Why a New Discovery About Homo Naledi has Far-Reaching Implications for Human Evolution

| By on The President's Notebook

Homo naledi skeletal specimens. Credit: Lee Roger Berger research team. Fair use via CC 4.0.

It has been two and a half years since paleontologist Lee Berger and associates announced the finding of  a new hominin species, Homo naledi.  The discovery was remarkable in part because it comprised the most extensive set of hominin fossils ever found (over 1500 specimens from at least 15 individuals). BioLogos summarized those findings in two reports in September 2015. The fossils were discovered deep in a remarkable cave network a short distance from Johannesburg, South Africa.   

Homo naledi was a fascinating species. The fossils have a conglomerate of ancient and modern characteristics. Their skulls had only a tiny primitive-looking braincase.   Its shoulders and fingers bore a resemblance to the ancient three to four million year old genus, Ardipithicus; they would have been ideally adapted for swinging from trees. In contrast, other parts were not much different than ours. Their feet for example were exquisitely suited for walking in a manner resembling how we do it,  and they had a bone in the wrist which, structured like ours, enabled the thumb and index finger to efficiently grip against each other.  

Given this anatomical mosaic, paleoanthropologists projected the age of the bones would turn out to be about two million years.  They were wrong. As shown in a paper just released (see here for a summary), multiple labs using various cross-checking techniques have demonstrated that the fossils are only about 300,000 years old. So that’s one important find, but there’s more. Another collection of fossils (undated so far) has been discovered in a neighboring cave—one not directly connected to the first, but like that one, deep in the network and exceedingly difficult to get to.

Graphic depicting part of the Rising Star Cave where the Homo naledi fossils were discovered. Credit: Paul H. G. M. Dirks et al, http://elifesciences.org/content/4/e09561. Fair use via CC 4.0.

There is much mystery here. How did these individuals end up in these two very hard-to-reach caves?  Except for some bird and small rodent fossils, there are no other animal fossils in the first cave, so their bodies were almost certainly not brought into the cave by predators. Berger and his collaborators think the bodies were placed in the caves for burial which, if true, would be amazing for a species with a brain only about one third the size of ours. Given that our own species was just emerging in Africa about 300,000 years ago, it is also shocking to find that we likely co-existed with a cousin species—one which, even though they could walk much like us, had Ardipithicus-like adaptations for swinging from trees.

This is a wonderful time to be studying human origins. Scholars used to think that there was a slow steady progression of one single species after another becoming more and more human-like through time. That’s not the way it was at all. Although these fossils give no evidence for when H. naledi went extinct, it’s clear it was our contemporary in Africa for at least a little while. There also were at least several other hominin species outside of Africa at that same time.  Some members of our species migrated out of Africa to Eurasia about 70,000 years ago, only to find that Homo neanderthalensis and the related, but distinctive Denisovans were already there. At the same time, the primitive diminutive species, H. florisiensis, occupied an island in Indonesia, and H. erectus was in eastern Asia.  Meanwhile, back in Africa, we know from genetic evidence that, in addition to H. naledi, another unknown hominin species was present and interbred with our species as recently as 30,000 years ago. So our lineage shared life on this planet with a whole set of other species up until just a few thousand generations ago.

I have just finished reading Almost Human by Lee Berger, a book that engagingly documents all aspects of the H. naledi discovery and investigation. The book ends with an Epilogue by John Hawks who describes a recent visit in which Berger takes him to one more cave in the complex. Upon entering the cave, Berger picks up a fist-sized rock and shows it to Hawks. There, embedded in the rock, is a hominin jaw bone with several large, nickel-sized teeth—a new, still undocumented discovery just waiting to be analyzed. “Here we go again,” Hawks says as the book draws to a close, hinting that we’ll soon be hearing about one more new species.

Closing Note from Deb Haarsma:

So, it is now quite certain that there were many hominin species (at least six that we know about, but likely quite a few more) that were contemporaries of our own.  This raises some fascinating questions, such as “What makes humans unique from the other species?” and “Why did H. sapiens survive and thrive while the others went extinct?” Human exceptionalism is an active area of research and BioLogos scholars take various approaches. But the discovery of H. naledi does not call into question the biblical teaching that God created humans in his image.  

Nor does the discovery call into question the scientific reality that humans evolved and share a common ancestor with H. naledi. The headlines and quotes from scientists call the discovery “surprising” and “shocking”—and it is, in terms of understanding the development of anatomical features among hominins.  But in larger terms, it is not surprising at all. This is how evolution works. Multiple related species often develop around the same time. In contrast to the frequently used image of a short ape evolving in linear steps toward a tall human, many life forms show evidence of a "bush" of related species. The question of exactly which early species led to which later species can be fiendishly challenging to work out, but their common ancestry is clear. The date of H. naledi is an exciting discovery that helps us better understand how and when God brought about our family of species.  

Notes

Citations

MLA

Falk, Darrel. "Why a New Discovery About Homo Naledi has Far-Reaching Implications for Human Evolution "
http://biologos.org/. N.p., 11 May. 2017. Web. 22 October 2017.

APA

Falk, D. (2017, May 11). Why a New Discovery About Homo Naledi has Far-Reaching Implications for Human Evolution
Retrieved October 22, 2017, from http://biologos.org/blogs/deborah-haarsma-the-presidents-notebook/why-a-new-discovery-about-homo-naledi-has-far-reaching-implications-for-human-evolution

References & Credits

1. To read more about contemporary scholarly research into our uniqueness as a species, see The Creative Spark: How Imagination Made Humans Exceptional by Agustin Fuentes (2017), as well as The Secret of Our Success: How Culture Is Driving Human Evolution, Domesticating Our Species, and Making Us Smarter  by Joseph Henrich (2015) and Masters of the Planet: The Search for Our Origins by Ian Tattersall (2012).

 

About the Author

Darrel Falk

Darrel Falk is former president of BioLogos and currently serves as BioLogos' Senior Advisor for Dialog. He is Professor of Biology, Emeritus at Point Loma Nazarene University and serves as Senior Fellow at The Colossian Forum. Falk is the author of Coming to Peace with Science.

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