What  is  Evolution?                              volution  is  a  biological  process  in  which            li                      living  organisms  gradually  change  and          d                      develop  over  time,  in  order  to  suit  the          n                      conditions  of    their  natural  environment.  Evolution  has  been  occurring  for  millions  of  years,  and  explains  how  every  individual  living  organism  has  evolved  from  a  single  type  of  micro-­‐organism  that  existed  millions  of  years  ago.  Evolution  is  a  key  process  for  the  survival  of  all  organisms,  and  explains  why  living  things  have  become  so  diverse  and  so  well  adapted  towards  their  environments.        

   Evolution  was  first  theorised  by  Charles  Darwin  who  was  a  naturalist  and    geologist  who  lived  from  1809  to    1882.  In  1831,  Darwin  embarked  on    a  5  year  voyage  on  the  H.M.S    Beagle,  where  he  was  assigned  to    survey  the  coast  of  South  America    for  the  British  Navy.  Although  he  joined  as  a  geologist,  Darwin  spent  most  of  the  time  observing  plants,  animals  and  fossils.  During  Darwin’s  time  in  the  Galápagos  Islands,  in  1835,  he  noted  that  the  finches  on  various  islands  had  developed  different  beaks,  which  were  adapted  to  the  available  food.  These  observations  led  to  his  theory  of  natural  selection,  which  held  that  the  survival  or  extinction  of  an  organism  is  determined  by  its  ability  to  adapt  to  its  environment—“survival  of  the  fittest”.  After  returning  home,  Darwin  began  writing  what  he  had  observed  on  his  journey,  and  in  1859,  he  published  his  theory  of  evolution.      

   

 

 

Fossil  Records    Fossils  are  the  remains  of  living  organisms  that  have  been  preserved  in  rock  over  large  periods  of  time.  Fossils  may  be  preserved  remains  of  an  organism  itself,  or  preserved  traces  that  were  left  by  the  organism  while  it  was  alive,  such  as  footprints  or  droppings.  Most  organisms  usually  rot  away  after  they  die,  due  to  scavengers  and  micro-­‐organisms  that  feed  upon  the  organism’s  flesh.  However,  this  process  cannot  take  place  if  there  is  no  oxygen  surrounding  the  dead  carcass,  because  without  oxygen,  organisms  would  not  be  able  to  live.  When  a  carcass  is  covered  in  rock  sediments  that  block  out  all  the  oxygen,  the  rotting  process  does  not  take  place,  and  the  carcass  is  preserved.  As  the  rock  sediments  harden  and  compress,  the  carcass  will  then  become  ‘fossilised’.                  

 When  fossils  are  discovered  under  the  ground,  scientists  can  calculate  approximately  how  long  the  fossil  has  existed  for.  There  are  two  main  ‘dating’  techniques  that  scientists  use.      One  technique  is  known  as  ‘relative  dating’  which  is  the  process  of  analysing  the  age  of  a  fossil,  by  comparing  its  location  of  depth  to  other  locations.      One  way  to  think  of  relative  dating  is  as  if  the  earth  was  a  layered  cake.  When  you    look  at  a  layered  cake,  you  know  that  the  layer  at  the  bottom  was  the  first    to  be  put  on  the  plate,  and  the  upper  layers  were  added  later  on.  In  the    same  way,  scientists  can  figure  out    the  relative  ages  of  fossils.  The    deeper  the  fossil,  the  older  it  is.                                                                                                          A  second  method  scientists  use  to  date  fossils  is  known  as  ‘radiometric  dating’  which  calculates  the  amount  of  nuclear  decay  in  the  rock  layer  that  a  particular  fossil  is  found  in.  Radiometric  dating  allows  scientists  to  calculate  the  approximate  age    

 

   

traits  can  drive  evolution,  if  they  are  desirable  to  the  organism’s  environment.      

