Transition from Sea to Land

Contributed by Michael Kaufman, Sterling Feeser, Cole Owens & Zach Vann

The Transition from Sea to Land

It might be shocking to hear that all of the species that inhabit land today came from ancestors that lived in the sea. In all species, mutations occur constantly by random chance. A mutation or the accumulation of many mutations can create a new physical trait whose prevalence is often determined by its ability to allow organisms to survive and reproduce. Mutations leading to traits that better allow organisms to survive and reproduce are often selected for and therefore rise in frequency with time. Because the transition from sea to land occurred, involving the accumulation of many new traits, it can be hypothesized that such land inhabiting traits provided some advantage.

One hypothesis for the nature of this advantage is the drying pond hypothesis, which suggests that droughts occurred, and fish were forced to move from one body of water to another. When a body of water dried out, the fish that already had random mutations leading to land-favoring traits were more able to reach another body of water via land and survive. Another hypothesis, the predator hypothesis, involves the idea that if species had random mutations enhancing their ability to survive on land, then they could better avoid predators. Overall, there are many hypotheses for why these traits may have been advantageous, but contradictory evidence hinders many of them, and therefore the truth behind this transitional process is still largely a mystery.

As this is one of the biggest transitions in the history of evolutionary biology, it is important to realize that drastic changes that lead to the formation of new species often involve the accumulation of many gradual mutations over time. As evidence of this, species with intermediate traits have existed. Amazingly, Tiktaalik roseae has characteristics that resemble both sea and land creatures. Tiktaalik had an intermediate structure between a fin and a limb as well as an enlarged pelvic bone compared to other fishes of the time, which is helpful for movement on land. Additionally, Tiktaalik had both gills and primitive lung structures, which were necessary to survive on both water and land respectively. Overall, the transition to land is a vitally important event that led to the development of many new species. However, because questions still remain about the certainty of the mechanistic theories, it is certain that proving exactly how and why the transition from land to sea occurred will be one of science’s greatest achievements.

“Waiting on the World to Change” Parody 

In order to emphasize that natural selection acts on random mutations and is not goal oriented, we made a parody of the song “Waiting on the World to Change” by John Mayer. Species in the sea did not choose to develop land favoring characteristics; rather all they could do was “wait” for mutations to arise before selection could act.

Waiting on the World to Change (Parody)


The change from sea to land
Is causing lots of talk
Some species evolved to swim or stand
And over time we learned to walk
Three hundred eighty-three million years ago
A landscape was emerging
And with fins with wrists and bigger hips
A new species was diverging
So we keep on waiting
Waiting on the world to change
We keep on waiting
Waiting on the world to change
You can beat the competition
As a species in transition
So we keep on waiting
Waiting on the world to change
Under natural selection
The fittest beasts will best survive
To reproduce and pass those better genes
That helped them to stay alive
Cause you can live under the water
Breathing through a set of gills
But if lungs arise with time
You can go wherever you will
That’s why we’re waiting
Waiting on the world to change
We keep on waiting
Waiting on the world to change
It doesn’t happen cause we want it
But with time we’re counting on it
So we keep on waiting
Waiting on the world to change
Tiktaalik roseae (repeat)
And we’re still waiting
Waiting on the world to change
We keep on waiting
Waiting on the world to change
The terrestrial population
Came from countless generations
So we keep on waiting
Waiting on the world to change
We keep on waiting
Waiting on the world to change
We keep on waiting
Waiting on the world to change
Waiting on the world to change (repeat)

For More Information:

“Recent Findings:Prologue- Fish Out of Water.” Devonian Times. N.p., n.d. Web. 15 Apr. 2014.

Scientific Articles

Daeschler, E.B., Shubin, N.H., Jenkins Jr, F.A. 2006. Devonian tetrapod-like fish and the evolution of the tetrapod body plan. Nature 440: 757-763.

Hagey, L.R., et al. 2010. Diversity of Bile Salts in Fish and Amphibians: Evolution of a Complex Biochemical Pathway. Physiological and Biochemical Zoology: PBZ 83.2: 308-321.

Harzsch, S., et al. 2011. Transition from marine to terrestrial ecologies: Changes in olfactory and tritocerebral neuropils in land-living isopods. Arthropod Structure & Development 40.3: 244-257.

Kleinteich, T., et al. 2014. Anatomy, Function, and Evolution of Jaw and Hyobranchial Muscles in Cryptobranchoid Salamander Larvae. Journal of Morphology 275:230–246.

Klussmann-Kolb, Annette, et al. 2008. From sea to land and beyond – New insights into the evolution of euthyneuran Gastropoda (Mollusca). BMC Evolutionary Biology 8: 57-73.

Schoch, R.R. and Witzmann, F. 2011. Bystrow’s Paradox- gills, fossils, and the fish-to-tetrapod transition. Acta Zoologica(stockholm) 92: 251-265.

Shubin, N.H., Daeschler, E.B., Jenkins Jr, F.A. 2006. The pectoral fin of Tiktaalik roseae and the origin of the tetrapod limb. Nature 440: 764-771.