Chapter  16:  Darwin’s  Theory  of  Evolution

Chapter  16:  Darwin’s  Theory  of  Evolution   Early  Ideas  

Early  scientists  believed  the  earth  was  only  a  few  thousand  years  old.  

Around  1800,  geological  studies  suggested  it  was  much,  much  older  (about  ________________________  years).  

Naturalist  _____________________  believed  that  individuals  change  and  acquire  features  that  help  them   become  more  successful.  

Prevailing  view:  If  an  animal  ___________________  a  trait  during  its  lifetime,  it  could  pass  it  on  to  its   offspring.  

Charles  Darwin  

What  was  Charles  Darwin’s  contribution  to  science?  

Darwin  developed  a  scientific  theory  of  biological  evolution  that  explains  how  modern  organisms   evolved  over  long  periods  of  time  through  descent  from  __________________________________________.  

______________________  -­‐  Process  of  change  over  time    

1831-­‐1836,  Darwin  toured  the  world  by  boat,  studying  and  collecting  specimens.  

Darwin’s  Observations  

What  three  patterns  of  biodiversity  did  Darwin  note?  

As  he  traveled,  Darwin  noticed  three  distinctive  patterns  of  biological  diversity:    

1. Species  vary  ________________________    

2. Species  vary  ________________________    

3. Species  vary  _________________________  

Species  Vary  Globally  

Different,  yet  similar,  species  inhabit  separate,  but  similar  _______________________.  

Species  Vary  Locally  

Different,  yet  ________________,  species  often  occupy  different  habitats  within  a  local  area.  

Diversity  of  tortoise  species  in  the  Galapagos  –  pg.  765,  figure  1.2   Finch  Beak  Tools  –  pg.  801,  figure  4.6  

Species  Vary  Over  Time  

Some  _______________________  animals  are  similar  to  living  species.    

Darwin  collected  _______________________,  preserved  remains  or  traces  of  ancient  organisms    

Artificial  Selection  

Darwin  realized  that  most  organisms  don’t  survive  and  reproduce.  

Which  individuals  survive  and  why?  

By  studying  plant  and  animal  breeders,  Darwin  came  up  with  the  idea  of  __________________________________.  

In  artificial  selection  (selective  breeding),  ____________________  provides  the  variation  and  humans  select   for  the  most  desired  traits.  

The  Struggle  for  Existence  

Darwin  realized  that  individuals  must  compete  for  _________________________.  

Hypothesized  that  some  variations  of  traits  are  better  suited  to  different  ______________________________  

than  others.    

______________________  –  how  well  an  organism  can  survive  and  reproduce  in  an  environment.  

______________________  –  heritable  characteristic  that  increases  an  organism’s  ability  to  survive  and   reproduce.  

“Survival  of  the  fittest”    

Only  those  that  survive  can  pass  on  their  genes.  

Natural  Selection  

Darwin  realized  that  _______________  can  act  on  traits.  

_____________________________________  –  nature  provides  the  variation   and  nature  selects  the  most  fit.  

Organisms  with  variations  most  suited  to  their  environment   survive  and  leave  more  offspring.  

Acts  only  on  ________________________  traits  because  they  are  the   only  ones  that  can  be  passed  on.  

Important:  Natural  selection  does  not  make  organisms  “better”  

and  it  doesn’t  move  in  a  fixed  direction.  

Natural  Selection  pg.  785,  Figure  3.2  –  Follow  the  animation  and  summarize  each  step,  below.  

What  is  happening  in  each  picture?  

Under  what  conditions  does  natural  selection  occur?  

Natural  selection  occurs  in  any  situation  in  which  more  individuals  are  born  than  can  ___________________,   there  is  natural  heritable  ________________________,  and  there  is  variable  __________________  among  individuals.  

If  environmental  conditions  change,  some  traits  that  were  once  _____________________  may  no  longer  be   useful  and  different  traits  may  be  selected  for  instead.  

If  conditions  change  faster  than  a  species  can  adapt  to  those  changes,  the  species  may  become  

___________________.  

Common  Descent  

What  does  Darwin’s  mechanism  for  evolution  suggest  about  living  and  extinct  species?  

Every  organism  alive  today  is  ___________________________  from  parents  who  survived  and  reproduced.  

Well-­‐adapted  species  survive  over  time.  

Over  many  generations,  ______________________  could  cause  successful  species  to  evolve  into  new  species.  

____________________________  –  living  species  are  all  descended  from  common  ancestors.  

Descent  with  modification  –  living  species  are  descended,  with  __________________________,    from  common   ancestors.  

According  to  the  principle  of  _____________________________,  all  species  –  living  and  extinct  –  are  descended   from  ancient  common  ancestors.  

For  evidence,  Darwin  looked  to  the  _______________________________.  

Constructed  an  ___________________________________  (aka  tree  of  life)  to  show  how  descent  with  modification   could  produce  the  diversity.  

