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

(system) #1
It looks like Homo naledi was around at the same time as modern humans.
This is a companion discussion topic for the original entry at https://biologos.org/blogs/deborah-haarsma-the-presidents-notebook/why-a-new-discovery-about-homo-naledi-has-far-reaching-implications-for-human-evolution

The moral law and socialization
(Jay Johnson) #2

Thank you for the excellent introduction to H. naledi. It spurred a little digging of my own, which turned up a couple of recent articles in New Scientist: one that discussed the age of H. naledi, and another that discussed its tiny but relatively advanced brain.

I have a question for @DeborahHaarsma and Dr. Falk that I hope they can answer for me.

Let me make sure I understand the basics. The H. naledi fossils are about 300,000 years old, which is roughly 100,000 years before anatomically modern humans appeared. Some speculate that the species might be as old as several million years, although that is unknown. H. naledi exhibits a strange mix of features, but it definitely has human-like hands and feet. It has a small brain, but definitely shows development in Brodmann Area 45, part of Broca’s area, which is linked to speech in modern humans. There is also a general expansion of the bottom surface of the frontal lobes, a region associated with empathy. Now, the researchers in the second article, who presented the findings just mentioned, speculate that these brain developments probably explain H. naledi’s burial of its dead, which is sophisticated (though not “symbolic”) behavior for a “small-brained” species.

My question is this: It sounds to me like H. naledi represents possibly the first known step in the reorganization of the human brain for greater communication and social abilities. Is that a fair statement?

Thank you!

[MOD CC @Jimpithecus @DarrelFalk]

(Darrel R Falk) #3

Thanks, Jay, for your follow-up reading and helpful comments and question. With regard to timing, Chris Stringer, a leading British paleontologist, says the following in the Nature summary cited in the posting: "The find shows there’s much to discover in Africa, which remains largely unexplored, Stringer says. At around 300,000 years ago, there were probably at least three kinds of humans across the continent, including early Homo sapiens, and H. naledi, he says. ‘Who knows what else might be out there?’ "

With regard to the analysis of the brain impressions on the skull, the “New Scientist” article you cite is summarizing discussions at a scientific meeting. Since none of the work has been submitted for publications and there is even a diversity of opinion among the investigators, it is too early to make hypotheses about the communication skills of Homo naledi. Some of the scientists are still skeptical about whether the bones were even purposely disposed of.

I also want to emphasize the mosaic nature of its body. Chris Stringer (again) in the Nature summary states the following: "The date is “astonishingly young for a species that still displays primitive characteristics found in fossils about 2 million years old”, says Chris Stringer, an anthropologist at the Natural History Museum in London. The brain of H. naledi came close in size to that of very early members of the Homo genus, and of ancient australopiths — and was only slightly larger than that of a chimpanzee. Its curved fingers and its shoulder, trunk and hip joints also seem ancient, Stringer says. “Yet the wrist, hands, legs and feet look more like those of Neanderthals and modern humans, and the teeth are relatively small and simple, and set in lightly built jawbones.” "

(Jay Johnson) #4

Yes, I suppose you’re right to tap the brakes in advance of published results. Dang you scientists and your overabundance of caution! Please rush to judgment faster! Haha.

I appreciate your response, and the further information and elucidation of the meaning. I will be curious to see the response to the published paper, when it eventually appears. Even after that, it could be a while before a consensus of opinion forms. Ah, well. Can’t rush the process…

(Larry Bunce) #5

The survival of an ancient species alongside later species is not unusual in the world. H nadeli seems well-adapted for life on the ground as well as life in trees, so it would have been at least as likely to survive as chimpanzees. If this species had first appeared 200,000 years ago, it might require a re-evaluation of the evolutionary lines leading to humans. If the various hominids were able to interbreed, the features that make up modern humans were in our gene pool long before we became H sapiens.

(Darrel R Falk) #6

Larry, I think your final point is quite important. We know there was some interbreeding that took place between Neanderthals and Sapiens and that at least some of the genetic variants introduced into our lineage at that point were helpful to survival in the higher latitudes, for example. Similarly we know there was interbreeding between Denisovans and Sapiens in Asia and at least some of those variants were also helpful (e.g. a variant that helps Tibetans to thrive at high altitudes is derived from Denisovans.) Here is a great article that summarizes this.

However, what about back in Africa, before the migration into Europe and Asia? We don’t have good data on that yet, but it would be surprising if that did not occur as well. Here are the final couple of sentences from a fine Scientific American article by Michael Hammer.

Many loose ends remain. Yet one thing is clear: the roots of modern humans trace back to not just a single ancestral population in Africa but to populations throughout the Old World. Although archaic humans have often been seen as rivals of modern humans, scientists now must seriously consider the possibility that they were the secret of H. sapiens’ success.

(Jay Johnson) #7

Hmmm. Just trying to make sure I understand both of you, so set me straight where necessary. I don’t think Larry’s point is technically correct, if he had in mind the interbreeding between humans and Neanderthal/Denisovans. As I understand Dr. Falk, this took place after Sapiens had migrated into Europe and Asia, which was long after anatomically modern humans appeared 200,000 years ago. Actually, though, the point about interbreeding coming after we already had left Africa is somewhat more interesting to me, because the features that make up present-day humans continued to be added to our gene pool well after we already had become cognitively modern humans.

Do you mean H. sapiens interbreeding with as-yet-undiscovered hominids prior to migrating out of Africa, or do you mean H. erectus interbreeding with other hominids? Just seeking some clarity.

(Darrel R Falk) #8

First of all, I want to clarify that there were likely only a few (at most) interbreeding events with Neanderthals or Denisovans which contributed to certain populations within the Sapiens lineage. The data on this are pretty solid (see the first of two books I discuss below).

However, onto the excellent question you pose. Since speciation is a gradual event occurring over many generations (See Dennis Venema’s “Evolution Basics” series), it is not possible to say precisely when H. sapiens became H. sapiens. What we do know is that 200,000 year-old skeletal remains that are extremely similar to ours have been found in eastern Africa. We have no paleontological details about our lineage for the couple of hundred thousand years prior to that… As I mentioned above, most paleontologists today think that there would have been other cousin species present and that some interbreeding may well have taken place. if so, our genetic characteristics may well have been shaped in part through these interbreeding events. If you (or others reading this) would like to learn more about current thinking on our genetic heritage, I recommend the book, “Ancestors in Our Genome,” by Eugene E. Harris. For people who are wondering why a Christian would even be thinking in terms of common descent from ancient ape-like ancestors, I recommend the book, “Human Evolution” by evangelical Christian, Graeme Finlay. Neither of the books are intended to be only for geneticists, but a good understanding of basic biology is certainly an asset. The latter book is the most important book I know of for laying out the very strong evidence for God having created humans through an evolutionary process that includes descent from earlier primates. It’s beautifully written, but not an easy read for the non-biologist.