Studies of gene expression in bees and humans suggest that who we become may be far more dependent on where we are and what we experience than we might have imagined.
What do honeybees and human beings have in common? We are highly social creatures. The human is entrenched in complex social structures from the nuclear family through political organization. Likewise, the honeybee lives in a socially stratified society. The queen bee has been likened to the matriarch of a family, with all of her little worker bees making up the other ladies of the house. They clean, cook and feed the young.
A less known factoid about the honeybee is that their behavior changes with age. As they get older, they transition from working in the hive to foraging. This transition, however, won’t happen if the ages of the bees are skewed. Ultimately, the needs of the hive determine the transitional timing of each individual worker bee.
This may not be interesting in and of itself, but it was the basis for highly interesting research at the University of Illinois. Dr. Gene Robinson and his group study the molecular basis of behavior using insects as models. We would expect behavior to be regulated by the brain, and we would expect neurons to play a pivotal role. Neurons are, after all, the most celebrated, star-quality brain cell. Robinson, however, doesn’t study neurons. He studies genes. And with his team he has found that genes also play a starring role in behavior. Genes are the coded instructions for most all of the molecular process that exists in an organism. They are made up of deoxyribonucleic acid, more popularly known as DNA, which is translated into ribonucleic acid (RNA) to control protein expression. In short, the importance of genes cannot be overemphasized. Gene expression, the reading of genes to produce and direct protein macromolecules, is responsible for outcomes on the level of the species and, also, the individual.
Experience dependence of Gene Expression in the Brain
That gene expression would play a direct role in behavior is surprising. One would expect changes in gene expression to happen very slowly over time, if at all. This isn’t the case. Robinson found that variations in behavior of the honeybee were accompanied by changed activity in thousands of brain-based genes (Whitfield et al). His team was even able to identify how changes in brain RNA influence behavior, correctly predicting the behavior of honeybees based on RNA profiles in 57 of 60 bees. Though we’re far from predicting human behavior based on RNA profiles, experts believe that the general mechanisms for control of behavior are similar in our brains – genes matter.
How might this rapid-fire change in gene expression manifest in changes in behavior? In addition to honeybees, Dr. Robinson has also studied the significantly more aggressive Killer bee. His research involved implanting baby bees from each hive into the other. As expected, the baby Killer bees exhibited the behavior of their hosts in the honeybee hive, and vice versa. Gene expression in the two groups of transplanted baby bees was more in line with their hosts than their siblings back home. This anomaly in expression became more pronounced the longer they stayed in their host hives.
These results indicate that gene expression in the brain is just as malleable and shaped by experience as neural connections (for example, see A Changing Brain is a Normal Brain and College in the Brain). Genes themselves cannot change, but how they are expressed can and does. These variations in gene expression can lead to drastically different outcomes. Importantly, gene expression is an essential step in neural plasticity, and response so environmental changes at the level of gene expression mean changes in the way neurons wire up and respond to stimuli. Plasticity at both the levels of genes and neuronal wiring are connected in a chain of events that shape behavior.
From Bees to Humans
We are not honeybees, but we share the basic mechanisms of DNA, RNA and protein creation. The role that gene expression plays in behavior illuminates the many levels of environmental influence on individual differences.
A 2004 study from the lab of Dr. Svante Paabo (Khaitavitch et al) reveals that our gene expression across the brains of individuals may vary more in humans than other species. Comparing the gene expression in post mortem human and chimpanzee brains, they found that expression in different cortex regions was more similar within each person’s brain than compared to the same regions in another person’s brain. They also found that the human brains contained more differences than the chimp brains, by roughly two-fold. Humans it appears, manifest far more variety.
This begs the question: would a transplanted human take on the characteristic of their host in much the same way as a honeybee? It is impossible to say for sure, but studies of identical twins shed some light on the matter. Though the more popular literature on twins separated at birth tends to concentrate on eerie similarities – such as dropping out of school at the same young age or marrying women with the same name – case studies on twins raised in different countries presents a different side of the coin.
US and SK always knew they were twins. Their South Korean parents could only afford to keep one of the girls, and the other was adopted by an American couple not three months after birth. When tested, both girls exhibited average IQs, high self-esteem and a preference for evening hours. Their personality tests, however, revealed marked differences. SK, raised in South Korea, scored much higher on both neuroticism and extroversion (a trait that can be measured physiologically in the EEG). Based on literature outlining the cultural expectations and outcomes in North Korea as compared to the United States, a higher score on neuroticism is to be expected. Given that her twin, raised as a minority in America, was “sensitive to the differences between herself and others,” their differences in regard to extroversion also align well with cultural factors.
Unfortunately, there are not enough twins raised in such varying cultures and we will never be able to study people the same way we study bees. However, our knowledge of gene expression in the brains of these little critters alongside evidence of the vast individual differences in the human brain presents the intriguing hypothesis that who we are is far more dependent on where we are and what we experience than we might have imagined.