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William Aird: Why Did Mammalian Red Blood Cells Give Up Their Nucleus?
William Aird/X
Apr 11, 2026, 13:35

William Aird: Why Did Mammalian Red Blood Cells Give Up Their Nucleus?

William Aird, Professor of Medicine at Harvard Medical School, shared a post on LinkedIn:

“Why did mammalian red cells give up their nucleus?

Most cells protect their nucleus.

Mammalian red cells do the opposite.

They eject it.

At first glance, this looks like a loss.

No DNA, no repair, no division. A finite lifespan.

But it is better understood as a trade-off.

Removing the nucleus allows the cell to remove something else too:

its mitochondria.

And with that, a potential conflict of interest.

A red cell that carries oxygen but also consumes it would compete with the tissues it serves.

By giving up mitochondria, the red cell commits fully to delivery.

It does not use the oxygen it transports.

It gives it away.

That same simplification has other consequences:

  •  more space for hemoglobin
  • greater deformability in narrow capillaries
  • fewer intracellular obstacles to diffusion
  • educed capacity to support viral replication

But the central idea is this:

the red cell becomes a specialist by subtraction.

It gives up autonomy to eliminate internal competition and to optimize a single function.

Not every organism makes this choice.

Other vertebrates retain nucleated red cells.

Their constraints are different.

Mammals chose another path.

One that favors efficiency of delivery over cellular independence.

What looks like loss is the elimination of internal conflict.”

Read more on The Blood Project.

William Aird: Why Did Mammalian Red Blood Cells Give Up Their Nucleus?

Find more posts featuring William Aird on Hemostasis Today.

 

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