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Episode 01 · pilot · “Why We Are Human”

The Ape That Never Grew Up

Human children take longer to grow up than the young of other primates. What does that have to do with the axolotl, an amphibian that gets by without growing up, and with foxes from Novosibirsk?

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Lectures are currently held in Russian.

Human brain organoids in a lab dish
Brain organoids · NIAID · CC BY 2.0 · Wikimedia Commons

The mystery

Why do we take so long to grow up?

A human baby stays helpless longer than the young of other primates, and the brain keeps maturing for years after birth. Is this a flaw of evolution — or its greatest trick?

I won’t give the answer away: we will piece it together from the clues.

Engraving of a Mexican axolotl
Axolotl · Popular Science Monthly, vol. 20, 1882 · Public domain · Wikimedia Commons

Clues

What’s in the episode

  1. Clue 1 · Mexico

    The axolotl

    An amphibian that gets by without growing up.

  2. Clue 2 · Novosibirsk, 1959

    Belyaev’s foxes

    They selected for temperament alone — and something else changed too.

A bold hypothesis: could humans have domesticated themselves? We weigh the arguments for and against.

  1. Clue 3 · Heidelberg

    A brain in a Petri dish

    Human and chimpanzee cortical organoids.

Live experiment

The audience is part of the experiment

The audience takes part from their phones — no apps needed. Your answers become part of the reveal.

  1. True or mythPhone voting on three popular claims about the brain.
  2. Whose organoid is it?Human or chimpanzee — the audience decides.
  3. A final question for the audienceOne last vote before the reveal.

How the voting works

After the reveal

What to take home

Why are we in such a hurry to grow up, if a long childhood is our evolutionary advantage? We will talk about curiosity, brain plasticity and what science says about learning as an adult.

Teaser at the end of the episode

The complete wiring diagram of a fly brain — and what happens if you sit it down at a poker table.

Bluffly: play against the fly right now

From my own lab

The research behind the episode

In Henrik Kaessmann’s lab I was working out a protocol for growing cortical organoids from human and chimpanzee cells, and along the way I made some preliminary findings:

  1. humans and chimpanzees run on different “clocks”: the optimal protocol days differ between human and chimpanzee;
  2. human organoids compensate better for a poor start;
  3. an organoid’s success is visible as early as days 9–12 from its neural rosettes, structures resembling the early neural tube;
  4. the cortical gene EMX1 was on average more active in humans (a trend);
  5. the “one organoid per well” format is cheaper and yields more cortex.

These are preliminary results: one cell line per species. A journal paper is in preparation.

Measured with qPCR analysed in Partly in qPioneer, partly in R

Who it’s for

For anyone curious about how we work

No background needed.

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Lectures are currently held in Russian.

Sources

Further reading

  1. Bolk L. Das Problem der Menschwerdung. Jena: Gustav Fischer, 1926
  2. Gould S. J. Ontogeny and Phylogeny. Cambridge, MA: Harvard University Press, 1977. ISBN 9780674639409
  3. Somel M. et al. Transcriptional neoteny in the human brain. PNAS, 2009
  4. Otani T. et al. 2D and 3D stem cell models of primate cortical development identify species-specific differences in progenitor behavior contributing to brain size. Cell Stem Cell, 2016
  5. Ponce de León M. S. et al. Neanderthal brain size at birth provides insights into the evolution of human life history. PNAS, 2008
  6. Takahashi K., Yamanaka S. Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors. Cell, 2006
  7. Takahashi K. et al. Induction of pluripotent stem cells from adult human fibroblasts by defined factors. Cell, 2007
  8. Lancaster M. A. et al. Cerebral organoids model human brain development and microcephaly. Nature, 2013
  9. Trut L., Oskina I., Kharlamova A. Animal evolution during domestication: the domesticated fox as a model. BioEssays, 2009
  10. Lord K. A. et al. The history of farm foxes undermines the animal domestication syndrome. Trends Ecol. Evol., 2020
  11. Wilkins A. S., Wrangham R. W., Fitch W. T. The “domestication syndrome” in mammals: a unified explanation based on neural crest cell behavior and genetics. Genetics, 2014
  12. Wrangham R. W. Two types of aggression in human evolution. PNAS, 2018
  13. Hare B., Wobber V., Wrangham R. The self-domestication hypothesis: evolution of bonobo psychology is due to selection against aggression. Anim. Behav., 2012
  14. Cieri R. L. et al. Craniofacial feminization, social tolerance, and the origins of behavioral modernity. Curr. Anthropol., 2014
  15. Zanella M. et al. Dosage analysis of the 7q11.23 Williams region identifies BAZ1B as a major human gene patterning the modern human face and underlying self-domestication. Sci. Adv., 2019
  16. Gopnik A. Childhood as a solution to explore–exploit tensions. Phil. Trans. R. Soc. B, 2020
  17. Gruber M. J., Gelman B. D., Ranganath C. States of curiosity modulate hippocampus-dependent learning via the dopaminergic circuit. Neuron, 2014
  18. Maguire E. A. et al. Navigation-related structural change in the hippocampi of taxi drivers. PNAS, 2000
  19. White J. G. et al. The structure of the nervous system of the nematode Caenorhabditis elegans. Phil. Trans. R. Soc. B, 1986
  20. Dorkenwald S. et al. Neuronal wiring diagram of an adult brain. Nature, 2024
  21. Shiu P. K. et al. A Drosophila computational brain model reveals sensorimotor processing. Nature, 2024
  22. Azevedo F. A. C. et al. Equal numbers of neuronal and nonneuronal cells make the human brain an isometrically scaled-up primate brain. J. Comp. Neurol., 2009
  23. Herculano-Houzel S. The human brain in numbers: a linearly scaled-up primate brain. Front. Hum. Neurosci., 2009

Next in the season

Episode 02

A Brain in a Dish: Can It Think?