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2.6: Macroevolution

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    Another word for macroevolution is speciation, the production of species, this is the level of evolution that Darwin studied, the kind that occurs over immense periods of time, where small changes accumulate to make life diverge into often drastically different forms. Now that we've introduced Mendel and cellular biology we can explain the two main pieces that Darwin was missing, heredity and variation.

    Hox genes

    Hox genes are a good example of one mechanism that enables drastic biological changes. Minor variations in the same small set of genes direct a zygote to grow into the shape of a worm, fly, mouse, or a human.

    Exercise \(\PageIndex{1}\)

    • Read Hox gene intro
    • Review Micro and Macro Evolution
    • Living things share common genes.
    • *Read about Human Accelerated Regions
    • *Article on the genes for arms and legs coming from fish


    “-patric” refers to geography. “allo” is Greek for other. Allopatric speciation happens when two populations are separated geographically; if you can't meet, you can't breed; in the absence of gene flow, variations accumulate through mutation and natural selection effects the two populations differently until they become separate species.

    Punctuated Equilibrium

    Darwin saw evolution as the gradual accumulation of changes, but looking closer at the fossil record, especially shellfish, later paleontologists began to question Darwin's ideas of phyletic gradualism, and proposed the theory of punctuated equilibrium, where the equilibrium of stasis or lack of change, is punctuated or broken by rapid evolutionary change. Remember that we are using the word "rapid" in a geological sense, usually it means hundreds of thousands of years.

    Exercise \(\PageIndex{2}\)

    Skim this intro to punctuated equilibrium

    This page titled 2.6: Macroevolution is shared under a CC BY-NC-ND 4.0 license and was authored, remixed, and/or curated by Arnie Daniel Schoenberg via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.