Kerbals are Kerbin's dominant species. As infants, they cling to the backs of their parents, much like infant apes on Earth. Until they are around 5 years old, Kerbals live on a combination of photosynthesis and some plant life. After age 5, Bacteria living on the plants accumulate in the gut of the Kerbal, and their waste becomes the Kerbal's primary food source. This is the reason for their ability to survive in space for such long periods. These bacteria need only minimal nutrients, usually provided in the form of plant matter. The word for this substance in Kerbal translates roughly to "Snacks". When not active for long periods, their metabolism slows. During this time, they once again perform photosynthesis alongside their slowed consumption. In this semi-hibernative state, a kerbal can live for months on the oxygen in their spacesuit, provided they are close enough to the sun. Kerbals Reproduce asexually. The entire species is androgynous, with no males or females. Kerbals can only breed for the period between their 54th year and their 82nd year on average. Once they have produced offspring, they typically enter old age. Kerbals will typically die after 96-118 years. However, if they do not breed, their lifespan is greatly extended. They may live for up to 200 years, but will experience declines in physical ability. Kerbals have sturdy legs to allow motion over the rough terrain of Kerbin. The ancestors of Kerbals did not begin walking upright until around 50,000 years ago, accounting for their unsteady gait.