Evolution: Class 12 Biology Chapter 6 Hinglish mein

Dhar ke paas Narmada valley mein ek rock todo, aur ho sakta hai tumhare haath mein lagbhag 15 cm chauda ek fossil dinosaur egg aa jaaye, jo dinosaurs ke yug ke bilkul aakhir mein diya gaya tha. Ab apni balcony par baithe pigeon ko dekho: woh dinosaurs ki us ek branch ka hissa hai jo aaj bhi zinda hai. Purani rock mein pade eggs aaj ke aasmaan ke birds se kaise jude hain? Yeh chapter is dhaage ko aur kai doosre dhaagon ko follow karta hai.

Evolutionary biology yeh poochti hai ki living world aaj jaisa hai, waisa kaise bana: pehli living cheezein kahan se aayi, species kyun badalti hain, aur aaj zinda laakhon species aapas mein kaise related hain. Iske jawab lagbhag chaar billion saal mein phaile hain, isliye hum aur bhi pehle se shuru karte hain, universe aur Earth se.

6.1 Life ka Origin

Light ko space paar karne mein time lagta hai, isliye telescope ek time machine bhi hai: billions of light-years door ki galaxy se aane wali light us galaxy ko waisa dikhati hai jaisi woh billions saal pehle thi. Aasmaan ki sabse purani light ikattha karke astronomers ne universe ki history dobara banayi hai aur uski age naapi hai, lagbhag 13.8 billion years.

Big Bang theory ke hisaab se universe ek bahut garam, dense state mein shuru hua aur tab se phailta aur thanda hota ja raha hai. Yeh khaali space mein hua koi explosion nahi tha: space khud phaila. Hydrogen aur helium ke nuclei pehle kuch minutes mein ban gaye. Agle kuch sau million saalon mein gravity ne gas ko stars aur galaxies mein ikattha kiya. Bhaari elements, jaise tumhari body ke carbon, oxygen aur iron, stars ke andar bane aur un stars ke khatam hone par bikhar gaye. Hamara Sun aur uske planets Milky Way galaxy mein aise hi ek cloud se bane, aur Earth lagbhag 4.54 billion saal pehle bani.

Young Earth garam thi, us par meteorites girte the aur woh volcanoes se dhaki thi. Uske andar se nikalti gases, zyadatar water vapour, carbon dioxide aur nitrogen, saath mein thodi hydrogen, methane aur ammonia, ne ek atmosphere banaya jismein free oxygen lagbhag nahi thi. Oxygen nahi thi to ozone layer bhi nahi thi, isliye tez ultraviolet light surface tak pahunchti thi. Jaise-jaise crust thanda hua, water vapour condense hokar bahut lambe time tak baarish ki tarah gira, aur gaddhon ko bhar kar pehle oceans bane.

Pehli life kahan se aayi? Do purane jawab mushkil hisse se bach nikalte hain. Panspermia, jo Greek thinkers se chala aa raha idea hai aur jise 1903 mein Svante Arrhenius ne phir se uthaya, kehta hai ki life ke 'seeds' space se tairte hue Earth tak aaye. Agar yeh sach bhi ho, to yeh sawaal ko bas kisi doosre planet par shift kar deta hai. Doosra jawab, spontaneous generation, yeh maanta tha ki living cheezein non-living matter se har waqt paida hoti rehti hain: sadte meat se maggots, keechad se frogs, baasi broth se microbes.

1668 mein Francesco Redi ne meat ke kuch jars ko gauze se dhaka aur baaki ko khula chhod diya; maggots sirf wahin aaye jahan flies meat tak pahunch sakti thi. Microbes ko rule out karna zyada mushkil tha, kyunki woh dikhte nahi aur har jagah hote hain. Louis Pasteur ne lagbhag 1860 mein aise flasks se yeh sawaal suljhaya jinki necks ko usne kheench kar S-shaped curve bana diya tha (Fig. 6.1).

Curved neck ne ek critic ki yeh objection khatam kar di ki ubaalne se hawa ki koi 'vital force' nasht ho jaati hai: yahan taazi hawa aaraam se broth tak pahunchi, phir bhi kuch nahi uga jab tak microbes andar nahi aaye. Conclusion yeh tha ki living cheezein sirf doosri living cheezon se hi paida hoti hain (biogenesis), aur isne spontaneous generation ko scientific idea ke roop mein khatam kar diya. Lekin isse yeh samajh nahi aaya ki bilkul pehli life kaise shuru hui.

1920s mein Russian biochemist Alexander Oparin aur British biologist J. B. S. Haldane ne alag-alag kaam karte hue suggest kiya ki life non-living matter se hi bani thi, lekin sirf ek baar, dheere-dheere, aur aaj se bilkul alag conditions mein. Pehla stage tha chemical evolution (रासायनिक विकास): lightning, ultraviolet light aur volcanic heat ne simple molecules ke beech reactions chalaye, jisse sugars, amino acids aur nucleotide bases bane jo seas mein ek patli 'soup' ki tarah jama ho gaye. Oxygen ka na hona zaroori tha, kyunki oxygen in naazuk molecules ko tod deti.

1953 mein Chicago mein Harold Urey ki laboratory ke student Stanley Miller ne is idea ko test kiya (Fig. 6.2). Unhone methane, ammonia aur hydrogen ko paani ke saath ek sterile glass loop mein band kiya. Ek flask mein ubalta paani vapour ko ghuma kar ek bade chamber mein bhejta tha, jahan electric sparks lightning ka kaam karte the. Ek condenser gases ko thanda karta tha, aur jo liquid banta woh ek trap mein jaakar wapas flask mein aa jaata. Ek hafte ke andar paani brown ho gaya, aur tests mein amino acids mile, jinmein glycine aur alanine bhi the, jo sirf simple gases aur energy se bane the.

