This question is courtesy of my ten year old daughter who meant to search “cornception” on YouTube but got autocorrected to “conception.” The videos that came up were fortunately educational in nature. Thanks for reading this far!
In: Biology
I just want to add to the other great specific answers that these biological don’t “know” anything, as your quotes imply.
You can think of biology as a chemical Rube Goldberg machine, where everything is a consequence of an upstream event, resulting in a domino effect.
So a chemical in the sperm reacts with a chemical in the egg, that causes it to release a chemical that reacts with the outer layer in a way that causes it to harden.
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