| Sažetak | Glavna teza teorije neutralnosti, da je većina evolucijskih promjena na molekularnoj razini rezultat nasumičnog genetičkog drifta selektivno neutralnih (ekvivalentnih) alela, imala je golem utjecaj na populacijsku genetiku. Tvorac teorije, Motoo Kimura, pritom ne negira značaj prirodne selekcije u evoluciji morfoloških i fizioloških karakteristika. Ipak, teorija je u početku bila potpuno neprihvatljiva za neodarviniste te je izazvala brojne rasprave. Iako danas brojni molekularni podaci govore u korist teorije, u vrijeme njena nastanka njihova dostupnost bila je ograničena, te stoga slobodno možemo tvrditi da je Kimurin rad bio vizionarski. Pretpostavka o konačnosti veličine prirodnih populacija bila je ključni korak u nastanku teorije. Što je populacija manja, to je snažnije djelovanje genetičkog drifta. No, stopa neutralne evolucije ne ovisi o veličini populacije, već o stopi nastanka neutralnih mutacija. Evolucijska stopa određenog proteina konstantna je u različitim linijama koje potječu od zajedničkog pretka, što je osnova molekularnog sata. Teorija neutralnosti ipak ne može objasniti sve evolucijske pojave. Postojeća genetička raznolikost populacija i vrsta često je bolje razjašnjena teorijom približne neutralnosti, koja uzima u obzir veličinu populacije i mogućnost istovremenog djelovanja drifta i selekcije. Pritom ishod evolucije ovisi o relativnoj snazi tih dviju sila. Uostalom, glavna razlika između "selekcionista" i "neutralista" je u tome koju od tih sila smatraju ključnim pokretačem evolucije. Teorija približne neutralnosti na neki način pomiruje ta dva stajališta. |
| Sažetak (engleski) | The main thesis of the neutral theory, which presumes that most of evolutionary changes on molecular level are driven by random genetic drift of selectively neutral (equivalent) alleles, had a huge influence on population genetics. Theory creator, Motoo Kimura, in doing so, doesn't deny significance of natural selection in evolution of morphological and physiological traits. Nevertheless, in the begining, the theory was completely unacceptable for neo-Darwinians and has caused many debates. By the time his theory firstly emerged, unlike now, there were only few molecular methods that could prove the theory so we can undoubtedly claim that Kimura's work was a visionary one. Presumption of finality of natural population was the crucial step towards the making of theory. The smaller the population is, the stronger is the effect of genetic drift. But the rate of neutral evolution doesn't depend on population size, but on the neutral mutation rate. The evolutionary rate of a given protein is constant in different lines that diverge from a common ancestor, so each protein evolves according to its own molecular clock. The neutral theory of molecular evolution can not explain all evolutionary phenomena. Present genetic diversity of populations and species is better explained by the nearly neutral theory, which considers the population size and the possibility of common influence of genetic drift and natural selection. The outcome of evolution depends on relative strength of above mentioned forces. After all, the main difference between "neutralists" and "selectionists" is relative importance of drift and selection, which is, in some way, conjoined into the nearly neutral theory. |
