If you, like me, spend your daily commute explaining Dune lore to unsuspecting strangers, then surely you must bump into the occasional normie who never heard about Fremen before. Where would you start? Because in terms of physical description, the first thing I usually bring up is the Eyes of Ibad.

While it’s certainly one of their most recognizable features - as you might well know -, it’s not a Fremen-exclusive. Anyone who has enough Spice in their system will be rocking the blue-within-blues, and the reverse is just as true → just because you’re born Fremen, you could have regular normal eyes. (e.g. the Museum Fremen at the end of Leto II’s rule)

Having said that, Dune: House Corrino does hint at the fact that Fremen eyes are somehow special, not only better but especially better in the dark.

It’s not made clear if that’s a Spice thing or a Fremen thing, but today we’re focusing only on the latter: the things Arrakis bred into the Fremen, whether it’s through genes or custom.

Evolutionary mutations

The Core Canon only hints at it, while the other books are not afraid to say it: the Fremen are built different. Millennia in the deep desert had its effect on them, and the survival of the fittest has had enough time for a bit of evolution to happen.

Unsurprisingly, their adaptations are all related to water.

Thick blood

The original book introduces us to the idea when Jessica meets Mapes and tries her new crysknife on the Shadout.

There was a thick welling of blood that stopped almost immediately. Ultrafast coagulation, Jessica thought. A moisture-conserving mutation?
‍— Dune [1965]

Mind the question mark at the end. In the Core Canon it’s a new thing, but if you read any of the Expanded Universe books, it’s taken as a given: Fremen don’t waste their water by bleeding.

Extended cycles

Speaking of bleeding, the Dune Encyclopedia details another mutation in this regard.

Over the generations, Fremen women's cycles didn't just lighten - they stretched out and settled at fifty-six days, double the Imperial norm, effectively halving a lifetime of water lost to it.

Education concerning this aspect of a Fremen girl's life, along with that involving such related issues as pregnancy, childbirth, and nursing, was considered too vital to be left to the individual parents. At puberty, the girls were taken on a week's retreat by the Reverend Mother of the sietch.
‍— Dune Encyclopedia [1984]

Long guts

Another piece of moisture-conserving mutation, this one confirmed by Leto II, a few pages into the start of his metamorphosis.

From his mother's genes he had that longer, larger Fremen large intestine to take back water from everything which came its way.
‍— Children of Dune [1976]

And to top this off, Hunters of Dune confirms that the plumbing always works in desert mode - even if a Fremen grows up “far from the arid wastelands of Arrakis, [their] body's metabolism […] still did not squander water.”

Desert conditioning

Dry eyes

Jessica, hearing the voices, felt the depth of the experience, realized what terrible inhibitions there must be against shedding tears.
‍— Dune [1965]

Paul giving moisture to the dead is probably one of the more famous scenes - but the reason Fremen are so in awe of it is that no crying is drilled into them since early childhood.

“She came out and touched him,” Harah said, “and he stopped crying. Everyone knows a Fremen baby must get his crying done at birth, if he’s in sietch because he can never cry again lest he betray us on hajr.”
‍— Dune [1965]

And the “great Fremen conditioning” goes incredibly deep.

Shooting blanks

And speaking of conditioning - the Dune Encyclopedia adds a rather unique one, that I’m duty-bound to pass along.

[…] the Fremen learned to separate the male orgasm from ejaculation. At the time they reached puberty, boys were given detailed instruction on the technique and were not considered to have entered into true adulthood before mastering it, whatever their other accomplishments.
‍— Dune Encyclopedia [1984]

To save moisture, yes, but more importantly, to keep women clear of the dangers of a late-stage pregnancy out on the move.

It’s clearly stated that men had to master this technique or stay celibate.