Updated 09/16/2026
Life does not exist in isolation. Throughout nature, organisms depend upon other organisms in extraordinarily complex relationships. Some are relatively loose ecological dependencies, while others involve intimate relationships known as symbiosis. When both organisms benefit, the relationship is called mutualism.
Pollination provides a familiar example. Many flowering plants depend upon animals such as bees to transfer pollen between flowers. The bee obtains food in the form of nectar or pollen, while the plant receives assistance with reproduction.
On an even larger scale, life participates in interconnected atmospheric cycles. Through photosynthesis, plants consume carbon dioxide and release oxygen. Humans and other aerobic organisms consume oxygen and release carbon dioxide through respiration. Although this global exchange is not technically classified as symbiosis, it demonstrates a fundamental characteristic of the living world:
Life depends upon life.
From a creation perspective, these interdependent systems raise an important origins question. If organisms gradually appeared independently over enormous periods of time, how did biological relationships arise when one organism eventually became strongly dependent upon another?
Cleaning Symbiosis: Don’t Eat the Cleaner
One remarkable example occurs on coral reefs.
Large reef fish allow much smaller cleaner fish and cleaner shrimp to approach their bodies, enter their mouths, and even move around their teeth and gills. Instead of eating these smaller animals, the client fish permits them to remove parasites and damaged tissue.
Carnivorous fish such as the Oriental sweetlip and the coral rock cod normally feed voraciously upon shrimps and smaller fish. But these photographs show them placidly allowing cleaner wrasse and cleaner shrimp to crawl around tongue, gill chamber and vicious-looking teeth—and the cleaners don’t seem to be at all reticent to enter the ‘jaws of death’. And when the wrasse and shrimp have finished picking off parasites, the large fish let the cleaners go again without eating them.
This is not merely anecdotal. Researchers describe marine cleaning interactions as a classic example of mutualism. Cleaner wrasse can perform thousands of interactions and consume large numbers of ectoparasites, while client fish receive the benefit of parasite removal.[1]
The interaction becomes particularly striking when the client is a predator capable of eating the cleaner.
The evolutionary explanation proposes that simpler interactions can become mutually beneficial and subsequently be strengthened through natural selection. Researchers have proposed, for example, that cleaning behavior may have originated as a simpler “by-product mutualism” before developing into the more specialized interactions observed today.[2]
But this explanation raises another question:
How does an initially undirected process establish the coordinated behaviors necessary for a predator to recognize a potential meal as a cleaner, tolerate its presence around vulnerable tissues, and allow it to leave uneaten, while the cleaner recognizes and safely approaches the predator?
Natural selection can preserve behaviors that already provide a reproductive advantage. The question of interest is how sufficiently coordinated behaviors arose in the first place.
Lichens: More Complicated Than We Thought
Lichens provide an even more intimate example of biological cooperation.
For generations, the standard description of a lichen was essentially a partnership between a fungus and a photosynthetic organism, usually a green alga or cyanobacterium. The photosynthetic partner produces organic compounds through photosynthesis, while the fungus provides the physical structure and helps obtain water and minerals.
Then researchers discovered that the story was more complicated.
A major 2016 study published in Science found previously unrecognized basidiomycete yeasts embedded within the cortex of many macrolichens.[3] This discovery challenged the traditional view that these lichens could adequately be understood simply as a partnership between one fungus and one photosynthetic partner.
Research continues to reveal just how complicated lichens really are. A 2025 review in the Annual Review of Microbiology noted that scientists still lack a dependable laboratory model for reconstructing a natural lichen from isolated partners and suggested investigating whether successful lichen formation may require additional microbial participants beyond the traditional fungal and photosynthetic partners.[4]
This does not establish that every lichen consists of three obligatory partners, nor that each partner is incapable of living independently. What it does demonstrate is that an organism once portrayed as a relatively simple two-member symbiosis can actually involve a much more complicated biological community.
The Origins Question
Evolutionary biology proposes that mutualistic relationships can develop incrementally when intermediate stages provide benefits to the organisms involved. That is a hypothesis that can be investigated.
But increasingly complex symbiotic systems raise an important question:
When two or more organisms have become highly dependent upon one another, what independently functional intermediate stages produced the coordinated biological structures and behaviors required for the relationship?
Simply identifying natural selection as the mechanism does not, by itself, demonstrate the historical sequence by which a particular interdependent system originated. From a creation perspective, the extraordinary integration seen throughout the living world is exactly what we would expect if organisms and their ecological relationships were created to function together. The evidence is the relationship itself. The disagreement concerns what best explains its origin.
Sources
1. Bshary, R., Oliveira, R. F., Oliveira, T. S. F., & Canário, A. V. M. (2007). “Do cleaning organisms reduce the stress response of client reef fish?” Frontiers in Zoology, 4, 21.
Read the study
2. Gingins, S., Werminghausen, J., Johnstone, R. A., Grutter, A. S., & Bshary, R. (2011). “Cleaning wrasse species vary with respect to dependency on the mutualism and behavioural adaptations in interactions.” Animal Behaviour, 82(5), 1067–1074.
Study abstract
3. Spribille, T., et al. (2016). “Basidiomycete yeasts in the cortex of ascomycete macrolichens.” Science, 353(6298), 488–492.
Read the study at PubMed Central
4. Belosokhov, A., & Spribille, T. (2025). “Making Fungal-Photobiont Symbioses in the Lab: Past, Present, and Future of the Elusive In Vitro Lichen.” Annual Review of Microbiology, 79, 713–730.
Read the review
