Editing Flagellum (section)

====Flagella and the intelligent design debate====
{{Main|Intelligent design|Irreducible complexity}}
Some authors have argued that flagella cannot have evolved, assuming that they can only function properly when all proteins are in place. In other words, the flagellar apparatus is "[[irreducible complexity|irreducibly complex]]".<ref>{{cite book |last1=Behe |first1=Michael J. |title=The edge of evolution: the search for the limits of Darwinism |date=2007 |publisher=Free Press |location=New York, NY |isbn=978-0-7432-9620-5}}</ref> However, many proteins can be deleted or mutated and the flagellum still works, though sometimes at reduced efficiency.<ref>{{cite journal |last1=Rajagopala |first1=Seesandra V |last2=Titz |first2=Björn |last3=Goll |first3=Johannes |last4=Parrish |first4=Jodi R |last5=Wohlbold |first5=Katrin |last6=McKevitt |first6=Matthew T |last7=Palzkill |first7=Timothy |last8=Mori |first8=Hirotada |last9=Finley |first9=Russell L |last10=Uetz |first10=Peter |title=The protein network of bacterial motility |journal=Molecular Systems Biology |date=January 2007 |volume=3 |issue=1 |page=128 |doi=10.1038/msb4100166 | pmid = 17667950 | pmc = 1943423}}</ref> Moreover, with many proteins unique to some number across species, diversity of bacterial flagella composition was higher than expected.<ref>{{cite journal |last1=Titz |first1=Björn |last2=Rajagopala |first2=Seesandra V. |last3=Ester |first3=Claudia |last4=Häuser |first4=Roman |last5=Uetz |first5=Peter |title=Novel Conserved Assembly Factor of the Bacterial Flagellum |journal=Journal of Bacteriology |date=November 2006 |volume=188 |issue=21 |pages=7700–7706 |doi=10.1128/JB.00820-06 | pmid = 16936039 | pmc = 1636259}}</ref> Hence, the flagellar apparatus is clearly very flexible in evolutionary terms and perfectly able to lose or gain protein components. For instance, a number of mutations have been found that ''increase'' the motility of ''E. coli''.<ref>{{cite journal |last1=Kakkanat |first1=Asha |last2=Phan |first2=Minh-Duy |last3=Lo |first3=Alvin W. |last4=Beatson |first4=Scott A. |last5=Schembri |first5=Mark A. |title=Novel genes associated with enhanced motility of Escherichia coli ST131 |journal=PLOS ONE |date=10 May 2017 |volume=12 |issue=5 |pages=e0176290 |doi=10.1371/journal.pone.0176290 | pmid = 28489862 | bibcode = 2017PLoSO..1276290K | pmc=5425062| doi-access = free }}</ref> Additional evidence for the evolution of bacterial flagella includes the existence of vestigial flagella, intermediate forms of flagella and patterns of similarities among flagellar protein sequences, including the observation that almost all of the core flagellar proteins have known homologies with non-flagellar proteins.<ref name="ReferenceA"/> Furthermore, several processes have been identified as playing important roles in flagellar evolution, including self-assembly of simple repeating subunits, gene duplication with subsequent divergence, recruitment of elements from other systems ('molecular bricolage') and recombination.<ref>{{cite journal |last1=Pallen |first1=M.J. |last2=Gophna |first2=U. |title=Bacterial Flagella and Type III Secretion: Case Studies in the Evolution of Complexity |journal=Genome Dynamics |date=2007 |volume=3 |pages=30–47 |doi=10.1159/000107602 | pmid = 18753783 | isbn = 978-3-8055-8340-4 }}</ref>