What is a consequence of improper human waste disposal?

Improper human waste disposal can lead to the attraction of disease-carrying pests, making this the correct answer. When waste is not managed appropriately, it creates a breeding ground for various pests, including flies and rodents, which can carry diseases. These pests thrive in unclean environments with readily available food sources, such as human waste. As a result, the presence of these pests can significantly increase the risk of spreading infectious diseases among humans and animals.

The other choices do not accurately reflect the consequences of improper waste disposal. For instance, increased cleanliness in the environment is unlikely when waste is improperly disposed of, as it leads to contamination and pollution. Additionally, while some animal populations may decline due to environmental degradation caused by waste, stating that improper disposal reduces animal populations oversimplifies the issue. Lastly, improving soil quality is not a consequence of improper waste disposal; in fact, it typically causes soil contamination, leading to detrimental effects on soil health.