Dr. Hendricks, a psychologist, believes that the differences between the genders can be attributed to the varying levels of estrogen and testosterone in males and females. In the context of the theoretical approaches to gender development, Dr. Hendricks is most likely a proponent of the approach.

Dr. Hendricks is most likely a proponent of the biological approach.

Explanation:

The biological approach basically suggests that gender and sex are not distinguishable from each other. Gendered behavior would be a result of biological sex; sex, in its turn, is a result of chromosomes and hormones, especially testosterone and estrogen - male and female, respectively. As we can see, Dr. Hendricks believes differences between the genders are due to differences in hormonal levels. It is safe to say Dr. Hendricks is a proponent of the biological approach.