Is the Ledi Jaw the Missing Link in Human Evolution?

Did God say, “Let us evolve man into our own image . . .”?

The Ledi jaw puts the human stamp on the evolutionary map much earlier than any other fossil. At least that’s what evolutionists are saying. Touted as the transitional form they need to span a pesky gap, the Ledi jaw has been classified as a species of Homo, the genus to which we belong. Paleontologists reporting in Science describe a number of human features that distinguish it from australopithecine apes. They believe this as-yet-unidentified human species fits somewhere in our evolutionary lineage but much earlier than any other Homo fossil.

The fossil, catalogued as LD 350-1, consists of the bottom portion of a left lower jawbone and five teeth. It was found in 2013 by Chalachew Seyoum, a student working with paleontologists William Kimbel and Brian Villmoare. They were working in the Ledi-Geraru region of Ethiopia’s Afar Triangle, about 12 miles from where the original Lucy—Australopithecus afarensis—was discovered.

The Lucy Connection

An extinct knuckle-walking ape, “Lucy” is generally depicted strolling about East Africa 3 million years ago on her two supposedly arched feet with tiny teeth smiling from her gorilla-like face and tiny brain. That image has created an imaginary place for Australopithecus afarensis in the human lineage. Homo fossils have also been found in East Africa. But until now there has been a big gap between the presumed appearance of Homo at around 2 million years and the latest evolutionary appearance of afarensis at around 3 million years. When, evolutionists have wondered, during this million-year gap did humanity’s ape-like ancestors develop whatever it is that makes them human enough to be called Homo? Villmoare says his team is arguing that the Ledi jaw links Lucy to the earliest humans, tracing “the most important transitions in human evolution.”1

Mind the Gap

The Ledi jaw (LD 350-1) has been assigned an age of 2.75 to 2.8 million years. By evolutionary reckoning, that would make it 400,000 years older than the oldest known Homo fossil (AL 666-1) but 200,000 years younger than Lucy’s youngest East African kin.2 “Previously, the oldest fossil attributed to the genus Homo was an upper jaw from Hadar, Ethiopia, dated to 2.35m years ago,” explains Kimbel, referring to the modern-appearing fossil maxilla known as AL 666-1, which Kimbel himself identified as Homo habilis in 1997.3 “So this new discovery pushes the human line back by 400,000 years or so,” he says, “very close to its likely ancestor.”4

“The Ledi jaw helps narrow the evolutionary gap between Australopithecus and early Homo,” Kimbel claims. “It's an excellent case of a transitional fossil in a critical time period in human evolution.”5 Furthermore, Kimbel’s associates report, in a separate paper, that animal fossils found in the same sediment layer as the Ledi jaw suggest the environment in which its owner lived had changed from forest to grassland. They therefore surmise that a change in the environment may somehow explain the selective advantage of developing a more human type of jaw, possibly paving the way to becoming human.6

If accepted by the evolutionary community at large, this discovery will add weight to the position of those who believe humans originated in East Africa. Proponents of South Africa’s Australopithecus sediba for a place as “oldest human ancestor” with an assigned age of 1.977 ± 0.002 million years will have to count this discovery their loss, as from an evolutionary point of view this new East African Homo fossil’s older dates and presumably primitive smile supersede it in the evolutionary race to become human.7

Humanity’s East African Roots . . . or Branches?

Celebrated by the simultaneous publication of three articles in two major scientific journals, an East African evolutionary origin for the human genus soared to the top of the charts as headlines announced the Ledi jaw was not only the oldest human but also a transitional form. “This narrows the time period in which we can now focus our search for the emergence of the human lineage,” explains Kimbel. “It’s very much a transitional form, as would be expected at that age. The chin looks backwards in time. But the shape of the teeth looks forward.”8

The combined studies in Science and Nature purport to link the Ledi jaw to a “younger” East African member of the human genus, Homo habilis OH-7, now reconstructed by paleontologist Fred Spoor. Homo habilis fossils consist of a confusing jumble of fragments about which there is no consensus among evolutionists. The signature (“holotype”) Homo habilis fossil is an East African specimen called OH-7 dated at 1.8 million years old, yet it bears little resemblance to AL 666-1, especially now that it has been reconstructed anew with a more “primitive” shape to its jaw.

