why "gem list" display two version numbers?

Question

I'm using

Ruby version 1.9.3-p327 RVM 1.16.17 gem 1.8.24

If I perform a :

gem list

I got following result.

Why do I have two version numbers for bundler (1.2.1, 1.1.3) ? :

*** LOCAL GEMS ***

actionmailer (3.2.9)
actionpack (3.2.9)
activemodel (3.2.9)
activerecord (3.2.9)
activeresource (3.2.9)
activesupport (3.2.9)
arel (3.0.2)
builder (3.0.4)
bundler (1.2.1, 1.1.3)
erubis (2.7.0)
hike (1.2.1)
i18n (0.6.1)
journey (1.0.4)
json (1.7.5)
mail (2.4.4)
mime-types (1.19)
multi_json (1.3.7)
polyglot (0.3.3)
rack (1.4.1)
rack-cache (1.2)
rack-ssl (1.3.2)
rack-test (0.6.2)
rails (3.2.9)
railties (3.2.9)
rake (0.9.2.2)
rdoc (3.12)
rubygems-bundler (1.0.2)
rvm (1.11.3.3)
sprockets (2.2.1)
thor (0.16.0)
tilt (1.3.3)
treetop (1.4.12)
tzinfo (0.3.35)

Answer 1

you can have multiple versions of gems - rubygems allows that!