Are people naturally unequal

Genes or environment? Why are people actually of different sizes?

It may seem mundane to most people, but our height is an exciting mystery to evolutionary biologists. The fact that we humans and other living beings can be so different in size is a phenomenon for which there was no real explanation, says Thomas Bosch, professor at the Christian Albrechts University in Kiel. You know that the body size is specific to the species, explains the zoologist. Humans have a certain size and, depending on the species, this is also the case.

In animals, whales are larger than guinea pigs and dogs. There is no dog as big as a whale and there is no guinea pig as big as a dog. A biological species has a fixed body size within fixed limits and fluctuations. It must be genetically determined somewhere.

Evolutionary biologist Thomas Bosch

But, puts it into perspective, when he walks through the pedestrian zone, people are not at all the same size, on the contrary. So how does that come about? A cohort study already established in 2017 how great the influence of our size genes actually is, explains the evolutionary biologist.

That work actually posited that about 30 percent is genetics. (...) Then 70 percent is not genetics. And that is what we have shown in our model organism, the freshwater polyp Hydra: What does it look like there?

Evolutionary biologist Thomas Bosch

So the freshwater polyp Hydra was the researchers' test system. Because they wanted to turn off some genes that could have something to do with height. Of course, that doesn't work with humans. Hydra is suitable for this because there are also animals of different sizes and the results can be transferred to other living things, even to humans. The researchers then carefully analyzed the genetic make-up of these tiny animals.

At the cellular level, we have found that indeed one of the environmental factors - temperature - has a huge impact on size.

Evolutionary biologist Thomas Bosch

One factor that determines our body size are influences from the environment. The lower the temperature, the larger the animals became. The researchers also analyzed the genes themselves in more detail and came across a few key genes. If they were switched off, the body size changed. From this, the researchers were able to derive a kind of basic plan for the creation of the size.

OObviously, the internal machinery of a cell, together with the regulators, make up the genetic machinery. The temperature is perceived by this genetic machinery and then converted into cell count, cell size and thus also body size.

Evolutionary biologist Thomas Bosch

Next, Bosch's team wants to focus on the environmental impact of our diet. Because it essentially determines the composition of our microbiome - the bacteria that are on and in us. There is even an initial interim result: It is obvious that the microbiome also has something to do with how big an individual becomes.