Babies With a Sense of Justice

I always find articles about cognitive development in babies to be fascinating, because they show the threshold of what we consider to be quintessential human traits. Now a study out of the University of British Columbia shows that somewhere between 5 and 8 months old, babies go from always preferring helpful individuals to preferring individuals who are helpful or not according to the behaviour of the recipient.

The research is pretty well described by LiveScience:

So the researchers set up a series of experiments using puppets to act out scenarios of helping and harming while each of 32 5-month-olds and 32 8-month-olds watched separately. After each experiment, the infants indicated their preference for the puppets’ behaviors by picking their favorite puppet to hold.

The puppets — a series of cheerful characters, including moose, elephants and a yellow duck — were first shown interacting in either nice or mean ways. One puppet would struggle to open a box containing a toy, while another either jumped in to help or cruelly slammed the lid shut.

Next, the infants watched as the puppet that had helped or hindered played with a ball and dropped it. A third puppet then came into the scene, either to take the puppet’s ball away or to hand it back…

The researchers wanted to know if the babies would prefer the ball-giving puppet or the one that took the ball away. They found that 5-month-olds always preferred the ball-giver, no matter whether the puppet that had dropped the ball had been mean or helpful in the previous scene. At this young age, the babies simply liked puppets to be nice in the moment.

But 8-month-olds were more discerning. They liked it when the third puppet gave the ball back to a previously helpful puppet. But they didn’t like it when the third puppet helped out a previously unhelpful puppet. In scenarios involving the mean, toy box-slamming puppet, 8-month-olds favored a third puppet taking its ball away by 13 to three.

The researchers then repeated the experiments with 32 toddlers ages 19 months to 23 months, this time adding a twist. The toddlers got to watch puppets being nice or mean to each other and then got to play the role of rewarder or punisher. Some toddlers were shown one nice puppet and one mean puppet and asked which they’d like to share a treat with. Others were shown a nice puppet and a mean puppet, both with treats, and were asked to take a treat away from one.

In all cases, the toddlers meted out justice according to the puppets’ earlier actions. Thirteen of 16 gave a treat to a nice puppet, while 14 of 16 took treats away from a mean puppet.

LiveScience also has a video of the puppet show and the babies choosing a puppet – it’s kind of adorable.

This finding is pretty cool. I wonder what the physical switch is that enables babies to be more discerning, if there is one distinct switch? For some small context, here’s a graph of a person’s change in brain weight over time, where blue is male and red is female:

Data from Dekaban, A.S. and Sadowsky, D., Changes in brain weights during the span of human life: relation of brain weights to body heights and body weights, Ann. Neurology, 4:345-356, 1978, via University of Washington

Notice that babies at the ages used in this experiment (5 or 8 months) have brains less than half the size of an adult, and maybe half that of a 3-year-old. They have a long way to go before everything clicks.

This study, to me, raises the question of which behaviours are learned, and which are ingrained. It seems clear here that a sense of justice, in the sense shown, is probably inherent, or at least the capability to learn it is. I’m also kind of surprised that the babies could distinguish between different puppets who were only distinguished by the colour of their clothes. It’s never caught my interest as a field of study, but I’m starting to understand why people might like developmental biology… 

A Mechanical DNA Clock Determines Embryos’ Segmentation

Researchers have discovered a mechanism for how animal embryos segment themselves (roughly from head to tail) with extreme precision and consistent timing: the DNA responsible for determining the fate of different segments unravels in the same order and with the same timing as the segmentation itself. Remember that DNA is generally twisted and looped up as tightly as possible, so that molecules that could span 6 feet end-to-end are crammed up into a few nanometres; specific DNA sequences get unwound when they’re needed so that they can be read and transcribed by proteins, and then have an effect on the cell. 

From Science Daily:

During the development of an embryo, everything happens at a specific moment. In about 48 hours, it will grow from the top to the bottom, one slice at a time — scientists call this the embryo’s segmentation. “We’re made up of thirty-odd horizontal slices,” explains Denis Duboule, a professor at EPFL and Unige. “These slices correspond more or less to the number of vertebrae we have.”

Every hour and a half, a new segment is built. The genes corresponding to the cervical vertebrae, the thoracic vertebrae, the lumbar vertebrae and the tailbone become activated at exactly the right moment one after another… How do the genes know how to launch themselves into action in such a perfectly synchronized manner? “We assumed that the DNA played the role of a kind of clock. But we didn’t understand how.”

Very specific genes, known as “Hox,” are involved in this process. Responsible for the formation of limbs and the spinal column, they have a remarkable characteristic. “Hox genes are situated one exactly after the other on the DNA strand, in four groups. First the neck, then the thorax, then the lumbar, and so on,” explains Duboule. “This unique arrangement inevitably had to play a role.”

The process is astonishingly simple. In the embryo’s first moments, the Hox genes are dormant, packaged like a spool of wound yarn on the DNA. When the time is right, the strand begins to unwind. When the embryo begins to form the upper levels, the genes encoding the formation of cervical vertebrae come off the spool and become activated. Then it is the thoracic vertebrae’s turn, and so on down to the tailbone. The DNA strand acts a bit like an old-fashioned computer punchcard, delivering specific instructions as it progressively goes through the machine.

“A new gene comes out of the spool every ninety minutes, which corresponds to the time needed for a new layer of the embryo to be built,” explains Duboule. “It takes two days for the strand to completely unwind; this is the same time that’s needed for all the layers of the embryo to be completed.”

This system is the first “mechanical” clock ever discovered in genetics. And it explains why the system is so remarkably precise.

I wanted to share this article both because it seems like a very novel discovery and because it touches on some DNA and development fundamentals, but to be honest it’s a bit confusing to me, and I wish I could read the actual article in Science for an explanation. This article basically reads like the embryo is one cell with one set of DNA, which, unless I’m thoroughly off the mark, is not the case during segmentation, by which I’m assuming they mean somitogenesis. This begs the question: in which cells are they noticing this Hox activity? How is this pattern being communicated between cells? 

I may be missing something obvious, but I wish this Science Daily article were clearer. Anyway, in conclusion, here’s an interesting time-keeping mechanism during embryogenesis 🙂

Side note: Apologies for the gap in posts since Thursday; like I said in the previous post, I was marathon cramming for my GRE biochemistry test on Saturday, and my brain has been hibernating since then. It’s slowly recovering from the trauma. Fear not, though, we won’t miss a thing: I’ll be going through every article in my RSS feed since Thursday, all 1000+. No science will escape us!