Why are siblings so different?
Two children from the same family can often be very different. If nature fully accounts for our behaviour then siblings should be identical, which can be evidence which contradicts the perception that our genes are what determine who we are. However if nurture fully accounts for our behaviour then siblings should also be identical, given that they are raised in the same environment. It is this debate that creates controversy around this topic.
Studies of twins reared apart
The Minnesota study of monozygotic (genetically identical) twins reared apart has been ongoing for decades, and has now concluded that monozygotic twins reared apart are about as similar as monozygotic twins reared together. This was based on several personality measures such as temperament, occupation, leisure time interests and social attitudes. These findings give strong support to the nature argument, in that they were the same despite being raised in different environments, meaning there identical genes must determine who they are.
Studies of adopted children
These studies lend more support to the argument that nature is of greater importance than nurture. Adoptive siblings share the same environment but not the same genes. Loehlin et al looked at the IQ of 200 adopted siblings. A correlation of 0.26 was found at 8 years old, but by the time the siblings were 18 there was no correlation. This displays some weak early similarities, but overall supports the nature argument in that the shared environment did not result in a shared IQ, meaning genes must determine our intelligence.
The unshared environment
In this uncertainty, the concept of the unshared environment offers explanation as to why sibling can become so different.
When we refer to environmental factors, we automatically assume that two people in the same home are sharing the same environment, when this is not necessarily true. An example of this is moving house. If one child is 12 at the time of the move, and the other is 5, the experience has different effects on each of them because of their age.
Another example that can be used is peer influences. Each sibling will have a different group of friends, and these friends play an important part in a child’s development. These peers will often determine factors such as music interest or social hobbies, all of which will shape the child as a person. This means it is very easy for siblings who have very different peer groups to become very different.
There are also other cases of unshared environments such as illness, accidents, teachers or hobbies that can make a person who they are. All of this is the force of nurture working, but unshared nurture.
I feel it is interesting to research how strongly nature impacts our personality and intelligence, however the issue with this research from a social standpoint is that it lessens the gravity of situational factors in development. When genes are a scapegoat, it is easier to discriminate and simple to dismiss personal responsibility. For the sake of basic research in psychology, understanding of sibling sameness regarding genes is essential, but it remains critical that the public gains insight into the weight of nurture. This is particularly important in policy making, and furthermore voting for those policy makers. Voters and their representatives must understand the situations that produce low performing or even criminal individuals. By giving weight to the environments people are often systematically cornered into helps to prevent categorizing people as critically flawed. Society often fails to identify situational factors (known as the fundamental attribution error); too often we claim: X people are all criminals. However, more accurately: Many X people receive lower quality resources from prenatal care to education to less occupational opportunity due to the remnants of historical segregation or even current discrimination which can lead to or even force said individuals into criminality or low-performance. When law makers and their supporters address or even discuss criminal justice, economic reform, social justice, healthcare, or even food distribution, the existence of unfair environments and the inherent qualities of their nurture must be at the forefront, so that these situations may be diminished, and not perpetuated, by new policies. Extensive, continual, and well -publicized research on the impact of nurture may eliminate stigmas and even make actual progress in closing socio-economic gaps.
It is very interesting that twins reared apart can be so similar. In class, we discussed two twins reared apart, Jim Lewis and Jim Springer. From the age of four weeks they were separated and finally reunited at age 39. I found it very interesting that both had very strange similarities. They discovered they both suffered from tension headaches, were prone to nail biting, smoked Salem cigarettes, drove the same type of car and even vacationed at the same beach in Florida.