The magnetic reversal probably had an impact on mutations since it would let in damaging cosmic rays.
You might want to check out the following books.
"The Magnetic Field of the Earth" by R.T. Merrill, M.W. McElhinny, and P.L. McFadden (Academic Press, 1996).
I'll quote a few things for your interest. p. 182 has a chart of the magnetic reversals for the last 18 M. years. In the last 10 M. years there have been 46 magnetic reversals. (.780, .990, 1.070, 1.770, 1.950, 2.140, 2.150, 2.581, 3.040, 3.110, 3.220, 3.330, 3.580, 4.180, 4.290, 4.480, 4.620, 4.800, 4.890, 4.980, 5.230, 5.894, 6.137, 6.269, 6.567, 6.935, 7.091, 7.135, 7.170, 7.341, 7.375, 7.432, 7.562, 7.650, 8.072, 8.225, 8.257, 8.699, 9.025, 9.230, 9.308, 9.580, 9.642, 9.740, 9.880, 9.920 ). Data from Cande and Kent (1995) which includes both marine magnetic anomaly records and magnetostratigraphic sections.
p. 184 There is an other time scale showing magnetic changes to 160 M years.
p.196 The Cretaceous Superchron, which extends from approximately 118 M years to 83 M years (Cande and Kent, 1995).
p. 244 Has a chart showing the Relative variations in the Earth's diople moment for the past 4 M year as determined from deep-sea sediment cores. There are 25 accepted magnetic reversals and drifting poles in this time period.
Another good book, "Reversals of the Earth's Magnetic Field", by J. A. Jacobs, sec. edition 1994, Cambridge University Press
From the present to .780 M. yrs.( identified as Brunhes/Matuyama) there are 10 contested observations of the variations of the magnetic poles. The times are: Githenburg flip 12,350, Mono 28,000, Lake Mungo 30,000, Laschamp 50,000, Blake 110,000, Lake Biwa I 176,000, Biwa II 292,000, Biwa III 380,000, Big Lost 575,000, and Delta 645,000.
My observation: In the last 65 M. years the evolution of the mammals had a lot of help/hinderance from the sun ( 46 times). I think that we had a lot of bad luck. The mutations, which, most of the times are bad, did happen to us.
I hope someone can make a believable story that would encourage scientific investigation and publications.
jal