Rosa Rubicondior: Creationism Refuted - What Caused Our Teeth To Shrink Until 690,000 Years Before 'Creation Week'

Changes in Diet Drove Physical Evolution in Early Humans | Dartmouth

A recent discovery by palaeoanthropologists, led by researchers from Dartmouth College, Hanover, New Hampshire, USA, highlights the stark difference between how a teleological thinker—such as a creationist—imagines evolution works and how it actually proceeds. The study found that the teeth of ancient hominins evolved over a period of some 700,000 years in response to the increasing availability of soft, starchy foods, which began to replace the coarse, fibrous plant matter they had previously consumed.

A teleological thinker—someone who sees purpose and agency in natural processes—would assume that something *caused* the teeth to evolve in order to better process the new food. However, as the theory of evolution predicts, any variation that improves efficiency in food processing or reduces the now-unnecessary cost of growing and maintaining large teeth will be favoured by natural selection. Over evolutionary time, such traits become more common. In the case of archaic hominins, this meant their teeth gradually became smaller.

Teleological thinkers often make the mistake of believing that asking, "Who or what told the teeth they needed to change?" or "How did the teeth know they had to evolve?" is a meaningful challenge to evolutionary theory. To them, it seems reasonable to assume a supernatural intelligence must be involved.

This simplistic view of evolution is actively encouraged by creationist pseudo-scientists such as William A. Dembski and his colleagues at the Discovery Institute, who claim that the genetic information resulting from such optimisation must have been intelligently designed because it is "specified" for a purpose. Of course, at every stage of human evolution, the genetic information that produced a particular tooth shape was necessarily "specified" for that outcome. Dembski never discloses this to his audience, nor does he attempt to correct the teleological bias on which his movement depends.

An interesting aspect of this discovery is that the evolutionary change in this case was driven not so much by environmental change - the starch foods had always been there - as by a change in behaviour - a case of meme-gene co-evolution, using the term 'meme' in the original sense as coined by Richard Dawkins in The Selfish Gene, to mean a unit of cultural inheritance - the analogue of the gene in genetic inheritance.

What Did Our Ancestors Eat? The diet of early primates and hominins evolved over millions of years, shaped by changing environments, anatomy, and behaviour

Early simians (30–40 million years ago) likely ate fruits, leaves, seeds, and insects, similar to many modern monkeys.
Miocene apes (~0–10 million years ago), ancestors of humans and great apes, were mainly frugivorous, with some fibrous vegetation and occasional animal protein.
Early hominins (7–4 million years ago) retained a largely plant-based diet, including roots, seeds, and tougher vegetation. Their thicker enamel and robust jaws suggest adaptations to hard or abrasive foods.
Australopithecines (~~4–2 million years ago) had a varied diet—fruits, tubers, nuts, and grasses—and large molars suited for grinding fibrous plant matter.
Paranthropus species evolved extreme chewing adaptations for processing tough, low-quality plant foods, likely as fallback during lean periods.
Early Homo (~.5 million years ago onwards) began eating more meat and marrow, aided by stone tools. Over time, their teeth reduced in size, reflecting a shift to softer, more processed foods—possibly including those softened by cooking.

By around 700,000 years ago, this dietary evolution was well advanced, as shown in recent research linking reduced tooth size in hominins to increased consumption of soft, starchy foods.

The discovery of this progressive change in hominin dentition is detailed in a recent paper in Science, and is also covered in a Dartmouth College news item.

Changes in Diet Drove Physical Evolution in Early Humans
Hominins had a taste for high-carb plants long before the teeth to eat them.
As early humans spread from lush African forests into grasslands, their need for ready sources of energy led them to develop a taste for grassy plants, especially grains and the starchy plant tissue hidden underground. But a new Dartmouth-led study shows that hominins began feasting on these carbohydrate-rich foods before they had the ideal teeth to do so. The study provides the first evidence from the human fossil record of behavioral drive, wherein behaviors beneficial for survival emerge before the physical adaptations that make it easier, the researchers report in .

The authors analyzed fossilized hominin teeth for carbon and oxygen isotopes left behind from eating plants known as graminoids, which includes grasses and sedges. They found that ancient humans gravitated toward consuming these plants far earlier than their teeth evolved to chew them efficiently.

It was not until 700,000 years later that evolution finally caught up in the form of longer molars like those that let modern humans easily chew tough plant fibers.

The findings suggest that the success of early humans stemmed from their ability to adapt to new environments despite their physical limitations, says Luke Fannin, Guarini ’25, a postdoctoral researcher at Dartmouth and lead author of the study.

We can definitively say that hominins were quite flexible when it came to behavior, and this was their advantage. As anthropologists, we talk about behavioral and morphological change as evolving in lockstep. But we found that behavior could be a force of evolution in its own right, with major repercussions for the morphological and dietary trajectory of hominins.

Luke D. Fannin, lead author.
Department of Anthropology
Dartmouth College, Hanover, NH, USA.

Nathaniel Dominy, the Charles Hansen Professor of Anthropology and senior author of the study, says isotope analysis overcomes the enduring challenge of identifying the factors that caused the emergence of new behaviors—behavior doesn’t fossilize.

