Editing Macroevolution (section)

=== Evolution of new organs and tissues ===
One of the main questions in evolutionary biology is how new structures evolve, such as new [[Organ (biology)|organs]]. Macroevolution is often thought to require the evolution of structures that are 'completely new'. However, fundamentally novel structures are not necessary for dramatic evolutionary change. As can be seen in [[Vertebrate|vertebrate evolution]], most "new" organs are actually not new—they are simply modifications of previously existing organs. For instance, the evolution of [[mammal]] diversity in the past 100 million years has not required any major innovation.<ref>{{Cite journal |last1=Meredith |first1=R. W. |last2=Janecka |first2=J. E. |last3=Gatesy |first3=J. |last4=Ryder |first4=O. A. |last5=Fisher |first5=C. A. |last6=Teeling |first6=E. C. |last7=Goodbla |first7=A. |last8=Eizirik |first8=E. |last9=Simao |first9=T. L. L. |last10=Stadler |first10=T. |last11=Rabosky |first11=D. L. |last12=Honeycutt |first12=R. L. |last13=Flynn |first13=J. J. |last14=Ingram |first14=C. M. |last15=Steiner |first15=C. |date=2011-10-28 |title=Impacts of the Cretaceous Terrestrial Revolution and KPg Extinction on Mammal Diversification |url=https://www.sciencemag.org/lookup/doi/10.1126/science.1211028 |journal=Science |language=en |volume=334 |issue=6055 |pages=521–524 |doi=10.1126/science.1211028 |pmid=21940861 |bibcode=2011Sci...334..521M |s2cid=38120449 |issn=0036-8075|url-access=subscription }}</ref> All of this diversity can be explained by modification of existing organs, such as the evolution of [[Tusk|elephant tusks]] from [[Incisor|incisors]]. Other examples include [[Bird wing|wings]] (modified limbs), [[feather]]s (modified [[reptile scale]]s),<ref>{{Cite journal |last1=Wu |first1=Ping |last2=Yan |first2=Jie |last3=Lai |first3=Yung-Chih |last4=Ng |first4=Chen Siang |last5=Li |first5=Ang |last6=Jiang |first6=Xueyuan |last7=Elsey |first7=Ruth M |last8=Widelitz |first8=Randall |last9=Bajpai |first9=Ruchi |last10=Li |first10=Wen-Hsiung |last11=Chuong |first11=Cheng-Ming |date=2017-11-21 |title=Multiple Regulatory Modules Are Required for Scale-to-Feather Conversion |url=|journal=Molecular Biology and Evolution |volume=35 |issue=2 |pages=417–430 |doi=10.1093/molbev/msx295 |issn=0737-4038 |pmc=5850302 |pmid=29177513}}</ref> [[lung]]s (modified [[swim bladder]]s, e.g. found in [[fish]]),<ref>{{Cite journal |last=Brainerd |first=E. L. |date=1999-12-01 |title=New perspectives on the evolution of lung ventilation mechanisms in vertebrates |url=|journal=Experimental Biology Online |language=en |volume=4 |issue=2 |pages=1–28 |doi=10.1007/s00898-999-0002-1 |bibcode=1999EvBO....4b...1B |s2cid=35368264 |issn=1430-3418}}</ref><ref>{{Cite journal |last1=Hoffman |first1=M. |last2=Taylor |first2=B. E. |last3=Harris |first3=M. B. |date=2016-04-01 |title=Evolution of lung breathing from a lungless primitive vertebrate |journal=Respiratory Physiology & Neurobiology |series=Physiology of respiratory networks of non-mammalian vertebrates |language=en |volume=224 |pages=11–16 |doi=10.1016/j.resp.2015.09.016 |issn=1569-9048 |pmc=5138057 |pmid=26476056}}</ref> or even the [[heart]] (a muscularized segment of a [[vein]]).<ref>{{Cite journal |last1=Jensen |first1=Bjarke |last2=Wang |first2=Tobias |last3=Christoffels |first3=Vincent M. |last4=Moorman |first4=Antoon F. M. |date=2013-04-01 |title=Evolution and development of the building plan of the vertebrate heart |journal=Biochimica et Biophysica Acta (BBA) - Molecular Cell Research |series=Cardiomyocyte Biology: Cardiac Pathways of Differentiation, Metabolism and Contraction |language=en |volume=1833 |issue=4 |pages=783–794 |doi=10.1016/j.bbamcr.2012.10.004 |pmid=23063530 |s2cid=28787569 |issn=0167-4889|doi-access=free }}</ref>

The same concept applies to the evolution of "novel" tissues. Even fundamental tissues such as [[bone]] can evolve from combining existing [[protein]]s ([[collagen]]) with calcium phosphate (specifically, [[Hydroxyapatite|hydroxy-apatite]]). This probably happened when certain cells that make collagen also accumulated calcium phosphate to get a proto-bone cell.<ref>{{Cite journal |last1=Wagner |first1=Darja Obradovic |last2=Aspenberg |first2=Per |date=2011-08-01 |title=Where did bone come from? |url=|journal=Acta Orthopaedica |volume=82 |issue=4 |pages=393–398 |doi=10.3109/17453674.2011.588861 |issn=1745-3674 |pmc=3237026 |pmid=21657973}}</ref>