Biologic evolution

Change in color of Yamato corbicula's husk.
The pattern of the color of the shell is different because of the
individual.
However, it is a process of changing because the shell finally becomes
black.
When you see the handle in the photograph
There are three kinds of (At present,) changes.
Type that blackens from edge of 1 and shell.
Type that blackens from 2 and husk top part.
The type (The husk top part : like yellow) that blackens from the tip of 3
and the shell.

It is imagined that a yellow corbicula is a prototype.
It
The reason for the color that is patterned of other corbiculas' shells basic
is that it is yellow.
It thinks basic yellow to be discoloration to brown by the external cause.
I think that it is difficult to think that a yellow corbicula is a new kind
corbicula.
Because
It is because a yellow corbicula doesn't exist in corbicula's Natai (big
individual to have grown up).
It was thought that it was difficult to think the one that did not exist to
be a new kind.