Monday, May 16, 2016

Book Review: The Human Advantage

Last Tuesday I faced a horrible dilemma as two books I'd been eagerly awaiting, Too Like the Lightning and The Age of the Em, both came out the same day.  Luckily I was nearly done with the book I'd been reading, The Human Advantage by Suzana Herculano-Houzel, so I could quickly finish that before moving on and I wasn't tortured by a third option of whether to just put it aside.

In some ways this book was a good complement to The Secret of Our Success since it's another book about humanity's place in the world.  But this one is much more about where we fit in with other species in terms of our brains and less about the story of how we got there.  The real meat of the book is how the author figured out a good way to measure the number of neurons in a brain and was able to do the first real comparisons across species as to the number of neurons in their heads.

The method was surprisingly simple as brilliant ideas sometimes are.  You can't just count the number of neurons in a small part of the brain and multiply because neuron density can vary quite a bit depending on where in someone's head you look.  The simple solution is just to stick a brain in a blender first.  Then you can sample and multiply to get a good count.  There's really more to it than that but that's the basic idea.

The interesting thing the author discovered is the way that the number of neurons in a brain varies with brain volume works very differently in primates than it does in pretty much all the other animals she looked at.  In most neurons are bigger in bigger brains and the number of neurons goes up as the 3/4 power.  But with primates neurons stay the same size and the brain volume and number of neurons are directly proportional.  The difference between 1 and 3/4 might not sound like much but different animals can vary in size but a factor of 10,000 easily which would give you a brain 10 times larger for one animal than another.

Another interesting discovery she was able to make was that the energy consumed by a brain is almost exactly proportional to the number of neurons in the brain, even though some brains have neurons that are much bigger than those in other brains.  She does on to describe the things about humans that let us get enough calories to support our huge brains in a chapter I would have found fascinating if I hadn't read The Secret of Our Success recently.

I did find a few annoyances.  The author made a big deal about the fact that the conventional wisdom was that human brains had 100 billion neurons but that she had discovered that humans really only had 86 billion.  Except that all her samples were from men between the ages of 50 and 70 and we know that humans lose neurons as they age to some extent.  And the largest of her 4 samples weighed in at 91 billion.  So we can't really be totally sure from her observations that the average number of human neurons isn't exactly 100 billion even before you consider reasonable amounts of rounding for a variable number.

The book was maybe longer than it needed to be and trying too hard to impress in places but I enjoyed it overall and I'm glad I read it.  There are a bunch of interesting facts about brains I haven't included here and another bunch of interesting anecdotes about how she got her hands on the different brains she examined.  So I'd recommend reading it but don't be afraid to skim.

Sunday, May 1, 2016

Eukaryotes and the Drake Equation

I bet a lot of the people reading this blog have heard of the Drake Equation but, as a recap, the idea is that given some assumptions you should be able to calculate how many alien civilizations there ought to be in the Milky Way.  There are a few problem with the way the equation is put together but in general it's hard make make assumptions strict enough that the galaxy shouldn't have lots of other civilizations.  And now that it's looking like most stars have planets that leads to the scary conclusion that maybe civilizations just don't last very long.

But thankfully I read a book recently that makes me a bit more hopeful.  A while ago I read Power, Sex, Suicide: Mitochondria and the Meaning of Life by Nick Lane which I really ought to have reviewed here because it was an excellent book.  It discusses how mitochondria allowed eukaryotic cells to become much larger than their forebears, the roll they plan in apoptosis or cell suicide, and how they effect how long various animals live.  But the important park in this blog post is how they were first created with one cell swallowing another and the two forming a symbiosis.

Without going into details (they're in the book!) it was sort of crazy that something like that could happen and result in a creature that was fit enough to survive.  I was recently looking at the timeline of life on Earth on Wikipedia and you can see that there.  The first simple cells appeared 4.1 billion years ago, just 400 million years after Earth got it's seas.  But it wasn't until 1.9 billion years ago, 2.2 billion years after life first appeared that we got eukaryotic cells.  So it looks like it took over 5 times as long for for complex cells to arise as it did for cells to in the first place.

If it had taken twice as long for simple cells to get going and the whole timeline of life on Earth was pushed back a half billion years then that wouldn't have been a big deal.  But if eukaryotes had taken twice as long to get going then the extra 2 billion years would push the arrival of complex life like us out to 6.5 billion years after the Earth formed by which point the sun will be hotter and there won't be liquid water on the surface any more.

So judging just by Earth's timeline we might go out into the wider universe to find that there are lots of bacteria out there but nothing big and complex enough to need a nucleus.  But of course all of this is still the thinnest speculation until we explore much more of the universe.

The very long run for SARS Covid 2

Many of the worst pandemics that afflict us are from pathogens that don't normally prey on humans.  Probably the most famous pandemic in...