** unset the colnames header argument
#+name: unset-colnames-example-input
| a | b |
|---+---|
| 1 | 2 |
| 3 | 4 |

Unlike most code blocks, Emacs Lisp has colnames set to "yes" in its
default header arguments.

#+begin_src emacs-lisp
  org-babel-default-header-args:emacs-lisp
#+end_src

#+RESULTS:
| (:hlines . yes) | (:colnames . no) |

As a result it has the following behavior by default.

#+begin_src emacs-lisp :var data=unset-colnames-example-input
  data
#+end_src

#+RESULTS:
| a | b |
|---+---|
| 1 | 2 |
| 3 | 4 |

If we wanted to unset this value, we could do the following.

#+begin_src emacs-lisp :var data=unset-colnames-example-input :colnames ()
  data
#+end_src

#+RESULTS:
| 1 | 2 |
| 3 | 4 |