It has long been presumed that there is a common cause at the genetic, cognitive, and neural levels for autism's characteristic triad of symptoms. However, there is increasing suspicion that autism is instead a complex disorder whose core aspects have distinct causes that often co-occur.
1 Transition metals are kinds of metals that have electrons in d or f orbitals. 2  Transition metals are in columns 3-12 of the periodic table and in the lanthanide and actinide series.  Most transition metals are lustrous, silvery, hard, and good conductors; however, properties may vary greatly.
Scientists can't seem to agree on what to call this group of metals (poor, other, post-transition) or which elements should be included. Typically the elements of the post-transition metals include any metal in groups 13, 14, and 15 which are aluminum, gallium, indium, tin, thallium, lead, and bismuth.