Human heritage: How we became who we are

Wolfgang Enard has a chimp on his desk. Or rather a bronze statue of one, sitting on a stack of books in the thinker pose. “We’re more alike than we sometimes like to admit,” says Enard. The Professor of Anthropology and Human Genetics has been researching the commonalities and differences in the genomes of humans and other animals for many years.

And yes, humans are animals. We are great apes, like chimpanzees, gorillas, and orangutans. Yet most non-experts feel uneasy about acknowledging our kinship with our ape cousins. Humans are somehow exceptional, are they not? Not the pinnacle of creation, perhaps, but at least the wunderkind of evolution. After all, we are the species that conquered the entire planet. But how did this come about?

The result of four billion years of evolution

“The question of our origin – our biological identity – is vitally important for many people,” affirms the evolutionary anthropologist. “It seems to have deep roots in the human psyche.” People find it easy to accept that there are various subspecies of flies that have interbred, but when it comes to our relationship with Neanderthals, for example, matters immediately get fraught.

The path from our primate ancestors to humans is difficult to reconstruct. We love stories where the main character purposefully gets from A to B. But evolution does not care about good storytelling. Our genome is our inheritance from over four billion years of evolution.

A huge variety of environmental conditions, ecological niches, and random coincidences have altered and shaped the genome in countless rounds of selection over this period. Many factors that play a role are intertwined and have continually influenced each other. And unraveling these threads is even more complicated for us humans than for other creatures.

The reason for this is cultural evolution, which operates much faster than genetic adaptation. It was kick-started by our marked aptitude for social learning. “If you place a really smart person alone in the middle of the jungle, they will die despite their brains.” As such, our intelligence alone cannot explain our huge influence on the world, clarifies Enard. “It’s the combination of individual brains that makes the difference. And that’s not only true for the modern world; it was ever thus.”

Cultural and genetic factors mutually influence each other

This cultural factor also began interacting reciprocally with biological processes in the course of hominization. The ability to understand complex relationships and interact socially with others requires a large brain. Conversely, a large brain needs a lot of energy and sufficient time to be filled with knowledge. Unlike muscle tissue, for example, a brain cannot decrease in size in bad times to save energy. It needs constant nourishment, even when not yet mature and dependent on parental help for survival.

In other words, the larger and more complex the brain of a child, the more effort that is required to successfully raise it. A cultural factor that came to bear here is the sharing of the child-rearing burden. Grandparents and other relatives helped furnish the constant energy input for the child’s developing brain. This created more scope for an even larger brain. The large brain and our increasingly complex social behavior thus mutually reinforced each other in a positive feedback loop. And though it might seem as if evolution had it all thought out for us, this is not how evolution works.

Evolution is not progress, but adaptation

Evolution does not think and does not plan ahead: “The famous picture of the ape that gradually stands upright to become a modern human – the continuous rise of the human – is one of the most iconic but also misleading images in scientific history.” Enard is referring to the March of Progress – the world-famous illustration of human evolution, which now adorns coffee mugs and T-shirts in all kinds of variations.

“The idea that evolution is progress is widely held, but like most stories of progress, it’s flat-out wrong.” Evolution never decided to make the brains of our ancestors bigger and bigger until they attained completion in modern humans. Whether brains become larger or otherwise change is renegotiated in every generation between a species and its environment. And whether humans, with their large, complex brains, are successful in the long run, remains to be seen.

What related species reveal about us

Brain sizes are in fact constantly changing in the universal tree of life. Humans are not the only ones to have developed big brains – this is also true of other animal groups such as dolphins. By comparing ourselves with such species – just as we do with our nearest relatives – we can try to understand the general mechanisms by which evolution produces larger brains. Indeed, this is one of the questions Enard explores in his research.

Such comparative approaches have become possible thanks to cutting-edge DNA sequencing technology. The development of the brain is made up of countless small genetic jigsaw pieces. If scientists identify one such piece, for example, by testing the effects of a specific genetic modification on lab mice, the next question is: Did this gene actually change in the course of evolution? Can a specific mutation be found along the stem lineage of primates? Did the dolphin develop the same mutation for its brain, or did it find another solution?