Spoor determined that OH-7 had a larger brain (729 to 824 milliliters) than ever before found in Homo habilis.9 Paradoxically, however, its reconstructed dental arcade is longer and narrower than previously thought, suggesting that its jaw may have jutted forward quite a bit. Until now AL 666-1, at 2.3 million years, was considered the oldest Homo. However, the jutting jaw on the OH-7 habilis is a “primitive” feature, while the AL 666-1 upper jaw has a curvature much like that of a modern human.

“AL 666-1 is simply too modern to be the ancestor of Homo habilis, which means Homo habilis has to have deeper roots than AL 666-1, extending back at least 2.3 million years,” Spoor says.10 Therefore, even though OH-7 is considered much younger than AL 666-1, Spoor says early Homo jaws varied a lot and concludes that OH-7’s Homo habilis ancestors must have been a vital link in the human evolution story reaching back to the still more primitive Ledi jaw. He says, “By discovering a new fossil and re-analysing an old one we have truly contributed to our knowledge of our own evolutionary period, stretching over a million years that had been shrouded in mystery.”11 Spoor’s reconstruction was published to coincide with the studies reporting the Ledi jaw because with its primitive features, evolutionists suggest, the puzzle pieces for an East African human evolutionary origin have now handily fallen into place.

Here the LD 350-1 mandible is shown from multiple angles (medial, lateral, top, bottom in A–D; a close-up of the teeth in E; scale bars = 1 cm). Analysis of the teeth shows their shapes and proportions to be typical of humans, not australopithecines. And though LD 350-1 lacks the protruding chin of modern humans, the front of the fossil does have a distinctive keel where the two portions of the human mandible are fused together as well as other anatomical features normally seen in humans, but not in australopithecines. Image reproduced from B. Villmoare et al., “Early Homo at 2.8 Ma from Ledi-Geraru, Afar, Ethiopia,” Science 347, no. 6228 (March 5, 2015): 1352–1355, doi: 10.1126/science.aaa1343.

---

On the left (A) is a jawbone from Australopithecus afarensis, and on the right (B) is LD 350-1. This view shows several features that distinguish LD 350-1 from afarensis. The mental foramen (an opening for a major nerve and blood vessels, indicated by red arrows) opens toward the front of the afarensis mandible in a hollowed out region. LD 350-1 lacks this depression, and the foramen opens toward the back. The robust vertical ramus of the afarensis mandible begins behind the second molar (M2), but the base of LD 350-1’s ramus begins behind the third molar (M3), as seen in humans. Also, the afarensis jaw narrows toward the back, but like human jaws the LD 350-1 does not. Image reproduced from Supplemental materials, figure S5, in B. Villmoare, “Early Homo at 2.8 Ma . . .,” Science (5 March 2015) doi: 10.1126/science.aaa1343.

Is It Homo, or Not?

The Ledi jaw is not, of course, a whole jaw, or even a whole lower jaw (mandible). It is the horizontal part of the left side of a mandible and parts of five teeth—three molars and two premolars. There is no cranium by which to judge brain size nor any facial bones by which to assess the jut of the jaw or brow. There isn’t enough of the jaw available to judge the curvature of the mandible or enough to assess the robustness of the vertical portion that attaches the mandible to the rest of the skull. Thus, while it certainly must be either a human’s jaw or an ape’s jaw, many of the criteria needed to answer “what is it?” are simply not available.

Looking for identifying clues in the part of the jawbone that is preserved, the team noted it differed from Australopithecus afarensis. Though its size is consistent with the smallest afarensis jaws, it lacks numerous features common to all afarensis mandibles and teeth. Specifically, the bony opening (mental foramen) through which a major nerve and blood vessels emerge near the chin is not located in the normal afarensis position12 but rather in the position most commonly seen in both archaic and modern humans. The Ledi jaw lacks a hollowed-out depression on the jaw behind the premolars, something all afarensis have.13 Though the mandible’s vertical ramus is not present, its base is set farther back than it is in afarensis, in the position ordinarily seen in archaic humans.14 The jaw’s overall proportions match those of humans, not afarensis, and it lacks the constricted dental arch of afarensis. The tooth anatomy fails to match that of known afarensis specimens in many respects, and the overall slimness, shape, and wear pattern of the teeth match that seen in humans. And though like afarensis the Ledi jaw lacks the protruding chin of most modern humans,15 this feature varies considerably among archaic humans, so not having a prominent chin isn’t really diagnostic of an evolutionary relationship with the extinct ape, particularly in the face of the jaw’s many human, non-australopithecine anatomical features. Furthermore, though its chin does not protrude, the Ledi jaw does have the typically human midline keel where the two halves of the mandible are joined together at the chin.16

