Sperm form and function: Beauty is in the eye of the beholder

Although clinical assessment schemes for sperm morphology increasingly use objective or "strict" criteria, many observers view sperm morphology too simplistically; and are unaware of the relationship between spermatozoa and their environment. "Normal" sperm morphology under the light microscope only indicates grossly normal spermiogenesis, not fertilizing ability. Rather than using sophisticated image analysis to describe idealized spermatozoa, we must recognize that abnormal sperm morphology is a symptom not the disease, and only reflects defective spermiogenesis. This review explores the nature of the physical world in which spermatozoa exist and how it impacts upon sperm biology.