Hvers vegna þolir maðurinn áfengi?

Skrifað um December 5, 2014 · in Almennt · 101 Comments

Fram að þessu hafa menn haldið, að áfengi hafi ekki fylgt manninum nema í um níu þúsund ár. Nú hafa bandarískir fræðimenn komizt að því, að áfengis hefur verið neytt í að minnsta kosti tíu miljón ár, og það því fylgt mannkyninu mun lengur en elztu menn muna.

Vitað er, að menn geta neytt áfengis (etanóls) án þess að veikjast, ef magn þess er innan ákveðinna marka. Forsenda fyrir því eru ákveðin prótín og enzýmið ADH4. Enda þótt öll fremdardýr (prímatar) hafi í sér enzýmið ADH4, geta ekki vissar tegundir, eins og lemúri (Lemur catta) og bavíani (Papio spp.), brotið niður áfengi, vegna þess að enzýmið í þeim er eilítið öðru vísi.

Áður var það trúa manna, að virkt enzým hefði fyrst þróazt meðal manna fyrir um níu þúsund árum. Hópur fræðimanna, undir foryztu Matthews Carrigans, líffræðings við Santa Fe College í Gainesville í Flórída, leitaði svo langt aftur sem 50 milljón ár til að finna fremdardýr með virkt enzým, en hafði ekki erindi sem erfiði. Virkni enzýmsins í þessum dýrum var mjög lítil. Það var ekki fyrr en mannapar, simpansi (Pan troglodytes) og górilla (Gorilla gorilla), sem komu fram fyrir um 10 millljón árum, voru athugaðir, að það fannst mikilvirkt ADH4-enzým, sem var um 40 sinnum virkara en í öðrum dýrum.

Einmitt á þeim tíma tók veðrátta að kólna og það hafði í för með sér, að það varð harðara á dalnum, og fremdardýrin urðu að laga sig að annars konar fæðu en áður. Það leiddi meðal annars til þess, að fremdardýrin urðu að leggja sér til munns ávexti, sem höfðu fallið niður úr trjánum. Og ávextir á jörðu niðri urðu fyrir áverkun baktería, sem breyttu sykri í alkóhól, sem safnaðist fyrir í þeim. Þau dýr, sem höfðu ekki virkt ADH4-enzým, urðu verulega ölvuð og hlutu skaða af, en hin, sem höfðu þróað með sér virkt enzým, gátu nýtt sér þessa fæðu. Genið, sem myndar virkt ADH4-enzým, erfðist meðal þessara apa og síðan til manna (Homo sapiens).

 

Heimild að þessum pistli er greinin: „Hominids adapted to metabolize ethanol long before human-directed fermentation,“ sem birtist í PNAS (The Proceedings of the National Academy of Sciences of the United States of America) og má lesa hér í heild:

http://intl.pnas.org/content/early/2014/11/26/1404167111

 

ÁHB / 5. desember 2014

 


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