For most of history, more people meant more power. I came across this X post that I initially found alarming for Western civilization:

But what I realized is that the argument is subtly incorrect, because it fails to recognize the important shifts happening.

It’s easy to see why a negative birth rate society is concerning to most. In “On the Origin of Species,” Darwin presents his famous four postulates argument. He frames these as sufficient conditions for natural selection to occur:

1. Variation among individuals

2. Heritability of that variation

3. Overproduction leading to competition

4. Differential reproductive success

Biologists today often treat these not only as sufficient, but also as necessary. So to a biologist, these conditions make clear why a society with a persistently negative birth rate is unsustainable. Without reproduction, traits cannot be propagated, and the lineage eventually disappears.

But the picture is shifting. Fertility rates are falling globally, yet lifespans are lengthening. Ray Kurzweil makes the popular argument that advances in medicine and technology suggest a possible future in which human life expectancy could increase faster than we age. Bryan Johnson speaks of a future where our top priority is simply “don’t die.”

This raises a question: does Darwin’s argument no longer hold up in a Kurzweilian world where we might not die of old age at all?

From Generations to Timesteps

Darwin’s framing relied on “generations” as the natural unit of evolutionary change. Evolution, he argues, is the process of the gene pool shifting from generation to generation. This was a reflection of his early understanding of biology, but our modern view on evolution has adapted over the last 100 years.

This raises a question: does Darwin’s argument no longer hold up in a Kurzweilian world where we might not die of old age at all? 

Generations are noisy to measure (organisms reproduce at different ages) and the distinction between parents and children is less fundamental than it appears. A “child” is simply a continuation of the biochemical process that ran in its parent, part of a continuous stream of life extending back to the origin of life itself.

The more precise discretization of evolution is therefore “timesteps” (t, t+1, t+2, …). Recast in these terms, Darwin’s “four” postulates become:

1. Variation exists at a given timestep

2. Traits or states persist across timesteps (retention)

3. (not necessary)

4. Certain traits are differentially favored in persistence or propagation

This version no longer requires reproduction per se, only continuity of adaptive traits across timesteps. And it no longer requires Darwin’s third postulate on competition. Instead, the fourth postulate implies some filtering or differential persistence mechanism exists. …