Evo-Devo: Combined Study of Evolution and Development


Since its beginnings as a single 1) ___, life has evolved into a spectacular array of shapes and sizes. How could such diversity of form arise out of evolution’s myriad random genetic mutations? The advent of molecular 2) ___ reinvigorated the study of developmental biology in the 1980s. The evo-devo quickly got scientists’ attention when early breakthroughs revealed that the same master genes were laying out fundamental body plans and parts across the animal kingdom. Genes are stretches of 3) ___ that can be switched on so that they will produce molecules known as proteins. Proteins can then do a number of jobs in the cell or outside it, working to make parts of organisms, switching other genes on and so on. When genes are switched on to produce 4) ___, they can do so at a low level in a limited area or they can crank out lots of protein in many cells. The development of an organism – how one end gets designated as the head or the tail, how feet are enticed to grow at the end of a leg rather than at the wrist – is controlled by a hierarchy of genes, with master genes at the top controlling a next tier of genes, controlling a next and so on. But the real interest for evolutionary biologists is that these hierarchies not only favor the evolution of certain forms but also disallow the growth of others, determining what can and cannot arise not only in the course of the growth of an embryo, but also over the history of life itself. There aren’t new genes arising every time a new species arises. Basically you take existing 5) ___ and processes and modify them, and that’s why humans and chimps can be 99% similar at the genome level and still be different in many ways. Evo-devo has also begun to shine a light on a phenomenon with which evolutionary biologists have long been familiar, the way in which different species will come up with similar solutions when confronted with the same challenges. One of evo-devo’s greatest strengths is its cross-disciplinary nature, bridging not only evolutionary and developmental studies but gaps as broad as those between fossil-hunting paleontologists and molecular biologists. Last year, evolutionary biologist (Univ. Chicago) Dr. Neil Shubin reported the discovery of a fossil fish on Ellesmere Island in northern Canada, that he named, Tiktaalik; special because it has a flat head with eyes on top and has gills and lungs. It’s an animal that’s exploring the interface between water and 6) ___. Tiktaalik was a stunning discovery because this water-loving fish bore wrists, an attribute thought to have been an innovation confined strictly to animals that had already made the transition to land. The genetic tools or toolkit genes for making limbs to walk on land appear to have been present long before 7) ___ made that critical leap. Then, Dr Shubin began a study of the living but ancient fish known as the paddlefish, finding that, these fish were turning on control genes known as Hox genes, in a manner characteristic of the four-limbed, land beasts known as 8) ___, which include cows, people, birds, rodents, etc. The potential for making fingers, hands and feet, crucial innovations used, in emerging from the water to a life of walking and crawling on land, appears to have been present in fish, long before they began flip-flopping their way out of the muck. The genetic tools to build fingers and toes were in place for a long time. Lacking were the 9) ___ conditions where these structures would be useful. Fingers arose when the right environments arose. Major events in 10) ___ like the transition from life in the water to life on land are not necessarily set off by the arising of the genetic mutations that will build the required body parts, or even the appearance of the body parts themselves. Instead, it is theorized that the right ecological situation, the right habitat in which such bold, new forms will prove to be particularly advantageous, may be what is required to set these major transitions in motion.


 1) cell; 2) biology; 3) DNA; 4) proteins; 5) genes; 6) land; 7) fish; 8) tetrapods; 9) environmental; 10) evolution


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