Tag / development

by Roslyn

Girls do science

One of the best things about maternity leave is watching my daughter learn new things, almost daily. A few weeks ago she realized she could control her feet. This week she’s using her hands to grab at objects and starting to pull them in for further, mouth-based inspection. It really is exponential – the more she learns, the more she is able to figure out.

Children also learn a lot from what they hear. And they are apparently sensitive to the particulars at a surprisingly young age. Take, for example, the phrase “some birds fly” vs. the generic version “birds fly”. Psychologists have shown that halflings as young as two years old can tell the difference between these two phrases, and they can also use the generic version appropriately. What’s more, when adults use generic language in conversation with very young children, the children are able to infer new categories and make predictions about the world. This has been shown in experiments where psychologists talk about new, fictional categories (like Zarpies and Ziblets) with children. The results of these studies suggest that children are essentialists: i.e., they tend to carve up the world into categories, and view members of the same category as sharing a deeper, inherent nature. And these categories are easily transmitted through language.

This can have some unintended consequences. In her book The Gardener and the Carpenter, Alison Gopnik describes a study by Susan Gelman and colleagues where mothers and their children were given pictures of people doing stereotyped (a girl sewing) and non-stereotyped (a girl driving a truck) activities, and their conversations were recorded and quantified. It turns out that even mothers who were feminists used generic language most of the time. Moreover, there was a correlation between how often mothers used generic language and how often their children did.

Worst of all, moms used generics that reinforced the very stereotypes they were trying to combat. As Gopnik puts it:

Saying “Girls can drive trucks” still implies that girls all belong in the same category with the same deep, underlying essence.

I can’t help but wonder how this might affect our daughter as she grows up.

Although her book is not meant to be prescriptive, Gopnik does say that we probably can’t avoid this by careful wording – it just wouldn’t work to try to consciously control our language. Instead, the best antidote may be to have children observe many examples and talk to many different people.

by Roslyn

Another reason for eggs

Roman soldiers used them for protein1. In Mexico, men steal them from endangered sea turtles for their supposed effects on virility2. Bird eggs and roe, the ripe ovaries of fish, have a rich balance of proteins, fats and minerals – nutritionally, almost everything a predator needs. The whole point of these things is to feed something for an extended period of time. It’s no wonder eggs are so delicious.

The applications go beyond adding energy to our diets and structure to baked foods. Laying hens also contribute to medicine. Fertilized chicken eggs are used to grow viruses for mass production of vaccines. In 2007, scientists figured out how to genetically engineer hens to incorporate certain cancer-fighting proteins right into their egg whites, in a more efficient way to manufacture drugs that has been dubbed “pharming“3.

This morning, enthusiasts have yet another reason to celebrate, since a new study suggests that bird eggs might hold even more promise for medical research.

It has to do with migration, but not the kind you’re used to hearing about with birds. Cellular migration refers to the movement of cells within an organism during growth or embryonic development. For a long time, biologists studying this behaviour focused on the movement of single cells in isolation. In the last decade, however, the focus shifted to cells moving in a large, cohesive group. This collective migration is a fundamental part of gastrulation and neural crest development – two of the necessary steps for turning a blob of cells into a fully formed embryo during development (watch a time lapse video of this process in zebrafish).

Collective cell movement, or epithelial migration, occurs on a grand scale during bird embryo development. Every fertilized egg contains a tiny blastula, the hollow ball of cells that will eventually become a fetus. Early on, the cells of outer blastoderm layer of the ball start to expand across the vitelline membrane that surrounds the egg yolk, in a process known as epiboly. Eventually, the expanding sheet of cells envelops the entire yolk – a requirement for the yolk sustain the embryo during its transformation from a ball of cells into a viable chick.

Bird embryo and yolk

A chicken embryo grows while attached to its yolk, because of epiboly. Modified from drawing by D.G. Mackean.

This around-the-yolk migration happens rapidly, within days. From the perspective of a single cell, it’s a feat that bioengineer Evan Zamir likens to “an ant walking across the earth”4. And we still don’t know exactly how birds do it, with their humongous yolks; so far, most research on epithelial migration has involved other organisms.

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