I totally forgot to include this neat video from Acapella Science in my January column for The Intergalactic Medicine Show.  Watch it before you read the rest of this.

https://www.youtube.com/watch?v=ydqReeTV_vk

The basics of the issue in biology are this:

1. All your cells have the same genes (genotype).
2. Yet you have at least 200 different cell types making up your tissues and organs (phenotype).
3. Wha???

Geneticists came up with those concepts at the level of the whole organism (the body), and biochemists eventually figured out that the genotype was coded in DNA, and the phenotype was mostly composed of proteins, allowing for that separation of function.  So that meant that each cell phenotype was expressing only a subset of the possible proteins that it could be using.

Developmental biologists spent a century working out what they called cell fate trees, with each branch point being a cell division, which are convenient points for deciding which genes to permanently turn off.  

[image link]

Then evolutionists noticed that 

1. hey, wait, those trees look a lot like our trees (except pointing down instead of up), and 
2. what if those developmental switches were the exact same genes responsible for the big changes in body shape that we see across evolutionary time?

"Man, you just wrinkled my brain."

                                             -Donald Glover on Community

Thus Evo-Devo was born.

RANDOM RESOURCES FOR FURTHER EXPLORATION

http://cellfinder.org/development

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0001939

http://www.wormbook.org/index.html

http://biomedicalcomputationreview.org/content/digging-deep-tree-life