Against parachute skepticism

  • Find all the relevant studies.*
  • Sort through them and throw out anything that looks dubious.
  • Weigh up the ones that find ‘pro’ and ‘con’ evidence, and decide how strong the cases are.

Parachute use did not reduce death or major traumatic injury when jumping from aircraft. (Yeh, 2018)

From (Smith, 2003), the great paper on parachute use.
The inimitable XKCD.
  • Child development research is not the same as popular ‘parenting advice’. In some cases, popular advice often tells people the opposite of what the research says.
  • For non-US readers: I am not trying to make a point about any religion(s). A majority of male newborns are circumcised in the US.



The Force of Evolution

Developmental Plasticity

From (Lafuente, 2019)
  • The fruit flies reflect a general biological rule that smaller forms are better suited to higher temperatures. (See Bergmann’s rule and its developmental-plasticity version, the Temperature Size Rule.)
  • For the butterfly Bicyclus anynana, lower temperatures happen in the dry season, when eyespots would interfere with camouflage (Lyytinen, 2003).

Life History Theory

From here. The ideas here date back to (Promislow, 1990).

Fast and Slow Strategies in Individuals

  • Some individuals follow faster strategies. They start having children earlier, have more children and invest less in them. They also live less long.
  • Some individuals follow slower strategies. They start having children later, have fewer children and invest more in them. They also live longer.
Developmental Plasticity II: The Revenge!

Where are the Switches?

In response to stress, the adrenal gland produces the hormone cortisol. More on that in a second.


  • Danger in the environment causes stress, which is reflected in increased cortisol levels.
  • In early life, large or sustained cortisol rises (& other similar changes) ‘flip switches’ in the stress response system.
  • These flipped switches result in different lifelong levels of hormones.
  • Those changes in hormone levels push an individual towards increased risk-taking, risky sexual behaviour and other parts of a faster evolutionary strategy.

The Nature of Danger

Neonatal Circumcision — the Experimental Evidence

From Gunnar (1981). Note broken y-axis.

Miani (2020)

Note Miani (2020) look at sensation-seeking as a proxy for risk-taking attitudes; the two are closely related.
  • Bollinger (2011). Found a link to alexithymia, or difficulty idenfitying emotions.
  • Bauer (2013) and Frisch (2015). Found links to autism.
  • Ullmann (2017). Looked at only 9 circumcised men (!) and found no significant results.
  • Studies on sexual function, reviewed in (Morris, 2013) which concludes circumcision had no effect.


Effect sizes are small. That doesn’t affect the argument in this article at all, but it may affect what you think about circumcision.
All the theoretical predictions were in the correct direction, although the results for trust and empathy were not statistically significant.

Parachute Skepticism

Partisans … systematically denigrate, depreciate and counterargue evidence that is contrary to their political views but accept uncritically the supportive evidence.

Which theories work?

  • theories that only ‘explain’ pre-existing data
  • theories that have made new predictions, later proven correct

Afterword: Reading about child development…

…or not reading about child development!

Only the Grinch could be skeptical of this parachute.

Key science, with sources. Minus bad statistics. Minus shaky methodology. Minus politicisation, left or right.

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