Which bug is nature selecting (evolving) AND tell why?

Natural selection is the process in nature by which organisms better adapted to their environment tend to survive and reproduce more than those less adapted to their environment. Forexample, treefrogs are sometimes eaten by snakes and birds
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Natural selection is the term that's used to refer to the natural evolution over time of a species in which only the genes that help it adapt and survive are present. This idea was reported by Charles Darwin, the researcher behind many of our modern concepts of evolution.

In natural selection, a population will show genetic traits over many generations that help it remain best suited to its environment. These can be physical, structural traits like a skeleton or musculature that helps it live in that setting, or can even by physiological traits such as the presence of an enzyme in the digestive tract to help it break down the available food sources.

Examples of Natural Selection:

1. Skeletal Adaptations

Giraffes, lizards, and many other known species adapted to their environments through genetic changes to their skeletons. This form of natural selection meant that members of the population who didn't develop and present these skeletal changes died out. For example, giraffes developed long necks to reach food sources higher up in trees, so members of the giraffe population who didn't develop a long neck died out. At the same time, certain lizards in one region developed longer leg bones to help it climb up during periods of flood and to escape predators in the ground; shorter legged lizards of the same population died out until only the lizards with the long legs survived..

2. Coloration

Many species have been studied who've adapted to their environment through adaptions in coloring. Once the optimal coloration is present, natural selection occurs when members of the species without the adaptive coloring died out more quickly and therefore didn't reproduce as abundantly. Some example include the deer mouse, the peppered moth, and the peacock.

3. Bacteria

Bacteria are a common research subject when studying evolution and adaptation because some colonies of bacteria can produce several generations in one day, letting researchers see a "fast forward" version of evolution and natural selection. Some observed bacteria have included some who've adapted to new food sources that were previously unusable, as bacteria that have adapted to the presence of deadly antibiotics and exhibited traits that let them not only survive, but reproduce to generate offspring that are also resistant to the antibiotic.

4. Physiological

Different species go through changes over time that help them adapt to different environments, and humans are no different. One of the physiological changes that different groups of human beings have made involves the ability to digest cow's milk. In regions where cattle are not raised, the human population is often lactose intolerant, lacking the enzyme to break down the milk. However, in regions where cattle are grown domestically and their milk is used as a chief part of the food supply, those humans as a whole produce the enzyme needed to digest milk.