“With the additional dimension of phylogeny and thanks to modern genomics, we have the ability today to investigate evolutionary patterns in a broader context.” For Enard, this broadening view is revolutionary. “Instead of observing just one branch, we can look at whole limbs and the entire tree of life.”

By now, it is pretty clear that our commonalities considerably outweigh our differences. All living creatures on planet Earth form one big colorful family. “Perhaps the most surprising discovery of biology over the past 50 years is how similar how we all are.” Fundamental molecular processes and development mechanisms are virtually identical for most organisms. Were this not the case, scientists could not use mice and flies as model organisms for humans.

Instead of just laying the gene sequences of various species alongside each other and comparing them, the LMU biologist is currently investigating how the respective genes are regulated. Specifically, he is studying how stem cells change into neurons – a process that happens in all mammals in the course of brain development. “We’re looking for groups of genes that are regulated the same in all species, as these are probably functionally relevant.” Differences in gene regulation, by contrast, could point to species-specific adaptations. To this end, Enard’s team uses so-called induced pluripotent stem cells, which allow these processes to be simulated cost-effectively in a Petri dish without animal suffering.

Obtaining stem cells non-invasively from ape urine

Procuring the samples is a challenge, however: The main donors of the stem cells are currently animals in zoos. “We considered trying it with hair roots,” recalls Enard, “but gorillas are not exactly thrilled when you pull out their hairs.” His team eventually found a fully non-invasive alternative – of which Enard is proud: “We developed a method for extracting stem cells from the urine of zoo animals.” Ape urine can easily be collected off the ground of the enclosure, and the cells the researchers obtain from the urine can be reprogrammed with excellent results. In the test tube, they become neural progenitor cells, which subsequently develop into brain cells.

Naturally, brain size alone is not the only key factor in anthropogenesis. The crucial thing is actually connecting these brains in networks. Our species solved this task by creating language. The development of language also has cultural and physical components. After all, the culturally acquired software that is “language” needs suitable biological hardware that can learn and generate the language.

The physical ability to speak rests on genetic and anatomical foundations – speech centers in the brain that are connected with suitably formed speech apparatus such that the latter can be consciously utilized. A wide variety of genes contribute to this functionality. Enard has investigated, for example, the transcription factor FOXP2, which is essential for human speech. Almost all animals possess the gene that codes for FOXP2 – including mice, songbirds, and chimpanzees.

And although lab mice with the human variant of FOXP2 do not begin to speak, they do exhibit conspicuous neural changes that are related to the reward system. Again, we can compare: Which mutations does the speaking human have which the non-speaking hominid lacks? And did songbirds come up with the same solution for their complex song, or different solutions?

Biological heritage of humans: not always up to date

Biology has become highly adept at following the traces of evolution and investigating how certain characteristics develop. Why is a whole other question, which researchers can generally only answer retrospectively by positing plausible hypotheses about selection and environmental conditions in the past.

In the course of cultural evolution, humans are now continually creating new environmental conditions for themselves – and at a rate that genetic adaptation cannot keep up with. It should not surprise us, then, if some gene remnants that once conferred an advantage no longer suit our modern lifestyle. Evolutionary anthropologist Enard refers to such cases as mismatches.

“A simple example is our genetically programmed craving for sugar,” says the LMU researcher. “Over millions of years of evolution, easily available sources of energy were rare and extremely valuable for our hunter-gatherer ancestors. Today, we’re a lot less active and sugar is suddenly available to excess – and so our genetic makeup no longer matches our circumstances.” In other words, our bodies no longer match the world in which we live. But we cannot turn back the clock. We have to learn to deal with the conditions we’ve created for ourselves.

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Prof. Dr. Wolfgang Enard is Chair of Anthropology and Human Genomics. Before coming to LMU, he completed his doctorate at the Max Planck Institute for Evolutionary Anthropology under subsequent Nobel Prize winner Svante Pääbo. After his PhD, he headed a research group at the same institute.

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