Sunday, April 10, 2005

Interpretation

I read an article about how those we believe to be the homo habilis had a complex social structure. How did we come to this conclusion? We know that they cared for their elderly, because we found the skull of a toothless "old" (he was forty) man who "would not have been able to chew the raw meat and fibrous plants which made up the creatures' normal diet." Why couldn't he just cook his meat? Because "the Dmanisi hominoids had no fire."

Here's the problem: how do we know that they had no fire? We don't. The way we "know" that they had no fire is because we assume that fire was first used by the homo erecti. Thus, anything that uses fire is defined as homo erectus or later. If we do find a homo habilis or earlier using fire, we assume that it was made by early homo erecti, or that they themselves were early homo erecti.

In a similar way, if we were to find, for example, a spear point inside a dinosaur fossil, the idea that humans and dinosaurs lived together would be rejected out of hand. Rather, with no evidence to the effect, we would assume that the fossil had been contaminated, because our pre-existing interpretation skews how we view the evidence.

The point is that most people view evidence as objective. They are "facts" and facts are objective and unchanging. The reality is that facts must be interpreted. The normal test used in the scientific method to help deal with interpretation is the simplicity test (which is in itself a form of bias). The simplicity test means that the most simple explanation is the one to be preferred. Which is the most simple explanation? That the homo habilis had learned how to cook.

5 Comments:

Blogger Noumenon said...

These scientists in your head are pretty simpleminded folk. You've got to wonder why they bother with the excavating and the arguing and the theorizing if at the end of it they're just going to "assume" fire was first used by homo erectus.

"we assume that fire was first used by the homo erecti. Thus, anything that uses fire is defined as homo erectus or later."

Does this sound like the kind of thought process an intellectually serious person would subscribe to? It's like saying, "Biologists assume that only ducks have webbed feet, so they would define platypuses as ducks." If the skull has no brow ridge and the inner ear bones are different, they're not going to call it homo erectus just because it's got its femur in a fire pit.

The first guy who finds it may assume that it's homo erectus, but that's not where the process stops. His job is to look for things he's not expecting. He probably wishes the skeleton would be homo habilis -- it would be great for his career to prove that homo habilis used fire.

(Here's another BBC article about the discovery of fire. Note the effort they go to to make sure the species really was using fire and not just camping where things burned -- mapping things around the site that weren't burned, checking whether the layers were far enough apart to be caused by seasonal wildfires. That's what scientists do, they don't only assume. Also, check out how excited they are to have another example of controlled fire being used before 500,000 BCE -- this is only the third they've ever found, and the earliest is 1,000,000 BCE. So I think they rule out fire in this 1.77 million-year-old based on the gradual trailing off of evidence. The same way you might assume that Egyptians 10,000 years before Tutankhamen wouldn't have writing. Part assumption, part induction.)

"The simplicity test means that the most simple explanation is the one to be preferred."

That's for two explanations that make the same predictions. For example, the simplest explanation of why galaxies spin is that gravity pulls them around the center, but scientists are going with a theory that posits enormous amounts of invisible dark matter instead. It's not simpler, but the simpler explanation can't explain galaxies spinning as fast as they do. If someone came up with a theory that explained the spinning and didn't require the dark matter, the simplicity test would be gratefully applied. (The dark matter theory is better than nothing, though -- even though it's unlikely, it opens up new areas of research like whether this dark matter causes gravitational lensing or not. It's testable.)

10:42 AM  
Blogger Octavo Dia said...

"they're not going to call it homo erectus just because it's got its femur in a fire pit."

Unless those darn homo erecti were cooking one up! Yet most of the time, all the evidence we have is a femur in a fire pit. Complete human skeletons are few and far between.

"He probably wishes the skeleton would be homo habilis -- it would be great for his career to prove that homo habilis used fire."

However, it is outside of the realm of interpreted possibility so if he didn't reject it, his colleagues would. Just like finding a spear point amount dinosaur bones would be interpreted as "contamination."

