Finally, something that makes sense about the possible evolution of Man:
http://iceagenow.info/2011/09/lightning-brain/

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     The speciation burst hypothesis offers a supported explanation of 
the variability of (evolutionary) rates as being primarily the result of 
the organisms exposure and sensitivity to ultraviolet light and/or 
cosmic rays.

     Any major disruption increasing the amount of exposure such as a 
geomagnetic reversal would also increase the evolutionary rate.

     Phenotypic characters show not only a remarkable variability in 
evolutionary rates ranging from very slow to very fast, but in some 
cases periods of stasis interspersed with shorter periods of accelerated 
evolution. Evolutionary hypotheses dealing with phenotypic characters 
are needed to explain this variability. Such a hypothesis is speciation 
burst.

     Any major disruption increasing exposure such as geomagnetic 
reversals would accelerate evolution by increasing the mutation rate. 
During a geomagnetic reversal which may last from 1,000-10,000 years the 
biological material of the earth is exposed to more intense cosmic 
radiation and/or ultraviolet light. As a consequence, mutations with 
none, small, or great phenotypic effect will appear in a relatively 
short period of time.

     Mutations with great phenotypic effect explain the absence of 
transitional forms (missing links). At the same time, due to the heavy 
genetic load and/or environmental changes, many species become extinct.

     Ultraviolet light and cosmic rays are known to produce chromosomal 
aberrations. Chromosomal aberrations are a causal factor for speciation 
events.

     Speciation would be expected to be faster closer to the polar 
regions due to the morphology of the geomagnetic field which affords 
lower protection from cosmic rays in these regions in comparison to the 
equator.

     Due to the protection afforded by water a progressively slower 
speciation-evolutionary rate would be expected moving from land to 
shallow water to deep water.

     Due to the reduced exposure to ultraviolet light, it would be 
expected that nocturnal creatures would evolve at a slower rate than 
diurnal ones.

     The intriguing periods of acceleration in evolution can be seen as 
the result of increased exposure to ultraviolet light and/or cosmic rays 
due to some major disruption such as geomagnetic reversals.

     Pronounced acceleration in speciation in Alcelaphini and molluscs, 
which are 2 different categories of organism, with different habitats, 
and such a pronounced difference in population sizes, occurred 
simultaneously with a period of frequent geomagnetic reversals.

At the time he published this, Dr Tsakas was with the Department of 
Genetics in the Agricultural College of Athens, Athens, Greece.

See entire paper, including citations:

Speciation burst hypothesis : an explanation for the variation in rates 
of phenotypic evolution
S.C. Tsakas and J.R. David
Genet. Sel. Evol.  18 3 (1986) 351-358
DOI: 10.1051/gse:19860309
[Abstract] [PDF (368.1 KB)]