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Our future, our universe, and other weighty topics

Thursday, June 29, 2017

Why Did They Call These Tiny-Brain Hominids “Almost Human”?

A recent book on paleontology is the book Almost Human: The Astonishing Tale of Homo naledi and the Discovery That Changed Our Human Story. The book is by two paleontologists named Lee Berger and John Hawks. They and their colleagues found some fossils of a species called Homo naledi.

So how does that fit into some scheme of human origins? On page 42 of the book, the authors have a diagram entitled, “A Depiction of the Family Tree of Hominin Species.” It's a quite wobbly-looking diagram, not something that should cause anyone to think that our scientists have human origins figured out very well. This is because the diagram is one of those “tree of ancestry” types of diagrams, but four of the nodes in the diagram are question marks.

The diagram makes these claims:

  • From Unknown Ancestor 1 there descended Paranthropus boisei, Paranthropus robustus, Austrolopithecus africanus, Austrolopithecus afarensis, and Unknown Ancestor 2.
  • From Unknown Ancestor 2 there descended Homo rudolfensis, Australopithecus sediba, Homo habilis, and Unknown Ancestor 3.
  • From Unknown Ancestor 3 there descended Homo erectus, Homo floresiensis, Homo naledi, and Unknown Ancestor 4.
  • From Unknown Ancestor 4 there descended modern humans, Neanderthals, and archaic African humans. 
So according to the diagram, there is not just one missing link, but four missing links. When you look at the diagram, it seems to have  quite a bit of arbitrary guesswork. If you do a Google image search for “Hominin family tree,” you will see other diagrams, some of which give a different story. The ancestry tree in an article at Britannica.com has even more question marks, having a total of 7 question marks, indicating seven missing links.

Credit: Britannica.com

The diagram in the Almost Human book puts Homo floresiensis in the left top of the “tree of ancestry,” claiming Homo floresiensis was close to being an offshoot of Homo erectus. A recent study rejects this positioning, claiming that Homo floresiensis has a completely different ancestry, and was an offshoot not of Homo erectus but Homo habilis. Given such a confusing hominid fossil record, with a large variety of different skulls found at different places around the world, it is no wonder that paleontologists often disagree with each other in drawing a tree of human ancestry.

Part of the uncertainty is because our paleontologists do not have what they would like to have. This is one of the dirty little secrets of modern evolutionary biology. Our evolutionary biologists do not have the DNA evidence they need to solidify the claims they make about human origins. The problem is that regular organic material rots in less than a few thousand years, and you can't get much DNA from a very old fossil bone. It has been estimated that the half-life of DNA is only about 500 years. So we don't have any adequate DNA evidence from Homo erectus or Homo habilis, which are claimed to be ancestors or evolutionary cousins of the human species. The oldest DNA from a claimed human ancestor is a scrap of DNA dating back 400,000 years. But this is only about 16,000 base pairs, and the human genome is 3.2 billion base pairs. Such a tiny scrap doesn't give you a hundredth of what you would need to genetically verify that such an organism was an ancestor of humans.

Imagine a trial in which the prosecution claimed that blood photographed at a crime scene is the blood of the person being tried. But imagine the blood was washed away by a thunderstorm before its DNA was checked, so no DNA match was made. That's the kind of position our evolutionary biologist is in. He really needs some complete Homo erectus DNA or Homo habilis DNA to back up his claims that these are human ancestors or human evolutionary cousins. But no such DNA exists, merely a rare scrap here and there.

We do have the complete DNA of modern humans and modern chimpanzees, and some argue that the similarity between these two implies that both had a common evolutionary ancestor. It is claimed that the protein-coding part of the human genome is 96% similar to the protein-coding part of the chimpanzee genome. But this refers to merely the building materials of proteins (amino acids), and is not based on a comparison of the full proteins, each of which has a 3D shape. No one knows for sure how proteins get their 3D shapes. This is the long-standing protein folding problem discussed here. When you look at the full proteins including their shapes, not just the amino acid building blocks specified in DNA, it turns out that chimpanzees and humans are not so similar. The scientific paper here is entitled “Eighty percent of proteins are different between humans and chimpanzees.”

Does the fact that hominid fossils can be arranged into a “tree of ancestry” diagram prove that they have an evolutionary relationship? Not really. Given any large random data set, and a person determined to show some “tree of ancestry,” it is usually possible for a “tree of ancestry” to be created. For example, if I go into the Yankee Stadium parking lot, and diligently start looking for cars that look like descendants of each other, I would be able to cherry-pick some cars and arrange them into a “tree of ancestry” showing what might look like a plausible evolutionary progression from one car model to another. But such a diagram (looking rather like the one below) would probably not be historically correct. 

But what about the fossils that Berger and Hawks found, the Homo naledi fossils? Are they, in fact, fossils of some species that was “almost human,” as the book title states? Not by a long shot. On page 193 of their book, the scientists finally give us an estimate of the brain size for the Homo naledi organisms corresponding to the fossils they found. It was about 560 cubic centimeters for a male, and about 450 cubic centimeters for a female. The average size of a male human brain is about 1350 cubic centimeters.

So far from being “almost human,” Homo naledi had a brain only about 41% of the size of the modern human brain. Which means that Homo naledi was apparently well short of being even half-human. So given that our paleontologists have written a book with the title Almost Human: The Astonishing Tale of Homo naledi and the Discovery That Changed Our Human Story, we must ask: why did they choose to call their book “Almost Human”? Is it because such a title would sell more copies than an accurate title such as “Not Even Half Human”?