Talk:K12 Human and Other Animal Development

From Embryology

About Discussion Page

This page is not intended to be used by students, though if you do find yourself here there are now secret answers to any worksheet questions. I use this page as a draft location to put links, information and references that may be useful on the actual page.


18th Century 2 theories

  • epigenesis - organs of the embryo are formed de novo (“from scratch”) at each generation (Aristotle and Harvey)
  • preformation - organs are already present, but in miniature form, within the oocyte or spermatozoa and “unrolled.” (Malpighi and 18th century scientists).


Other Species Stages

Chicken: Chicken stages | Hamburger Hamilton Stages | Witschi Stages

Rat: Rat Development Stages

Rabbit: Rabbit Stages

Fly: Fly Stages

Exercise Documents

  1. Exercise 1 - Embryo Size File:K12_Comparative_Embryology_Exercise_1.doc | File:K12_Comparative_Embryology_Exercise_1.pdf
  2. Exercise 2 - Embryo Stages File:K12_Comparative_Embryology_Exercise_2.doc | File:K12_Comparative_Embryology_Exercise_2.pdf
  3. Exercise 3 - Embryo Stages File:K12_Comparative_Embryology_Exercise_3.doc | File:K12_Comparative_Embryology_Exercise_3.pdf

Online Resources


These references are not suitable for K12 level of this topic. I will identify a good simplified review, when I find one.

Morphological evolution and embryonic developmental diversity in metazoa

Development. 2010 Feb;137(4):531-9.

Salazar-Ciudad I. Source Grup de Genòmica, Bioinformàtica i Evolució, Departament de Genètica i Microbiologia, Universitat Autònoma de Barcelona, Cerdanyola del Valles, Spain.


Most studies of pattern formation and morphogenesis in metazoans focus on a small number of model species, despite the fact that information about a wide range of species and developmental stages has accumulated in recent years. By contrast, this article attempts to use this broad knowledge base to arrive at a classification of developmental types through which metazoan body plans are generated. This classification scheme pays particular attention to the diverse ways by which cell signalling and morphogenetic movements depend on each other, and leads to several testable hypotheses regarding morphological variation within and between species, as well as metazoan evolution.

PMID 20110318

Gavin Rylands de Beer: how embryology foreshadowed the dilemmas of the genome

Nat Rev Genet. 2006 Nov;7(11):892-8.

Horder TJ.

Source Department of Physiology, Anatomy and Genetics, University of Oxford OX1 3QX, UK.


Gavin de Beer is remembered, at best, as a shadowy figure among those who gradually built up our current view of evolution and the role of genetics. This view derives from the Modern Synthesis - the recognition that emerged in the 1930s that genetics can adequately explain Darwinian evolution and speciation through natural selection. I argue that de Beer's theories of embryology had a crucial role in the Modern Synthesis, and that his work indirectly continues to influence how we think about the genome, evolution and developmental biology.

PMID 17047688 Nat Rev Genet.

Good discussion of historic background to comparative embryology in relation to evolution.

Mark Q. Martindale: shedding new light on developmental diversity

Int J Dev Biol. 2011;55(3):237-42. Hejnol A. Source Sars International Centre for Marine Molecular Biology, Bergen, Norway.


The Saint-Petersburg Society of Naturalists awarded the 2009 "Alexander Kowalevsky Medal" to Mark Q. Martindale, Professor of Organismal Biology at the University of Hawaii and Director of the Kewalo Marine Laboratory, Honolulu. This international award inaugurated first in 1910 was re-established only in 2001. In memory of Alexander Onufrievich Kowalevsky, it is awarded to outstanding zoologists and embryologists who have made great contributions to the field of embryology and developmental biology from an evolutionary perspective. Mark Q. Martindale has worked on a wide range of animals, mostly marine species, in contrast to many evo-devo researchers who often use a single "well-established" model organism. His work demonstrates how the insights gained by studying less "popular" animal taxa not only complement, but also significantly enrich our knowledge of the evolution of metazoan body plans and of the events that have led to the current animal diversity.

PMID 21710431

Darwinian evolution in the light of genomics

Nucleic Acids Res. 2009 Mar;37(4):1011-34. Epub 2009 Feb 12.

Koonin EV. Source National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD, USA.


Comparative genomics and systems biology offer unprecedented opportunities for testing central tenets of evolutionary biology formulated by Darwin in the Origin of Species in 1859 and expanded in the Modern Synthesis 100 years later. Evolutionary-genomic studies show that natural selection is only one of the forces that shape genome evolution and is not quantitatively dominant, whereas non-adaptive processes are much more prominent than previously suspected. Major contributions of horizontal gene transfer and diverse selfish genetic elements to genome evolution undermine the Tree of Life concept. An adequate depiction of evolution requires the more complex concept of a network or 'forest' of life. There is no consistent tendency of evolution towards increased genomic complexity, and when complexity increases, this appears to be a non-adaptive consequence of evolution under weak purifying selection rather than an adaptation. Several universals of genome evolution were discovered including the invariant distributions of evolutionary rates among orthologous genes from diverse genomes and of paralogous gene family sizes, and the negative correlation between gene expression level and sequence evolution rate. Simple, non-adaptive models of evolution explain some of these universals, suggesting that a new synthesis of evolutionary biology might become feasible in a not so remote future.

PMID 19213802

Ernest Everett Just, Johannes Holtfreter, and the origin of certain concepts in embryo morphogenesis

Mol Reprod Dev. 2009 Oct;76(10):912-21.

Byrnes WM. Source

Department of Biochemistry and Molecular Biology, Howard University College of Medicine, Washington, District of Columbia 20059, USA.


Ernest E. Just (1883-1941) is best known for his discovery of the "wave of negativity" that sweeps of the sea urchin egg during fertilization, and his elucidation of what are known as the fast and slow blocks to polyspermy. Just's contemporary Johannes Holtfreter (1901-1992) is known for his pioneering work in amphibian morphogenesis, which helped to lay the foundation for modern vertebrate developmental biology. This paper, after briefly describing the life and scientific contributions of Just, argues that his work and ideas strongly influenced two of the concepts for which Holtfreter is best known: tissue affinity and autoneuralization (or autoinduction). Specifically, this paper argues that, first, Just's experiments demonstrating developmental stage-specific changes in the adhesiveness of the blastomeres of cleavage embryos helped lay the foundation for Holtfreter's concept of tissue affinity and, second, Just's notion of the intrinsic irritability of the egg cell, which is evident in experimental parthenogenesis, strongly informed Holtfreter's concept of the nonspecific induction of neural tissue formation in amphibian gastrula ectoderm explants, a phenomenon known as autoinduction. Acknowledgment of these contributions by Just in no way diminishes the importance of Holtfreter's groundbreaking work. It does, however, extend the impact of Just's work into the area of embryo morphogenesis. It connects Just to Holtfreter and positions his work as an antecedent to embryo research that continues to this day.

(c) 2009 Wiley-Liss, Inc.

PMID 19610071