Extract
From any perspective, sperm are remarkable. We now know of course that sperm do not contain a tiny version of the adult (the appealing homunculus imagined by Nicholas Hartsoeker in the 17th century, Pinto-Correia 1997). Instead, sperm comprise a head of highly condensed DNA, an acrosome cap, virtually no cytoplasm, and a long tail partially encased within a sheath of specialized mitochondria. Then there is their extraordinary journey, with some sperm cast out into the external environment and some placed directly within the potentially hostile territory of the female. Finally, a series of complex processes ensues, leading to fusion of sperm and egg nuclei and the ultimate formation of a zygote. What is mind-boggling is how often the situation is absolutely nothing like the above. Sperm are the most variable cell type known (Jamieson 1987). They may have no tail or many tails; possess hooks, coils, spikes, balloons, and other widgets; vary in the presence of a nucleus, acrosome, and source of fuel for propulsion. To cap it all even if they are one of the minuscule percentage of sperm to reach their target, their DNA may still be ignominiously shoved aside.
