Party animal? Don't blame your genes
Genes shape our health and appearance more than they shape our personality, suggests a new study of thousands of people in a genetically isolated part of the world.
According to the study, published in the August issue of PLoS Genetics, genetics account for roughly 51% of a person's height, weight and body shape, 25% of cardiovascular function and about 40% of certain blood characteristics, such as sugar and cholesterol levels.
But genes only account for about 19% of many documented personality traits, such as neuroticism, extraversion, agreeableness and conscientiousness.
"My personal view is that we have evolved to have very diverse personalities and that, compared to other traits, personality may be much less deterministic than other human characteristics," says Associate Professor Gonçalo Abecasis, one of the study's authors.
"My view is that both genes and environment will play smaller roles than random factors."
Abecasis, a scientist at the Center for Statistical Genetics at the University of Michigan, and his colleagues examined 6148 people from the Mediterranean island of Sardinia, where many residents are related.
Roughly 95% of people in the study had Sardinian grandparents, and the test group included 5000 pairs of siblings.
The researchers believe their study is the largest ever published for the traits they examined.
The scientists took blood samples, gave physical exams, and asked participants to fill out standard personality questionnaires.
They also measured liver and thyroid function, electrolyte levels, cholesterol, blood glucose and more.
To figure out the degree to which each trait was affected by genetics, the researchers first calculated the amount of DNA shared by each pair of relatives.
For example, the DNA of identical twins is almost 100% identical, siblings average 50% similarity, and uncle-nephew pairs usually have about 25% similarity. Cousins share, on average, about 12.5% of their DNA.
The researchers then compared this information with the health, weight, personality and other data.
Computer models matched these traits with relatedness to find how much of each trait appeared to be affected by genetics.
While the study found genetic effects often determine whether a person will be heavy or thin, the researchers say we cannot always blame our genes for weight problems.
Dr David Schlessinger, who also worked on the study and is a senior scientist at the National Institute on Aging, says that "lifestyle has led to the current epidemic of obesity".
"It does appear, however, that some individuals have a genetic constitution that is more resistant to the modern diet and lifestyle than others," Schlessinger adds.
Personality and disease
Cross-examination of all of the data revealed that personality traits do not appear to be linked to blood and heart health. For example, anger-prone people don't appear to suffer more heart problems than mellow people do.
"What is unusual [about the study] ... is its size and integration of a large amount of trait information into the analysis," says Dr Wayne Frankel, senior staff scientist at The Jackson Laboratory in Maine.
"It is important that the heritability of related traits be considered together, in order to improve the power of gene-identification experiments in future."
Abecasis and his colleagues next hope to identify the particular genes that are responsible for each of the traits they studied.