1. ovulation
   1. a pre-existing egg becomes mature
   2. sperm competition
2. fertilization
   1. one sperm is allowed to enter egg
   2. cell division
   3. cell differentiation
   4. form fetal gonad
      1. hormone input determined by M/F genes
      2. differentiate female reproductive anatomy
      3. (differentiate MALE anatomy ONLY if male hormones are present)
      4. brain develops toward end of fetal period
         1. brain differentiation
         2. overproduction of neurons and synapses
3. birth (to about age two)
   1. continued brain growth
   2. begin mylination of neural fibers
   3. begin pruning (loss) of surplus neurons and synapses
   4. form self-identity including gender identity
      1. based on anatomy and neural "programming"
      2. self observations and comparisons
      3. behavior of others toward self (socialization)
4. adolescence (triggered by hormones)
   1. gender identity established
   2. erotic imagery established
   3. secondary sex characteristics emerging
   4. sexual activities increase
      1. length of estrus in nonhumans varies greatly
   5. sex differences maximized during periods of high fertility
      1. (these differences may have unforseen consequences in the life of contemporary humans)