The Efficiency of the Human Brain and AI

Fascinating post quoting Elon Musk on the efficiency of the brain and the potential efficiency of AI:

Well, we have a clear example of efficient power, efficient compute, which is the human brain. Our brains use about 20 watts of power, and only about 10 watts is higher brain function. Half of it is just housekeeping, keeping your heart going and breathing.

So you’ve got maybe 10 watts of higher brain function in a human, and we’ve managed to build civilization with 10 watts of a biological computer. Given that humans are capable of inventing general relativity and quantum mechanics, inventing aircraft, lasers, the internet, and discovering physics with a 10-watt meat computer, there’s clearly a massive opportunity for improving the efficiency of AI compute. Right now, even a hundred-megawatt or gigawatt AI supercomputer can’t do everything a human can do. But we already have the proof that true intelligence can emerge from just 10 watts. That should lead you to one conclusion, AI can get a lot more efficient.

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Steve Stewart-Williams explains his aversion to the term “Gender.”

Steve Stewart-Williams explains "Why I'm not a Fan of Gender." Excerpt from his upcoming bok, "A Billion Years of Sex Differences":

Many social scientists draw a distinction between sex and gender where, roughly speaking, sex refers to biological aspects of female and male, and gender refers to social aspects. ... I’m not a fan of the concept of gender, which I think confuses more than it enlightens.

There are several reasons for this. The first is that the term has multiple meanings. Sometimes gender refers to female–male differences that are (supposedly) shaped by nurture rather than nature; sometimes it refers to masculinity and femininity; sometimes it refers to psychological profiles that are more common in one sex than the other; sometimes it refers to widely held stereotypes of the sexes; sometimes it refers to the roles that society provides for females and males; sometimes it refers to people’s gender identity (their sense of themselves as a boy or a girl or a man or a woman); and sometimes it’s just a polite synonym for sex: a term that makes it clear that you’re talking about biological sex rather than the fun kind of sex. The profusion of partially overlapping meanings makes it difficult to know what people using the term are actually talking about. It’s like trying to juggle jelly.

A second reason I prefer not to partake of gender is that, even if we could agree on a definition, most of those on offer are profoundly flawed. Take, for example, the idea that gender refers to female–male differences due to nurture rather than nature. An initial problem is that this is invariably assumed rather than demonstrated; indeed, describing a female–male difference as a gender difference often seems to be a way to settle the nature–nurture issue by definitional stipulation rather than arguments and evidence. . . .

Other definitions of gender face similar problems. Consider, for example, the idea that gender refers to psychological profiles loosely linked to sex: Men tend to be stoic and assertive, for instance, whereas women tend to be caring and emotional. This definition is assumed by people who argue that there are multiple distinct genders, rather than just the two vanilla options of man and woman. Again, this doesn’t strike me as a useful way to construe things. The problem is that it involves imposing categories – even if more than just two – on what is actually continuous psychological variation. No two human beings have exactly the same psychological profiles, so the logical endpoint of this approach is that there are as many genders as there are human beings – and we’re really just talking about personality.

I've subscribed to Steve's excellent Substack for the past year and highly recommend it.

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How Much ATP Does a Human Body Produce Every Day?

Today I learned that the human body makes its weight in ATP (a key component of the Krebs cycle") every day. When I read this I wondered if it could possibly be true. Here's what Grok had to say:

My Query to Grok: Is it true that we make our body weight worth of ATP every day?

Yes, it's true. The human body turns over (produces and consumes) an amount of ATP roughly equivalent to its own body weight each day, though the exact figure varies by activity level and individual.

At any given moment, the body contains only about 250 grams of ATP (plus some ADP). However, ATP is rapidly recycled: it's hydrolyzed to ADP + phosphate to release energy, then resynthesized using energy from food. This cycle happens thousands of times per day per molecule.

Reliable sources estimate daily ATP turnover as:

    • 50–75 kg for an average adult (often cited as ~100–150 moles of ATP hydrolyzed and regenerated daily).

    • Around 50 kg in sources like Wikipedia.

    • ~60 kg in BioNumbers database.

    • Up to 100 kg or more during high activity in some physiology texts.

For a typical 70 kg person, this is approximately one body weight's worth per day at rest or moderate activity. During intense exercise, the rate can increase dramatically (e.g., up to 0.5–1 kg per minute). The key point is the enormous flux: even though net ATP storage is tiny—your cells are constantly churning through it to power everything from muscle contraction to brain function.

This fact is widely accepted in biochemistry and physiology textbooks and is often used to illustrate how dynamic cellular energy metabolism is.

Tutorial on the Krebs Cycle (Also from Grok):

The Krebs cycle, also known as the citric acid cycle or tricarboxylic acid (TCA) cycle, is a central metabolic pathway in cellular respiration that occurs within the mitochondria of eukaryotic cells, efficiently converting nutrients from carbohydrates, fats, and proteins into usable energy. It begins when acetyl-CoA—derived primarily from the breakdown of glucose via glycolysis—combines with oxaloacetate to form citrate, initiating a series of eight enzymatic reactions that systematically oxidize the molecule, releasing carbon dioxide as a byproduct (which we exhale) and generating high-energy electron carriers like NADH and FADH2, along with a small amount of ATP directly through substrate-level phosphorylation. These electron carriers then feed into the electron transport chain to produce the bulk of the cell's ATP via oxidative phosphorylation, yielding up to 38 ATP molecules per glucose molecule overall. The cycle is highly efficient, regenerating oxaloacetate to allow continuous operation, and it's tightly regulated by factors like ATP levels and enzyme inhibitors to match the cell's energy demands, playing a crucial role not only in energy production but also in providing intermediates for biosynthesis of amino acids, nucleotides, and other essential compounds.
 

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