Is experiment ke variations, doosre gas mixtures ke saath aur sparks ki jagah ultraviolet light ya heat ke saath, se tab se DNA aur RNA mein milne wale bases, simple sugars aur woh fatty molecules bhi bane hain jo membranes bana sakte hain. 2008 mein jab Miller ke rakhe samples ko modern instruments se dobara analyse kiya gaya, to unmein 20 se zyada alag amino acids mile. Geologists ab maante hain ki early atmosphere mein methane aur ammonia utne nahi the jitna Miller ne maana tha, isliye researchers hot springs aur deep-sea vents ko bhi study karte hain, jahan heat aur minerals waisi hi chemistry chala sakte hain. Main lesson wahi rehta hai: life ke molecules simple ingredients aur energy ke source se aasaani se ban jaate hain.

Chemistry biology kaise bani? Yahan evidence kam hai, aur scientists clues se reasoning karte hain. Ek living cell ko aisa molecule chahiye jo information store kare aur reactions ko tez bhi kare. RNA dono kar sakta hai: kuch RNA molecules (ribozymes) catalysts ka kaam karte hain, aur ek RNA strand copying ke liye template ban sakta hai. Isse ek early 'RNA world' ka pata chalta hai jismein molecules khud ki copy banate the. Fatty molecules paani mein apne aap khokhle bubbles bana lete hain, aur aise bubbles ke andar phansa RNA simple protocells banata. Jab protocell badh sakta, divide ho sakta aur apna RNA aage de sakta, tab natural selection shuru ho sakti thi.

Cells ka sabse purana evidence lagbhag 3.5 se 3.7 billion saal purana hai: microbial mats (stromatolites) ke banaye layered mounds aur biological signature wala carbon. Yeh sea mein rehne wale simple prokaryotes the; zameen aur billions saal tak bina life ke rahi. Life non-living chemistry se natural processes ke zariye bani, yeh science ki working consensus hai (ise kabhi-kabhi abiogenesis kehte hain); protocell se asli cell tak ka exact raasta abhi bhi research mein hai.

6.2 Evolution of Life Forms – Ek Theory

Ek purana view, special creation, maanta tha ki species fixed hain. Is view ke hisaab se har tarah ka organism apne aaj ke roop mein alag se banaya gaya, tab se koi kind na aaya na gayab hua, aur Earth sirf kuch hazaar saal purani hai. Nineteenth-century geology aur biology ne har point ke khilaaf evidence paaya: rock layers jinhe banne mein millions saal lage, aisi species ke fossils jo ab exist nahi karti, aur living species jo ek doosre se bas thoda sa alag hain.

Charles Darwin ne 1831 se 1836 tak paanch saal HMS Beagle par bitaye, jab woh South America ke coasts ka survey karke duniya ke charon taraf ghooma. Argentina mein unhone giant extinct mammals ki haddiyaan khod nikaali jo wahan aaj bhi rehne wale armadillos aur sloths ke bahut bade versions jaise dikhte the. Galápagos Islands par birds aur tortoises ek island se doosre island par thode alag the, phir bhi sab South American mainland ki species jaise the. England lautkar unhone do decades ek explanation ko test karne mein lagaye: species fixed nahi hain, balki pehle ki species se dheere-dheere modification ke saath descend karti hain.

Unka proposed process hai natural selection. Halki ret par rehne wale deer mice socho. Unke coat colours alag-alag hote hain, yeh variation inherit hota hai, aur owls un mice ko pakadte hain jo alag dikhte hain. Achhe se match karne wale mice zyada bachche paalte hain, isliye agli generation average mein thodi halki hoti hai; yeh kai generations tak dohrao aur population badal jaati hai. Yahan success offspring se gini jaati hai. Darwinian fitness matlab reproductive success, yaani ek individual kitne zinda bachne wale bachche chhodta hai, na ki khud mein strength ya speed.

Is theory ke do bade implications hain, aur dono baad mein confirm hue. Har do species, chahe tiger aur mango tree hi kyun na hon, agar kaafi peeche jaao to ek common ancestor share karti hain, isliye saari life ek family tree banati hai (Fig. 6.3). Aur kyunki aisa change dheema hota hai, Earth bahut purani honi chahiye: radiometric dating ab use 4.54 billion saal ka batati hai, na ki kuch hazaar saal jaisa pehle maana jaata tha. Isiliye rock record life ka calendar bhi hai.

6.3 Evolution ke Evidences kya hain?

Evolution ka evidence kai independent sources se aata hai: rocks, embryos, anatomy, molecules, breeders ke records aur aankhon ke saamne hota change. Inmein se koi bhi is idea ko galat saabit kar sakta tha. Iske bajaye, sab ek hi kahani sunate hain.

Fossils

Fossil (जीवाश्म) bahut purane samay ke kisi organism ke bache hue remains ya nishaan hain. Zyadatar hard parts hote hain, jaise bones, shells, teeth ya wood, jo patthar ban gaye, lekin footprints, burrows aur leaf impressions bhi fossils hain. Zyadatar fossils sedimentary rock mein bante hain, jahan mitti aur ret layers mein jamti hain aur dheere-dheere sakht hoti hain. Bina chhede gaye rock mein har layer apne neeche wali layer se nayi hoti hai (Fig. 6.4).

