Sean Carroll (University of Wisconsin) provides a captivating and enlightening account of the latest findings in evolutionary developmental biology ("evo devo").  It explains how genetics really works to turn DNA into the visible traits and physical forms of living things.  The book is a must-read for anyone who is "interested in the origins of complexity".  Have you have ever wondered why there are so many similarities between us and other animals or why in the midst of multitudes, there are so few, common patterns (e.g. two eyes, five fingers, etc.)?  This is the place to start.

Here is a bit of what I grasped from his richly exampled book.

All creatures begin as a single cell that divides and differentiates.  As this embryonic development gets underway, chemical markers identify the location of the cell in 3 dimensions much like a globe: longitude, latitude, and altitude.  Each cell knows where it is relative to the others--its global position.

There are regulatory genes that, based on the cell's position, trigger a cascading series of cell development.  These regulatory genes are ancient and nearly identical in all animals.  At the very onset, the embryo divides into a "head" and "tail", and into "topside" and "bottomside", and "left and right".  Within the "tail" section, cells further subdivide into segments.  The future site of arms and legs are marked very early, when the embryo just looks like a blob.  Later these marked cells trigger growth of limbs, which involve their own cascading sequence of genetic triggers.

The key things to note:  The foundational genes that organize the body pattern is the same or similar in almost all animals, especially vertebrates.  These body patterns begin forming in the first few hours of embryo formation.  Therefore these common basic genes are shared across an incredibly vast variety of creatures large and small.  Thus it is no coincidence that we have so much in common with even a fruit fly.

In fact, the same proteins involved in the production of a fruit fly's eyes are used in the formation of our eyes; the same proteins, if disrupted, cause birth defects in humans.  The underlying chemical system is the same in all living things.  This is to be expected given that we know that DNA is shared by all living things.  But what this means is that not only is nature using the same "paper and pencil" but is using the same drawings as a starting point, and "simply" embellishing the drawings with more and more layers and details, or sometimes stretching or repeating patterns to suit a different need.