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Why are sperm usually motile while eggs are usually nonmotile?

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Study the different ways mushrooms release spores and watch mold hyphae spread across bread — Reproduction Fungi produce billions of spores that give rise to new generations of fungi.

The distinction between motile sperm and nonmotile eggs is a result of an evolutionary division of labor designed to ensure successful fertilization and the development of new organisms.1

These two gametes serve different, specialized functions:

Sperm (Male Gametes): To maximize the probability of encountering an egg, sperm are produced in enormous numbers and are highly motile. They possess a flagellum—a whiplike tail—that allows them to travel through the reproductive tract to reach the egg.12
Eggs (Female Gametes): Eggs are typically nonmotile and large, as their primary role is to store nutritional reserves. These reserves are essential for the developing embryo to survive and grow before it can fend for itself.1

Essentially, the requirements for fertilization—bringing gametes together—and the requirements for development—accumulating energy reserves—are difficult for a single cell type to satisfy simultaneously. Evolution has therefore favored the production of many small, mobile sperm to seek out and fertilize the larger, nutrient-rich, and stationary eggs.1