Morphological evidence of marine adaptations in human kidneys
Marcel F Williams 2006 Med.Hypoth.66:247-257
doi 10.1016/j.mehy.2005.09.024

Amongst primates, kidneys normally exhibiting lobulated, multi-pyramidal medullas is a unique attribute of the human species.
Kidneys naturally multi-pyramidal in their medullary morphology are rare in terrestrial mammals,
but kidneys with lobulated medullas do occur in elephants, bears, rhinos, bison, cattle, pigs & okapis.
Kidneys characterized with multi-pyramidal medullas are common in aquatic mammals, and nearly universal in marine mammals.
To avoid the deleterious effects of saline water dehydration, marine mammals have adaptively thickened the medullas of their kidneys:
this enhances their ability to concentrate excretory salts in the urine.
The lobulation of the kidney's medullary region in marine mammals appears to be an adaptation to expand the surface area between the medulla & the enveloping outer cortex,
it increases the volume of marine dietary induced hypertonic plasma that can be immediately processed for the excretion of excess salts & nitrogenous waste.
A phylogenetic review of freshwater aquatic mammals suggests:
most, if not all, non-marine aquatic mammals inherited the medullary pyramids of their kidneys from ancestors who originally inhabited, or frequented, marine environments, suggesting:
most, if not all, aquatic mammals exhibiting kidneys with lobulated medullas are either marine-adapted, or are descended from marine antecedents.
A phylogenetic review of non-human terrestrial mammals possessing kidneys with multi-pyramidal medullas suggests:
bears, elephants & possibly rhinos, also, inherited their lobulated medullas from semi-aquatic marine ancestors.
That several terrestrial mammalian spp of semi-aquatic marine ancestry exhibit kidneys with multipyramidal medullas, may suggest:
humans could have, also, inherited the lobulated medullas of their kidneys from coastal marine ancestors.
A specialized marine diet in ancient human ancestry could, also, explain the re-activation & enumeration of corporeal eccrine sweat-glands & the copious secretion of salt tears.
Human substantial loss of genetic variation vs other hominoids, + the apparent isolation of early-Pliocene human ancestors from particular retro-viruses that infected all other African primate spp, may suggest:
such a semi-aquatic marine phase, during the emergence of Homo, may have occurred on an island off the coast of Africa during the early-Pliocene.

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Very interesting article, excellent IMO except the last sentence:
our Pliocene ancestors followed the S-Asian not E-Afr.coasts (e.g. early-Pleist.Mojokerto).
And yes, not unikely, H.erectus or their immediate ancestors (early-Pleist.?) lived temporarily on an island.