Chapter 6 The Best Laid (Body) Plans Your Inner Fish By Neil Shubin

The Blastocyst Starts as ball of 16 cells Starts as ball of 16 cells No clear body plan No clear body plan Implants itself on the walls of the uterus Implants itself on the walls of the uterus Photo from:

Three Germ Layers Endoderm Endoderm –Inner Ex: Digestive tract Ex: Digestive tract Mesoderm Mesoderm –Middle Ex: Skeleton, muscles Ex: Skeleton, muscles Ectoderm Ectoderm –Outer Ex: Skin, nervous system Ex: Skin, nervous system

Ontogeny Recapitulates Phylogeny As animals go through development they track their evolutionary history As animals go through development they track their evolutionary history Compares human embryo in “reptile stage” to adult reptile. Compares human embryo in “reptile stage” to adult reptile. Photo from:

Experimentation- The Organizer Noggin Noggin –Type of organizer gene – When injected into an embyro would double the body axes. Organizer Organizer Made up of DNA Made up of DNA Same function in every animal Same function in every animal

Symmetry in bodies Most animals’ bodies are laid out on axes Most animals’ bodies are laid out on axes –Sea anemones- radial symmetry –Humans- bilateral symmetry Sea anemones have primitive versions of our body plan genes Sea anemones have primitive versions of our body plan genes Photo from: ling_on_the_southe/nudibranchs/

Citations Neil Shubin. Your Inner Fish, a Journey into the 3.5-Billion-Year History of the Human Body Pantheon Books. New York. ISBN: ISBN - 13: Pages