The Importance of Studying the Skeleton in Evolution

The occurrence of an internal skeleton, in definite relations to the other organ systems, and the articulation of the body into homologous segments, are points in the general organization of Vertebrates to which especial weight must be given. This metameric structure is more or less definitely expressed in most of the organs, and as it extends to the axial skeleton, the latter also gradually articulates into separate segments, the vertebrae. The latter, however, must be regarded only as the p...

 Practice Walking Helps Infants Walk Earlier

In fact, contrary to all of the early anecdotes claiming that practice has no effect on the onset of walking, one carefully controlled study has shown that special exercise can indeed accelerate it. In this study, a group of newborns were given just ten minutes per day of "practice walking." Every day between one and nine weeks of age, the baby would be held upright by a parent, with his feet on a table, and allowed to exercise his stepping reflex. Two additional groups of babies received, re...

 An Experiment With a Tadpole's Development

An early classic experiment by the Nobel Prize-winning embryologist Roger Sperry illustrates the principle perfectly. Sperry and a colleague took a tadpole and removed a tiny square of skin from the back. They removed another square, the same size, from the belly. They then regrafted the two squares, but each in the other's place: the belly skin was grafted on the back, and the back skin on the belly. When the tadpole grew up into a frog, the result was rather pretty, as experiments in embryo...