Wednesday, June 14, 2017

The Oldest Fossils of Homo Sapiens as Evidence for Evolution

Having debated scientific creationists and intelligent-design proponents who deny the evidence for evolutionary science, I have thought a lot about what counts as evidence for evolution, and about whether any evidence could settle this debate.  I have been thinking more about that in recent weeks when the journals Nature and Science have published articles reporting the discovery of the earliest known Homo sapiens fossils and the identification of the genes responsible for the splitting of the Galapagos flightless cormorant from all other cormorants about two million years ago. 

One might think that evidence like this strongly supports evolution. But I doubt that any scientific creationists or intelligent-design proponents are going to change their minds because of this.  Why not?  Is there something wrong with the evidence?  Or is there something wrong with the critics of evolution such that they are not open to considering such evidence?  Do the critics have any fossil or genetic evidence that demonstrates how, when, and where the Creator or the Intelligent Designer created Homo sapiens or flightless cormorants?  Or would some of the critics say that the Creator or Intelligent Designer created separate "kinds" of animals and then allowed natural evolution to create separate species--including human beings and flightless cormorants--within the boundaries of those "kinds"?

First, consider the new fossil evidence for human evolution.  Articles in Nature have reported the discovery of the oldest known fossils of our Homo sapiens ancestors at a site in Morocco called Jebel Irhoud (Hublin et al. 2017; Richter et al. 2017; Stringer and Galway-Witham 2017).  An article in The New York Times summarizes these reports. 

These fossil skulls have been dated at about 300,000 years.  They are in the same sedimentary layer with flint blades for spears that have been burned with fire.  So there is evidence of the controlled use of fire and refined use of hunting tools.  Although these early Homo sapiens have the flat faces very similar to humans today, their brain structures are different in that these early human skulls are elongated rather than showing the distinctly round shape of human brain cases today.

Here we see the evolutionary steps in ancient human fossil skulls.  A is a skull found in Spain that is about 430,000 years old.  It is thought to be an early form of Neanderthal.  It has the characteristic Neanderthal brow-ridge.  But it also has the smaller brain size of earlier ancestors

B is a late Neanderthal skull that is about  60,000 to 40,000 years oldAlthough Neanderthal is no longer believed to be a direct human ancestor, there is evidence of hybridization from the mating of Neanderthal and human beings, so that the human genome today has some Neanderthal genes.  

C is one of the Jebel Irhoud fossils, dated at around 350,000 to 280,000 years old, which is thought to represent an early form of Homo sapiens.  The face has the delicate and flat features characteristic of modern humans.  But the braincase has an older form--an elongated shape rather than the more rounded form of the modern human braincase.

D is a Homo sapiens fossil that is approximately 20,000 years old, which shows the rounded braincase.  This rounded braincase could indicate some distinctive traits in the modern human brain that support the uniquely human cognitive capacities that constitute the human mind, but no one knows exactly what the shape and size of the human braincase means for human thought.

Notice that the dates for such fossils is always "approximate."  Dating fossils so far into deep history is always open to doubt.  As I have indicated in a previous post, creationist critics of evolution like Ken Ham argue that there can be no absolute proof in "historical science" (based on what we can only speculate happened in the deep past) as opposed to "observational science" (based on what we can all see in the present or judge from records of the recent past).  So here, Ham would say that his "biblical worldview" tells him that these fossils cannot be older than 6,000 years, because that is the age of the Earth. 

The dating of the Jebel Irhoud fossils was done by thermoluminescence: assuming that the flint blades were burned in a fire, heating those blades produces light that is detectable in the laboratory, and that light indicates the accumulated radiation dose since the blades were first burned, which then can date the blades.  Since the blades were found in the same sedimentary layer as the fossil skulls, the thermoluminescence dating of the blades can date the fossils.  Someone like Ham can complain that there are a lot of dubious assumptions and inferences in this dating method.

Finding old human fossils in Africa seems to confirm Charles Darwin's belief that human evolution originated in Africa.  Although he did not have any human fossil evidence available to him at the time, he inferred that since the primate species most closely related to human beings--the great apes--were in Africa, that pointed to Africa as the likely place of origin for human beings.

In his article for The New York Times, Carl Zimmer says that these new human fossils discovered in Morocco "rewrites the story of mankind's origins."  That does indicate a problem, however, in that it illustrates how unpredictable and accidental these discoveries are.  It seems that the evolutionary story of mankind's origins is being rewritten every year or so when some new fossil is discovered.  The fundamental problem is the rarity of these human fossils and their fragmentary character.  For example, a few years ago, I wrote a post on the discovery of the only complete adult hominid skull from the Early Pleistocene, which illustrates the how limited the human fossil record is.

But still there is enough of a fossil record that can be combined with comparative studies of human and primate genomes to trace at least a rough outline of the descent of the human species from common ancestors shared with the higher primates--particularly, chimpanzees and bonobos.

In fact, this paleontological and genetic evidence of human common descent from ancient primate ancestors is so persuasive that even many scientific creationists and intelligent-design proponents now must admit that the evolutionary account of human origins from primate ancestors is scientifically confirmed.  As I have indicated in some previous posts (here and here), creationists like Ken Ham and Todd Wood and intelligent-design theorists like Michael Behe accept the natural evolution of species at or below the taxonomic level of families.  For Ham and Wood, this is because the Creator did not separately create all species, but rather created all "kinds" of animals and plants, and then allowed natural evolution by natural selection to create separate species within these "kinds."  Behe is explicit in affirming that the evidence for the evolution of the human species from primate ancestors is compelling, and there was no need for intervention by an Intelligent Designer.  If biblical "kinds" correspond to "families" in modern taxonomical classification, as Ham and Wood say, then God created the family of Hominidae, which includes chimpanzees, bonobos, gorillas, orangutans, and humans.  The human species could have evolved naturally from some common ancestor shared with chimpanzees and bonobos.

So here it seems that the evidence of human evolution really does support Darwinian science in its rejection of the theory of special creation.


Hublin, Jean-Jacques, et al. 2017. "New Fossils from Jebel Irhoud, Morocco, and the Pan-African Origin of Homo sapiens." Nature 546: 289-92.

Richter, Daniel, et al. 2017. "The Age of the Hominin Fossils from Jebel Irhoud, Morocco, and the Origins of the Middle Stone Age." Nature 546: 293-96.

Stringer, Chris, and Julia Galway-Witham. 2017. "On the Origin of Our Species." Nature 546: 212-13.

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