I've been thinking about Goro's nipples way too long.
Edit: Goro from Mortal Kombat.
To achieve equal proficiency across all four upper limbs, the Shokan torso is elongated and stacked with two distinct sets of pectoralis major muscles. The upper pecs drive the top arms, while a lower, visible set of raw muscle anchors the bottom arms to a modified sternum.
Shokan males (like Goro) possess vestigial nipples, proving that embryos are conceived using a gender-neutral baseline blueprint before hormonal differentiation occurs.
Shokan females (like Sheeva) possess a single set of breasts sitting over the top pectoral muscles. The lower pecs remain un-breasted, leaving a wide, muscular upper abdomen.
Due to the massive skeletal and muscular frame of a Shokan fetus, internal human-like gestation would severely compromise a female warrior's combat readiness.
Shokan reproduce via internal mammalian fertilization but quickly secrete a leathery, vascular, porous external "womb" egg. This egg absorbs oxygen and nutrients externally, allowing the mother to immediately return to the battlefield.
Managing four independent, quadridextrous limbs requires massive brain processing power. Consequently, the Shokan brain prioritizes a hyper-developed motor cortex at the expense of the prefrontal cortex, resulting in a species that is highly intelligent in combat but culturally static and lacking in abstract inventive drive.
Hatchlings emerge with fully synchronized arm development. They learn to crawl using a hexapod (insect-like) tripod gait, rapidly building the massive caloric-burning muscle walls required for upright walking.
Motherhood is viewed not as a peaceful retreat, but as a strategic military deployment. A nursing mother's body is the fuel refinery creating the next generation's muscle mass, earning her a distinct, highly respected warrior status.
Parental and elder hierarchies are rooted entirely in the track record of breeding viable killers. Rearing a "weakling" or a child with non-combat interests is viewed as a genetic and disciplinary failure, stigmatizing the mother as a bad warrior and a liability to the tribe.
All of this explains why their species has not evolved over thousands of years. They are stuck in an everlasting combat ready, cull the weak mindset and lifestyle.