title: filled / open circle by group
body: <p>I have trouble making a filled / open circle plot by group. </p>
  
  <p>My data looks like:</p>
  
  <pre><code>Body_weight  Gender
  50            M
  60            M 
  55            M
  45            F
  43            F
  42            F
  </code></pre>
  
  <p>I want to plot the male weights in filled circle and the female weights in open.</p>
  
  <p>I tried: </p>
  
  <pre><code>ggplot(data, aes(x=Gender, y=Body_weight))+
   geom_point(aes(fill=Gender))
  </code></pre>
  
  <p>But, this only gives filled circles for both gender.
  I have no idea why this does not work.</p>
  
  <p><code>geom_point(aes(shape=Gender))</code> works and gives a circle / triangle plot. </p>