Comment by moralestapia
3 days ago
It's not, the guy is just making stuff up.
A lot of what's behind that "selection" there is still unknown; in principle all sperm are, more or less, the same.
There's also so many external effects in play that no single sperm cell may actually have a significant advantage over others; e.g. the behavior of the seminal fluid (ph, viscosity), the physical location of the egg, etc.
The cartoonish image of sperm swimming towards the egg is pretty much that ... a cartoon. In reality, they're pretty much drifting and their movement is much more like brownian motion than anything else [1].
Reminds me of this sperm race thing that took the spotlight a month ago, after watching the videos [2] ... come on, man.
Only someone who is extremely ignorant and/or is lacking severely on their mental abilities (bordering on idiocy), would believe that thing was true.
1: When the sperm is really close to the egg, however, there seems to be a hormone gradient that guides the sperm, preferentially, towards it.
There’s a big difference between mostly the same and actually the same. A sperm that doesn’t move is extremely unlikely to fertilize an egg. Thus, 1 is a test for fitness among a tiny percentage of total sperm but still a large number.
Length of survival is dependent on factors largely put side of sperms control, but sperm lifespan does test for massive genetic abnormality.
So yes 99% never get a chance to compete, but meaningful competition still occurs.