**Core Concept**
Sexual differentiation in human embryos is a complex process influenced by genetic and hormonal factors. The presence of the Y chromosome and the subsequent production of androgens play crucial roles in the development of male external genitalia. In contrast, female sexual differentiation is characterized by the absence of androgenic influence, allowing for the development of female external genitalia.

**Why the Correct Answer is Right**
Male sexual differentiation occurs earlier than females due to the presence of the SRY gene on the Y chromosome. This gene initiates the production of testis-determining factor (TDF), which triggers the development of testes in the genital ridge. Testes then produce anti-Müllerian hormone (AMH) and androgens, leading to the differentiation of Wolffian ducts and the development of male external genitalia. In contrast, female embryos lack the SRY gene and develop ovaries, which produce estrogens and inhibit the development of male external genitalia. The earlier onset of androgen production in male embryos allows for the earlier development of male external genitalia.

**Why Each Wrong Option is Incorrect**
**Option A:** Gonadal development begins at the 6th week of intrauterine life, not the 5th week. While gonads do begin to form at this time, the process of sexual differentiation is initiated earlier, around the 4th to 5th week.

**Option B:** The Y chromosome determines the differentiation of testes, not ovaries. The presence of the SRY gene on the Y chromosome triggers the development of testes, which then produce AMH and androgens to differentiate the Wolffian ducts and external genitalia.

**Option C:** Female external genitalia development is not completed by 10 weeks. While the basic structure of female external genitalia is established by this time, further development and differentiation occur throughout embryonic and fetal life.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the presence of the Y chromosome and the SRY gene are essential for male sexual differentiation. The absence of these genetic factors leads to the development of female external genitalia. This understanding is crucial for diagnosing and managing disorders of sex development (DSD).

**✓ Correct Answer: D. Male sexual differentiation occurs earlier than females**