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Evo Devo and the Mechanism of Evolution

Evolution, in the macroscopic sense, has probably been explained to you time and time again in your science classes as tiny changes that over time build up and create differences among species. From a single common ancestor, different species evolve, eventually creating the huge diversity of life we see today. But have you ever considered how that change comes about? Evo devo allows us to understand how various species evolve and how different species are related. It can help us answer questions, such as: how does a fin evolve into a hand? What kind of signaling in proteins allows those tiny changes to accumulate? Can new genes arise in our DNA, and, if so, how?fish

Evolutionary developmental biology, commonly and playfully known as “evo devo”, aims to answer these questions of how various phenomena in evolution occur [1]. Evo devo is relatively new; it emerged in the 1990s [4]. However, since its initiation, evolutionary developmental biology has tremendously impacted the scientific community. By combining the fields of evolutionary biology and developmental biology, as well as other fields such as embryology, zoology, and molecular biology, evo devo is a field that helps us understand the tiny biological details behind huge ecological changes [4].

At first glance, evo devo seems an odd synthesis of fields: what could studying an embryo’s growth tell us about how (for example) dinosaurs became chickens? The connection is clear once one looks at the issue from the microscopic perspective —the DNA. Since fetal development is the first step in an organism’s growth, changes in gene expression in this initial stage influence the organism throughout its life. By tracking those changes, scientists can discover how structures in a species over time change in form and function–and, if enough of these changes take place, how a new species is created [1].

To understand the finer details of this science, let us explore the example from the beginning of this article: how a fish’s fin turns into a limb. First, scientists studying evo devo must tackle the development part: how a fish’s fin forms in the first place. Early evo devo scientists discovered that in many organisms, organization of limbs during fetal development is controlled by small groups of genes called homeoboxes [1]. These genes send out proteins that tell other cells where to form different limbs [6]. In fish fins, three different homeobox groups are expressed in the same area, each directing a different type of cellular development such as bone and skin [6].

Now, the evolution side: how a fin becomes a limb. The common explanation is that evolution is the result of mutations. The same three homeoboxes that create fish fins also create fingered limbs [6]. The difference is in protein signaling. The proteins that are expressed in your hand are given different instructions than in a fish’s fin; signaling occurs in different areas [6]. The new positioning of the proteins creates the spread-out and divided pattern that you can see in your own hands.Untitled

There are actually many more changes involved in the evolution of limbs from fins than there are with any large-scale evolutionary change. The same genes are used to create similar structures – such as fins and hands – but their differences in nucleotide sequence – the version of the gene – results in different amounts and formations of the proteins. Evo devo therefore explains another commonly-cited yet oft-unexplained scientific tidbit: the high genetic similarity between the genomes of humans and seemingly dissimilar animals. Gene for gene, humans are 96% the same as chimpanzees [2], 90% the same as cats [5], and about 50% the same as fruit flies [3]. The great variation in phenotype between these organisms is clearly not the simple result of genes, but the result of the different ways those genes are expressed.

Interdisciplinary science strengthens connections, bridges gaps, and lends new insights to the scientific community as a whole. Examining how a signal impacts a gene, which impacts an organism and thus the species’s evolution, reminds us that proteomics, genetics, embryology, and ecology are not wholly separate: they all fall within the umbrella of biology. The impact of evo devo on our understanding of both evolution and development thus illustrates a key point: science works best when it works together.

References:

[1] Carroll, Sean B. Endless Forms Most Beautiful: The New Science of Evo Devo and the Making of the Animal Kingdom. New York: Norton & Company, 2005.

[2] Nunes, Maria D.S., Saad Arif, Christian Schlotterer, and Alistair P. McGregor. “A Perspective on Micro-Evo-Devo: Progress and Potential.” Genetics 195 (2013): 625-634. doi: 10.1534/genetics.113.156463

[3] Greenspan, Ralph J. and Herman A. Dierick. “Am Not I a Fly Like Thee? From Genes in Fruit Flies to Behaviour in Humans.” Human Molecular Genetics 13, no. 2 (2004): R267-R273. doi: doi:10.1093/hmg/ddh248

[4] Gibbons, Ann. “Bonobos Join Chimps as Closest Human Relatives.” American Association for the Advancement of Science. Last modified June 13, 2012.

[5] Pontius, Joan U., et al. “Initial Sequence and Comparative Analysis of the Cat Genome.” Genome Research 17 (2007): 1675-1689. doi: 10.1101/gr.6380007

[6] Yano, Tohru and Koji Tamura. “The Making of Differences between Fins and Limbs.” Journal of Anatomy 222 (2013): 100-113. doi: 10.1111/j.1469-7580.2012.01491.x

Image References:

[1] “Royal Angelfish – Pygoplites Diacanthus.” Flickr. July 4, 2009. Accessed March 19, 2015. https://www.flickr.com/photos/berndhoppe/3664955558/in/photolist-6zRRAW-6zyFKz-oUrSgb-6aMTTt-6AAoKW-7sCdsM-g6hQR9-5ABJtE-9jfrT3-67bzKM-a3wmBj-dXfs1U-pFTdrb-9nxdyP-5NB3Fu-6xGxvg-6mVQv7-bRW9Yp-aifguG-ekX1e9.

[2] “Micah’s DNA.” Flickr. July 16, 2010. Accessed March 19, 2015. https://www.flickr.com/photos/micahb37/3080247531/in/photolist-5Gc5h4-Fxw4-93S5sV-2wa6R-iUKgF8-7JQMKU-5xwJgw-PVMKy-7242M6-3PaAeV-66bBcj-DYEj6-n9QpT-EV6Tu-ga3Pn-4adoJP-nKUJMQ-3kmmTE-9bk7CS-4rKYZk-8DHjAj-3q7wHy-7K4AjU-5cenX-bquTfb-8Met9-8UwdR-87Wwmc-bUqM6a-jbEnG-beGnKg-7KoAby-hhtxEE-4UaQAV-87woEB-7JQMHY-jbEnH-bXb8Y5-6DCAiL-ERLaB-ERLGj-8jGj4J-Gjib1-ERLFN-7i92zp-7xrrvu-82Yji1-4gqRir-7iNL6N-dQ9dME.

 

Acacia Ackles is a freshman at George Washington University. She is currently undeclared but plans in majoring in biology or chemistry, and has a special interest in genetics. Follow The Triple Helix Online on Twitter and join us on Facebook

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