Thus, while too incomplete to make a definitive judgment, this fossil appears to fit within the normal range of human variation, justifying its probable identification as Homo. It is unfortunate that the descendants of Adam and Eve, thanks to evolutionary biases, have long been subdivided into multiple species of Homo instead of simply varieties of Homo sapiens. It is likewise unfortunate that, also due to evolutionary thinking, it is possible for paleontologists to “count as Homo” fossils that may be too fragmentary, sparse, and distorted to accurately identify. Nevertheless, though there is not enough left of the Ledi jaw’s owner to know what variety of human he or she was, it is not unreasonable to think he or she was a person, an archaic human.

A Transitional Form?

Could the Ledi jaw’s owner have been a transitional form? No. Evolutionists strain to see something ape-like in the array of Homo traits in the Ledi jaw because its position in the fossil record is so “far back” they think it must be their much sought-after transitional form. Since it lacks a protruding chin no one would suggest this fossil belonged to a modern human, but the lack thereof does not demonstrate that it is Australopithecus afarensis or an ape descended from it or even a less-evolved part of the human lineage. The relatively chinless jaw is simply not typical of modern humans. Nothing about this fossil indicates that its owner still had one foot in the ape-camp and was only in the process of evolving into a full-fledged human.

The Ledi jaw’s bid to be Homo or an early transition to Homo rests largely on the fact that its assigned dates place it in the desired gap between the ape Lucy and archaic varieties of humans. Had its host sediment been dated substantially older, its human features would likely have been ignored or explained away. Evolutionists have been known to dismiss fossil evidence of very early Homo, no matter how similar to modern man, if the stratigraphically assigned dates are too old to fit into the evolutionary schema.

The Ledi jaw wouldn’t even be close to being the oldest “Homo” if certain other fossil bones and footprints that are virtually identical to modern man were rightly recognized as Homo sapiens. For example, the Laetoli footprints are claimed to be 3.66 million years old and are virtually identical to modern man’s footprints, but no evolutionist considers them to be human because they are simply too old. The Kanapoi elbow fossil from the Lake Rudolf region of northern Kenya is the distal end of a humerus that is indistinguishable from Homo sapiens, but it is considered to be australopithecine in origin because it is also too old at 4.0–4.5 million years to be considered human. These assigned dates, based on a host of worldview-based unverifiable assumptions, blind evolutionists to the true identity of fossils like these. In truth, humans have been around since the sixth day of the Creation Week, the first two people having been created by God the same day as the land animals.

God’s Word is clear that God made all kinds of land animals as well as Adam and Eve on Day Six of the Creation Week about 6,000 years ago. He made both the animals and humans to reproduce and vary only within their created kinds, as we see them do today through the observational science of biology. God made the first man and woman in His own image (Genesis 1:26–27) on the same day as the animals. By His own eyewitness account preserved in the Bible, He created the first man from the “dust of the ground” (Genesis 2:7) and the first woman from Adam’s side (Genesis 2:18-23). He did not make them from ape-like ancestors through evolutionary processes.

So Old?

The authors report in Science that the Ledi jaw is 2.75 to 2.8 million years old. How they dated it is straightforward. This age is largely based on radiometric dating of the volcanic rock layers between which the site of the discovery is more or less sandwiched, though offset by a fault. The date is then derived after estimating the rate at which sediment accumulated for thousands of years. While this sounds simple enough, the unverifiable assumptions required to actually come up with these numbers are legion.

The fossil was found in a silt bed located between two layers (tuffs) of volcanic ash, the Gurumaha Tuff bed 10 meters below and the Lee Adoyta Tuff bed above. The thickness of the sediment between the two tuffs and the supposed time it took to accumulate was used to calculate a sedimentation rate of 14–30 cm per thousand years. The Gurumaha Tuff bed was Ar-Ar dated at 2.842 ± 0.007 million years (ago). At the estimated sedimentation rate of 14–30 cm per thousand years, the 10 meters of sediment took about 34,000–71,500 years to accumulate.17 So 2,842,000 years minus 34,000 or 71,000 years, and rounding the figures, gives an age for the fossil of 2.75–2.80 million years.

