Many years ago I was working on a project that, if I recall correctly, used the basic idea of the mouse-elephant curve to test out some statistical feature of reality or some such thing. Or the reverse. Either way, the point is I was using the mouse-elephant curve data.

What is the mouse-elephant curve? This:

You take all the mammals from mouse to elephant, and plot their metabolic rate or, if you like, brain volume, or any other metric, against body mass. You may or may not log an axis. The final result is supposed to be a straight line that approximates all the points. Then, you can measure how “off” any given species is by calculating its residual, or, how far off the line it is. One well known outcome of this procedure is the term “relative brain size” which shows that humans have ginormous brains compared to everything else on the mouse-elephant curve, even though they do not have the largest absolute brain size. (Never mind that cebus monkeys have larger relative brains.)

Anyway, I was working on this and talking about it with my friend Mark Pagel who is a statistics expert and a biologist, and he said something like, “That’s OK, but this is all theoretical, the mouse-elephant curve is made up.”

“What ever do you mean,” I asked.

“The metabolic rate scales to mass the way it does because body surface area scales allometrically to mass, right?”

“Ah, right… so?”

“How many of the animals on the mouse elephant curve have ever been measured for body surface area?” he asked.

“Uh…. eleven?”

“Zero, I’d bet.”

And that is when I realized that we know noting about anything.

Think about this for a second. You can find decades old texts explaining that mammals use XY chromosome compliments to determine sex. But where was the database for all mammals that showed the karyotype for each species? Nowhere. No one had done that. We probably had humans, mice, all the other lab animals of which there are probably about a dozen species, and the farm animals, of which there are probably fewer than a dozen species. That might seem like a good sample, but almost every farm mammal is a bovid, then you add horses, then you add close relatives in the old world murid family, and some closely related primates. Who knows, maybe they had more than that. But there could easily have been some subset of mammals that had independently and subsequent to their split from other mammals evolved a different chromosomal system. (There actually are multiple systems in mammals if you count ALL the mammals, but I’m speaking here of placental mammals.)

OK, maybe that is not easy to imagine, but it is possible to imagine.

The thing is, when it comes to organismic biology, we have made a huge mistake. Lots of research was done on a relatively small number of species, then rather suddenly, the fields of ecology and organismic biology were sidelines and everything became genetics. Genetics is nice and all, but it is not possible to directly answer every single question with just genetics.

This is why I was happy to see the beginnings of a project to cat scan all the cats, and along with the cats, all the other vertebrates.

I quickly add that even though the project is billed as scanning all the verts, and has in its various forms been called “scan all the frogs” or “scan all the vertebrates” etc, it is not that at all. At most, this project will scan a large but incomplete sample of genera, not species. And it really is a problem that they are claiming that they are scanning everything when they simply are not, because this will cause people to think this job is getting done when it is not.

Also, they are scanning a minimal number in each group, and only the available museum specimens. Museum collections are notoriously biased and there may be other problems with 3D morphology as well. Ultimately, a really useful project will scan a full range of development, multiple individuals at each stage, both sexes, etc. And, of I’m sure the folks doing this project understand this. And, eventually this may get done.

I wonder if it will be possible to use these scans to develop surface area estimates for several species of mammal ranging in size from, say, a mouse to an elephant? Of course not … there are no preserved elephats, or for that matter, any large mammal, so all of those critters are not part of this “scan everything” project…. πŸ™


The resulting 3D renderings will be uploaded to an existing digital depository, MorphoSource, created by Doug Boyer, an evolutionary anthropologist at Duke University in Durham, North Carolina, where they will be freely available for research in fields such as comparative anatomy, evolution, developmental biology, and biomimetics.

You can find out more about the project by clicking here, and depending on if you have a subscription, get either a summary or a more detailed accounting.


  1. #1 Li D
    August 25, 2017

    Question for knowledgable readers.
    Is there a simple method to accurately determine surface area?
    Weight and volume are easy peasy but its doing my head in trying to think of a simple foolproof methodology.
    Obviously things like fur or feathers complicate a calculation.
    And some species might have a very high surface area for special reasons. Like a ballooning spider.
    Any help appreciated. Thanks.

  2. #2 Richard Simons
    August 26, 2017

    Li D: dip them in paint and determine the change in weight? πŸ™‚

  3. #3 Li D
    August 27, 2017

    #2 Thats a damn clever idea. Thankyou.

  4. #4 Lionel A
    August 27, 2017

    Li D #3

    #2 does not overcome the fur & feathers problem though.

    Surface area of an animal with feathers almost becomes a problem involving fractals (ever carried out macro-photography of a feather) β€” now there is an idea.

  5. #5 Lionel A
    August 27, 2017

    Many other threads of interest in Richard Dawkins’ book The Ancestor’s Tale β€” review which should be studied quietly for it could be a long read but well worth the effort.

    One of the interesting ‘brain size’ discourses is to do with the seemingly disproportionate proportion of brains used to deal with senses through organs and body parts of particular utility to the owners, like hands with humans and and the nose and whiskers of burrowing animals.

    Given one of Dawkins’ diversions in this book, as mentioned in the review, it is probably fortunate that Dawkins put this book to bed before the advent of Trump as POTUS.

  6. #6 Greg Laden
    August 27, 2017

    Dipping in paint is a great idea for individuals within a species. Between species, the surfaces may vary too much.

    I would suggest 3D surface topography with scanners and then basic 3D software.

    Right,the proportion of total brain volume as function of different areas’ enlargement matters a great deal. Thus, brain size comparisons at some point need to be done within higher-order but not too-higher order taxonomic groups (i.e., within simian primates, or within major groups of rodents, etc.)

  7. #7 Wow
    August 27, 2017

    Emulsion or water based? Matt or silk?

    To be a little serious, you need to shave them first. Which they may object to a bit. And you’d need a lot of different sizes of bespoke safety razor!

  8. #8 Raucous Indignation
    August 27, 2017

    That’s true of Medicine too. We medical types used digoxin for heart failure for more than a hundred years. Over that time the predominant cause of heart failure changed from rheumatic valvular heart disease to ischemic cardiomyopathy. When I was but a wee doctor, everyone with heart failure form ischemic cardiomyopathy was prescribed digoxin, but there was little data for its use in that setting. All the cardiologist knew this and knew the history of the changing cause of heart failure. They even taught that to all the young doctors, but digoxin was still widely used. It took a long time for the science to catch up to the common dogma.

    Now we just paint the failing heart. Water-based semi-gloss finishes are preferred unless contraindicated.

  9. #9 Wow
    August 27, 2017

    Wouldn’t that be the dogma having to catch up with the science? The dogma was “use digoxin”. The science said “The cause is different to the one this was tested against”, but the dogma would not condone looking again.