How Does Embryology Provide Evidence For Evolution?

Evolution is the study of how different types of living organisms adapt and change over time. New species continually emerge while others go extinct in response to fluctuating environmental conditions.

Embryology and evolution evidence work in tandem to support the theory that all life evolved from a common ancestor, possibly answering questions like why you had a tail before you were born.

In the mid-1800s, Charles Darwin and **Alfred Wallace** independently concluded that inherited variations in traits, such as a bird's beak shape, may provide better odds of survival in a given niche. Organisms without the advantageous variation are less likely to survive and pass on their genes.

Since the heyday of Darwinism, considerable scientific evidence has emerged supporting the theory of evolution, including embryology, although the mechanisms of mutation and change are more complex than previously understood.

Theories, such as the theory of evolution, are evidence-based ideas widely held by the scientific community. According to Charles Darwin in Origin of the Species, organisms descend and diversify from one common ancestor. Organisms change and adapt over time as a result of inherited physical and behavioral characteristics that are passed down from parent to offspring.

Through the process of natural selection and survival of the fittest, certain traits are more likely to be inherited than other traits.

Embryology is the study and analysis of embryos. Evidence of an evolutionary common ancestor is seen in the similarity of embryos in markedly different species. Darwin used the science of embryology to support his conclusions.

Embryos and the development of embryos of various species within a class are similar even if their adult forms look nothing alike. For instance, chicken embryos and human embryos look similar in the first few stages of embryonic development.

These early similarities are attributed to the 60 percent of protein-coding genes that humans and chickens inherited from a common ancestor.

Evolutionary developmental biology ("evo-devo") dates back to Alexander Kowalevsky's discovery in the 19th century that embryonic stages of development aid in the classification of organisms. Kowalevsky suggested that sea squirts called tunicates should be classified as chordates instead of mollusks because tunicate larvae have notochords and form neural tubes, making them more like chordates and vertebrate embryos. DNA analysis of the tunicate genome has since proven Kowalevsky correct.

German scientist Ernest Haeckel is known for the ideas of "biogenetic law" and "ontogeny recapitulates phylogeny." Haeckel's drawings of embryos suggested that an organism recapitulates (repeats) stages of its evolutionary history during embryonic stages of development.

Haeckel's controversial comparative embryology drawings released in 1874 showed a developing human embryo passing through stages that resembled different animals, such as embryonic fish, chickens and rabbits.

The notion of recapitulation drew plenty of critics, notably Karl von Baer, who also took a disliking to Darwin's ideas. Embryologist von Baer stressed the differences between vertebrate and invertebrate embryonic development that refuted Haeckel's conclusions.

Modern evo-devo experts like Michael Richardson agree there are similarities in the embryonic development of related species, but mainly at the molecular level.

Darwin's theory of biological evolution noted that all vertebrates have gill slits and tails in early stages of embryo formation, even though these features may be lost or modified in the adult-form phenotype.

For instance, human embryos have a tail that becomes the tail bone. This pattern indicates that all vertebrates stem from a common ancestor that developed that way, and everything diverged from there.

Many embryology and evolution questions can be answered through the study of comparative anatomy. Homologous structures in embryonic development suggest that ancestral structure was maintained as things diversified.

Examples found in comparative anatomy include the forelimbs of humans and the flippers of a whale, which supports the idea of common descent. Although a human arm and bat wing look different, the process of embryonic development is similar.