Introduction to evolution

The lion's yawn

Why do female hyenas have a penis? Why do we choose fattening foods if we are stressed out? These and 17 others evolutionary questions are covered in the book ‘Why starlings pick flowers and why trembling mice are smarter’. Journalist Monica Wesseling wrote it in collaboration with scientists from the RUG’s GELIFES research institute.
By Tim Bakker / Translation by Traci White

It all started with a question posed by author Monica Wesseling: why do lions yawn?

GELIFES did not have the answer, but they did know that mice are right- or left-paw preferring.

After that first conversation, it was just one unusual story after another.

An example: if we are stressed out, we need food. After the September 11th attacks, sales of hamburgers and pizzas spiked in the United States.

Or: children who were born just after 1944 are more prone to being overweight. Why? Because their mothers had too little to eat during pregnancy.

Some researchers struggled a bit with the fact that their stories were being popularised for the sake of a book.

To that end, Wesseling says, ‘Of course they are first and foremost researchers, and they do not deal in absolutes.’

Fundamental research is gradually disappearing from the agenda, says GELIFES’ Ton Groothuis, and that is a shame. ‘We can only really recognise its value in hindsight.’

Reading time: 6 minutes (1,008 words)

It all started with a question posed by author Monica Wesseling: why do lions yawn? Wesseling, who wrote a series of nature stories for Dutch newspaper Trouw, called Ton Groothuis, a behavioural biologist and director of the Groningen Institute for Evolutionary Life Sciences (GELIFES), for the answer. ‘But he didn’t know, either’, Wessling says. ‘So I asked him, ‘what do you know, then?’ And then he started telling me about his research into right- or left-paw preference in mice.’

It was a very pleasant conversation, as Groothuis recalls. ‘We swapped stories and I told her about how we do a lot of this kind of research at GELIFES. I don’t know who came up with the idea first, but we both found ourselves thinking quite quickly: why don’t we make a book about it?’


Wesseling has previously written two books full of facts about animals. ‘I’m curious’, she says. ‘And I have a passion for nature and the ecological interactions between living things. This was the first time that I was describing research, but in principle, it’s the same. It’s still about asking questions.’

This book also differs conceptually from the first two. ‘I had written short passages that were around 150 words in the other books. This book has more in-depth explanations of scientific research, so the focus is different.’

Wesseling began writing in May and travelled to Groningen by train for nine weeks in a row. ‘I had planned two two-hour-long interviews with the researchers from the institute. It was so nice to see how enthusiastic they were about their areas of expertise. Some researchers struggled a bit with the fact that their stories were being popularised. Of course they are first and foremost researchers, and they do not deal in absolutes.’

Under pressure

That is the appropriate stance for a researcher to take, but it is also one that can be difficult to maintain in the modern academic climate, Groothuis says. ‘You get asked very quickly, ‘what can we do with this?’ Researchers are under pressure, and they are tempted to draw broader conclusions. But the objective should not be to translate research done on every mouse in the lab into something for people, because we know that the results would differ if we were to do testing on wild mice instead. Eventually, you want to be able to extrapolate that research, but in a well-founded way.’

Fundamental research is gradually disappearing from the agenda, says Ton Groothuis, and that is a shame. We can only really recognise its value in hindsight, and it is truly interesting unto itself. More importantly, there is a far greater need for fundamental research than the general public may think. We want to better understand the world around us, regardless of how applicable it may be.’

That is also part of his motivation to collaborate with the book. ‘It’s a good way to show the outside world – and the tax payers – what we do.’ Wesseling seconds that. ‘We wanted to get people wondering. We wanted them to think that they had never thought about that.’


The book explores how, following the September 11th attacks, sales of hamburgers, pizzas and chocolate pudding spiked in the United States. Makes sense: when we think of comfort food, we are not thinking about carrots and apples. But the neurobiologists in Groningen thought that it was strange that we reach for fattening foods in stressful situations. Eating unhealthily every once in a while is not a bad thing, but chronic stress can lead to obesity and the threat of countless other ailments. Where does that urge to snack come from?

And why is it that female hyenas, the greater guinea pig and certain other lesser primates have penises? Well, technically a pseudopenis: the females cannot use them for reproduction and they burst open during labour, which can lead to infection and stillbirth. Has nature made a mistake in these cases?

No, Groothuis says. Evolution is no accident.


Groothuis: ‘The research that we do here is part of the adaptive life research programme. Organisms adapt to constantly changing conditions. That is not a cognitive process, but rather genetic. It’s in our DNA. When mutations are advantageous for survival, these organisms will eventually be able to reproduce more easily. Over time, that results in broader dissemination of a mutation.’

That is a process that takes place not over one or two generations but rather thousands of years, depending on the species. ‘We used to think that adaptations would happen over the course of roughly 50,000 years, but we know now that it can go a little more quickly than that.’


That process is even further expedited through epigenetics. Our DNA code does not change so fast, but how it is expressed does change. ‘And there are different ways to read that code’, Groothuis explains.

‘One famous example is the children who were born just after the Dutch famine of 1944. Their mothers had very little to eat while they were pregnant, so they physically prepared their children for a life of scarcity. More food became available after the war, so there was a difference between the reality and the psychical conditions that their motherhood prepared them for. This mismatch led to all kinds of problems, including obesity. It was eventually possible to determine the exact trimester of pregnancy where the famine began.’

Many questions

The fact that this occurs in animals is well known. But how it works is a question that remains to be answered. Much research still has to be done, and that is not always simple. Hyenas are difficult to keep in a lab, so research can only be done on the guinea pigs. The answer to the question of ‘why’ eventually came from the janitors who complained about how sticky their cages were. It seems that the guinea pigs use their penis to give off a scent so as to communicate with each other.

And our need for comfort food can also be explained away. Fattening and sweet foods increase sensitivity for serotonin, a neurotransmitter. But always eating fatty foods does not appear to be a sustainable solution because it brings many other health issues along with it.

As for why lions yawn, the Groningen team cannot say. And that is also not explained in the book. But Wesseling was able to find the answer elsewhere: ‘They do it at the moment that they stop being stressed out.’


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