Myths and misconceptions about evolution. Let's talk about evolution. You've probably heard that some people consider it controversial, even though most scientists don't. But even if you aren't one of those people and you think you have a pretty good understanding of evolution, chances are you still believe some things about it that aren't entirely right, things like, "Evolution is organisms adapting to their environment." This was an earlier, now discredited, theory of evolution. Almost 60 years before Darwin published his book, Jean-Baptiste Lamarck proposed that creatures evolve by developing certain traits over their lifetimes and then passing those on to their offspring. For example, he thought that because giraffes spent their lives stretching to reach leaves on higher branches, their children would be born with longer necks. But we know now that's not how genetic inheritance works. In fact, individual organisms don't evolve at all. Instead, random genetic mutations cause some giraffes to be born with longer necks, and that gives them a better chance to survive than the ones who weren't so lucky, which brings us to "survival of the fittest". This makes it sound like evolution always favors the biggest, strongest, or fastest creatures, which is not really the case. For one thing, evolutionary fitness is just a matter of how well-suited they are to their current environment. If all the tall trees suddenly died out and only short grass was left, all those long-necked giraffes would be at a disadvantage. Secondly, survival is not how evolution occurs, reproduction is. And the world if full of creatures like the male anglerfish, which is so small and ill-suited for survival at birth that it has to quickly find a mate before it dies. But at least we can say that if an organism dies without reproducing, it's evolutionarily useless, right? Wrong! Remember, natural selection happens not at the organism level, but at the genetic level, and the same gene that exists in one organism will also exist in its relatives. So, a gene that makes an animal altruistically sacrifice itself to help the survival and future reproduction of its siblings or cousins, can become more widespread than one that is solely concerned with self-preservation. Anything that lets more copies of the gene pass on to the next generation will serve its purpose, except evolutionary purpose. One of the most difficult things to keep in mind about evolution is that when we say things like, "Genes want to make more copies of themselves," or even, "natural selection," we're actually using metaphors. A gene doesn't want anything, and there's no outside mechanism that selects which genes are best to preserve. All that happens is that random genetic mutations cause the organisms carrying them to behave or develop in different ways. Some of those ways result in more copies of the mutated gene being passed on, and so forth. Nor is there any predetermined plan progressing towards an ideal form. It's not ideal for the human eye to have a blind spot where the optic nerve exits the retina, but that's how it developed, starting from a simple photoreceptor cell. In retrospect, it would have been much more advantageous for humans to crave nutrients and vitamins rather than just calories. But over the millenia,
Mitovi i zablude o evoluciji. Hajde da pričamo o evoluciji. Verovatno ste čuli da neki ljudi misle da je ideja sporna iako se mnogi naučnici sa tim ne slažu. Čak i ako ne pripadate tim ljudima i mislite da prilično dobro razumete evoluciju verovatno i dalje verujete u neke stvari koje nisu sasvim tačne, poput: "Evolucija predstavlja prilagođavanje organizma okruženju." Ovo je jedna zastarela, sada odbačena, teorija evolucije. Gotovo 60 godina pre nego što je Darvin objavio svoju knjigu, Žan Baptist Lamark je rekao da bića evoluiraju tako što razvijaju određene karakteristike tokom života i onda ih prenose na potomstvo. On je mislio, na primer, da zato što žirafe provode život istežući se da dohvate lišće na visokim granama, njihovi mladunci će se roditi sa dužim vratovima. Ali danas znamo da genetika ne funkcioniše tako. U stvari, jedinka ne evoluira uopšte. Zapravo, slučajne genetske mutacije dovode to toga da se neke žirafe rađaju sa dužim vratovima i to im daje bolje šanse da prežive nego one koje nisu imale toliko sreće, što nas dovodi do "preživljavanje najsposobnijih". Ovo zvuči kao da evolucija uvek bira najveće, najjače ili najbrže jedinke, što u stvari nije slučaj. Prvo, evoluciona spremnost se odnosi na to koliko je jedinka prilagođena trenutnom okruženju. Ako bi svo visoko drveće iznenada nestalo i ostala samo trava sve one dugovrate žirafe ne bi više bile u prednosti. Drugo, evolucija se ne ostvaruje kroz preživljavanje već kroz razmnožavanje. I svet je pun stvorenja poput mužjaka morskog đavola, koji je toliko mali i nespreman da preživi na rođenju da mora brzo da nađe partnera pre nego što umre. Ali barem možemo reći da ako organizam umre, a nije se razmnožio pre toga on je evolutivno beskoristan, zar ne? Pogrešno! Zapamtite, prirodna selekcija se ne događa na nivou organizma već na genetskom nivou, a gen koji postoji u jednom organizmu postoji i kod njegovih rođaka. Dakle, gen koji podstiče neku životinju da se žrtvuje kako bi pomogla preživljavanje i buduće razmnožavanje svoje braće, sestara ili rođaka, može postati rasprostranjenija nego životinje koje su usmerene na samo-preživljavanje. Sve što obezbeđuje da se što više kopija gena prenese na sledeću generaciju će poslužiti svrsi, izuzev evolucionoj svrsi. Treba imati na umu da kada kažemo stvari poput: "Geni žele da naprave što više svojih kopija" ili "prirodna selekcija", mi, u stvari, koristimo metafore. Geni ne žele ništa i ne postoji spoljni mehanizam koji određuje koji geni su najbolji i treba ih sačuvati. Sve što se događa je da nasumične genetske mutacije utiču na organizam koji ih poseduje da se ponaša ili razvija na drugačiji način. Neke od posledica su da se više kopija mutiranih gena prenosi na sledeću generaciju i tako dalje. Niti postoji neki predodređeni plan po kome se ide ka savršenoj formi. Za ljudsko oko nije savršeno da ima slepu mrlju gde optički nerv izlazi iz mrežnjače, ali oko se tako razvilo od jednostavne fotoreceptorske ćelije. Opšte uzev, možda bi za ljude bilo mnogo bolje da su razvili potrebu za hranljivim materijama i vitaminima nego samo za kalorijama. Ali tokom vekova,
during which our ancestors evolved, calories were scarce, and there was nothing to anticipate that this would later change so quickly. So, evolution proceeds blindly, step by step by step, creating all of the diversity we see in the natural world.
tokom kojih su naši preci evoluirali, kalorija nije bilo dovoljno i ništa nije moglo nagovestiti da će se ovo kasnije tako brzo promeniti. Dakle, evolucija nastupa slepo, korak po korak, po korak, stvarajući svu raznovrsnost koju vidimo oko nas.