During the late 19th century, Ernst Haeckel 's recapitulation theory , or "biogenetic fundamental law", was widely accepted. It was often expressed as " ontogeny recapitulates phylogeny", . the development of a single organism during its lifetime, from germ to adult, successively mirrors the adult stages of successive ancestors of the species to which it belongs. But this theory has long been rejected.   Instead, ontogeny evolves – the phylogenetic history of a species cannot be read directly from its ontogeny, as Haeckel thought would be possible, but characters from ontogeny can be (and have been) used as data for phylogenetic analyses; the more closely related two species are, the more apomorphies their embryos share.
Phylogenetic networks are used when bifurcating trees are not suitable, due to these complications which suggest a more reticulate evolutionary history of the organisms sampled.
Birgit Meldal gives an introduction to the Complex Portal . The Complex Portal provides manually curated summaries about macromolecular complexes, including lists of participants, function and property information as well as cross-references. This...
"Why do evolutionary biologists care who's related to whom,
and how do scientists find out how different animals are related?"
Scientists care because phylogeny is the fundamental product of evolution . Therefore, a phylogenetic hypothesis is essential if you want to understand biological phenomena, most of which have an evolutionary explanation. Since many scientists would like to know how animal diversity and animal body plans came to be, presently there is a great deal of work on resolving the evolutionary relationships among the major groups of animals. Much of this research has relied upon morphological characters, especially those expressed in early development (. embryological characters). More recently, a significant advance in our understanding of animal phylogeny has been brought about by the study of molecules (in particular genes and their protein products) contained within animal cells. The phylogeny presented here is a relatively conservative guess based upon various published studies of 18S ribosomal RNA sequence data. As you can see, there are quite a few unresolved branches, and therefore a great deal of work to be done in this area. Note that the phylum Porifera (the sponges) is paraphyletic . A few lines of independent evidence suggest that one group of sponges is actually more closely related to non-sponge animals than it is to the other sponges. This is an important finding for it implies that the lineage leading to all other animals (including ourseleves!) was directly descended from an animal with a sponge body and a sponge life style. Visit the Tree of Life for more information concerning the systematics of animals . For some classic images of invertebrate animals and protists, created in the 19th century by the great zoologist Rudolph Leuckart, click here to visit the Marine Biological Laboratory at Woods Hole, Massachusetts. Sources:
Oceans Research begins its new research endeavor focusing on land and river wildlife. Similarly to its sister department, the Wildlife Research Unit’s model utilises its internship to provide funds and manpower to the different research projects.