All things must change to something new, something strange. ~ American poet Henry Wadsworth Longfellow
Variation in organisms of the same species is ubiquitous, in every facet of existence, from genotype to phenotype and mentotype. Diversity is an essential aspect of Nature. From an evolutionary perspective, diversity enhances survivability during times of stress.
More variable populations are less vulnerable to environmental changes, show decreased fluctuations in population size, have superior establishment success, larger distribution ranges, and are less extinction prone. ~ Swedish evolutionary biologists Anders Forsman & Lena Wennersten
While the specific mechanics and effects of individual variation are multifarious, variations ultimately originate with the environment: both within an organism and externally. The genome may define the deck of playable cards, but the cards played are dealt by intimate ecological interaction – in a word: adaptation.
New species arise through a variety of evolutionary mechanisms. ~ American biologist Margaret Ptacek & American zoologist Shala Hankison
Speciation is the process of a new species originating, as a population of similar organisms establish a collective pool of reproductive identity.
Speciation is a series of processes. ~ Margaret Ptacek & Shala Hankison
During speciation, sex chromosomes often accumulate interspecific genetic incompatibilities faster than the rest of the genome. ~ American geneticist Colin Meiklejoh et al
Speciation is both prodded and checked by the environment. In other words, environmental influences parameterize evolution. Intrinsic factors include an organism’s own preferences and tolerances, and its ecological interactions: with its own kind, competitors, possible cohorts, prey/foodstuffs, and predators.
Interactions between species are important catalysts of the evolutionary processes that generate the diversity of life. ~ Canadian evolutionary biologist Jeffrey Joy
In animals, differing local food supplies can drive speciation between populations, even those live close by. Closely related animal species seldom prefer the same food. This lessens competition between them, even as there is often overlap in what related species will eat.
Diet affects gut flora composition, which has cascade effects throughout the body. Environmental exposures frequently alter the microbiome. This can sway host behaviors and preferences. As microbes are particular about their associations, they may induce speciation in their hosts to avoid intermingling with what they consider undesirables. While it is known that the microbiome influences host behaviors, the processes in toto are little understood besides that communications at the cellular level are involved.
Extrinsic factors provoking speciation are environmental upheavals which influence prospects for survival: habitat changes of all sorts, including climate. These most immediately affect nutrient supply and can challenge the tolerances that an organism has.