How do embryonic external genital structures develop into male or female anatomy?

During the first eight weeks of development, human embryos are in an "indifferent stage," where external genitalia appear identical across all sexes. These structures consist of a genital tubercle and a pair of urogenital folds flanked by genital swellings.123

Starting around the third month, these rudiments differentiate based on genetic and hormonal influences.34

Male Development

Under the influence of masculinizing factors, the structures transform as follows:
* Penis: Formed by the combination of the genital tubercle and the united urogenital folds, which also enclose the urethra.3
* Scrotum: Formed by the genital swellings, which shift toward the anus and fuse.3

Female Development

In the absence of androgenic effects, the structures develop along a female pathway:
* Clitoris: The genital tubercle remains small and does not contain the urethra.3
* Vulva: The urogenital folds remain unclosed to form the lesser vulvar lips, while the genital swellings remain unshifted and unfused to become the greater lips.3

This process highlights that all embryos possess the potential for either anatomical path, with sexual differentiation driven by specific hormonal signals during gestation.4