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The evolution of flagella is of great interest to biologists because the three known varieties of flagella – (eukaryotic, bacterial, and archaeal) each represent a sophisticated cellular structure that requires the interaction of many different systems.
A flagellum (/ f l ə ˈ dʒ ɛ l əm /; pl.: flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores (), and from a wide range of microorganisms to provide motility.
Furthermore, extensive virus evolution seems to have preceded the LUCA, since the jelly-roll structure of capsid proteins is shared by RNA and DNA viruses across all three domains of life. [ 75 ] [ 76 ] LUCA's viruses were probably mainly dsDNA viruses in the groups called Duplodnaviria and Varidnaviria .
This last idea has not received much acceptance, because flagella lack DNA and do not show ultrastructural similarities to bacteria or to archaea (see also: Evolution of flagella and Prokaryotic cytoskeleton). According to Margulis and Dorion Sagan, [20] "Life did not take over the globe by combat, but by networking" (i.e., by cooperation).
Viral evolution is a subfield of evolutionary biology and virology concerned with the evolution of viruses. [ 1 ] [ 2 ] Viruses have short generation times, and many—in particular RNA viruses —have relatively high mutation rates (on the order of one point mutation or more per genome per round of replication).
Typically, one flagellum is very short, and does not protrude from the cell, while the other is long enough to be seen with light microscopy. In some species, such as Euglena mutabilis, both flagella are "non-emergent"—entirely confined to the interior of the cell's reservoir—and consequently cannot be seen in the light microscope.
The flagellum of choanoflagellates is surrounded by microvilli at its base. Movement of the flagellum creates water currents that can propel free-swimming choanoflagellates through the water column and trap bacteria and detritus against the microvilli, where these foodstuffs are engulfed.
Evolution of flagella – Origin of three known varieties of flagella; Evolution of mammalian auditory ossicles – Middle ear bones evolved from jaw bones; Evolution of nervous systems – Origin and subsequent variation and development of neurons and neural tissues and organs