22/08/2025
Fertilization is not just a race where the fastest s***m wins—it's a far more selective and complex process.
Research shows that the egg, along with its surrounding follicular fluid, releases chemical signals (chemoattractants) that actively guide s***m toward it.
However, not all s***m are attracted equally.
These chemical cues often show preference for s***m from certain males, even if they're not the egg's partner, indicating a form of selective fertilization called gamete-mediated mate choice or cryptic female choice.
This selection is influenced by biological compatibility, such as immune system gene diversity (like HLA compatibility), and is designed to increase the chances of producing a healthy embryo.
The egg’s outer layer, the zona pellucida, also plays a role in screening s***m before allowing entry.
Molecules like progesterone, secreted by the cells around the egg, help direct the right s***m via a process called chemotaxis.
In short, the egg is not a passive target—it uses chemistry to select which s***m succeeds.
This overturns the old myth of fertilization being a purely competitive race among s***m, emphasizing instead the egg's active and selective role in reproduction.
