254  MENTAL  EVOLUTION  IN  MAN,

no  proof  that  the  agglutinative  languages  did  not  start  from
an  isolating  type,  and  thereafter  proceed  on  a  different  line
of  development  in  accordance  with  their  different  "genius,"
or  method  of  growth.  Naturalists  entertain  no  doubt  that
two  different  types  of  morphological  structure,  b  and  j3,  are
both  descended  from  a  common  parent  form  B,  even  though
b  has  "advanced"  in  one  line  of  change  and  /3  in  another,  so
that  both  are  now  equally  efficient  from  a  morphological
point  of  view.  Why,  then,  should  a  philologist  dispute  genetic
relationship  in  what  appears  to  be  a  precisely  analogous  case,
on  the  sole  ground  that  b  is,  to  his  thinking,  no  less  psycho-
logically efficient  a  language  than  /3  ?

Lastly,  as  I  have  before  indicated,  it  appears  to  me
impossible  to  dispute  that  every  agglutinative  language,  in
whatever  measure  it  can  be  proved  to  be  agglutinative,  in
that  measure  is  thereby  proved  to  have  been  derived  from  a
language  less  agglutinative,  and  therefore  more  isolating.
And,  similarly,  in  whatever  measure  an  inflective  language
can  be  proved  to  inflect  its  agglutinated  words,  in  that
measure  is  it  thereby  proved  to  have  been  derived  from  a
language  less  inflective,  or  a  language  whose  agglutinations
had  not  yet  undergone  so  much  of  the  inflective  modification.
On  the  other  hand,  as  there  is  no  necessary  reason  why  an
isolating  language  should  develop  into  an  agglutinative,  or  an
agglutinative  into  an  inflectional,  it  may  very  well  be  that  the
higher  evolution  of  isolating  tongues  has  proceeded  collaterally
with  that  of  agglutinative,  while  the  higher  evolution  of  agglu-
tinative has  proceeded  collaterally  with  that  of  inflectional.