Anthropologists often assume behaviors on the basis of morphological traits, but these traits can take a long time—a half-million years or more––to appear in the fossil record, but these chemical signatures are an unmistakable remnant of grass-eating that is independent of morphology. They show a significant lag between this novel feeding behavior and the need for longer molar teeth to meet the physical challenge of chewing and digesting tough plant tissues.

Professor Nathaniel Dominy, corresponding author.
Department of Anthropology
Dartmouth College, Hanover, NH, USA.

The team analyzed the teeth of various hominin species, beginning with the distant human relative Australopithecus afarensis, to track how the consumption of different parts of graminoids progressed over millennia. For comparison, they also analyzed the fossilized teeth of two extinct primate species that lived around the same time—giant terrestrial baboon-like monkeys called theropiths and small leaf-eating monkeys called colobines.

All three species veered away from fruits, flowers, and insects toward grasses and sedges between 3.4 million to 4.8 million years ago, the researchers report. This was despite lacking the teeth and digestive systems optimal for eating these tougher plants.

Hominins and the two primates exhibited similar plant diets until 2.3 million years ago when carbon and oxygen isotopes in hominin teeth changed abruptly, the study found. This plummet in both isotope ratios suggests that the human ancestor at the time, Homo rudolfensis, cut back on grasses and consumed more oxygen-depleted water.

The researchers lay out three possible explanations for this spike, including that these hominins drank far more water than other primates and savanna animals, or that they suddenly adopted a hippopotamus-like lifestyle of being submerged in water all day and eating at night.

The explanation most consistent with what’s known about early human behavior, they report, is that later hominins gained regular access to underground plant organs known as tubers, bulbs, and corms. Oxygen-depleted water also is found in these bulging appendages that many graminoids use for storing large amounts of carbohydrates safely away from plant-eating animals.

The transition from grasses to these high-energy plant tissues would make sense for a species growing in population and physical size, Fannin says. These underground caches were plentiful, less risky than hunting, and provided more nutrients for early humans’ expanding brains. Having already adopted stone tools, ancient humans could dig up tubers, bulbs, and corms while facing little competition from other animals.

We propose that this shift to underground foods was a signal moment in our evolution. It created a glut of carbs that were perennial—our ancestors could access them at any time of year to feed themselves and other people.

Luke D. Fannin

Measurements of hominin teeth showed that while they became consistently smaller—shrinking about 5% every 1,000 years—molars grew longer, the researchers report. Hominins’ dietary shift toward graminoids outpaced that physical change for most of their history.

But the study found that the ratio flipped about 2 million years ago with Homo habilis and Homo ergaster, whose teeth exhibited a spurt of change in shape and size more suited to eating cooked tissues, such as roasted tubers.

Graminoids are ubiquitous across many ecosystems. Wherever they were, hominins would have been able to maximize the nutrients derived from these plants as their teeth became more efficient at breaking them down, Dominy says.

One of the burning questions in anthropology is what did hominins do differently that other primates didn’t do? This work shows that the ability to exploit grass tissues may be our secret sauce. Even now, our global economy turns on a few species of grass—rice, wheat, corn, and barley, Our ancestors did something completely unexpected that changed the game for the history of species on Earth.

Professor Nathaniel Dominy

Publication:
Luke D. Fannin et al.
Behavior drives morphological change during human evolution. Science 389, 488-493 (2025). DOI:10.1126/science.ado2359

Abstract
Dietary shifts and corresponding morphological changes can sometimes evolve in succession, not concurrently—an evolutionary process called behavioral drive. Detecting behavioral drive in the fossil record is challenging because it is difficult to measure behaviors independently from corresponding morphologies. To solve this problem, we focused on a puzzling behavior in the fossil record of some primates: eating graminoid plants. We report carbon and oxygen isotope ratios from fossil cercopithecid monkeys and integrate the data into a view of hominin dietary evolution, finding that changes in graminivorous behavior preceded corresponding changes in dental morphology by ~700,000 years. Decoupling diets and morphologies in time was conducive to determining when and to exploring why dietary changes helped to propel human evolution.

Luke D. Fannin et al.
Behavior drives morphological change during human evolution. Science 389, 488-493 (2025). DOI:10.1126/science.ado2359

© 2025 the American Association for the Advancement of Science.
Reprinted under the terms of s60 of the Copyright, Designs and Patents Act 1988.

The progressive reduction in tooth size observed in hominin fossils over hundreds of thousands of years is a clear example of evolutionary adaptation through natural selection. As early humans shifted from a diet of coarse, fibrous vegetation to softer, starchy foods—likely facilitated by cooking and food processing—large, robust teeth became less necessary. Individuals with slightly smaller teeth may have had a slight energetic advantage, investing fewer resources in growing and maintaining unnecessary dental tissue. Over many generations, these traits became more common in the population.

This gradual, adaptive change is exactly what evolutionary theory predicts: variation exists within populations, and environmental pressures shape which traits are favoured. There is no foresight, planning, or guiding hand involved—only differential survival and reproduction over deep time.

In contrast, creationist explanations, which rely on the assumption of intelligent design or supernatural intervention, cannot account for the stepwise, incremental nature of these changes. They ask teleological questions—such as “how did the teeth know to evolve?”—which misunderstand the basic mechanism of evolution. Fossil evidence like this undermines such views by showing a continuous, natural process requiring no designer, just ordinary biology playing out across vast timescales.

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