Measuring evolution's waistline

Jun 03, 2011
Figure 1: The funnel-like model (left) and the hourglass model (right) are two competing theories that explain how developmental processes are conserved during evolution. In the funnel-like model, conservation occurs at the earliest embryonic stage (bottom) but in the hourglass model it occurs during the middle. Credit: 2011 Naoki Irie and Shigeru Kuratani

Nearly 150 years ago, noted German biologist Ernst Haeckel made the bold assertion that ‘ontogeny recapitulates phylogeny’: in other words, morphological changes that occur during an organism’s embryonic development mirror its evolutionary history.

This concept has long since been debunked, but has nevertheless provided useful starting points for considering the yet-unsolved question of how the developmental process has evolved. Naoki Irie of the RIKEN Center for Developmental Biology (CDB) in Kobe has pondered this problem since graduate school. “My main interest then and now has been to understand the basic or common rules of how animal bodies develop,” he says.

Now, as a postdoctoral fellow in Shigeru Kuratani’s laboratory at CDB, Irie has conducted an ambitious comparative analysis of four vertebrate species with the aim of resolving an ongoing debate over two prevailing evolutionary models1 (Fig. 1). The ‘funnel-like’ model, informed in part by Haeckel’s thinking, suggests that the process of vertebrate embryonic development is very similar across species at the earliest stages, but increasingly differs at later stages. In contrast, the ‘hourglass’ model suggests that the earliest and latest stages of development differ considerably, whereas the greatest similarity is observed at the intermediate stages where organ development and body patterning take place.

To resolve this so-called ‘evo-devo’ debate, Irie and Kuratani analyzed changes in expression levels of thousands of evolutionarily conserved genes at different developmental points in the mouse, chicken, frog and zebrafish. The data provided striking support for the hourglass model, with gene transcription levels most similar at the intermediate stage known as ‘pharyngula’, where the animal has developed primitive precursors of the heart, kidney, brain and other tissues. They observed particularly strong conservation of activity among the Hox genes, which contribute to limb development, as well as several growth factor genes.

These findings offer new fuel for the evo-devo debate, but also raise complicated questions. “It is puzzling for me how vertebrate embryos established differences in early developmental stages while conserving the mid-embryonic stages,” says Irie. “It’s obvious that later developmental stages will not exist if earlier stages fail to develop successfully.” 

Irie now hopes to obtain further support for the hourglass model by expanding his approach to include well-characterized invertebrate species, such as the fruit fly. He also intends to dig deeper into the nuts and bolts of development. “We would like to go down to the level of tissues and primordial organs to find which structures have been conserved during ,” he says.

Explore further: New insights in survival strategies of bacteria

More information: Irie, N. & Kuratani, S. Comparative transcriptome analysis reveals vertebrate phylotypic period during organogenesis. Nature Communications 2, 248 (2011). doi:10.1038/ncomms1248

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User comments : 8

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FrankHerbert
1 / 5 (54) Jun 03, 2011
Why would God give human embryos gills and a tail? Is that really intelligent design?
210
1.8 / 5 (16) Jun 03, 2011
Why would God give human embryos gills and a tail? Is that really intelligent design?

God requires, REQUIRES faith in order to find him - that is not a realm of science, pure and simple."Now Faith is the substance of things hoped for the evidence of things not seen. Hebrews 11:1."
SCIENCE is our toolbox to understand those things we can measure, infer, and see essential cause and effect, the rhyme and reason for the phenomena in our realm of existence that we choose to understand. Why did God do something? In yur private meditations ASK Him & seek D answer! MEANWHILE, back at the ranch, we have the honor and duty as sentient beings to gather as much data as is available and progressively advance our little but noble species further away from doubt and fear.
Faith is a different tool for a much different realm of thought, but, there are faith-filled scientists who marvel at our universe and seek the wisdom to solve problems, and ask HARD questions.
word-to-ya-muthas
Doug_Huffman
2.1 / 5 (11) Jun 03, 2011
God is the sound of one hand clapping, a koan.
DontBeBlind
1 / 5 (8) Jun 03, 2011
Why would God give human embryos gills and a tail? Is that really intelligent design?


You can make a better system? Id love to see what you can come up with! :)
Bigblumpkin36
5 / 5 (3) Jun 03, 2011
Human's were a mistake, a good one though. What other living thing has the chance to think of concisness and the atomic universe and so on. I have the sense that religous people need to open their eyes not a bible or some precher of inteligent design. The greeks new more than most people today.
FrankHerbert
0.9 / 5 (50) Jun 03, 2011
Why would God give human embryos gills and a tail? Is that really intelligent design?


You can make a better system? Id love to see what you can come up with! :)


Not me, but Craig Venter is as we speak!
jsn3604
not rated yet Jun 03, 2011
Human's were a mistake, a good one though. What other living thing has the chance to think of concisness and the atomic universe and so on. I have the sense that religous people need to open their eyes not a bible or some precher of inteligent design. The greeks new more than most people today.


Greeks also had a lot of things wrong, later discovered during the Renaissance.
mjo
not rated yet Jun 06, 2011
Why does every article with "evolution" in the title draw so many idiots? Keep faith in the church, and leave science to the scientists.