These calculations depend on lots of assumptions! To begin with they don’t really know how many sediment layers there are between the Gurumaha Tuff and Lee Adoyta Tuff beds because these two tuff beds are found in different adjacent sedimentary layer sequences separated by a fault. Because the Lee Adoyta Tuff bed yields a younger Ar-Ar age than the Gurumaha Tuff bed and because of the evidence of which way the layers moved on each side of the fault, they only know the Lee Adoyta Tuff bed is higher in the combined sequence than both the fossil-bearing silt bed and the Gurumaha Tuff bed 10 meters below it. Therefore, they can only guess at the total thickness of sedimentary layers between the two tuff beds! Then to estimate the rate of sediment accumulation, they have to assume that the sedimentation rate was similar to that similarly calculated for the apparently underlying Hadar Formation outcrop more than 10 km away to the southwest.

The researchers are of course assuming the sediments accumulated slowly. Yet, for all they know, these sediment layers could have accumulated within a few days or weeks! For starters, tuff beds do not accumulate calmly. They result from huge, violent volcanic eruptions, actually explosions, probably much more violent and larger than the May 1980 Mount St. Helens eruption. So each of these tuff beds could have accumulated in the space of an hour. And the overlying the siltstone bed containing the fossil is a meter-thick, cross-bedded, sandy conglomerate bed. This siltstone would have required rapid deposition by fast-moving waters; therefore, it would have been deposited within hours. And there are sandstone, claystone, and siltstone beds in the 10 meters between the Gurumaha Tuff bed and the fossil-bearing siltstone bed. Each of these sorts of beds, based on observational evidence (local storms and floods) and experimental evidence (sedimentation in flumes) in the present could have formed within hours to days. So much for 14 to 30 cm per thousand years!

But what about those so-precisely dated Ar-Ar ages for those tuff beds? Not only are the assumptions on which those dates are based unverifiable, some are demonstrably wrong. The 2.842 ± 0.007 million years for the Gurumaha Tuff bed was based on averaging the Ar-Ar ages obtained for each of 23 feldspar crystals. According to the published report, the feldspar crystals extracted from the Gurumaha Tuff and Lee Adoyta Tuff beds were dated by calibrating their Ar (argon) isotopic contents against standard samples of supposedly known age, in this case feldspar crystals from the Alder Creek Rhyolite in California with a reference age of 1.202 ± 0.012 million years, adjusted for the age of the Fish Canyon Tuff in Colorado of 28.201 ± 0.046 million years. However, the ages for these Alder Creek Rhyolite and Fish Canyon Tuff standards were determined by adjusting the Ar-Ar ages of their feldspar crystals to agree with the U-Pb ages of zircon crystals extracted from the same rocks! Now both these rocks formed from “granitic” magmas that explosively erupted at the earth’s surface, and it is well known that the zircon crystals in such “granitic” magmas could have formed well before the eruptions and well before the feldspar crystals. Therefore they may not be the same apparent age. Furthermore, Ar is a gas, which is independently present in erupting volcanic gases without being produced by radioactive decay of parent potassium, and it is thus incorporated in the resultant minerals that crystallize from the erupting magmas. For example, feldspar crystals extracted in 1996 from a lava flow that had erupted from Mount St. Helens in 1986 (and so were observationally only 10 years old) yielded a K-Ar age of 350,000 years! In other words, nearly all the Ar gas in those feldspar crystals was not from radioactive decay of parent potassium (K). So how do we know that most of the Ar gas in the feldspar crystals extracted from the Gurumaha Tuff and Lee Adoyta Tuff beds and that in the Alder Creek Rhyolite and Fish Canyon Tuff “standards” was not also inherited from volcanic gases and is not due to radioactive decay of parent potassium?

Clearly all of this radioactive dating work depends on assumptions that are completely unverifiable or demonstrably wrong. The initial Ar contents of the feldspar crystals are not known, yet Ar not derived from radioactive decay is known to be inherited by the crystals when they form. And the decay rates of the parent potassium and uranium are known to not have been constant but faster in the past.18 (Read more about it in “Radiometric Dating: Back to Basics,” “Radiometric Dating: Problems with the Assumptions,” and “Radiometric Dating: Making Sense of the Patterns.”)

