natural selection theory of darwin

Sadaf naseer 's assingment

1. Sadaf neseer (zoologist)

2. DARWINISM
IntroductionDarwinismisatheoryofbiologicalevolutiondeveloped
bytheEnglishnaturalistcharlisDarwin.(1809-1882).andotherstatingthat
allspeciesoforganismariseanddevelopedthroughthenaturelselection
ofsmallinheritingvariationsthatincreasetheindividual’sabilityto
competesurviveandreproduce.
Definition
“Thetheoryofevolutionbynaturelselection1
st
formulatedinDarwin’s
bookoriginofspeciesin1859istheprocessbywhichanorganismchange

3. overtimeasaresultofchangeinheritablephysicalandbehavioralchange”
Thebasicideapopulationsandspeciesoforganismchangeover
time.inthe1850centuryDarwinwroteandinfluentialand
controvefialbookcalledontheoriginofspecies.
JoinedcrewHMSBeagle-1831-1836
Collectedfloraandfauna
Astonishedbydiversityoflife
Galapagosislands–smallgroupofislands1000kmWestofSouth-
America
Verydifferentclimate
Uniqueanimals–tortoises,iguanas,finches
•Observedadaptationsofplantsinthenaturalenvironments
•Birth&survivalofdifferentspecies
•Fossilsofdifferentspeciesthatgotextinct

4. •Fossilsofspeciesthathavesimilaritytotheexistingspecies
•AtGalapagostortoisevariableinlook(long/shortneck)andweight
•Iguanasondifferentislandshadvariableappearance
•Thebeakofthefincheswerevariableadaptedforeatingseeds,nuts,
berries,insectsetc.
Darwinfinches

5. Voyageofthebeagle

9. Naturelselectionmeansomestartingmaterialandthatstarting
materialisheritablevariationsfornaturalselectionactona
feather,theremustalreadybevariations(differencesamong
individual)forthatfeather.Alsothedifferenceshavetobe
heritabledeterminedbytheorganismgenes.

10. Naturelselectiondependentsonthe
environment
Naturelselectiondoesnotfavortraitthatarecomehow
inherentlysuperiorinstead,itfavortraitsthatarebeneficial(that
ishelpanorganismsurviveandreproducemoreeffectivelythan

11. itspeers)isarespecificenvironment.traitsthatarehelpfulinone
environmentmight
actuallybeharmfuloneanother.

12. ConceptofDarwinofnaturelselection
moreoffspringareproducethancan
survive
Organismsarecapableofproducingmoreoffspringthentheir
environmentcansupportthusthereiscompetitionforlimited

13. processineachgeneration.
Offspringvaryinthereheritabletraits
Theoffspringinanygenerationwillbeslightlydifferentfromonanotherin
theirtraits(colorsizeshapeetc.)andmanyofthesefeatherswillbe
heritable)
Variations
Variationsisthekeyingredientforthesurvivalof
species.
Thosespecieswhohavesuitablevariationsthatbenefitsthem
havehigherchancesofsurvivalthanthosespecieswhohaveno
variationsorwholackbeneficialvariations.Henceastheresultof
variationspeciespossessmorphologicalandcharacter
differences.
•Continuousvariations–slowasaresultofgenetic
recombination
•Discontinuousvariations–suddenduetomutations

14. StruggleforExistence–Aspopulationincrease
geometricallyandresourcesincreasearithmetically,organism
struggleorcompetefortheavailableresourceslikefood,space
andmate.
•Competitionmaybeinterspecific–betweenthespecies;
intraspecific–withinthespeciesandenvironmentali.e.withthe
environmentalfactors.
Survivalofthespecies
Afteraparticulartimeperiod,thechangeorvariationacquiredby
speciesresultinnaturalselection.thismeansthatnatureselect
thebeneficialvariations.Andincreasethesurvivalrateof
offspringhavingthosecharacter.

15. ExamplesinfavorofnaturalSelection
•Skeletaladaptationsinanimals-Giraffes,lizards,andmany
otherknownspeciesadaptedtotheirenvironmentsthrough
geneticchangestotheirskeletonse.g.
•Giraffesdevelopedlongneckstoreachfoodsourceshigherup
intrees,somembersofthegiraffepopulationwhodidn'tdevelop
alongneckdiedout

16. Darwinism–Objection/demerits
•Darwincouldnotexplaintheoriginandcauseofvariationswhich
aregeneratedduringevolution.Hewasnotclearaboutheritable
andnon-heritablevariations.
•Neutralvariationse.g.fingerprintscouldnotbeexplainedby
Darwinism.
•Darwinismdonotexplainroleofmutations
•Heemphasizedsurvivalofthefittestorganisms.Hecouldnot
explainarrivalofthefittest.
•TheprincipleofinheritancewasnotpresentduringDarwin,
HenceDarwinbelievedinthetheoryof'pangenesis’.Pangenesis
theorypostulatedthateverypartofthebodyemitstinyparticles

17. calledgemmuleswhichmigratetothegonadsandaretransferred
tooffspring.
•Therearenoevidencesfrompaleontology,molecularbiology,
biochemistryinthefavoroftheDarwinism

18. Sadaf naseer