Comments on: Did humans trade guts for brains?

By: Jess Tauber

Jess Tauber — Mon, 09 Jan 2012 21:18:13 +0000

There is a difference not just in the overall mass of muscles in humans vs. other apes, but also in how they operate. In nonhuman apes there is a strong bias towards firing muscle groups all at once, in parallel, thus a power-heavy operation. In humans we go for serial firings, which is much ore finesse-heavy. My guess is that our cognitive modes have a similar split, so that we can handle all sorts of shades of meanings, nonliterality, etc., while the other apes are limited to the concrete, and absolute.

By: amphiox

amphiox — Fri, 11 Nov 2011 21:22:43 +0000

Why isn’t the positive relationship between brain and gut size in primates generally supportive of the original theory — assuming that humans do not follow this trend? Only humans cook/process food extensively with tools, so it would not obviously be a surprise that they were the only outlier.

Could one postulate that the relationship held true in humans up to the moment cooking was invented (the beginning of brain enlargement in the human lineage predates the earliest evidence for use of fire and cooking), but then the advent of cooking caused the “rules to change”, decoupling the brain-gut relationship, leading to human brains getting even bigger while gut size stayed constant, thus pushing humans into being the outlier?

By: edelauna

edelauna — Fri, 11 Nov 2011 14:43:52 +0000

Not to undermine the seriousness of the issue, but I would think that obesity discussions are off topic here.

Wouldn’t the gut that processes, breaks down and extracts energy from our food be different than the “gut” i.e. Omentum which stores energy.

The goal of the study is to determine if humans sacrificed an energy extraction ability compared against other species.

By: Alex

Alex — Fri, 11 Nov 2011 09:28:03 +0000

@JMW regarding the ‘natural habitat’ of humans, if you were measuring body composition of an ant species that survived from the energy provided by domesticated aphids or the fungus it cultivates would you also go back and study only the ants that didn’t cultivate domesticates to be a more ‘natural’ study? While I agree it doesn’t make sense to use an extreme outlier population to define the norms of a species, I think we have to be careful what we call natural and unnatural.

By: Flavio Garboggini

Flavio Garboggini — Thu, 10 Nov 2011 23:22:49 +0000

The trade-off was less muscles , more brains . We are five times weaker than our cousins the big apes . The difference is in the chemistry of the muscles .

By: SP

SP — Thu, 10 Nov 2011 10:57:44 +0000

Why isn’t the positive relationship between brain and gut size in primates generally supportive of the original theory — assuming that humans do not follow this trend? Only humans cook/process food extensively with tools, so it would not obviously be a surprise that they were the only outlier.

By: Jayarava

Jayarava — Thu, 10 Nov 2011 09:10:34 +0000

Cooking. That’s how we extract more energy from our food that any other animal. Cooking makes food easier to digest.

By: Karin Isler

Karin Isler — Thu, 10 Nov 2011 07:42:24 +0000

Unortunately, there is to our knowledge no published value of body fat content in a natural population of human (e.g. hunter-gatherers). BMI data are available, but the predictive power of BMR for body fat content is weak. It would be great to have such data, but they may be difficult to obtain (measuring in living individuals would require calibration with a few cadavers first, which is ethically problematic). From non-quantitative reports is seems, however, that temporal fat storage is abundant also in natural populations of humans.
The 14-26% are however not from obese people, but healthy, fit, younger adults. males is about 15%, females about 25%. Obese would mean much more, 30-50% or more.
Also, keep in mind that the non-human primate values are also not from natural populations, but usually from zoo animals, that may be rather slim from an illness, or rather fat from lack of training. This induces a high amount of error variation. We completely agree that to assess the case of primates, further studies with better samples are needed.

By: JMW

JMW — Wed, 09 Nov 2011 20:49:13 +0000

I have to ask…what population of humans were used to establish that 14-26% of body weight is made up of fat? As Carol notes, western populations (especially that of the U.S.) are obese. What needed to be measured was the percentage of body weight made up of fat in humans in their “natural habitat” – i.e., before we developed agriculture, animal husbandry, scientific farming, etc.

By: eyebeam

eyebeam — Wed, 09 Nov 2011 19:49:46 +0000

Humans don’t have smaller guts – they’ve extended them outside their bodies, through technological means.