When a lineage splits into multiple line of descents, then, it leads to speciation. It is a process by which a single population evolves into different species. The process of speciation leads to the development of two or more species as the lineages are splitted. These two evolved species are genetically independent.
Hence, the blank can be filled with 'speciation'.
Answer:
Soil erosion causes siltation in rivers, dams, etc. In some areas, huge river deltas are formed (such as River Nile delta) because of soil erosion. Such places are good for agriculture but not good for urbanization. However, some people do not care about it, they just want to construct buildings on alluvium type soils.
Neurotransmitters is the word you're looking for.
The statement that highlights and describes in detail the key features of an aquatic animal would be produce qualitative data analysis as we will describe its external features such as color size etc.