There are a lot of traits and behaviors that separate hominins from great apes and the other species on earth. One of the most important ones is our ability to walk upright. The ability to walk upright appears to be the first of the major differences between hominins and great apes to develop. It is theorized that this then set off a cascade of adaptations including the huge increase in brain power that led to humans becoming the dominant species on the planet. The change from walking on four legs to two required a lot of morphological changes throughout the body. One of those changes was the location of the foramen magnum on the skull. The foramen magnum is the opening in the skull through which the spinal cord passes through to join the brain. In animals that walk on four legs the foramen magnum is positioned towards the back of the skull so that the spinal cord exits from the back of the skull instead of underneath it. This is not true for animals that walk on two feet. For these species the foramen magnum is positioned beneath the skull so that the spinal cord exits downward and can act as the framework to support an upright body. The earliest example of this is seen in Sahelanthropus tchadensis a hominin discovered Chad in 2001. The only fossil remains found were a skull which dates back 6-7 million years ago. However, even though we don’t have a skeleton to examine we can still infer that this hominin was at least partly bipedal due to the foramen magnum being located on the underside of the skull. Another important morphological change that lead to hominins walking upright is the shape of the spine. Our spine, and most other bipedal hominins’, is shaped like an s where the lumbar portion curves in, the thoracic portion is curved out, and the cervical portion which continues the thoracic curvature up to the skull. The inward curvature of the lumbar spine, also called lordosis, is integral in maintain an upright posture. It distributes weight so that our center of gravity is roughly at our body’s midpoint. It also adds a significant amount of support so that our bodies don’t crumple from trying to support the added weight of our upper body. One other difference between hominins and great apes is our knees, specifically the way we can lock our knees. The ability to lock our knees allows us to be much more energetically efficient when we walk upright compared to apes and chimps. Since apes and chimps can’t lock their knees, they have to expend more energy on each stride to keep their balance and not topple over when their weight shifts to the one leg on the ground. Examining fossil remains can provide context to how modern humans developed and why certain traits were lost or passed on. Using either relative or chronometric dating we can establish a timeline of hominins starting with ourselves and dating back millions of years. Examining which ancestors survived and which ancestors died out can let us pinpoint which particular adaptations made humans so special.