您的问题是因为您一次更改了所有.descContainer元素上的类，而不仅仅是与单击的.showDesc相关的类。
为了解决这个问题，你需要使用DOM遍历来获取closest('.feedContainer)，然后next()来获取你想要切换的元素，就像这样：

$(".showDesc").click(function() {
  var $target = $(this).closest('.feedContainer').next(".descContainer").toggleClass("show");
  $(".descContainer").not($target).removeClass('show'); // hide other open elements
});

.descContainer {
  position: relative;
  padding: 24px 40px 24px 24px;
  border-top: 1px solid rgba(0, 0, 0, .08);
  display: none;
  line-height: 24px;
  background-color: #fdfdfd;
}

.descContainer.show {
  position: relative;
  padding: 24px 40px 24px 24px;
  border-top: 1px solid rgba(0, 0, 0, .08);
  display: block;
  line-height: 24px;
  background-color: #fdfdfd;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<main>
  <section>
    <article class="feedBox mainSmooth">
      <div class="feedContainer">
        <div class="feedContent">
          <h3>Title</h3>
          <div class="feedButtonContainer"></div>
          <ul class="list-inline feedExtras">
            <li class="">
              <a class="mainSmooth showDesc">show description</a>
            </li>
          </ul>
        </div>
      </div>
      <div class="descContainer">
        <div>Description Text</div>
      </div>
    </article>
    <article class="feedBox mainSmooth">
      <div class="feedContainer">
        <div class="feedContent">
          <h3>Title</h3>
          <div class="feedButtonContainer"></div>
          <ul class="list-inline feedExtras">
            <li class="">
              <a class="mainSmooth showDesc">show description</a>
            </li>
          </ul>
        </div>
      </div>
      <div class="descContainer">
        <div>Description Text</div>
      </div>
    </article>
  </section>
</main>

你不需要jQuery，甚至不需要javascript，使用：target CSS伪类在HTML +上设置id和内部链接就可以了。

.descContainer {
        position: relative;
        padding: 24px 40px 24px 24px;
        border-top: 1px solid rgba(0,0,0,.08);
        line-height: 24px;
        display:none;
    }

    .descContainer:target {
        display:block;
    }

<main>
    <section>
    <article class="feedBox mainSmooth" style="display: block;">

    <div class="feedContainer">

    <div class="feedContent">

    <h3>Title</h3>


    <div class="feedButtonContainer">
    </div>


    <ul class="list-inline feedExtras">
    <li class="">
    <a class="mainSmooth showDesc" href="#1">show description</a>
    </li>
    </ul>

    </div>

    </div>

    <div class="descContainer" id="1">

    <div>Description Text</div>

    </div>

    </article>

    <article class="feedBox mainSmooth" style="display: block;">

    <div class="feedContainer">

    <div class="feedContent">

    <h3>Title</h3>


    <div class="feedButtonContainer">
    </div>


    <ul class="list-inline feedExtras">
    <li class="">
    <a class="mainSmooth showDesc" href="#2">show description</a>
    </li>
    </ul>

    </div>

    </div>

    <div class="descContainer" id="2">

    <div>Description Text</div>

    </div>

    </article>

    </section>

    </main>