Before I can explain about Kobolds and Ogres, I have to explain about the Planes.
At the dawn of what could narrowly be called History, as the Power of the Elemental Kings began to wane, formless intelligences coalesced in the voids left behind.
Some of these Spirits loved Order, and they gathered together, concentrating their power and their ideals in a vast, blindingly pure light: the Beacon. Infinitely, unreachably far from the Beacon, there is a place where all Order dissolves, a roiling blackness of gathered Entropy: the Abyss.
Around each of these, new Spirits took form, attuned to their own environments. So some favored the light. Some favored the dark. Over the rubble of the Elemental Crossroads, under the infant stars, they clashed.
Away from the ideological purity of their homes, the Spirits were forced to adapt, over time becoming Creatures. They spread across the sky, the land, the ocean, having traded some of their eternal essence to adapt to a material environment.
In this way the First Ones came into being, creatures with a footing in the world but still unmistakeably of Order or of Chaos. From the First Ones arose the Successors, who were even more a part of the world but even less able to express their essential being apart from the material.
Great embodiments of Sloth from the Abyss became the cruel Ogres. Impulsiveness developed into the skittish Kobold. Ogres breed in pairs, male and female, but slowly and rarely. Kobolds, though, reproduce on their own, ossifying bodily to produce a clutch of eggs.
No one knows whether jealousy or fear or something undefined drove the first Ogre Magi to experiment on the Kobold, or whether captive rivals or volunteers of their own families were combined with the smaller creature. What is known, which has come down in oral tradition from the dim days of the Successors, is that Ogres combined with Kobolds to create the Orcs.
Ecology of the Orc - Biology Textbook Graphic Descriptions Incoming
Consider the Orc female Yolanda approaching physical maturity, age 10. She is not much different from her brother Paolo externally, but within her, hormones are producing major changes. As her first ovulation cycle approaches in the height of the summer, her hips widen and soften; she will find it increasingly painful to walk as the days grow longer. Menarche is a sacred time for the entire clan, and they rally around Yolanda to make her comfortable and keep her fed since she cannot do it herself. The Shaman chant over her and give her herbs to relieve her pain.
Yolanda's destiny is to be the mother of a new clan stronghold. The clan has known this was coming. The Clan Mother now finalizes the Pioneer Consort who will journey with Yolanda once her menstrual cycle has finished. Packs and wagons are prepared, and 20 to 30 Orcs, including a Shaman, will escort Yolanda and her Consort to her new home. They will establish a new outpost of the clan. Next summer, she will reproduce.
Paolo's physical maturity manifests differently. With food he puts on muscle, becoming better at hunting and fighting. His metabolism is efficient at growth, but this comes at a cost. Orc males rapidly deteriorate as they approach 40 years of age, and 50 is never reached.
As the height of her 11th summer approaches, Yolanda's reproductive hormones are even stronger. Her hips widen and soften to an even greater degree; as she enters estrus, she is incapable of walking. She is made comfortable by her young clan in her lair. Her body emits a mixture of intense pheromones, exposure to which over many days will ready her Consort for breeding; Orcs cannot otherwise present sexually. The Shaman oversees the conception rites.
If all goes well, 12-48 whelps grow within Yolanda. One of these, the largest, will be a daughter, the rest sons. Yolanda grows to enormous size over the next 6 months, from roughly 100 pounds to 600 pounds, becoming completely immobile. Her womb overgrows her legs, but her hands and arms become wickedly powerful; her nails, strong curved talons. Her breasts swell with milk. She constantly demands food, trinkets and entertainment.
When the nights have grown cold and long, the litter is born, with the Shaman acting as midwife. Yolanda's abdomen is now massive folds of skin. Her legs have been mangled and softened during gestation. She will never stand or walk again.
Yolanda can bear a litter every year. Typically, however, after the seventh, the Clan Mother's hair will turn white. As her mother and the Shaman had told her, this means her fertility is at its end. But they also told her that there is another way.
They told her that her seventh daughter will steal her fertile essence when she enters the world. They told her that the Shaman can repair this, with her permission. The Shaman takes the newborn Orc daughter, a Princess of the Clan like her, and prepares her specially, according to the ancient rite. Yolanda knows it to be the truth. She consumes the consecrated flesh, blood and bones of her nameless daughter, and her hair returns to its lustrous black. She will be fertile again in the summer. As long as her clan can support a Shaman and a Consort, she can do this every single year, remaining young and fertile forever.