous Coward said...

I'm no expert but I would argue that a virus in a cell is alive since it satisfies both conditions. A virus outside a cell is not alive, or at least it's dormant like a spore....

kamel said...

Then I guess the question is: Are these requirements that you list (replicates, evolves) the minimal definition of life? Are they both necessary and sufficient?

If a virus outside a cell is not alive, what about other species that can't reproduce? Ligers, for example. Are they alive? (I know, strictly speaking, not all ligers are sterile, but for the sake of argument...)

Anonymous said...

Well a hybrid has all the necessary machinery to do both...