The risks and benefits of older siblings

The theory is well known in biology. Having children sometimes comes at the expense of your own fitness: your future health, fertility or survival. So adult life is one big decision, one trade offas the biologists say. For example, laying more eggs sometimes results in birds ultimately fewer offspring because the ‘costs’ for the mother appear to be too high. And sometimes bird parents abandon their healthy young, for example if the partner has died. In this way they save themselves for the future. They therefore try to optimize their reproduction throughout their entire lives.

But what about people?

That is the question that Scottish PhD student Euan Young has focused on for four years. On November 17, he will defend his dissertation at the University of Groningen. And in the week before that, one of his editorials appears in the magazine Science Advances. Mothers don’t always compromise on their own fitness, the article concludes – only when conditions are tough. Mothers who had children during the Great Finnish Famine (1866-1868) lived on average six months less per child they had in their entire lives.

“People are a lot more complicated to research than animals, in this context,” says Young in a café near the Groningen Martini Tower. “People have all kinds of complicating factors that determine how many children they have. Especially nowadays, but also in the past: cultural practices, socio-economic factors… We try to unravel all these factors – including genetics.”

It’s easy to experiment with birds, Young notes. Taking eggs away or adding them, for example. “But that is of course not possible with people. For historical research on people, we have to rely on sources such as church archives. But they do not tell us whether people were sick or healthy, or what they died from. These sources are also very different in nature, which makes it difficult to combine them. And because naming was sometimes complex, genealogical research is often first necessary to find out who exactly was related to whom.”

Sibling effects

For their studies of contemporary humans, researchers use large biobanks, such as Lifelines: a database with genetic, lifestyle and health data of more than 160,000 people in the Northern Netherlands. “It’s whole data heavy research,” says Young. “I mainly sat behind the computer. But at the same time it was very exciting. And it is getting attention. After our article about Swiss brothers and sisters, we immediately received a call from a journalist from Nature.”

That article was based on Swiss church archives dating back more than three centuries and covering more than 45,000 people. The study was a follow-up to one previous Finnish study with more than 100,000 ‘records’. “That study showed that those who had more older brothers were more likely to survive,” says Young. “Why? We can only speculate, but maybe because the brothers helped on the land. But if you were a girl and you were close in age to more than one big brother, then that was actually a disadvantage. Maybe because boys received preferential treatment.”

The Swiss data in Young’s research also suggested that older brothers were a disadvantage if you were a girl, but that older sisters were an advantage. “That is probably why we found no effect overall.”

A Swiss amateur genealogist spent thirty years of his life sifting through and transcribing those archives, says Young: “In a super small handwriting, which allowed a lot of data to fit in one book. But you first have to digitize it again before you can apply analyzes to it.” One of his PhD supervisors, the Dutchman Erik Postma from the University of Exeter in the United Kingdom, had connections in that region because he worked for a time in Switzerland. “That’s how he got that data. And so he put together that database.” With a laugh: “Luckily that had all already happened by the time I knocked on the door.”

Evolutionary forces

Young’s research is a special European collaboration, he notes. “I have a Dutch supervisor in England, a British supervisor in Groningen and a Finnish supervisor in Finland.” Hannah Dugdale from the University of Groningen is a professor in ‘evolutionary medicine’, a relatively new field, Young explains. “That is the field that looks at people through evolutionary glasses.” But here in Groningen, that research is not part of medicine, but of biology: Dugdale’s office is next to that of the bird biologists. “And my Finnish supervisor Virpi Lummaa looks at aging in elephants, among other things. But she has also compiled the Finnish church database.”

Their new field sheds a refreshing light on illness and health, Young explains. “It offers new perspectives. For example, on genes that cause cancer: how can they persist in a population? Do they sometimes also do something else, which is actually an advantage? For example, provide protection against another disease? This research identifies risk factors and the evolutionary forces that have contributed to them. Forces that we all still have to deal with today.”

How did Young himself actually end up in this field? “I first studied marine biology in Aberdeen, Scotland,” he says. “For my master’s degree I went to Exeter, in the far south west of England: about as far away as you can go in our country. Ten hours by train from Scotland.” That master’s degree was in evolutionary and behavioral ecology – in the animal context. “My supervisor was Erik Postma; he put me in touch with Groningen.”

Big life topics

How does he find Groningen, as a foreigner? “Great fun. So I was used to cities in far-flung corners,” he says with a grin. “I had a nice time here. I was part of a PhD committee that organizes all kinds of activities for PhD students. And as an English speaker, I am privileged. Everything here is in English.” Yet he has learned very good Dutch in those four years, as it turns out when he orders a glass of water. His hard ‘g’ is flawless. “Yes, that’s because we have them in Scotland too, right.” He lets him grate it nice and sharply: “Loch…”

And what is on the agenda now, after his promotion in mid-November? “I would like to stay in science for a while,” Young answers. “It’s a tough world, but I find the research very interesting. Working with those large databases, but also the content. That historical context, the biological questions…”

Young hopes for a postdoc position in France: his partner is doing research in Paris. “I am now trying to get funding for research into diseases, reproduction and aging. In people, or in animals. It remains fascinating, those interactions between genes and health and those major life topics. We now have more and more cool methods to uncover those interactions.”

Give a gift





Part





Email the editor