Re: How we evolved: From a Few Genes, Life's Myriad Shapes
BumbleBeeBoogie wrote:June 26, 2007
From a Few Genes, Life's Myriad Shapes
By CAROL KAESUK YOON
New York Times
But how could such bills evolve from a simple finch beak? Scientists had assumed that the dramatic alterations in beak shape, height, width and strength would require the accumulation of many chance mutations in many different genes. But evo-devo has revealed that getting a fancy new beak can be simpler than anyone had imagined.
What Dr. Tabin and colleagues found, when looking at the range of beak shapes and sizes across different finch species, was that the thicker and taller and more robust a beak, the more strongly it expressed a gene known as BMP4 early in development. The BMP4 gene (its abbreviation stands for bone morphogenetic protein, No. 4) produces the BMP4 protein, which can signal cells to begin producing bone. But BMP4 is multitalented and can also act to direct early development, laying out a variety of architectural plans including signaling which part of the embryo is to be the backside and which the belly side. To verify that the BMP4 gene itself could indeed trigger the growth of grander, bigger, nut-crushing beaks, researchers artificially cranked up the production of BMP4 in the developing beaks of chicken embryos. The chicks began growing wider, taller, more robust beaks similar to those of a nut-cracking finch.
In the finches with long, probing beaks, researchers found at work a different gene, known as calmodulin. As with BMP4, the more that calmodulin was expressed, the longer the beak became. When scientists artificially increased calmodulin in chicken embryos, the chicks began growing extended beaks, just like a cactus driller.
So, with just these two genes, not tens or hundreds, the scientists found the potential to recreate beaks, massive or stubby or elongated.
I don't get it. How do successive generations of the same BMP4 gene lead to an increasing change in morphology?
Let's see, a chance combining of existing genes (due to random chance or mixing of parents genes) leads to an overly active BMP4 which not only increases robustness of a beak, but also induces an architectural change which guides the robustness. So you get a single individual with a slightly larger beak without necessarily needing a specific gene mutation.
Fine, that part makes sense. But the beak won't get any *more* robust in the next generation, will it?
If the exact same BMP4 gene is passed on to a whole population of offspring, then won't the whole population have the same sized bill as the original overactive BMP4 gene expressed?
How does this discovery add anything to the evolution of new features, other than to realize that a single gene can alter multiple attributes at once?