Palaeontological evidence, yaani fossils se mila evidence, rocks mein life ke order par tika hai. Sabse gehre fossil wale rocks mein sirf single-celled life hai. Upar ki layers mein soft-bodied animals, phir shelled invertebrates, fish, land plants, amphibians, reptiles, mammals aur sabse naye rocks mein humans aate hain. Har group pehli baar ek khaas level par dikhta hai, aur kai upar jaakar gayab ho jaate hain kyunki woh extinct ho gaye: birds ke alawa dinosaurs sirf lagbhag 230 se 66 million saal purane rocks mein milte hain. Fixed, kabhi na badalne wali species ki duniya aisa koi sequence nahi chhodti.

Fossils beech ke forms bhi dikhate hain. Tiktaalik, ek fish jiski neck aur mazboot limb jaise fins thi, lagbhag 375 million saal purane rocks se mili. Archaeopteryx, lagbhag 150 million saal purana, ke feathers aur wings the lekin teeth, claws wali ungliyaan aur ek lambi haddi wali poonch bhi thi, jo chhote dinosaurs aur birds ko jodti hai.

Hum yeh ages kaise jaante hain? Radiometric dating se, jo tum physics mein padh chuke ho. Ek radioactive isotope apni half-life se tay ek fixed rate par decay hota hai, isliye sample mein bacha fraction ek clock ka kaam karta hai. Carbon-14, jiski half-life 5730 years hai, lagbhag 50,000 saal tak purane remains ko date karta hai. Purane rocks ke liye dheeme clocks chahiye, jaise potassium-40 (half-life 1.25 billion years), jise fossil ke upar aur neeche ki volcanic ash layers par use karte hain.

Embryos

1860s mein Ernst Haeckel ne claim kiya ki ek embryo apne ancestors ke adult forms ko dohraata hai, yaani human embryo ek 'fish stage' aur ek 'reptile stage' se guzarta hai. Dhyaan se compare karne par yeh galat nikla. Decades pehle Karl Ernst von Baer ne dekha tha ki ek animal ka embryo related animals ke embryos jaisa dikhta hai, unke adults jaisa kabhi nahi, aur jo features ek bade group mein common hain woh development mein un features se pehle aate hain jo ek chhote group ke khaas hain.

Embryos asal mein shared ancestry dikhate hain. Development ke shuru mein har vertebrate embryo, chahe fish ho, bird ho ya human, ki neck region mein grooves se alag ki gayi pharyngeal arches ki ek series hoti hai, jinhe aksar loosely gill slits kehte hain. Fish mein yeh gill supports ban jaati hain. Mammals mein wahi embryonic tissues jaw ke hisse, middle ear ki teen chhoti haddiyaan, aur thymus jaisi glands ban jaate hain. Ek hi shared starting kit, jo har group mein alag tarah se reshape hui, bilkul wahi hai jo common ancestor se descent predict karta hai.

Comparative anatomy: homology aur analogy

Bat ke wing mein thumb aur finger bones kyun hone chahiye? Udne ke liye inki koi zaroorat nahi. Fig. 6.5 mein human, bat, dolphin aur horse ke forelimbs haddi se haddi match karte hain: shoulder par ek humerus, phir radius aur ulna, carpals aur metacarpals, aur tip par phalanges, jabki yeh pakadte, udte, tairte aur daudte hain. Sabse simple explanation inheritance hai: in chaaron mammals ko yeh limb plan ek common four-legged ancestor se mila, aur phir selection ne iske parts ko lamba, chhota ya jod diya. Aise structures homologous organs (समजात अंग) hain, aur jo process related forms ko alag-alag disha mein le jaata hai woh divergent evolution hai. Yahi reasoning body ke andar bhi lagti hai: frog, crocodile aur human ke brains ek jaise teen main regions se bane hain.

Plants mein bhi homology dikhti hai. Bougainvillea ke thorns aur Cucurbita (gourd family) ke tendrils bilkul alag dikhte hain, phir bhi dono leaf ke axil se ugte hain, isliye dono modified shoots hain. Isi tarah garden pea ke climbing tendrils aur Opuntia ke spines, dono modified leaves ya leaves ke hisse hain.

Ab shark aur dolphin ko compare karo. Dono streamlined hain, peeth par fin aur ek powerful tail ke saath, phir bhi ek fish hai aur doosra hawa mein saans lene wala mammal, jiska skeleton aur fins bilkul alag tarah se bane hain. Jo features ek jaise dikhte hain ya ek jaisa kaam karte hain lekin structure aur origin mein alag hain, woh analogous organs (समरूप अंग) hain. Yeh convergent evolution se bante hain: jab unrelated lineages ek hi physical problem ka saamna karti hain, jaise paani mein tez chalna, to selection milte-julte solutions tak pahunchti hai.

Molecules

Sabse gehri samaantaayein chemical hain. Saari cellular life apne genes DNA mein store karti hai, jo same chaar bases se bana hai, aur lagbhag same genetic code se unhe same 20 amino acids wale proteins mein padhti hai. Same kaam wale proteins, jaise respiration mein cytochrome c, ke sequences species ke beech bahut milte-julte hote hain, aur evolutionary doori ke saath differences badhte hain. DNA compare karne se wahi family tree milta hai jo anatomy aur fossils suggest karte hain (Table 6.1).

Artificial selection

Breeders is process ka fast-forward version chalate hain. Kaunse plants ya animals reproduce karenge yeh chunkar, logon ne kuch hazaar saalon mein crops aur livestock ko naya roop de diya hai. Europe ke coast ka ek wild plant, wild cabbage (Brassica oleracea), har baar alag hisse ko favour karke chhe jaani-pehchaani sabziyon mein badal diya gaya hai (Table 6.2). Darwin, jo khud pigeons breed karne ke shaukeen the, ne On the Origin of Species isi tarah ke evidence se shuru ki: breeding dikhati hai ki populations mein kitna heritable variation hota hai, aur nature ke paas us par kaam karne ke liye kahin zyada lamba time raha hai.

