Embryology is the study and analysis of embryos. Ancient Greek philosopher, Aristotle, was the first to study biology systematically, including embryology. Through observation and logic, Aristotle was the first to describe that embryos emerge from undifferentiated material.
Centuries later, Charles Darwin ran with Aristotle’s link between embryology and evolution. In the Origin of Species, Darwin argued –
“[The] leading facts in embryology … are second to none in importance.”
Ontogeny
Darwin developed the field of evolutionary embryology by fusing embryo observations of Karl Ernst von Baer and Fritz Müller and German biologist Ernest Haeckel‘s embryo drawings. Haeckel coined the now-famous term “ontogeny” and the phrase –
“Ontogeny recapitulates phylogeny.”
Ontogeny means the biological process of origination and development from fertilization, while phylogeny implies an evolutionary relationship based on apparent similarities.
In other words, a species’ embryological development (ontogeny) retraces the species’ entire evolutionary development (phylogeny). “Ontogeny recapitulates phylogeny” is like a re-run movie of the species’ evolutionary history within each embryo.
Phylogeny
Phylogeny represents family relationships comprising Earth’s biosphere – graphically illustrated as a tree. While life’s first common ancestor is at the root, the trunk and branches represent its descendants’ successive lineages.
Diverging branches at the tree nodes indicate a split, a speciation event, from a single ancestral lineage. The most recent species to emerge top each branch. Darwin’s “slight, successive,” but now extinct, transitional links form the tree branches.
Similarities
Similarities drive the development of phylogenies. If different species share common ancestors, descendants will share similarities inherited from those ancestors – known as homologies.
In the Origin of Species, Darwin explains how embryology and homology are evidence supporting his theory of common ancestry–
“We have distinct evidence in their embryological, homologous [similarities], and rudimentary structures, that within each kingdom all the members are descended from a single progenitor.”
Common ancestry explains these embryonic similarities: in other words, present-day embryonic similarities between species demonstrate relatedness to a common ancestor.
Scientific Validation
As a subcategory of Evolution and Science, evidence from embryology is essential for validating the theory of evolution scientifically.
Testing the Evidence
To understand how evidence from the embryology research evidence challenges the theory of evolution, click to read the following posted articles –
Each article will describe what evidence was found and why it scientifically draws into question the validity of the theory of evolution, using the reporters own words.
Darwin Then and Now is an educational resource on the intersection of evolution and science and the challenges facing the theory of evolution.
Refer to the Glossary for the definition of terms.
