what does this first book deals with?
It is a vivid travel memoir as well as a detailed scientific field journal covering biology, geology, and anthropology.
The Voyage of the Beagle
The book is a vivid travel memoir as well as a detailed scientific field journal covering biology, geology, and anthropology that demonstrates Darwin's keen powers of observation, written at a time when Western Europeans were exploring and charting the whole world. 
the process of natural selection principles and applications It is the differential survival and reproduction of individuals due to differences in phenotype. what does this selection refers to? A mechanism of evolution. what do you mean by this last term? It is change in the heritable characteristics of biological populations over successive generations. is there is any specific theory related to the previous selection process? Yes, Darwin's theory. what is stated in this theory? He defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved". who was this above person you previously mentioned? He was an English naturalist, geologist and biologist, best known for his contributions to the science of evolution. has he written any book? "The Voyage of the Beagle", "On the Origin of Species", "The Descent of Man","The Expression of the Emotions in Man and Animals", " The Power of Movement in Plants" and others.
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The Voyage of the Beagle [SEP] Introduction
Although Darwin revisited some areas during the expedition, for clarity the chapters of the book are ordered by reference to places and locations rather than by date. Darwin's notes made during the voyage include comments hinting at his changing views on the fixity of species. On his return, he wrote the book based on these notes, at a time when he was first developing his theories of evolution through common descent and natural selection. The book includes some suggestions of his ideas, particularly in the second edition of 1845.