Natural selection ko hote hue dekha gaya

England ka peppered moth (Biston betularia) din mein tree trunks par baithta hai. Zyadatar individuals halke rang ke aur chitte wale the, jo bark par lage halke lichens se match karte the. 1848 mein Manchester ke paas ek dark (melanic) moth record kiya gaya. Jab coal ke dhuen ne lichens ko maar diya aur trunks kaale kar diye, to pale moths alag dikhne lage aur birds unhe kha gaye, jabki dark moths chhup gaye. 1890s tak Manchester ke paas lagbhag 98 % moths dark the (Fig. 6.6).

Yeh shift, jise industrial melanism kehte hain, 1950s mein clean-air laws aane ke baad ulti chal padi: lichens wapas aaye, bark halki hui aur dark moths phir se rare ho gaye. Bina pollution wale countryside mein dark moths hamesha kam hi the. Field studies ne confirm kiya ki birds un moths ko zyada pakadte hain jo apne background se alag dikhte hain, aur 2016 mein geneticists ne dark form ko cortex naam ke gene ke ek single mutation tak trace kiya jo lagbhag 1819 mein aaya tha. Is poore samay dono forms bane rahe; badla to bas unka ratio. Lichens khud bhi useful pollution indicators hain, kyunki zyadatar species sulfur dioxide se polluted hawa mein ug nahi sakti.

Aaj insaan kai species mein evolution chala rahe hain, aksar anjaane mein. Ek khet par saal-dar-saal same pesticide spray karo, aur jo rare insects use jhel paate hain woh lagbhag saare offspring chhodte hain; kuch hi seasons mein pesticide kaam karna band kar deta hai. India mein pink bollworm ne Bt cotton ke aane ke lagbhag ek decade ke andar uske against resistance evolve kar li. Weeds herbicides ko, mosquitoes DDT ko aur bacteria antibiotics ko isi tarah resist karte hain (neeche ke steps). Biologists aise insaan ke laaye change ko anthropogenic evolution kehte hain, aur yeh tez hota hai kyunki selection bahut tagdi hoti hai aur generations chhoti hoti hain.

In examples ka ek common lesson hai: evolution ka koi goal nahi aur koi foresight nahi. Mutations sanyog se aate hain, aur kaunse phailenge yeh us waqt ke environment par depend karta hai. Evolution ek stochastic process hai, jise chance events aur selection shape karte hain, kisi target ki taraf planned march nahi.

6.4 Adaptive Radiation kya hai?

1835 mein Beagle ne Ecuador se lagbhag 900 km west mein Galápagos Islands par paanch hafte bitaye. Darwin ne wahan chhote, phike rang ke birds collect kiye, bina yeh samjhe ki woh kareebi relatives hain. London lautne par ornithologist John Gould ne dikhaya ki woh alag lekin related species ka ek group hain, har ek ki apni tarah ki beak. Aaj hum in Darwin's finches ki lagbhag 18 species ginte hain. Sab ek seed-eating ancestor se descend hui hain jo pichhle kuch million saalon mein American mainland se islands tak pahuncha.

Har species khaane ke alag tareeke ke liye suited hai (Fig. 6.7). Ground finches gehri, mazboot beaks se seeds todte hain, aur beak jitni badi, utna sakht seed woh khol sakti hai. Cactus finches lambi, nukeeli beaks se cactus flowers mein khojbeen karte hain. Tree finches insects ko kuchalte hain, warbler finch patli, tez beak se leaves par se chhote insects chunta hai, aur vegetarian finch moti, mudi hui beak se buds aur fruit nochta hai. Woodpecker finch to beak mein cactus ka kaanta pakad kar bark se grubs bhi nikaalta hai.

Ek ancestor se kai species ka evolve hona, jab uske descendants alag habitats ya ways of life mein phail jaate hain, adaptive radiation (अनुकूली विकिरण) kehlaata hai. Darwin's finches iska textbook example hain, kyunki islands par kai khaali niches the aur competitors kam the.

Australia ek poore continent ke scale par adaptive radiation dikhata hai. Doosre land masses se tens of millions saal tak alag rehne ki wajah se yeh pouch wale mammals, yaani marsupials, ka ghar bana, jo lagbhag har mammalian way of life mein phail gaye: ghaas charne wale kangaroos, bil khodne wale wombats, patte khaane wale koalas, glide karne wale sugar gliders, termites khaane wala numbat, ret mein 'tairne' wala marsupial mole, aur predators jaise quolls, Tasmanian devil aur ab extinct ho chuka thylacine, yaani Tasmanian wolf.

Inmein se kai marsupials doosre continents ke placental mammals jaise hi dikhte aur jeete hain (Table 6.4). Thylacine wolf jaisa dikhta tha, aur sugar glider lagbhag flying squirrel ki copy hai. Dono groups sirf door ke rishtedaar hain, kyunki unka last common ancestor 160 million saal se bhi pehle jeeta tha, lekin milte-julte ways of life ne milti-julti body forms select ki. Yeh convergent evolution hai: alag continents par do alag adaptive radiations, jo matching solutions tak pahunchi.

6.5 Biological Evolution

Natural selection ke liye teen ingredients chahiye: variation, inheritance aur unequal reproductive success. Pehli cells mein teeno pehle se the, kyunki kuch cells apne aas-paas ke chemicals ko doosron se behtar use karti hongi, isliye selection utni hi purani hai jitni cellular life.

