Preadaptations (aka exaptations) are features that perform a function but was not produced by natural selection for its current use. It could be argued that an exaptation forms as a result of co-option from a preadaptation, however Daniel Dennett denies exaptation differs from preadaptation. A simple example of a preadaptation is a feather that evolved (through natural selection) for warmth and was coopted into a new function, flight. The genomes of various ancient organisms have been sequenced and it is interesting to view the presence of several preadaptations in the genomes of these creatures. The purpose of this thread is to highlight several of these interesting findings. If anyone come across any interesting findings, post it here . Various trees of life exist. For example: 1 2 3 4 5 6 7 For the purpose of this thread, tree #2 (Dhushara, trevol.jpg) will be used as it is a nice representation of the evolution of animals (especially vertebrates). Horizontal gene transfer and endosymbiotic events are however not clear and tree #7 (Doolittle) is probably a better way of looking at evolution. Therefore keep #2 and #7 in mind and try and piece them together. Preadaptations in the genome of the choanoflagellate, Monosiga brevicollis: Choanoflagellates (link) are single-celled organisms thought to be most closely related to animals. The divergence time of this organism was about >600 million years ago (Link) (Blue circle in image). Please Register or Log in to view the hidden image! Tyrosine Kinases are crucial for multicellular life to exist and play pivotal roles in diverse cellular activities including growth, differentiation, metabolism, adhesion, motility, death (link). More than 90 Protein Tyrosine Kinases (PTKs) have been found in the human genome. Interestingly Monosiga brevicollis has a tyrosine kinase signaling network more elaborate and diverse than found in any known metazoan. Adherens junctions are also crucial components of multicellular life and function to communicate and adhere together in tissues. Even though Monosiga brevicollis are single-celled and do not form colonial assemblages, it is interesting to know they posses about 23 cadherins genes (Cadherins) usually associated with multicellular organisms. Calcium signaling toolkits also play a crucial role in multicellular signaling. Calcium signaling plays a crucial part in contraction, metabolism, secretion, neuronal excitability, cell death, differentiation and proliferation. Thus, it is also interesting to note that Monosiga brevicollis has an extensive calcium signaling toolkit and emerged before the evolution of multicellular animals. Tyrosine kinases, calcium signaling, and adherens junctions all play a part in neural signaling and other multecellular systems. Monosiga brevicollis does not have a nervous system. Thus it is also interesting to find the presence of the hedgehog gene in the genome of Monosiga brevicollis. Signaling by Sonic hedgehog (Shh) controls important developmental processes, including neural stem cell proliferation. (Link). Nice article: Multigene Phylogeny of Choanozoa and the Origin of Animals Compare the hedgehog gene of Monosiga brevicollis to that of humans. Another interesting fact about the genome of the Monosiga brevicollis is noted in this article. (Emphasis mine) Fascinating multicellular preadaptations very early on in the evolution of single-celled organisms. Please Register or Log in to view the hidden image!