You did your postdoc with the zoologist Michael Akam at Cambridge. In an era when biochemistry predominates, the study of whole animals can sometimes seem like a throwback to another century. Why did you choose it?
Because I wanted to take the findings in my dissertation to the next step. The dissertation examined how germ cells behaved in one animal. At Cambridge, I asked how germ cells behaved in all animals and how they evolved. To do that, I studied sea urchins, crustaceans and sea anemones in the lab. Then I read the historic literature, just about everything published on the germ cells of hundreds of different species.
Throughout my career, I’ve tried to build on previous findings, and that sometimes means going outside of the original discipline or stretching its definitions. Right now, in my lab, we’re trying to understand the evolution of development by considering more than genes.
We are incorporating ecology and environment into our studies. Instead of just studying fruit flies in isolation, we are looking at the microbes that live inside the flies and the plants that the flies feed on. With this work, we hope to understand how the developmental processes can evolve in real-life environments.
What would you say are the most important findings to come from your Harvard lab?
First, showing that cell-cell signaling is not an unusual way for animals to generate embryonic germ cells — that is, cells that will become eggs and sperm. The idea that dominated textbooks for most of the 20th century was that in insects and most other animals, a “germ plasm” in the egg established a distinct lineage of germ cells very early in development. But we showed that in crickets, body cells are induced to change into germ cells by signals from the surrounding tissues. That’s what happens in mice and other mammals, too, but it was thought to be a novel mechanism that appeared rarely in evolution.
Second, discovering in 2020 that the long-lost relatives of oskar, a gene very famous for its essential role in insect reproduction, were actually from bacteria, not just from earlier animals. This gene evolved by fusion of bacterial genome sequences with animal genome sequences. It suggests that the forerunners to oskar had very different functions, possibly in the development of the nervous system, and that further study of how it evolved its new purpose could be highly informative.
Third, falsifying century-old “laws” that predicted the shapes of biological structures. Insect eggs vary tremendously, by eight orders of magnitude in size and with wildly different shapes. Previous assumptions were that a universal “law” of some kind, that applied to all animals, could explain the evolution of the shapes and sizes of cells and of structures made of cells. In the case of eggs, there were many previous hypotheses about what these laws were, including, for example, that the dimensions of the eggs reflected the requirements of the developmental rate or the adult body size for each species.
But we constructed an unparalleled data set of over 10,000 measurements of insect eggs and found that what really best predicted the size and shape of an egg was where it would be laid. Eggs laid on the ground or under leaves are basically elliptical. Eggs laid in the water tend to be smaller and more spherical. Parasitoid eggs laid inside other insects are also small but asymmetrical.
How did you come to move your work from Cambridge to Harvard?
In 2003, Harvard invited me to give a seminar. Afterward, people said, “Do you know that there’s an assistant professorship opening in evolutionary developmental biology? You should apply.”
I was perfectly happy at Cambridge. I had just gotten four years’ worth of funding for research. Frankly, I didn’t think I’d get the job because I had a pretty clear idea of what Harvard was looking for and it didn’t look like me. I was surprised to receive an offer.
Within a few years, you won tenure. In fact, you became the first Black woman to be tenured in the biological sciences at Harvard’s Faculty of Arts and Sciences. Did that feel good — or like a burden?
Both. Listen, this was not the first time in my life that I’ve been a “first.” Being the only Black woman in an all-white environment is essentially the story of my professional life. My chosen field of work is predominantly white. Often, whenever I do anything professionally, I’m the first Black woman to have done it. That’s not a reflection on me. That’s a reflection on the field.
Have you experienced any bias at Harvard?
I have not experienced a huge amount of deliberate blockage or targeted discrimination. But things often happen. I’ll turn up at the door for something and am told to use the service entrance. “Oh, I’m here for the [Harvard] Corporation dinner,” I explain. “Oh yes, the service entrance is around the back.”
Or I’m the keynote speaker at a conference. I’ll go to the front desk and hear, “Are you waiting for someone?”
It’s so constant. Saying that we should react like “it’s water off a duck’s back” implies that there’s no residue left behind. There’s a huge buildup of scar tissue. I can’t use my brain space to hold every single one of those because I need my brain space to do other things.
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