Yeh kitni tez kaam karti hai, yeh generation time par depend karta hai. Ek bacterium lagbhag 20–30 minutes mein divide ho sakta hai, isliye ek culture ek din mein darjanon generations se guzarta hai, jabki ek elephant ko apna pehla bachcha paida karne mein ek decade se bhi zyada lagta hai. 1988 se biologist Richard Lenski aur unki team ne E. coli ke baarah flasks ko glucose ki diet par evolve hote rakha hai. Unke medium mein citrate bhi hai, jise normal E. coli oxygen hone par use nahi kar sakta. Lagbhag 31,500 generations ke baad ek population ne citrate khaane ki ability evolve kar li aur tezi se badhi. Itna bada change ek mammal mein laakhon saal leta; bacteria mein isne lagbhag pandrah saal liye.

Sirf genes mein likhe differences hi aage ja sakte hain, isliye sirf inherited traits hi select ho sakte hain. Jo bacterium drug se sirf isliye bacha kyunki woh aise kone mein tha jahan drug pahuncha hi nahi, woh aage kuch useful nahi deta. Adapted hona, yaani kisi khaas environment mein zinda rehne aur reproduce karne ke liye achhe se suited hona, inherited differences par selection ke kai rounds ka result hai.

Sab milakar, Darwin ki theory do pillars par khadi hai: branching descent, jismein saari species common ancestors ke ek tree se related hain (Fig. 6.3), aur natural selection, woh main process jo har lineage ko uske aas-paas ke liye fit karta hai.

Giraffe ki neck itni lambi kyun hai? Darwin ki book se aadhi sadi pehle, 1809 mein, Jean-Baptiste Lamarck ne do rules par tika ek jawab diya. Jo organs zyada use hote hain woh badhte hain, aur jo bekaar pade rehte hain woh murjha jaate hain (use and disuse). Aur ek animal apni life mein is tarah jo bhi paata ya khota hai, woh apne bachchon ko de deta hai (inheritance of acquired characters). Is view ke hisaab se giraffes ki har generation ne sabse oonche patton tak pahunchne ke liye kheench kar neck mein thodi length jodi jo uske bachchon ne inherit ki.

Yeh idea fail hota hai kyunki life ke dauraan aaye changes eggs aur sperm tak nahi pahunchte. 1880s mein August Weismann ne kai generations tak mice ki poonch kaati, aur har baar bachche normal poonch ke saath hi paida hue. Isi wajah se ek wrestler ke mote kaan ya weightlifter ki muscles inherit nahi hote. Giraffe ka Darwinian explanation alag hai: jo bachche thodi lambi neck ke saath paida hue, woh sookhe mausam mein zyada khaane tak pahunche, behtar zinda rahe aur khud zyada bachche chhode.

Ek aur ingredient economics se aaya. 1798 mein Thomas Malthus ne argue kiya ki human populations apni food supply se tez badhti hain. Darwin ne 1838 mein Malthus ko padha aur samjha ki yeh argument poori nature par lagta hai. Unki reasoning ko paanch observations aur teen inferences mein rakha ja sakta hai (Fig. 6.8).

Dono hisson ko jodo to selection se bacha nahi ja sakta. Jab har offspring zinda nahi bach sakta, to jinke inherited traits unke aas-paas ke liye suit karte hain, woh average mein agli generation ke parents bante hain. Ise hazaaron generations tak dohrao aur population ka average character usi direction mein shift ho jaata hai jise environment favour karta hai. Isiliye Darwin ki book ka title hai On the Origin of Species by Means of Natural Selection: geological time tak jama hui yahi roz ki chhantai naye species bana sakti hai.

6.6 Evolution ka Mechanism

Darwin ki theory mein ek gap tha: woh nahi bata sakte the ki variation kahan se aata hai ya kaise inherit hota hai. Inherited 'factors' par Mendel ka kaam (1866), yaani Chapter 4 ke genes, 1900 tak kisi ki nazar mein nahi aaya, aur Darwin ko iske baare mein kabhi pata nahi chala. Lagbhag usi samay Amsterdam ke paas ke khet mein Dutch botanist Hugo de Vries ko aise evening primroses (Oenothera lamarckiana) mile jo apne padosiyon se bilkul alag the, zyada lambe ya chaude patton wale, aur jo true breed karte the. Unhone aise achaanak heritable changes ko mutations (उत्परिवर्तन) naam diya.

In plants se de Vries ne apni mutation theory (1901) banayi: ek nayi species achaanak, ek badi chhalaang mein aati hai, jise unhone saltation kaha. Darwin ne selection se chhante gaye chhote differences ke dheere-dheere jama hone ki kalpana ki thi; de Vries ne in chhalaangon ko hi evolution ka engine bana diya. Mazedaar baat yeh hai ki unke zyadatar primrose 'mutants' single genes ke change se nahi, balki chromosomes ke unusual behaviour se aaye the, jaise chromosomes ke extra sets.

Dono views ko 1930s aur 1940s mein population genetics ne milaya. R. A. Fisher, J. B. S. Haldane aur Sewall Wright ne mathematically dikhaya ki selection se chhante gaye chhote heritable differences population ko jaldi badal sakte hain, aur Theodosius Dobzhansky aur Ernst Mayr ne ise wild species se joda. Iska result, modern synthesis, kehta hai ki mutation aur recombination variation dete hain jabki selection, drift aur gene flow use shape karte hain. Haldane baad mein India mein bas gaye, Indian citizen bane aur Kolkata aur Bhubaneswar mein apni research jaari rakhi.

Synthesis ka ek central point yeh hai ki mutations zaroorat ke hisaab se random hote hain: ek organism woh mutation paida nahi kar sakta jo uska environment maangta hai. Joshua aur Esther Lederberg ne 1952 mein ise badi safaai se dikhaya (Fig. 6.9). Unhone bacterial colonies wali plate par ek velvet pad dabaya aur wahi pattern antibiotic streptomycin wali plates par chhaap diya. Resistant colonies har copy par same positions par ugi, isliye resistant cells original plate par drug se milne se pehle hi maujood the.

