Perje se ubraja među najčudesnije pojave u životinjskom svijetu. Predivni u svojoj složenosti, i osjetljivosti u konstrukciji, dovoljno su jaki da drže ptice hiljadama kilometara u visinama. Kao i sve stvari u prirodi, perje je evoluiralo kroz milione godina u svoj današnji oblik. Teško je zamisliti kako se to desilo. Kako su, inače, izgledali posredni oblici? Kakva je korist polu-krila prekrivenog polu-perjem? Zahvaljujući nauci, znamo da su ptice živući dinosauri. Može se vidjeti srodnost njihovih kostura. Pojedini dinosauri dijele anatomske osobine sa pticama i ne nalazimo ih kod drugih životinja, npr. jadac. Tokom kasnih '90-ih, paleontolozi su počeli tražiti dokaze za tu ideju: dinosaure s ostacima perja koji su opstali na njihovim tijelima. Naučnici su od tada pronašli desetke vrsta dinosaura s ostacima perja. Neki su sitni poput golubova, a neki su bili kao školski autobus. Ako posmatramo njihovu srodnost na porodičnom stablu, evolucija perja ne izgleda tako nemoguće. Najudaljeniji ptičji pernati srodnici imali su ravno perje poput žice. Zatim su se te žice razdvojile u proste grančice. Kod mnogih vrsta dinosaura, to perje je evoluiralo u još komplikovanije perje, koje i danas vidimo na pticama. U isto vrijeme perje se proširilo duž tijela dinosaura, mijenjajući se od rijetkog paperja u gusto perje, koje je dosezalo čak i do nogu. Neki od fosila su očuvali i molekule koje daju boje. Oni otkrivaju divnu paletu boja: sjajno tamno perje koje podsjeća na vrane, naizmjenične crne i bijele pruge, ili kapi žarko crvene boje. Neki dinosauri su imali visoke krijeste na glavi, a drugi veliko i dramatično perje na repu. Ipak, nijedan od ovih dinosaura nije mogao iskoristiti perje za let - ruke su im bile previše kratke a ostatak tijela je bio previše težak. Ali ptice ne koriste perje samo za letenje. Šljuka koristi perje kako bi se savršeno uklopila u okolinu. Noj širi svoja krila iznad gnijezda kako bi zaštitio mlade. Paun eksponira svoje veličanstveno perje na repu da bi privukao paunice. Perje je moglo služiti za te funkcije čak i kod dinosaura. Ali, kako su poletjeli pernati dinosauri još uvijek je misterij. Ako su dinosauri sa sitnim perjem mahali rukama penjući se uzbrdo, njihovo perje bi im dalo dodatni podstrijek kako bi brže trčali. Ovo dešavanje u fizici moglo je dovesti do evolucije dužih ruku kod dinosaura, što bi im omogućilo brže trčanje i čak kraći let. S vremenom su njihove ruke zamijenila krila. Tek tada, vjerovatno 50 miliona godina nakon što je perje nalik na žicu evoluiralo, dinosauri su odletjeli prema nebu.
Feathers are some of the most remarkable things ever made by an animal. They are gorgeous in their complexity, delicate in their construction, and yet strong enough to hold a bird thousands of feet in the air. Like all things in nature, feathers evolved over millions of years into their modern form. It could be hard to imagine how this could have happened. After all, what did the intermediate forms look like? What good is half a wing, festooned with half-feathers? Thanks to science, we now know that birds are living dinosaurs. You can see the kinship in their skeletons. Certain dinosaurs share some anatomical details with birds found in no other animals, such as wish bones. And in the late 1990s, paleontologists started digging up some compelling support for that idea: dinosaurs with bits of feathers still preserved on their bodies. Since then, scientists have found dozens of species of dinosaurs with remnants of feathers. Some were as small as pigeons, and some were the size of a school bus. If you look at how they are related on a family tree, the evolution of feathers doesn't seem quite so impossible. The most distant feathered relatives of birds had straight feathers that looked like wires. Then these wires split apart, producing simple branches. In many dinosaur lineages, these simple feathers evolved into more intricate ones, including some that we see today on birds. At the same time, the feathers spread across the bodies of dinosaurs, turning from sparse patches of fuzz into dense plumage, which even extended down to their legs. A few fossils even preserved some of the molecules that give feathers color. They reveal a beautiful range of colors: glossy, dark plumage, reminiscent of crows, alternating strips of black and white, or splashes of bright red. Some dinosaurs had high crests on their heads, and others had long, dramatic tail feathers. Now, none of these dinosaurs could use their feathers to fly - their arms were too short and the rest of their bodies were far too heavy. But, birds don't just use feathers to fly. A woodcock uses feathers to blend in perfectly with its forest backdrop. An ostrich stretches its wings over its nest to shade its young. A peacock displays its magnificent tail feathers to attract peahens. Feathers could have served these functions for dinosaurs too. Exactly how feathered dinosaurs took flight is still a bit of a mystery. But if a small-feathered dinosaur flapped its arms as it ran up an incline, its feathers would have provided extra lift to help it run faster. This accident of physics might have led to the evolution of longer dinosaur arms, which would let them run faster and even leap short distances through the air. Eventually, their arms stretched out into wings. Only then, perhaps 50 million years after the first wiry feathers evolved, did feathers lift those dinosaurs into the sky.