The evolution of erect posture, or bipedalism, in hominins brought about a suite of significant anatomical and physiological changes, resulting in both evolutionary advantages (gains) and disadvantages (losses).

Gains of Erect Posture:

1. Freeing the Hands: Perhaps the most crucial gain was the liberation of the forelimbs, allowing for tool use, carrying objects (food, infants), and complex manipulation. This was a critical step in human technological and cognitive development.
2. Enhanced Vision: Standing upright provided a wider field of vision, aiding in spotting predators, prey, and resources in open environments like the savanna.
3. Efficient Locomotion: Bipedalism is energetically more efficient for long-distance travel than quadrupedalism in certain contexts, especially for sustained walking or running.
4. Thermoregulation: A reduced surface area exposed to direct sunlight and increased exposure to cooling breezes helped in regulating body temperature, particularly in hot, open environments.
5. Display and Communication: Erect posture could have facilitated social signaling and display.

Losses of Erect Posture:

1. Skeletal Stress: The upright stance places considerable stress on the vertebral column, pelvis, knees, and feet, leading to common human ailments like lower back pain, knee problems, and flat feet.
2. Birthing Difficulties: The narrowing of the birth canal due to pelvic restructuring for bipedalism, combined with the increasing brain size of hominin infants, led to a more difficult and prolonged birthing process, often requiring assistance.
3. Vulnerability: Loss of speed and agility compared to many quadrupeds, and a higher center of gravity, can make bipedal individuals more vulnerable to falls and certain types of predation.
4. Circulatory Challenges: Maintaining blood flow against gravity to the brain requires a more robust circulatory system and can contribute to issues like varicose veins.

In summary, while bipedalism conferred immense evolutionary advantages that were foundational to human development, it also introduced specific anatomical vulnerabilities and challenges.