6.7 Hardy–Weinberg Principle

Genetics ki nazar se evolution ek population ke genetic make-up ka generations ke saath badalna hai. Aisa change pakadne ke liye hamein ek baseline chahiye: jab koi cheez population ke genes ko dhakel nahi rahi, tab unka kya hota hai? Woh baseline Hardy–Weinberg principle hai, jise 1908 mein English mathematician G. H. Hardy aur German physician Wilhelm Weinberg ne alag-alag nikaala.

Gene pool aur allele frequencies

Socho ki population ke har member ke har gene ki har copy ek shared reservoir mein hai: yeh population ka gene pool hai. Do alleles, $A$ aur $a$, wale ek gene ke liye $N$ individuals ki diploid population mein $2N$ copies hoti hain. In copies mein jitna hissa $A$ hai, woh $A$ ki allele frequency hai, jise $p$ likhte hain, aur jitna hissa $a$ hai woh $q$ hai. Sirf do alleles hon to har copy ya to ek hai ya doosri.

Randomly mate karne wali population mein har offspring gene pool se randomly nikle do gametes se banta hai. Egg mein $A$ hone ka chance $p$ hai aur sperm mein $A$ hone ka chance bhi $p$ hai, isliye $AA$ offspring ka chance $p\times p=p^2$ hai. Neeche ki derivation argument poora karti hai (Fig. 6.10).

Jo population in conditions ko poora karti hai woh Hardy–Weinberg (genetic) equilibrium mein hai: uska gene pool nahi badalta. Yeh principle isiliye useful hai kyunki asli populations shayad hi kabhi har condition poori karti hain, isliye isse hatna is baat ka sign hai ki evolution chal raha hai.

Equilibrium ko kya bigaadta hai

Agar naapi gayi genotype frequencies $p^2$, $2pq$ aur $q^2$ se alag hain, ya allele frequencies generations ke beech badalti hain, to population par kuch kaam kar raha hai, aur difference ka size aur direction isse kya ho raha hai iska ishara dete hain. Aam taur par paanch forces gini jaati hain jo population ko equilibrium se door dhakel sakti hain:

1. Gene flow (gene migration): khet ke beech udta pollen, ya herds ke beech jaate animals, ek gene pool se doosre mein alleles le jaate hain. Jab aisa baar-baar hota hai, to judi populations genetically milti-julti rehti hain.
2. Genetic drift (आनुवंशिक विचलन): allele frequencies chance se badalti hain kyunki sirf kuch individuals hi sanyog se breed kar paate hain. Drift chhoti populations mein strong hota hai aur bahut badi populations mein na ke barabar.
3. Mutation: naye alleles banata hai. Yeh variation ka asli source hai lekin akele frequencies ko bahut dheere badalta hai.
4. Genetic recombination: gamete formation ke dauraan crossing over aur independent assortment alleles ko naye combinations mein phente hain, aur selection ko kaam karne ke liye naya variation dete hain.
5. Natural selection: jo genotypes behtar zinda rehte aur reproduce karte hain, woh agli generation mein zyada alleles dete hain.

Non-random mating, jaise relatives ke beech mating, bhi equilibrium bigaadti hai: yeh homozygotes ka hissa badhati hai, lekin akele allele frequencies nahi badalti.

Drift sabse zyada tab dikhta hai jab population sirf kuch individuals se hokar guzarti hai. Agar ek chhota group nikal kar nayi population banata hai, jaise kisi island par, to uska gene pool purane gene pool ka ek chhota chance sample hota hai: kuch alleles zyada ho jaate hain aur kuch bilkul gayab. Yeh founder effect hai (Fig. 6.13). Jo population ghatkar kuch survivors tak reh jaaye aur phir wapas badhe, woh bhi aise hi bottleneck se guzarti hai.

India mein iske zabardast examples hain. Gir ke Asiatic lions twentieth century ki shuruaat mein ghatkar kuch darjan reh gaye the; ab woh saikdon mein hain lekin unmein bahut kam genetic variation hai. Cheetahs, jinhe haal hi mein Madhya Pradesh ke Kuno National Park mein dobara laaya gaya, purane bottlenecks se guzre hain aur itne ek jaise hain ki unrelated cheetahs ke beech skin grafts aksar accept ho jaate hain. Agar founder population isolated bhi ho, to drift aur selection use itna aage le ja sakte hain ki woh nayi species ban jaaye.

Selection trait ko teen tareekon se shape karti hai

Kai traits, jaise body size, beak depth aur birth weight, continuously vary karte hain, isliye population mein values ek bell-shaped curve banati hain. Selection aise curve par teen tareekon se kaam kar sakti hai (Fig. 6.15). Har case mein yeh gene pool mein allele frequencies badalti hai, isiliye Hardy–Weinberg ke matlab mein yeh evolution hai.

• Stabilising selection average ko favour karti hai aur dono extremes hata deti hai, isliye curve lamba aur patla ho jaata hai jabki uska mean wahin rehta hai. Human birth weight lambe samay tak iska classic case tha: average se bahut halke ya bahut bhaari babies ke bachne ke chances kam the.
• Directional selection ek extreme ko favour karti hai, isliye poora curve us taraf shift ho jaata hai. 1977 mein Galápagos ke Daphne Major island par ek bhayankar sookhe ke baad zyadatar bade, sakht seeds hi bache; gehri beaks wale medium ground finches bach gaye, aur unke offspring ki beaks naapne laayak gehri thi.
• Disruptive selection beech ke bajaye dono extremes ko favour karti hai, isliye curve do peaks mein bant sakta hai. Cameroon ke black-bellied seedcrackers ki bills ya to chhoti hoti hain ya badi, jo naram ya sakht seeds ke liye suited hain; beech wali bills wale birds dono ko achhe se handle nahi kar paate.

