Advantages + disadvantages of bipedalism

Advantages

Efficient Energy Expenditure: Bipedalism is more energy efficient than quadrupedal locomotion over distances. This means this energy can be put into other things (e.g. reproduction)

Increased Endurance: Bipedalism allows for sustained, endurance-based locomotion, enabling humans to cover long distances efficiently. This adaptation was advantageous to earlier hominins as they migrated across varied landscapes in search of food and resources/useful for hunter gatherers when using persistence hunting, hunting their prey to exhaustion

Freeing of Hands: Walking upright frees hands for carrying objects, manipulating tools, and performing complex tasks. Eventually leading to greater dexterity—positive feedback loop (freed hands, better tools, better access to resources, increased diet, increased nutrients for brain, brain development, increase ability to manipulate hands)

Enhanced Visual Field: Walking upright elevates head and eyes, providing broader field of view compared to quadrupedal locomotion—allowing them to detect predators, prey, and other environmental cues from a distance

Thermoregulation: Walking upright exposes less surface area of the body to direct sunlight, reducing heat absorption and aiding in thermoregulation. This adaptation is particularly advantageous in hot open environments where minimising heat stress is crucial for survival

Disadvantages

Increased Risk of Back Problems: Walking upright places greater stress on the lower back and spine compared to quadrupedal locomotion. Upright posture of bipedalism requires the spine to support to the weight of the upper body, which can lead to issues such as lower back pain, herniated discs, and other musculoskeletal problems

Decreases Stability and Balance: Bipedalism requires a narrower base of support compared to quadrupedal locomotion, which a decrease stability and balance, especially on uneven or slippery surfaces. This increased risk of falls and injuries is exacerbated by the elevated centre of gravity associated with walking upright

Slower Speeds: While bipedal locomotion is energy efficient over long distances, it is generally slower than quadrupedal locomotion, particularly in sprinting or chasing. This reduced speed may be a disadvantage when hunting prey or escaping predators

Increased Vulnerability to Predators: Walking upright exposes vulnerable body parts, such as the abdomen and groin, to potential predators

Greater Risk of Joint and Foot Injuries: Bipedalism places increased stress on the lower limbs and feet, because the entire weight of the body is shifted from foot to foot (or knee to knee) leading to higher risk of joint injuries, such as knee and ankle sprains as well as foot problems such as plantar fasciitis and stress fractures. The human foot, with its arch structure, is particularly susceptible to overuse injuries associated with bipedal locomotion.

Pregnancy and Childbirth Challenges: The narrow birth canal and changes in pelvic shape can pose challenges during pregnancy and childbirth. The upright posture of bipedalism requires careful, positioning and coordination of the pelvis and birth canal increasing the risk of complications during labour.

The advantages outweigh the disadvantages. As such individuals with alleles for more efficient bipedal features show greater survival chances and as such are more likely to reproduce offspring that are more likely to survive so these alleles are selected for.