Comparative embryology is the branch of

embryology Embryology (from Ancient Greek, Greek ἔμβρυον, ''embryon'', "the unborn, embryo"; and -λογία, ''-logy, -logia'') is the branch of animal biology that studies the Prenatal development (biology), prenatal development of gametes (sex ...

that compares and contrasts

embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...

s of different species, showing how all animals are related.

History

Aristotle Aristotle (; 384–322 BC) was an Ancient Greek philosophy, Ancient Greek philosopher and polymath. His writings cover a broad range of subjects spanning the natural sciences, philosophy, linguistics, economics, politics, psychology, a ...

was the earliest person in recorded history to study embryos. Observing embryos of different species, he described how animals born in eggs (

oviparous Oviparous animals are animals that reproduce by depositing fertilized zygotes outside the body (i.e., by laying or spawning) in metabolically independent incubation organs known as eggs, which nurture the embryo into moving offsprings kno ...

ly) and by live birth (

viviparous In animals, viviparity is development of the embryo inside the body of the mother, with the maternal circulation providing for the metabolic needs of the embryo's development, until the mother gives birth to a fully or partially developed juve ...

ly) developed differently. He discovered there were two main ways the egg cell divided: holoblastically, where the whole egg divided and became the creature; and

meroblastic In embryology, cleavage is the division of cells in the early development of the embryo, following fertilization. The zygotes of many species undergo rapid cell cycles with no significant overall growth, producing a cluster of cells the same siz ...

ally, where only part of the egg became the creature. Further advances in comparative embryology did not come until the invention of the microscope. Since then, many people, from

Ernst Haeckel Ernst Heinrich Philipp August Haeckel (; ; 16 February 1834 – 9 August 1919) was a German zoologist, natural history, naturalist, eugenics, eugenicist, Philosophy, philosopher, physician, professor, marine biology, marine biologist and artist ...

Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English Natural history#Before 1900, naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all speci ...

, have contributed to the field.

Misconceptions

Many erroneous theories were formed in the early years of comparative embryology. For example, German biologist and philosopher

proposed that all organisms went through a "re-run" of evolution he said that 'ontogeny repeats phylogeny' while in development. Haeckel believed that to become a

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

, an embryo had to begin as a single-celled organism, then evolve into a fish, then an amphibian, a reptile, and finally a mammal. The theory was widely accepted, then disproved many years later.

Objectives

The field of comparative embryology aims to understand how embryos develop, and to research the inter-relatedness of animals. It has bolstered

evolutionary theory Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certai ...

by demonstrating that all

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

s develop similarly and have a putative common ancestor.

References

* Comparative Embryolo

Retrieved 5/21/14 * Embryolo

Retrieved 5/21/14 * Comparative Embryology: The Vertebrate Bo

Retrieved 5/22/14 * Embryolo

Retrieved 5/22/14 * Evidence for Evoluti

Retrieved 5/22/14 * Comparative Studies Insigh

Retrieved 5/23/13

External links

Medpedia Article
{{Webarchive, url=https://web.archive.org/web/20210421142517/http://wiki.medpedia.com/Comparative_Embryology , date=2021-04-21 Embryology

History

Misconceptions

Objectives

See also

References

External links