6.8 Evolution ki Ek Chhoti Kahani

Deep time ki kalpana karna mushkil hai, isliye Earth ke 4.54 billion saalon ko ek 24-hour din mein samet do. Pehli cells subah lagbhag 4:30 baje aati hain. Photosynthesis se bani oxygen hawa mein lagbhag 11:20 baje badhti hai. Pehli complex (eukaryotic) cells dopahar mein aati hain. Shells aur skeletons wale animals raat 9 baje ke baad hi dikhte hain, aur dinosaurs lagbhag 10:45 se 11:39 p.m. tak raaj karte hain. Hamari species aadhi raat se lagbhag chhe second pehle aati hai; farming, ek second ke paanchve hisse pehle.

Us din ke zyadatar hisse mein life microscopic thi, aur uski sabse badi khoj thi oxygen chhodne wala photosynthesis. Aaj ke cyanobacteria jaise microbes ne sunlight se paani se electrons kheenchna shuru kiya, wahi reaction jo tumne Class 11 mein photosynthesis ki light reaction ke roop mein padha, aur by-product ke roop mein oxygen chhodi. Pehle oxygen ne seas mein ghule iron ko zang lagaya, jisse layered iron-rich rocks bani jinhe banded iron formations kehte hain; Odisha aur Jharkhand ka kaafi iron ore isi tarah ki rocks se aata hai. Baad mein hi yeh hawa mein badhi, jisse ozone shield aur oxygen par jeene wali cells mumkin hui. Kai cells wali life aur bhi baad mein aayi.

Lagbhag 539 million saal pehle, Cambrian period ki shuruaat mein, shells, legs aur eyes wale animals fossil record mein achaanak dikhte hain, aur kuch tens of millions saal ke andar lagbhag har major invertebrate group maujood hota hai. Pehle vertebrates, jawless fish, lagbhag 520 million saal pehle tak aate hain; jaws wali fish baad mein aati hain. Plants animals se pehle zameen par pahunche: lagbhag 470 million saal pehle tak chhote moss jaise plants, phir sakht stems aur roots wale vascular plants (Fig. 6.16). Jab animals rengte hue kinaare par aaye, to unhe khilaane aur chhupaane ke liye hari-bhari zameen intezaar kar rahi thi.

Fish ke ek group, lobe-fins, ke paas haddiyon ke sahaare wale muscular fins the. Lagbhag 375 million saal pehle uthle, kam oxygen wale paani mein jo lobe-fins khud ko upar utha sakte the aur hawa nigal sakte the, unse pehle four-legged animals bane, jo frogs aur salamanders jaise amphibians ke ancestors the. Maana jaata tha ki coelacanth group ki lobe-finned fish dinosaurs ke saath khatam ho gayi thi, 1938 tak.

Amphibians ko eggs dene ke liye paani mein lautna padta hai. Lagbhag 312 million saal pehle reptiles ne ek mazboot solution evolve kiya, shelled (amniotic) egg, jiski membranes embryo ko sookhi zameen par bhi geela rakhti hain. Isi beech Carboniferous period ke daldali jungle mein giant club mosses aur tree ferns (pteridophytes) uge, mare aur dab gaye, aur dheere-dheere aaj khode jaane wale coal mein badal gaye. 252 million saal pehle ke sabse bade extinction ke baad reptiles zameen par, samundar mein (fish-shaped ichthyosaurs, jo dinosaurs nahi balki marine reptiles the) aur hawa mein (pterosaurs) diversify hue.

Dinosaurs lagbhag 230 million saal pehle aaye, lagbhag 165 million saal jiye aur us samay ke zyadatar hisse mein zameen par raaj kiya. Tyrannosaurus rex, aakhri dinosaurs mein se ek, lagbhag 12 m lamba tha aur uske daant kelon jitne bade the. Phir 66 million saal pehle lagbhag 10 km chauda ek asteroid aaj ke Mexico mein takraya. Is impact ne, usi samay ke aas-paas India mein Deccan Traps banane wale vishaal volcanic eruptions ke saath milkar, achaanak climate catastrophe paida kiya, aur lagbhag teen-chauthai species gayab ho gayi, jinmein har na udne wala dinosaur shaamil tha. Chhote feathered dinosaurs ka ek group bach gaya: birds. Crocodiles, lizards, snakes aur turtles doosri reptile lines hain jo bach nikli.

Mammals lagbhag dinosaurs jitne hi purane hain. Sabse pehle, lagbhag 205 million saal pehle, shrew ke size ke insect khaane wale the jo raat mein active rehte the, aur 100 million saal se zyada tak mammals chhote hi rahe. Asteroid ne yeh badal diya. Impact ke 10–15 million saal ke andar fur, doodh pine wale bachchon aur tez senses wale mammals khaali niches mein grazers, browsers, predators aur bats ban kar phail gaye; zyadatar species apne bachchon ko janam tak maa ke andar rakhne lagi.

Khiskte continents ne tay kiya ki kaunsa group kahan phala-phoola. South America tens of millions saal tak akela khiskta raha aur usne apne khaas animals evolve kiye: horses jaise dikhne wale hoofed litopterns, hippos jaise toxodonts, giant ground sloths aur chhoti car jitne bade armoured glyptodonts. Lagbhag 3 million saal pehle Panama par ek land bridge bana; cats, dogs, bears aur deer south ki taraf phaile, aur zyadatar purane South American groups khatam ho gaye. Iske ulat Australia, Antarctica se alag hone ke baad se hi ek island continent raha hai, isliye uske marsupials ka saamna kisi placental rival se tab tak nahi hua jab tak insaan aur unke animals nahi aaye (Section 6.4).