Thus, if one doesn’t know the starting conditions for these radioactive “clocks” and how fast these “clocks” ticked in the past, then how can they be trusted to tell the time—the ages—of these crystals and their host rocks?

Who, What, When, How?

So when did the owner of LD 350-1 walk the earth? The historical record in Genesis enables us to know it was sometime after the global Flood, which occurred about 4,350 years ago, and the subsequent dispersion from Babel. And nothing that can be concluded from the scientific data swirling about the Ledi jaw truly disputes that.

Who was the Ledi jaw’s owner? If, as it appears from the fragmentary evidence, the jaw belonged to a person, that person was merely a variant of modern Homo sapiens and thus our ancestral relative descended from Noah and his three sons after the Flood. And where did the Ledi jaw’s owner come from?

Humans did not originate in East Africa. Humanity began with Adam and Eve about 6,000 years ago in Eden and got its second start after the global Flood, but not in East Africa. The jaw’s owner or equally human forebears must have traveled to Africa after the confusion of languages at Babel, where Noah’s descendants stubbornly remained for a time. Those people who eventually emigrated from Babel to post-Flood Africa would have found a climate different from that of today.

What kind of place was it? Owing to the recent Flood and resulting unstable climate, the LD 350-1 probably lived in a much wetter Africa than today, in a climate that was rapidly changing. And a wetter climate could have well provoked locally catastrophic sediment accumulation between explosive volcanic eruptions unlike any occurring in the region today. The fossils sharing LD 350-1’s host sediment offer some clues about the ecology of the time. By comparing the mammals buried nearby to those in 182 different modern African national parks, game reserves, and protected areas including habitats that are open versus closed and wet versus dry, the researchers reasonably suggest the Ledi jaw’s owner lived in an open savannah grassland. But that doesn’t mean the jaw’s owner was a descendant of Lucy on an evolutionary path to personhood!

The Path to Personhood or Life After Babel?

Evolutionists feel compelled to identify fossils like LD 350-1 according to their presupposition that humanity evolved over millions of years from lower animals through various lineages. And given the extremely fragmentary, distorted, and incomplete nature of some of the fossils that are sometimes classified as Homo, it is important to point out that not everything that gets called Homo really is! However, all humans—all true members of Homo—are descended from Adam and Eve. The evolutionary determination to subdivide varieties of humans into various species is based on evolutionary claims, when in reality all humans would best be called Homo sapiens regardless of their variations. Nevertheless, we are stuck with the terminology that calls the descendants of various people descended like us from Adam and from Noah via the dispersion from Babel by names that imply they are unrelated. Truly, however, when it comes to a fossil like this one, the real question should not be “where in the evolutionary history of humans does it fit?” but rather “does it fit within the norms for human beings or not?” Though limited by its incompleteness, analysis of LD 350-1 suggests it belonged to a person.

But several things can be said with absolute certainty. First of all, the fossil is not 2.75–2.80 million years old, since the Earth is only about 6,000 years old and the global Flood occurred about 4,350 years ago. Claims to the contrary are biased by unverifiable, worldview-based assumptions. Secondly, it is not a transitional form, intermediate between Australopithecus and Homo. It is only by superimposing evolutionary presuppositions on this fossil that anyone can interpret it as a transitional form. God created all the kinds of land animals and Adam and Eve on the sixth day of the Creation Week, each designed to reproduce and vary only within its created kind. Adam and Eve were created in the image of God, him from the dust of the ground and her from a portion of Adam’s body. They did not evolve, and neither did their descendants.

The sediments of Africa—East or South—will never reveal humanity’s roots, though they may on occasion yield parts of a long-dead person who inhabited the post-Flood world as well as extinct animals like “Lucy” that also lived in that world. But viewing the fossils and sediment layers through unverifiable presuppositions about a human evolutionary path requiring millions of years sadly distorts our understanding of who we are and where we came from. We know from God’s Word that all people who have ever lived are descendants of Adam, and, except for the sinless Son of God Jesus Christ, all people have inherited not only Adam’s physical humanness but also his sinful nature. Yet through Jesus Christ God grants us the grace through faith to have a wonderful future, eternal life, in a place without death and sin, with Him. While we explore humanity’s history, we would be wise to also ponder our personal future and place our faith and trust in our Creator and Savior.