title: Connecting two points with curved lines (s-ish curve) in R
body: <p>Suppose I would like to produce a kind of tree structure like the one below:</p>
  
  <pre><code>plot(0, type="n",xlim=c(0, 5), ylim=c(-3, 8), axes=FALSE, xlab="", ylab="", main="")
  points(1, 2.5)
  points(3, 5)
  points(3, 0)
  lines(c(1, 3), c(2.5, 5))
  lines(c(1, 3), c(2.5, 0))
  text(1, 2.5, adj=1, label="Parent   ")
  text(3, 5, adj=0, label="   Child 1")
  text(3, 0, adj=0, label="   Child 2")
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/PgrAU.png" rel="noreferrer"><img src="https://i.stack.imgur.com/PgrAU.png" alt="enter image description here"></a></p>
  
  <p>I wonder if there is a way in <code>R</code> where we can produce curved lines that resemble varying degrees of a S-curve like the ones below. Crucially it would be great if it would be possible to create such lines without resorting to <code>ggplot</code>.</p>
  
  <p><a href="https://i.stack.imgur.com/gNnAq.png" rel="noreferrer"><img src="https://i.stack.imgur.com/gNnAq.png" alt="enter image description here"></a> </p>
  
  <p><strong>EDIT removed and made into an answer</strong></p>