Kuch mammals wapas samundar mein chale gaye. Whales aur dolphins four-legged, hoofed land mammals se descend hue hain, seals bear jaise carnivores se, aur dugongs aur manatees (sea cows) elephants ke relatives se. India mein aaj bhi Gulf of Mannar aur Andaman Islands ke aas-paas dugongs hain. Horses, elephants aur dogs ki fossil histories bhi achhe se documented hain jinhe tum khud explore kar sakte ho; Exercise 10 whales ko trace karti hai.

6.9 Insaan ka Origin aur Evolution

Lagbhag 15 million saal pehle Africa, Europe aur Asia ke jungle mein kai tarah ke apes rehte the. Tumhari textbook inmein se do ke naam leti hai. Dryopithecus ek European ape tha jo pedon par chadhta tha. Ramapithecus ko 1934 mein India ki Siwalik Hills mein mile jaws se describe kiya gaya aur lambe samay tak use early human ancestor maana gaya, lekin baad mein behtar fossils ne dikhaya ki woh Sivapithecus ke saath aata hai, jo aaj ke orangutans ka relative hai. Dono human line ke chimpanzee line se alag hone se bahut pehle jiye, aur DNA aur fossils is split ko lagbhag 6–7 million saal pehle rakhte hain.

Us split ke baad human branch ke members ko hominins kehte hain (tumhari textbook purana word hominids use karti hai). Sabse purane, jaise Chad ka Sahelanthropus, lagbhag 7 million saal purana, sirf kuch haddiyon se jaane jaate hain. Lagbhag 4 aur 3 million saal pehle ke beech australopithecines ('southern apes') East Africa mein seedhe khade hokar chalte the aur pedon par bhi chadhte the. Ethiopia ka skeleton jise Lucy naam diya gaya, 3.2 million saal purana hai, aur Tanzania ke Laetoli mein volcanic ash mein dabe footprints 3.66 million saal pehle seedhe chalne walon ko dikhate hain. Woh lagbhag 1–1.5 m lambe the, unke brains lagbhag 400–500 cc ke the, kaafi had tak chimpanzee jaise, aur woh zyadatar plant food khaate the.

Lagbhag 2.4 million saal pehle East Africa mein Homo habilis ('handy man') aata hai, thode bade, lagbhag 550–700 cc ke brain ke saath, aur pebbles se flakes tod kar banaye simple stone tools ke saath (Fig. 6.17). Is samay ki animal bones par cut marks dikhate hain ki early Homo aise tools se meat aur marrow tak pahunchta tha, shayad plants ikattha karne ke saath-saath scavenging karke bhi.

Homo erectus ('upright man') lagbhag 1.9 million saal pehle aata hai, hamare jaise body, lagbhag 600–1100 cc (average lagbhag 900 cc) ke brain aur dhyaan se shape kiye hand-axes ke saath. Yeh regularly meat khaata tha, shayad aag use karta tha, aur Africa se bahar phailne wala pehla hominin tha, jo China aur Java tak pahuncha, jahan 1891 mein pehle fossils, jinhe Java Man naam diya gaya, khode gaye. India mein 1982 mein Madhya Pradesh mein Narmada river par Hathnora mein mili ek fossil skull-cap lagbhag isi stage ke ek archaic human ki hai.

Neanderthals (Homo neanderthalensis) lagbhag 400,000 se 40,000 saal pehle tak Europe aur western aur central Asia mein rehte the. Unke brains hamare jitne ya usse bhi bade the, lagbhag 1200–1750 cc. Neanderthals apne murdon ko dafnaate the, zakhmi saathiyon ki dekhbhaal karte the, achhe stone tools banate the aur ice-age ki sardiyon mein animal hides pehente the.

Hamari apni species, Homo sapiens, Africa mein bani: sabse purane fossils, Morocco ke Jebel Irhoud se, lagbhag 300,000 saal purane hain. Modern humans ke groups lagbhag 70,000–50,000 saal pehle se Africa se bahar phaile, India, Australia aur Europe tak pahunche aur kaafi baad mein Americas tak. Raaste mein woh Neanderthals se mile aur unke saath interbreed kiya, isliye Africa ke bahar ki ancestry wale zyadatar logon ka lagbhag 1–2 % DNA Neanderthal hai. Saare living humans ek hi species ke hain aur populations ke beech genetic difference bahut kam hai; zyadatar human genetic variation groups ke beech nahi, balki kisi bhi ek group ke andar milta hai.

Art, gehne aur door-door tak trade modern humans ke saath phaile. Sabse purani jaani-maani cave paintings, Indonesia ke Sulawesi island par, 45,000 saal se zyada purani hain. India mein Madhya Pradesh ke Raisen district mein Bhimbetka ke rock shelters, jo UNESCO World Heritage Site hain, par animals, shikaar aur naach ki paintings hain, jinmein sabse purani kam se kam 10,000 saal purani hain. Farming lagbhag 11,000–12,000 saal pehle western Asia mein shuru hui jab last ice age khatam hua, aur lagbhag 9000 saal pehle tak Bolan Pass ke paas Mehrgarh ke log wheat aur barley ugaate the aur cattle paalte the. Farming ke baad gaon, kasbe aur shehar aaye; us point se hamari species ka record zyadatar palaeontologists nahi, balki archaeologists aur historians padhte hain.