Reality → Life → Evolution → Natural selection
Through the very gradual, long-term process of natural selection, 'traits' of the biologically 'fittest' [1] will become more common in a population's gene pool and may eventually lead to 'speciation' [2] . The process is influenced by environmental factors (e.g., climate, geography, habitat), migrations (gene flow), and sexual behavior (e.g., male competition or female choice), but is also subjected to chance (genetic drift). The process may not be random, but it has no direction and no goal. All species go extinct or evolve into new ones. Adaptation can be very beneficial, but also carries big risks.
The 'fittest' individual produces the most surviving offsprings and is not necessarily the strongest, healthiest, or in any other way remarkable member of a group.
A species is commonly regarded as a group of interbreeding organisms, comprising a 'population' as a sub-group living in a defined geographical area with a smaller gene pool than the species. To pinpoint speciation (the evolutionary splitting of a lineage or emergence of a new species) is a challenging task aided by genomic analysis.