Final answer:
Option (a), To limit human population growth sustainably, decreasing the birth rate is the most effective method. Increasing carrying capacity has historically led to population growth, but without sustainable practices, it can lead to resource depletion and environmental harm.
Step-by-step explanation:
The most sustainable method for limiting human population growth is decreasing birth rate. Increasing the carrying capacity of the environment by developing advanced food production methods and engineering high-quality shelters has allowed more people to survive, which contributes to population growth. On the other hand, decreasing birth rate would involve a conscious effort to reduce the number of births and consequently slow down population growth without directly harming the existing population.
It is important to understand that while increasing carrying capacity allows more people to live, it can also lead to further strain on resources if population growth outpaces the advances in technology and resource management. Activities that decrease carrying capacity, such as overexploitation of resources and unsustainable practices, contribute to environmental degradation and ultimately limit the number of individuals that an area can sustain. Therefore, efforts should be focused on sustainable practices, which include managing birth rates to align with the available resources and carrying capacity.
Using language, as mentioned in option d of question 21, is not a way that humans have increased the carrying capacity of the environment in the same direct manner as agriculture or domestication of animals. However, language has been pivotal for knowledge transfer, allowing for collaboration and innovation in other areas that do increase carrying capacity.