Option 1: Deforestation is the removal or clearing of trees from a forested area. This process disrupts the natural habitats of many organisms and can lead to a loss of biodiversity. Deforestation generally has a negative impact on the ecological balance.

Option 2: Developing new breeds of cultivated plants and domesticated animals can have both positive and negative effects on the ecological balance. While it may enhance productivity and meet human needs, it can also disrupt natural ecosystems if not done sustainably. Therefore, though this option may contribute to ecological balance in some cases, it is not always the case.

Option 3: Using insecticides and pesticides is a common method to control pests and increase agricultural yield. However, these chemicals can have harmful effects on non-target organisms and disrupt the natural balance of ecosystems. Thus, this option does not maintain ecological balance.

Option 4: Understanding the delicate balance in the relative number of organisms is the correct answer. By recognizing and respecting the relationships between different organisms and their roles in the ecosystem, humans can make informed decisions that help maintain ecological balance. This option promotes sustainable practices to preserve the environment and conserve biodiversity.