Introduction:

Sloths are arboreal mammals that defecate on the ground, increasing the risk of predation. There are several hypotheses that try to explain why they undergo this risk.

Objective:

To critically review all the hypotheses and to propose a new hypothesis that is compatible with all known data.

Methods:

I verified the assumptions and implications of five hypotheses against the literature available February, 2021.

Results:

Previous hypotheses either lack reliable supporting data, or are contradicted by published data. Here I propose that defecation on the ground is an ancestral behavior that persists in all sloth species because there has not been enough natural selection against it.

Conclusions:

Current knowledge of sloth biology is compatible with the hypothesis that there has not been enough selective pressure for sloths to abandon defecation on the ground.