 One  example  of  a  mutation  that  has  driven  evolution,  is  the  blue  eye  colour  in  us  humans.  Once  upon  a  time,  all  humans  had  brown  eyes,  but  a  mutation  in  the  sequence  of  our  DNA  resulted  in  some  of  us  obtaining  blue  eyes.  Given  that  this  trait  was  not  harmful,  it  was  able  to  be  passed  on  through  many  generations,  resulting  in  the  large  population                                                                              of  blue  eyed  people  we    see  today.              Diversification  Reproduction,  heredity  and  mutations  all  cause  individual  organisms  to  have  unique  sets  of  DNA.  This  uniqueness  in  the  DNA  causes  every  organism  to  have  a  unique  set  of  traits  and  a  unique  set  of  characteristics.  This  uniqueness  causes  a  species  to  become  incredibly  diverse  and  it  is  this  diversity  that  is  important  for  the  survival  of  the  species.  By  having  a  diverse  group  of  organisms,  it  is  more  likely  that  the  species  would  continue  to  thrive,  given  that  changes  in  the  environment  would  cause  some  of  the  organisms  to  die  out.  When  every  individual  is  different,  it  is  more  likely  that  organisms  with  desirable  sets  of  characteristics  will  survive,  while  organisms  with  undesirable  sets  of  characteristics  will  die  out.      Natural  Selection  This  process  by  which  weaker  organisms  die  out,  while  others  continue  to  thrive,  is  known  as  natural  selection.  Natural  selection  is  the  key  biological  process  towards  evolution,  as  it  removes  the  weak,  and  selects  the  desirable,  allowing  distinct  traits  to  be  passed  on  through    many  generations.  It  is  these  filtered  combinations  of  desirable  sets  of  DNA  that  allow  organisms  to  develop  over  time.  Natural  selection      

 

of  a  fossil,  given  that  the  rate  of  nuclear  decay  takes  place  at  a  predictable  rate.  Nuclear  decay  is  basically  the  rate  at  which  objects  emit  radiation.  Older  layers  of  rock  that  are  found  deeper  in  the  Earth  have  emitted  more  radiation  compared  to  rocks  near  the  surface.  Given  that  the  rate  of  nuclear  decay  is  predictable,  scientists  can  calculate  the  approximate  date  of  a  fossil,  by  measuring  how  much  radiation  it  has  emitted.            By  analysing  fossils,  scientists  are  able  to  examine  evidence  of  life  that  existed  millions  of  years  ago,  as  well  as  identify  how  particular  organisms  have  changed  over  specific  periods  of  time.      Reproduction  and  Heredity  Every  organism’s  characteristics  is  determined  by  its  DNA,  which  stands  for  deoxyribonucleic  acid.  DNA  is  a  long  chemical  molecule,    consisting  of  genes,  that  “codes”    for  all  the  characteristics  of  an    organism.  Although  animals  of    the  same  species  may  look  the    same,  they  each  have  a  unique  set  of  DNA,  which  codes  for  unique  sets    of  traits  and  characteristics.  This  uniqueness  is  generally  caused  by  reproduction  and  heredity.  When  two  organisms  reproduce,  the  offspring  will  inherit  half  of  their  DNA  from  the  father  and  half  from  the  mother.  This  passing  down  of  DNA  is  known  as  heredity.  When  random  shuffles  of  this  DNA  are  combined,  organisms  with  unique  combinations  of  genes  will  be  created,  resulting  in  unique  traits  and  characteristics.  

   Mutations  Mutations  are  random  changes  in  the  sequence  of  DNA  that  result  from  mistakes  during  the  copying  process  of  the  code.  Mutations  may  have  no  affect  on  the  organism,  depending  on  what  section  has  been  changed,  and  how  this  section    has  been  changed.  However,  mutations  can  also  be  detrimental  or  beneficial,  given  that  they  bring  upon  new  traits  and  characteristics.  These  new      

   

   

