As presented in the 4th module, there are concrete evidences of both genetics’ and environment’s significance in an individual’s intelligence. The public in general has been fascinated by “twin studies” of which the findings were viewed promising. It says:
Evidence of genetic influences:
- Twin studies suggest that identical twins IQ’s are more similar than those of fraternal twins (Promin & Spinath, 2004).
- Siblings reared together in the same home have IQ’s that are more similar than those of adopted children raised together in the same environment (McGue & others, 1993).
Evidence of environmental influences:
- Identical twins reared apart have IQ’s that are less similar than identical twins reared in the same environment (McGue & others, 1993).
- School attendance has an impact on IQ scores (Ceci, 2001).
- Children who are breastfed during the first three to five months of life score higher on IQ tests at age 6 than same-age children who were not breastfed (Reinberg, 2008).
In line with this concern, let me share what I’ve read in my psychology book about the surprising natural tendencies of a twin to be similar in many things.
Let’s consider a startling example that involves identical twins, who have 100% of their genes in common. Jim Lewis and Jim Springer were identical twins reunited at the age of 39 after being separated since infancy (Holden, 1980). To their shock, both had married and later divorced women named Linda. Their second wives were both named Betty. Both had sons named James Allan and dogs named Toy. Both chain-smoked Salem cigarettes, worked as sheriffs’ deputies, drove Chevrolets, chewed their fingernails, enjoyed stock car racing, had basement workshops, and had built circular white benches around trees in their yards.
Could there possibly be genes for marrying women named Linda or Betty or for having basement workshops that account for the similarities between these twins, who had never before met each other? Genetic researchers think not. Instead, people with identical genes may have similar temperaments and talents that cause them to choose similar environments (Bouchard & Loehlin, 2001; Johnson, McGue, Krueger, & Bouchard, 2004). For example, both of the Jim twins may have wood- working talent that causes them to build work- shops in their basements and circular benches in their yards.
I was really surprised and amazed after reading this story. It does show how powerful genetics is. Hope you do the same. God bless!:D
Kendra Cherry. Psychology By Category. Retrieved June 14, 2013 from http://Psychology.About.Com/Od/Intelligence/F/Int-Influences.Htm
Hoeksema, S. N. (2011) Interactions between Genes and Environment. Abnormal Psychology (5th Edition, p. 26). New York: McGraw Hill Companies, Inc.