Sibling species (also known as aphanic species) are species that are very similar in appearance, in behavior and in other characteristics, but they are reproductively isolated. In other words, sibling species are pairs or groups of genetically closely related species which are often morphologically indistinguishable, but are reproductively isolated, meaning that while they may interbreed, the offspring cannot reproduce.
Sibling species may arise as a result of allopatric speciation through geographic isolation, parapatric speciation, or sympatric speciation. The important thing to note is that sibling species are in fact separate biological species. The biological species concept, proposed by Ernst Mayr in 1942, emphasizes reproductive isolation as the basis of defining a species. The definition states: "A species is defined as a population or group of populations whose members have the potential to interbreed with one another in nature and to produce viable offspring, but cannot produce viable, fertile offspring with members of other species." Mayr, a proponent of allopatric speciation, hypothesized that adaptive genetic changes that accumulate between allopatric populations cause negative epistasis in hybrids, resulting in sterility of the offspring.
Scientists traditionally pairs or groups of species as sibling species based upon morphology, biogeography, and anatomical studies, but recent advances in DNA testing and molecular phylogeny have made it possible to better determine whether two or more species are in reality sibling species.
Famous quotes containing the words sibling and/or species:
“Unfortunately, life may sometimes seem unfair to middle children, some of whom feel like an afterthought to a brilliant older sibling and unable to captivate the family’s attention like the darling baby. Yet the middle position offers great training for the real world of lowered expectations, negotiation, and compromise. Middle children who often must break the mold set by an older sibling may thereby learn to challenge family values and seek their own identity.”
—Marianne E. Neifert (20th century)
“Can it then be doubted, but that God, who is infinitely fine Spirit, and withal intelligent, can make and change all species and kind of body as he pleaseth? But I dare not say, that this is the way by which God Almighty worketh, because it is past my apprehension: yet it serves very well to demonstrate, that the omnipotence of God implieth no contradiction.”
—Thomas Hobbes (1579–1688)