In Lumina Evolutiei: Selectia cumulativa / Cumulative selection

Teoria selectiei cumulative (sau “actiunea cumulativa a selectiei naturale”) este maniera prin care speciile evolueaza in timp. Evolutia este un proces de selectie cumulativa, nu un proces "pas cu pas". Putem exemplifica acest lucru prin experimentul Shakespeare-maimuta. In al sau eseu, "Ceasornicarul orb", Richard Dawkins se foloseste de acest experiment pentru a demonstra faptul ca teoria evolutiei a lui Charles Darwin este un proces cumulativ, si nu unul "pas cu pas". In acest experiment, o maimuta este asezata in fata unui calculator si lasata sa loveasca tastele la intamplare pana cand pe ecran rezulta textul (versul) din Shakespeare dorit, "METHINKS IT IS LIKE A WEASEL". Deruland experimentul avand la dispozitie un numar infinit de maimute, procesul ar dura multe milioane de ani. Daca privim experimentul Shakespeare-maimuta ca pe un proces “pas cu pas”, realizam ca intervalul de timp si sansa necesare pentru a ajunge la rezultatul dorit (versul din Shakespeare) fac din acest proces o explicatie foarte implauzibila pentru evolutia speciilor. Cu toate acestea, daca modificam experimentul, astfel incat acesta sa imite conditiile naturale de mediu, rezultatul dorit este atins. Modificare consta intr-o selectie (pastrare) a acelei propozitii aleatorii introduse de catre maimuta care este cea mai apropiata de versul din Shakespeare dorit. Apoi maimuta incearca sa copieze respectiva propozitie (ereditate), dar nereusind in intregime, o schimba in mica masura (mutatie). Este selectat cel mai bun rezultat, iar procesul se repeta pana cand maimuta ajunge la versul din Shakespeare. Folosind acest proces de selectie cumulativa, sunt necesari doar 40-60 de pasi pana cand se ajunge la rezultatul dorit.

Generation 1: WDLMNLT DTJBKWIRZREZLMQCO P
Generation 2: WDLTMNLT DTJBSWIRZREZLMQCO P
Generation 10: MDLDMNLS ITJISWHRZREZ MECS P
Generation 20: MELDINLS IT ISWPRKE Z WECSEL
Generation 30: METHINGS IT ISWLIKE B WECSEL
Generation 40: METHINKS IT IS LIKE I WEASEL
Generation 43: METHINKS IT IS LIKE A WEASEL

Vezi si http://gygess.blogspot.com/2007/04/cumulative-selection-selectie.html

The theory of cumulative selection is the manner by which species evolve over time. The process of evolution is a cumulative selection, not a single-step process. This can be exemplified by looking at The Shakespeare Monkey Experiment. In his essay The Blind Watchmaker, Richard Dawkins uses this experiment to prove that Charles Darwin's theory of evolution is a cumulative process rather than a single-step process. This experiment involves placing monkeys in front of a computer, then letting them hit keys randomly until they come up text from Shakespeare ("METHINKS IT IS LIKE A WEASEL"). With an infinite amount of monkeys this process would take million and millions of years. When looking at the Shakespeare Monkey Experiment as a single-step process one realizes that the amount of time and chance required make it an improbable explanation for the evolution of species up to this point. However, if one changes the process slightly to imitate environmental conditions that would preserve certain mutations and eradicate others, the desired end is achieved. This alteration involves looking at the sentences the monkeys produced, choosing the one that most resembles something from Shakespeare. The monkey then attempts to copy this sentence. It is unable to duplicate the sentence, however, and the sentences change. The best sentence is picked out and the process is repeated until the monkey comes up with a sentence from Shakespeare. Using this process of cumulative selection, the desired sentence only takes forty-sixty steps (as opposed to millions of years). This is a probable time frame to explain the evolution of plants and animals that exist today.