Related Experiment Video
Updated: Jul 5, 2026
08:12
Micro-dissection of Enamel Organ from Mandibular Incisor of Rats Exposed to Environmental Toxicants
Published on: March 29, 2018
Intraspecific variation in M1 enamel development in modern humans: implications for human evolution
1Department of Archaeology, University of Sheffield, Sheffield S1 4ET, England, UK. p.mahoney@sheffield.ac.uk
Journal of Human Evolution
|April 29, 2008
Summary
Modern human molar enamel development shows cusps form at different rates and thicknesses, influencing tooth mechanics. Enamel secretion rates increase from inner to outer layers, with some individual variations noted.
Area of Science:
- Paleoanthropology
- Developmental Biology
- Dental Morphology
Background:
- Understanding enamel development is crucial for reconstructing hominoid evolution and function.
- Individual cusp formation timing and enamel thickness vary significantly across primate species.
Purpose of the Study:
- To document enamel development timing, sequence, and thickness in modern human lower first molars (M(1)s).
- To compare these findings with existing data from modern and fossil species.
- To investigate the relationship between enamel formation rates, thickness, and molar morphology.
Main Methods:
- Analysis of 15 unworn permanent lower first molars (M(1)s) from modern human juveniles.
- Documentation of enamel development for individual cusps (protoconid, hypoconid, metaconid, entoconid).
- Comparison of data with published literature on modern and fossil species.
Main Results:
- Enamel crown formation initiated in the protoconid and completed in the hypoconid.
- Protoconid and hypoconid exhibited significantly longer formation times and thicker enamel than metaconid and entoconid.
- Enamel secretion rates increased from inner to outer enamel, with one case showing an anomalous trajectory possibly linked to illness.
Conclusions:
- Differences in cusp formation times, initiation, and completion correlate with enamel thickness and molar mechanics.
- The observed slow molar formation in modern humans may reflect extended growth periods.
- The relationship between enamel formation rates and thickness appears consistent across several primate taxa.
Related Concept Videos
01:15Teeth
The formation of teeth, also known as odontogenesis, is a complex process that begins in utero, around the sixth week of embryonic development. There are three stages to this process: the bud stage, the cap stage, and the bell stage.
In the bud stage, the tooth germ (an aggregation of cells) starts to form in the developing jawbone. During the cap stage, the tooth germ differentiates into enamel organ, dental papilla, and dental sac, which will later develop into the tooth's enamel, dentin and...
In the bud stage, the tooth germ (an aggregation of cells) starts to form in the developing jawbone. During the cap stage, the tooth germ differentiates into enamel organ, dental papilla, and dental sac, which will later develop into the tooth's enamel, dentin and...
02:31Synteny and Evolution
John H. Renwick first coined the term “synteny” in 1971, which refers to the genes present on the same chromosomes, even if they are not genetically linked. The species with common ancestry tend to show conserved syntenic regions. Therefore, the concept of synteny is nowadays used to describe the evolutionary relationship between species.
Around 80 million years ago, the human and mice lineages diverged from the common ancestor. During the course of evolution, the ancestral chromosome underwent...
Around 80 million years ago, the human and mice lineages diverged from the common ancestor. During the course of evolution, the ancestral chromosome underwent...
02:55The Evidence for Evolution
Genetic variations accumulating within populations over generations give rise to biological evolution. Evolutionary changes can result in the formation of novel varieties and entire new species. These changes are responsible for the diverse forms of life inhabiting the planet. The evidence for evolution suggests that all living organisms descended from common ancestors.The collection of fossils within sedimentary rocks give a record of common ancestry and often depicts the history of evolution.
01:38Limits to Natural Selection
Organisms that are well-adapted to their environment are more likely to survive and reproduce. However, natural selection does not lead to perfectly adapted organisms. Several factors constrain natural selection.For one, natural selection can only act upon existing genetic variation. Hypothetically, redtusks may enhance elephant survival by deterring ivory-seeking poachers. However, if there are no gene variants—or alleles—for redtusks, natural selection cannot increase the prevalence of...
01:24Evolution of New Traits in Microbes
Microorganisms evolve rapidly due to their large population sizes and short generation times, often exhibiting measurable changes within days under laboratory conditions. Natural selection acts on standing genetic variation, enabling the retention and amplification of beneficial traits that confer fitness advantages in changing environments.Adaptive Pigment Regulation in RhodobacterIn Rhodobacter, a genus of purple non-sulfur bacteria, light-harvesting pigments such as bacteriochlorophyll and...
02:37Gene Duplication and Divergence
The seminal work of Ohno in 1970 popularized the idea of gene duplication and divergence. DNA sequence comparison studies reveal that a large portion of the genes in bacteria, archaebacteria, and eukaryotes was generated by gene duplication and divergence, indicating its critical role in evolution.
The duplicated copies of the gene are called Paralogs. Paralogs with similar sequences and functions form a gene family. Across several species, a large number of gene families are characterized.
The duplicated copies of the gene are called Paralogs. Paralogs with similar sequences and functions form a gene family. Across several species, a large number of gene families are characterized.