How does the coloration of beetles explain darwin's dangerous idea

Not sure what you mean by dangerous. Charles Darwin had a theory on evolution called Natural Selection. This theory of his essentially states that the organisms that adapt best and most successfully to changes in their surroundings are more likely to survive. A coloration change in beetles would explain this because the color change may help them blend in with their surroundings better, thus escaping predators and having a greater chance of survival. These beetles, due to their success, will become prevalent, meaning that the other beetles will phase out because they have not adapted well to the environment.

the abdomen (less formally called the belly, stomach, tummy or midriff) constitutes the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. the region occupied by the abdomen is termed the abdominal cavity. the stomach secretes acid and enzymes that digest food. ridges of muscle tissue called rugae line the stomach. the stomach muscles contract periodically, churning food to enhance digestion. the pyloric sphincter is a muscular valve that opens to allow food to pass from the stomach to the small intestine.

answer: tributaries flow into rivers.

wetland is a biome that develops when the water gets accumulated in a land exhibiting a huge depression. these form either seasonally or permanently. the water in the wetland comes from rivers, lakes, ocean, flood, rain or other sources. the wetlands includes mangroves, marshes and peatland.

tributaries flow into the rivers develops a wetland because such water will get deposited in the depression and will restrict the original flow of tributary water. hence, water with low drainage current combines with the river water.