# A simple analytical model for Neanderthal disappearance due to genetic dilution by recurrent small-scale immigrations of modern humans

## TL;DR

This paper proposes that small-scale immigration of modern humans into Neanderthal populations led to their genetic disappearance over thousands of years.

## Contribution

A new analytical model showing genetic dilution from recurrent immigration can explain Neanderthal disappearance without requiring catastrophic events.

## Key findings

- Recurrent small-scale immigration of Homo sapiens could lead to nearly complete genetic substitution of Neanderthals over 10,000–30,000 years.
- The model aligns with archaeological evidence and genetic introgression patterns in present-day Eurasian populations.
- Genetic admixture is proposed as a key mechanism for Neanderthal disappearance without needing selective advantage or environmental catastrophe.

## Abstract

The disappearance of Neanderthals remains a subject of intense debate, with competing hypotheses attributing their demise to demographic decline, environmental change, competition with Homo sapiens, or genetic assimilation. Here, we present a mathematical model demonstrating that small-scale Homo sapiens immigrations into Neanderthal populations, providing recurrent gene mixing, could have led to almost complete genetic substitution over 10,000–30,000 years. Our model, grounded in neutral species drift, does not require selective advantage or catastrophic events but shows that sustained gene flow from a demographically larger species could account for Neanderthals’ genetic absorption into modern humans within a time-frame consistent with archaeological evidence. This scenario aligns with growing evidence of interbreeding and genetic introgression through recurrent H. sapiens immigration waves, providing a parsimonious explanation for the observed patterns of Neanderthal ancestry in present-day Eurasian populations. Although other factors may have contributed to the decline of Neanderthals, our results highlight genetic admixture as a possible key mechanism driving their disappearance.