5) Sean B. Carroll, a leading investigator in the field of evolutionary developmental biology. (by Theodor Zbinden)

      Sean Carroll is nationally and internationally recognized investigator in the forefront of the evolutionary developmental biology (evo-devo) field.  Born in 1960 in Toledo, Ohio, he received his bachelor at the Washington University in St. Louis and his Ph. D. at Tufts University in Massachusetts.  Now Carroll studies the evolution of cis-regulation in the context of biological development at the University of Wisconsin-Madison.  He also is member of the Howard Hughes Medical Institute (HHMI).

Carroll answers the question of what is evo-devo with “form is a product of development, and changing form requires changes in development. Species diverge because of changes in their DNA.  Evo-devo research tries to understand the genetic and developmental basis of change over time and to link genetic change to changes in appearance”.

Thirty years ago, the general expectation in science was: the more recent the animal, the more complex the creature, and the more genes involved in building its body.  Now we know that it doesn’t completely depend on how many genes are present in the genome but how they are deployed.  Evolution of traits involves genes acting as a network which are linked through non coding DNA.  An example of such traits is seen in the Three-spined Stickleback Fish, a salt water fish which invaded fresh water, now found in fresh and salt waters in Alaska areas.  The salt water fish has a full body armor including spines for protection against predators.  However spines are disadvantageous in the fresh water, because the Stickleback predator dragon fly larva, can grape them.  This fact eliminated the expression of the spine gene Pitx1 in the fresh water fish, while the marine form maintains expression of the Pitx1 gene.  This is a typical example of evo-devo biology.

 Three-spined stickleback fish, marine and fresh water form.

The left image shows the skeletal differences between marine and freshwater sticklebacks. On the right are preserved specimens stained red. Note the strong divergence in morphology between the marine and freshwater forms, which can arise in just 13 generations (David Kingsley).

Activation and inactivation of the spine gene Pitx1 in the three spinal stickleback fish:

Graphic from Sahpiro's paper in Nature.  As you can see Pitx1 has four different promoters, each for specific tissues. In the spikeless sticklebacks one such promoter has undergone a mutation leaving it ineffective. In other words a mutation in one small piece of DNA related to one gene can cause such a major morphological change that a fish loses its defining characteristic. (David Winter)