CapitalistImperialistPig

Things to think about: Mice are rodents, and the rodent and primate lines separated a long time ago, probably on the order of about 75 million years ago. Mice are small-brained; they possess a neocortex but it is much smaller relative to that of primates, and, of course, minuscule in comparison to ours. Yet, comparison of mouse and human genomes reveals that greater than 99 percent of all genes in the human have a mouse counterpart, and vice versa. In fact, 96 percent of all genes in the human are found in the exact same relative order in human chromosomes as in the mouse chromosomes. This is a remarkable degree of similarity. These figures tell us that in the course of 75 million years of mammalian evolution, and at least 55 million years of primate evolution, our genome and that of a rodent contain essentially the same genes in mostly the same organization. Carroll, Sean B.. Endless Forms Most Beautiful: The New Science of Evo Devo (pp. 269-270). W. W. Norton & Company. Kindle Ed...

My thoughts upon reading Endless Forms Most Beautiful , by Sean B. Carroll In the middle ages, says Prof Carroll, Europeans started eating with two knives, using one to spear their food and another to cut it. This redundancy opened an opportunity for one knife evolve to be more specialized for spearing, while sacrificing the cutting function. This division into knife and fork was followed by many more in sufficiently posh dining facilities - a veritable Cambrian explosion of cutlery. A similar redundancy made room for arthropod specializations. Early arthropods had so-called biramous, or forked limbs, lots of them, but each fairly similar to all the others. Each consisted of a lower, leg-like limb used for walking, digging, or swimming, and an upper gill branch, used for absorbing oxygen. The most dramatic arthropod changes have taken place in those who moved onto land. In the case of insects, only six legs have been retained, but many others have been converted to other uses: mou...

Olivia Judson's latest New York Times column/blog called The Wild Side talks about "hopeful monsters." The term was introduced in the 1930s by a geneticist called Richard Goldschmidt. He was interested in the question of how radical changes in morphology evolve. As an example of radical change, he gave flatfish — the flounder and its relations. These are descended from fish with the usual fishy symmetry: the same left-right symmetry that we have. Larval flounders have it, too. But as adults, flounders have a profound asymmetry — one side has been completely flattened. What’s more, they have deformed, twisted skulls, and an eye that has migrated from one side of the face to the other. It’s as though you had both eyes on the same side of your nose. How did they get this way? Goldschmidt speculated that big changes like this could be caused in one step by a mutation acting on the developing embryo. Most such mutations, he suggested, would produce individuals that were pla...

My thoughts upon reading Endless Forms Most Beautiful , by Sean B. Carroll Where should we look for the well laid plans that sculpt mice and men so differently? Well in the genome, of course, but there we meet a problem. Men and mice each have about the same number of genes, about 25,000. The conundrum gets worse. The genes are not only the same in number, but for most purposes they are the nearly the very same genes, producing very similar proteins. The answer to this and many other puzzles of development, form, and evolution seems to be that it's in the switches that turn those genes on and off. If we think of the genes as the keys on an old fashioned player piano, the switches are the piano roll. It's the sequence of switching that orchestrates the notes into the symphony of development. For the most part, man and mouse are built out of the same cell types and tissues - different architectures built out of the same old Lego blocks.

Reading Endless Forms Most Beautiful , by Sean B. Carroll Some unicellular creatures called dinoflagellates are remarkable for their ability to change shape and mode of existence in response to environmental conditions. Their shape changing skills are nothing compared to those of a more familiar cell, however. Each human (or mouse, elephant, or frog) cell has the instruction set for turning itself into a blood, bone, brain, or skin cell. The story of how they manage these feats is the tale of embryonic development, and it is a remarkable tale indeed. When people set out to build something, we gather parts from afield, and bring them together in carefully (in my case, usually not carefully enough!)planned sequence and pattern, but an embryo assembles itself from the inside. The method is both elegant and instructive. First, the egg and early embryo establish a set of internal coordinates. These internal coordinates are specified in terms of chemical gradients, and are initially ...

Wherein Captain Imperio meets evo devo (Hat tip to Changcho) Modularity is the law in biology, and indeed in the universe. Somehow those ancient Greeks rightly guessed that the world was made of universal tinkertoys. The funny thing is that it works at seemingly every level. Everything is made of atoms, and atoms are made of even fewer and simpler parts: electrons, protons, and neutrons, each of which is identical to all the other members of its species. At larger scales are stars and their solar systems, which assemble to build Galaxies, which in turn form clusters. Above and below, we can't quite be sure - though protons and neutrons are made of quarks. But this post is about life, because I have started reading Endless Forms Most Beautiful: The New Science Of Evo Devo And The Making Of The Animal Kingdom by Sean B. Carroll. All the life we know inhabits one planet around one star, and it, like everything else, is made of atoms, but there is a lot more to its modularity. All tha...