pip install markdownでエラー

前提

evervimを使用するために，pythonのmarkdownパッケージをインストールしようとしています．

pip install markdown

を実行した結果，エラーが発生し，インストール出来ません．
環境は以下のとおりです．

• El Captan(OS X 10.11.4)
• python2.7
• pip 1.5.6

以下にpip.logの内容を示します．
（10000字の制約があるので途中省略しています．）

ネットで調べてみたのですが，どういうエラーかわからず，自力で解決できませんでした．
どのようにすればよろしいでしょうか？
アドバイスのほど，よろしくお願いいたします．

------------------------------------------------------------
/usr/local/bin/pip run on Thu Apr 14 00:05:41 2016
Downloading/unpacking markdown
  Getting page https://pypi.python.org/simple/markdown/
  URLs to search for versions for markdown:
  * https://pypi.python.org/simple/markdown/
  Analyzing links from page https://pypi.python.org/simple/markdown/
    Skipping link https://pypi.python.org/packages/any/M/Markdown/Markdown-2.0.1.win32.exe#md5

---------------------中略---------------------


    Converting docs/extensions/wikilinks.txt -> build/docs/extensions/wikilinks.html
    running install_lib
    copying build/lib/markdown/__init__.py -> /lib/python2.7/site-packages/markdown
    error: could not delete '/lib/python2.7/site-packages/markdown/__init__.py': Permission denied
    Complete output from command /usr/local/opt/python/bin/python2.7 -c "import setuptools, tokenize;__file__='/private/var/folders/kw/s2s66jl17l7634cyv1r17spm0000gn/T/pip_build_mk_mkee/markdown/setup.py';exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /var/folders/kw/s2s66jl17l7634cyv1r17spm0000gn/T/pip-v_8a_Y-record/install-record.txt --single-version-externally-managed --compile:
    running install

running build

running build_py

creating build

creating build/lib

creating build/lib/markdown

copying markdown/__init__.py -> build/lib/markdown

copying markdown/__main__.py -> build/lib/markdown

copying markdown/__version__.py -> build/lib/markdown

copying markdown/blockparser.py -> build/lib/markdown

copying markdown/blockprocessors.py -> build/lib/markdown

copying markdown/inlinepatterns.py -> build/lib/markdown

copying markdown/odict.py -> build/lib/markdown

copying markdown/postprocessors.py -> build/lib/markdown

copying markdown/preprocessors.py -> build/lib/markdown

copying markdown/serializers.py -> build/lib/markdown

copying markdown/treeprocessors.py -> build/lib/markdown

copying markdown/util.py -> build/lib/markdown

creating build/lib/markdown/extensions

---------------------中略---------------------

Converting docs/extensions/wikilinks.txt -> build/docs/extensions/wikilinks.html

running install_lib

copying build/lib/markdown/__init__.py -> /lib/python2.7/site-packages/markdown

error: could not delete '/lib/python2.7/site-packages/markdown/__init__.py': Permission denied

----------------------------------------
Cleaning up...
  Removing temporary dir /private/var/folders/kw/s2s66jl17l7634cyv1r17spm0000gn/T/pip_build_mk_mkee...
Command /usr/local/opt/python/bin/python2.7 -c "import setuptools, tokenize;__file__='/private/var/folders/kw/s2s66jl17l7634cyv1r17spm0000gn/T/pip_build_mk_mkee/markdown/setup.py';exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /var/folders/kw/s2s66jl17l7634cyv1r17spm0000gn/T/pip-v_8a_Y-record/install-record.txt --single-version-externally-managed --compile failed with error code 1 in /private/var/folders/kw/s2s66jl17l7634cyv1r17spm0000gn/T/pip_build_mk_mkee/markdown
Exception information:
Traceback (most recent call last):
  File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pip-1.5.6-py2.7.egg/pip/basecommand.py", line 122, in main
    status = self.run(options, args)
  File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pip-1.5.6-py2.7.egg/pip/commands/install.py", line 283, in run
    requirement_set.install(install_options, global_options, root=options.root_path)
  File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pip-1.5.6-py2.7.egg/pip/req.py", line 1435, in install
    requirement.install(install_options, global_options, *args, **kwargs)
  File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pip-1.5.6-py2.7.egg/pip/req.py", line 706, in install
    cwd=self.source_dir, filter_stdout=self._filter_install, show_stdout=False)
  File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pip-1.5.6-py2.7.egg/pip/util.py", line 697, in call_subprocess
    % (command_desc, proc.returncode, cwd))
InstallationError: Command /usr/local/opt/python/bin/python2.7 -c "import setuptools, tokenize;__file__='/private/var/folders/kw/s2s66jl17l7634cyv1r17spm0000gn/T/pip_build_mk_mkee/markdown/setup.py';exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /var/folders/kw/s2s66jl17l7634cyv1r17spm0000gn/T/pip-v_8a_Y-record/install-record.txt --single-version-externally-managed --compile failed with error code 1 in /private/var/folders/kw/s2s66jl17l7634cyv1r17spm0000gn/T/pip_build_mk_mkee/markdown

2016/04/14追記内容

pipのアップデートを試したところ，エラーが発生したため，
brewでpythonを再インストールしました．
その結果，

• python: ver2.7.11
• pip: ver8.0.2

がインストールされました．

ですが，再インストール後も
pipのアップデートやmarkdownパッケージのインストールでPermissionのエラーが出てしまいます．

% pip install --upgrade pip
IOError: [Errno 13] Permission denied: '/lib/python2.7/site-packages/pip/__init__.py'

% pip install markdown
IOError: [Errno 13] Permission denied: '/lib/python2.7/site-packages/markdown/__init__.py'

試しに，

sudo pip install --upgrade pip

を実行したところ，インストールは完了しましたが，pipコマンドを実行するたびに

Traceback (most recent call last):
  File "/usr/local/bin/pip", line 5, in <module>
    from pkg_resources import load_entry_point
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 3130, in <module>
    @_call_aside
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 3116, in _call_aside
    f(*args, **kwargs)
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 3143, in _initialize_master_working_set
    working_set = WorkingSet._build_master()
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 642, in _build_master
    ws.require(__requires__)
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 943, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 830, in resolve
    raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound: The 'pip==8.0.2' distribution was not found and is required by the application

というエラーが出てpipコマンドが使用できなくなってしまいました．
再びpipをpythonごと再インストールし，--userオプションでmarkdownをインストールするしか無いのでしょうか？

2016/04/20追記

指示されたコマンドを実行した結果，以下のようになりました．

% ls -la /usr/local/lib/python2.7/ | grep -i site-
drwxr-xr-x   19 mk_mkee  admin    646 Apr 14 21:24 site-packages

特に/usr/local/lib/python2.7/以下の権限は触っておらず，ログインユーザにも権限があると思うのですが，
この状態でpip installを実行しても，Permissionエラーとなります．．．

% pip install markdown
OSError: [Errno 13] Permission denied: '/lib/python2.7/site-packages/markdown'