 

is  generally  caused  by  an  organism’s  natural  environment.  As  this  environment  changes  over  time,  the  organisms  too  must  change  in  order  to  survive.      Types  of  Natural  Selection:  There  are  three  main  types  of  Natural  Selection  processes,  which  include:  Disruptive  Selection  Where  natural  selection  causes  a  species  to  become  divided  into  two  distinct  groups,  based  upon  their  favorable  phenotypes.  (A  phenotype  is  an  organism’s  observable  set  of  characteristics,  which  is  determined  by  its  DNA)    Stabilising  Selection    Where  natural  selection  causes  genetic  diversity  to  decrease  and  the  population  mean  stabilizes  on  a  single  particular  phenotype.      Directional  Selection  Where  one  extreme  phenotype  is  favored  over  other  phenotypes.        The  Peppered  Moth:  The  peppered  moth  is  an  example  of  a  species  that  has  changed  due  to  the  process  of  natural  selection.  Before  the  industrial  revolution,  the  majority  of  the  peppered  moths  were  lightly  coloured.  This  allowed  them  to  blend  in  and  camouflage  in  the  lichen-­‐covered  trees  that  surrounded  their  natural  environment.  This  camouflage  allowed  these  moths  to  hide  from  predators  such  as  birds.  However,  some  of  the  peppered  moths  were  darkly  coloured,  which  resulted  in  more  of  these  types  of  moths  to  be  eaten  by  predators.    

 Once  the  industrial  revolution  began,  many  factories  were  established  all  throughout  the  land.  These  factories  then  caused  many  of  the  trees  to  become  darker,  due  to  pollution  caused  by  the  exhaust  gases.  This  change  in  colour  amongst  the  trees  allowed  the  darkly  coloured    

moths  to  camouflage  instead  of  the  lightly  coloured  moths.  This  resulted  in  more  of  the  lightly  coloured  moths  to  be  eaten,  and  less  of  the  dark  to  be  eaten.  This  process  of  natural  selection  has  now  caused  the  majority  of  the  peppered  moths  to  be  darkly  coloured.    Speciation  Speciation  is  the  process  by  which  natural  selection  causes  new  and  distinct  species  to  form.  Speciation  is  caused  by  disruptive  selection,  in  which  a  species  is  divided  into  two  distinct  groups.  This  division  between  a  species  can  often  prevent  them  from  breeding  with  each  other,  which  causes  traits  to  be  passed  on  differently.  This  split  into  two  separate  groups  can  eventually  result  in  entirely  new  species  to  be  formed.      Types  of  Speciation:  There  are  two  particular  types  of  speciation.  These  include:  Allopatric  Speciation  Speciation  that  occurs  when  biological  populations  of  the  same  species  become  isolated  from  each  other  to  an  extent  that  prevents  reproduction.  This  causes  two  distinct  groups  to  form,  and  when  these  groups  continue  to  breed  with  each  other  while  ignoring  the  other  group,  they  will  eventually  become  different  species.    Sympatric  Speciation  Speciation  where  new  species  evolve  from  a  single  ancestral  species  while  inhabiting  the  same  geographical  region    Is  The  Evolution  Theory  Accurate?  Although  evolution  is  recognised  as  a  key  biological  process,  there  are  many  people  who  believe  that  it  is  false  and  inaccurate.  Such  beliefs  generally  revolve  around  either  religion  or  scientific  flaws  that  contradict  the  theory.    Firstly,  many  religions,  particularly  Christian  based  religions,  state  that  all  the  diversity  found  amongst  living  organisms  was  created  by  a  God  or  a  spiritual  being.  Although  scientists  have  gathered  large  amounts  of  evidence  towards  proving  that  evolution  is  accurate,  many  religious  followers  argue,  and  refuse  to  believe  that  evolution  is  accurate.      Secondly,  the  theory  of  evolution  has  many  

   