Variation  and  Mutation  

In  order  for  some  individuals  to  be  more  fit  than  others,  individuals  have  to  be  different.  

Differences  are  caused  by  ______________________.  

Mutations  can  be  ____________________  or  caused  by  ____________________  like  radiation  or  chemicals.  

Mutations  often  lead  to  no  change  in  phenotype  (__________________),  but  sometimes  they  are  positive  or   negative.  

If  a  mutation  is  “good”  it  will  stay  in  the  ________________________  because  it  helped  the  individual  survive   and  reproduce.  

If  a  mutation  is  “bad”  it  will  likely  not  stay  in  the  gene  pool  because  the  individual  who  had  it  did  not   survive  to  pass  it  on.  

BIG  PICTURE  

In  nature  there  is  ______________________.  

________________________  cause  more  variety  (good  or  bad).  

The  more  suited  (fit)  an  organism  is  to  its  environment,  the   more  likely  it  will  survive.  

Individuals  that  _____________________  can  pass  on  their  traits.  

Less  fit  individuals  will  die  off  and  cannot  pass  on  their  

“less  fit”  traits.  

If  an  environment  _____________________,  what  is  “fit”  may   change,  too.  

Evidence  of  Evolution  

Evidence  that  supports  evolution  comes  from:  

1. ________________________________________  

2. Physical  Structures  

3. ______________________________________  

4. Genetics  and  Molecular  Biology    

Biogeography  

How  does  the  geographic  distribution  of  species  today  relate  to  their  evolutionary  history?  

Patterns  in  the  _______________________________________  of  living  and  fossil  species  tell  us  how  modern   organisms  evolved  from  their  ancestors.  

__________________________  –  study  of  where  organisms  live  now  and  where  their  ancestors  lived  in  the  past.  

Biogeography  shows  how  closely  related  species  _______________________________  in  slightly  different   environments.  

Biogeography  also  shows  how  different  species  develop  similar  traits  from  being  in  similar   ___________________________________.  (Ex:  flightless  birds)  

Physical  Structures  

By  Darwin’s  time,  scientists  had  noted  that  all  vertebrate  limbs  had  the  same  basic  _______________________.  

By  studying  physical  structures  of  organisms,  scientists  can  deduce  _____________________________  between   species.  

Homologous  Structures  

Homologous  structures  –  structures  that  are  shared  by  related  species  because  they  were  inherited   from  a  _______________________________________.  

Homo  =  _______________,  so  homologous  =  same  structure    

Homologous  structures  have  similar  _______________________  but  often  have  different  ________________________.  

Shows  common  ancestry  because  DNA  contains  instructions  on  how  to  build  structures.  

Homologous  structures  evolved  from  a  common  ancestor  but  have  changed  over  time  as  each   organism’s  ____________________________________  changed.  

Analogous  Structures  

_________________________________________  –  structures  that  have  the  same  or  similar  function,  but  are  built   differently.  

Opposite  idea  of  homologous  structures.  

Examples:    

• Flippers  are  used  to  swim  but  can  be  built  differently.  

• Wings  are  used  to  fly  but  can  be  built  differently.  

Does  not  show  common  ancestry,  only  indicates  the  organisms  evolved  in  similar  ________________________.  

Homologous  =   Same  

______________,   different  

___________________.

Analogous  =   different  

__________________,   same  

_________________

Vestigial  Structure  

Vestigial  structures  are  inherited  from  ____________________________________,  but  have  lost  much  or  all  of   their  original  function  due  to  changes  in  the  environment.  

Example:  Human  coccyx  is  a  much-­‐reduced  version  of  an  ancestral  tail.  

Why  would  an  organism  possess  structures  with  little  or  no  function?  

The  presence  of  vestigial  structures  does  not  affect  __________________________,  so  there  is  no  selective   pressure  for  them  to  be  removed.  

Evidence  From  Fossils,  pg.  793,  figure  4.1    

Embryology  

By  studying  vertebrate  __________________,  similar  patterns  of  embryological  ______________________________  

suggest  that  organisms  descended  from  a  common  ancestor.  

Genetics  &  Molecular  Biology  

How  can  molecular  biology  be  used  to  trace  the  process  of  evolution?  

At  the  molecular  level,  the  _____________________________________________________  and  similar  molecules  provide   evidence  of  common  descent.  

All  living  things  use  _________  and  ___________.  

The  more  closely  related  organisms  are,  the  more  _________________________  their  DNA  is.  

In  this  sequence  of  DNA,  how  many  differences  are  there  between  the  DNA  of  humans  and   chimpanzees?  ______________________  

Between  humans  and  orangutans?  __________________________  

Based  on  this  sequence  of  DNA,  which  species  is  most  closely-­‐related  to  humans?  _________________________  

Which  are  more  closely-­‐related,  rats  and  dogs  or  dogs  and  cows?  ___________________________________________