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On H. naledi, Separating Fact from Interpretation

Homo_naledi_assembled_skull.jpg

The subject of human origins is a sensitive one, stirring up strong emotions on all sides. Most people come at the question with a pre-formed point of view about our ancestry and when they want the date of the appearance of the first human to be.

But that doesn’t mean they are free to superimpose their preferred point of view on the data, or view it only through lenses of their own prescription. That’s not the way science is supposed to be done.

Why am I, an advocate of intelligent design, arguing so passionately for objectivity in science? Because that’s actually what we are about — following the evidence where it leads.

I fear that the latest celebrated fossil find, H. naledi, will be used to further the agendas of those who have a stake in the issue. A certain denial of the evidence is possible. So is a certain overeager interpretation.

So what do I think of the H. naledi fossils?

I don’t know. It’s too soon to say. I tend to find the argument for the creature’s intelligence convincing, based on the apparently deliberate depositing of bodies in that isolated cave, but I am open to persuasion otherwise, if there is other evidence to account for it. I don’t know what the mixed traits, human and australopithicene, mean, or what to make of the small skulls. If the paleoanthropologists can’t agree, how am I to make an informed judgment? The age of the find may make it all moot. If H. naledi is less than 2 million years old, she will be younger than Homo erectus, with his almost completely human form. Then H. naledi becomes merely a curiosity, a side road traveled by some ancient hominin group.

Let’s let the evidence speak for itself.

What Does the Most Recent “Human” Fossil Find Actually Mean?

Before we begin, probably most of you have watched the crime shows CSI or Bones. These two shows leave the impression that all kinds of definite, factual information can be gathered from bones. That’s true, but there are limits. There are facts, and legitimate inferences. Then there is interpretation, and spin, the way these things are reported to advance an agenda.

What do we know for a fact or as a legitimate inference? Everything in italics below is a matter of interpretation.

1. Many bones were found in a nearly inaccessible cave in South Africa. They appear to be fossils with mixed traits. The shoulders and pelvis seem to be australopithicene in character, while the teeth, legs, and feet appear to be more like the genus Homo.

2. Many bones were found in that nearly inaccessible cave. This may be due to non-intentional natural causes, or perhaps the bones were intentionally placed there by someone (by their own species — who knows?). The latter would argue for some special care of the dead, and perhaps intelligence like ours (or not — for another point of view see an article by primatologist Frans de Waal in the New York Times). It also depends on whether there was ever another possible route into the cave, or some sort of natural disaster that collected them in one place.

3. Very few bones of small mammals or birds were found in the cave, which argues against both another previous form of access, or a natural disaster that swept them away.

4. The fossils represent many individuals, because multiple bones of the same type have been found.

5. The fossil skulls are small. How this is interpreted depends on the point of view of the interpreter.

What Don’t We Know?

1. How old are the fossils? This matters because if the bones are 3 million years old and from a single species, they would represent the oldest fossils with traits of our genus Homo, and traits of the australopithicenes. Under some interpretations, this might make them the missing link.

If the fossils are younger than 2 million years, the story remains interesting but not nearly so important. Why? Because that would make them younger than the oldest known Homo fossils, Homo erectus, whose morphology was almost exactly like ours. That would make Homo naledi an interesting side branch among hominins, but definitely not the missing link between us and an ape-like ancestor, if such a thing ever existed. (See our book Science and Human Origins.)

2. Does the find represent a single species with mixed traits, or is it a mixture of two species? The authors of the paper claim that all the fossils are definitely of the same species, with any differences due to sexual dimorphism and age. (Sexual dimorphism means the sexes look different from one another. Think of how gorilla babies, full-grown male silverbacks, and adult females look compared to each other.) Other scientists doubt that claim, and say the differences indicate separate species. See my post earlier this week.

This particular dispute may, at least, be resolved with more specimens and time for analysis. In some cases the bones are still articulated, and other bones can be pieced together. Can they be pieced together in two ways or only one? No one knows for sure yet, though there are strongly held points of view.

Now for My Interpretation of It All

1. What impact, if any, should this discovery have on our view of human origins? It depends on whether you are convinced common descent is true. If you already believe we came from a chimp-like ancestor, you will see this as confirmation.

2. If you doubt common descent, and/or have considered our arguments against the possibility of unguided evolution, nothing has changed. Intelligent design had to be involved. The basic mechanism of Darwinian evolution is still incapable of unguided evolution. And the question of whether we share an ancestor with chimps will not be decided one way or the other by this fossil find. Finding a fossil with intermediate traits does not mean there is a bridge from there to full humanity.

Fossils tell patchy stories. It’s like opening the pages of a book at random, a page at a time, sampling maybe ten brief passages. You may notice character names that appear on some of the pages. Certain events past and present may be suggested by what you read. Now you must write the plot of the book based on your snippets of information.

Let me ask you, how likely is it that what you write actually matches the plot of the book?

Image: Homo naledi, assembled skull, by Berger et al. 2015 [CC BY 4.0], via Wikimedia Commons.