                                                                                                                 

scientific  contradictions.  One  contradiction  exists  between  ‘punctuated  equilibrium’  and  ‘gradualism’.  Punctuated  equilibrium  is  a  scientific  hypothesis  that  suggests  evolutionary  development  is  marked  by  periods  of  rapid  speciation  followed  by  long  periods  of  little  to  no  change.  Gradualism,  on  the  other  hand,  states  that  evolution  is  a  gradual  process  that  occurs  over  long  periods  of  time.  These  two  contradicting  ideas  show  how  evolution  has  its  flaws,  and  how  it  may  in  fact  be  inaccurate.      A  second  contradiction  within  the  theory  of  evolution  exists  between  ‘microevolution’  and  ‘macroevolution’.  Studies  have  shown  that  organisms  are  able  to  adapt  to  their  environments  through  the  process  of  natural  selection.  These  small  changes  that  allow  a  species  to  thrive,  is  known  as  microevolution.  However,  long  term  evolution,  where  new  species  are  formed  through  speciation  is  known  as  macroevolution.  Macroevolution  suggests  that  micro-­‐organisms  can  develop  into  multicellular  organisms  such  as  humans.  This,  however,  is  hard  for  scientists  to  prove  in  the  laboratory.  It  is  this  large  difference  between  micro  and  macro  evolution  that  has  caused  debate  upon  whether  new  organisms  can  actually  be  formed  through  evolution.      Although  the  theory  of  evolution  has  its  flaws,  it  is  safe  to  say  that  evolution  is  accurate,  given  that  there  is  more  information  supporting  it,  than  there  is  evidence  contradicting  it.  Such  supporting  evidence  includes;  the  process  of  natural  selection  discovered  by  Charles  Darwin,  the  evidence  of  pre-­‐historical  life  through  fossils,  how  traits  and  characteristics  can  be  passed  on  through  heredity,  how  mutations  can  influence  changes  in  genetic  constitution,  and  how  natural  selection  can  cause  new  species  to  form.                  Case  Study  –  Darwin’s  Finches  One  particular  case  study  that  displays  all  the  aspects  of  natural  selection,  speciation  and  of  course  evolution,  is  Darwin’s  Finches,  which  are  the  group  of  birds  that  Charles  Darwin  studied  while  he  was  on  the  Galápagos  Islands.      In  the  early  1800s,  a  small  group  of  finches,  from  the  same  species,  migrated  to  the  Galápagos  Islands.  These  finches  found  themselves  in  an  environment  that  was  completely  new  to  them,  where  there  was  a    

large  supply  of  food,  and  a  very  small  amount  of  predators.  The  finches  soon  began  to  rapidly  reproduce,  causing  them  to  spread  out  all  throughout  the  islands.  However,  this  large  increase  in  population  caused  the  food  supply  of  the  islands  to  become  incredibly  scarce.  

 This  scarcity  in  food  supply  then  caused  natural  selection  to  take  place.  The  diversification  caused  by  the  excess  breeding  allowed  the  finches  to  have  many  different  variations  of  beaks.  The  finches  with  long  thin  beaks  were  able  to  easily  dig  for  worms,  while  finches  with  thick  strong  beaks  were  able  to  crack  seeds.  This  disruptive  selection  caused  these  particular  finches  to  split  into  two  distinct  groups,  while  finches  with  undesirable  beaks  were  killed  off  due  to  starvation.    

   The  individuals  amongst  each  of  the  groups  began  to  breed  with  each  other,  while  ignoring  the  finches  from  the  opposing  group.  Over  the  course  of  many  generations,  these  beneficial  characteristics  were  enhanced  due  to  more  instances  of  natural  selection.  Eventually,  the  differences  between  the  worm  diggers  and  the  seed  cracker  became  so  large,  that  they  were  no  longer  able  to  breed  with  each  other,  thus  resulting  in  two  distinct  species  to  be  formed,  ‘speciation’.            

 

 

As  of  today,  there  are  14  different  species  of  finch  on  the  Galápagos  Islands,  all  of  which  descended  from  the  original  group  of  stranded  finches.  By  examining  this  particular  group  of  organisms,  we  can  see  how;  excess  production  of  offspring,  genetic  recombination  through  heredity,  diversification,  and  natural  selection  all  influence  organisms  to  evolve.        

 

Written By Oliver Read

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