"So I think they rule out fire in this 1.77 million-year-old based on the gradual trailing off of evidence…. Part assumption, part induction."

The problem arises because of the cumulative effect of assumptions. How do they know that the skeleton is 1.77 million years old? You can't carbon date anything that old (I believe that's around 300+ half lives), and our other dating techniques test rocks, not (formerly) living things. Other ways of dating include dating the strata the bones are in and dating the fossils which surround it. Due to things like floods, which can wipe away dozens of layers in a few hours, the only place that the entire geological column exists is in a textbook. Thus, to determine which strata is which, we assume that the fossils will remain relatively homogenous throughout the world. We date the rocks using one of our other dating methods, only using the expected (assumed) age of the fossils as a rough guide. Thus our assumption about the age of the fossils is used to shape our dating of the rocks, and the dates we assign to the rocks is given to the fossils. The fossils are then used to date the strata, which we then use to date the bones.

"For example, the simplest explanation of why galaxies spin is that gravity pulls them around the center, but scientists are going with a theory that posits enormous amounts of invisible dark matter instead."

I actually don't have a problem with dark matter. All it means is that the only stuff we can "see" is that which emits a fair amount of radiation. Thus stuff like planets, comets, asteroids, moons, etc., don't show up, and if our solar system is any guide, there's quite a bit of it floating around. I do have a problem with dark energy—it just smacks of ether to me.

12:16 AM  
Blogger Octavo Dia said...

"These scientists in your head are pretty simpleminded folk."

Not simple minded, just closed minded in an area where I think they should be open minded. I recognize the need to be closed minded, but my interpretation of the evidence disagrees with theirs.

8:28 AM  
Blogger Noumenon said...

"However, it is outside of the realm of interpreted possibility so if he didn't reject it, his colleagues would. Just like finding a spear point amount dinosaur bones would be interpreted as 'contamination.'"

I completely understand that progress in science sometimes only happens when the old scientists die off. I also understand that sometimes people can only see what they're expecting when the evidence is right in front of their face. However, I am hearing you talk about scientists as though they always, automatically do this because they are blindly "close-minded."

Those are not the scientists I know. They are close-minded the way you and I are close-minded; we believe we're open-minded, and yet certain possibilities seem almost impossible for us to believe. (Plus the added conflict of interest from their paychecks, but that's what tenure is for.)

For example, homo habilis taking care of its old people is a "highly unusual" and "totally new" hypothesis, and yet they're entertaining it, based on this one piece of evidence. They're going to scrutinize the heck out of that skull, and propose all kinds of other interpretations, but they're going to allow that maybe homo habilis had the social structures of homo erectus, even though all the other evidence said they were primitive.

I can't say they would do the same for the speared dinosaur, because of the heavy political implications of that (though I could see them throwing it out there to people saying, "This looks just like a speared dinosaur, can you tell me why it's not?") This, though, is a totally internal debate for them, and all they really care about is the truth between homo habilis and homo erectus. (Or maybe, it'll bring them closer to realizing they're all the same species. It's easy for me to be open-minded about that, though, since I haven't spent years studying all the differences between the various species. Try being open-minded on whether Lutherans and ELCA Lutherans are the same breed.)

On fossil strata, the age might be suspect but the order isn't, so whether it's 1.77 million or 177,000 years old, it's still twice as far down as the earliest evidence we have of people using fire.

1:28 AM  
Blogger Noumenon said...

Here's another BBC article on ancient use of fire. Maybe homo habilis did know how to cook. Scientists are open to that.

Note how they analyze bones to find out whether they've been cooked or not. Electron Spin Resonance (ESR) tests on the free radicals tells whether the organic structures in the bone were decomposed by heat, and even how long and hot the heat was applied. That is the kind of work that inspired my defense of scientists in the comments to this post. They don't just "assume" that fire was first used by homo erecti. They have multiple sources of evidence: excavating, chemical analysis, and skeleton remains, and it all has to point in the same direction. If we had find after find like these two that point to an earlier date for fire, I think scientists would have no problem admitting that homo habilis had fire.

3:14 AM  

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