Red Blood Cells Reveal Complex Design

One of the occupational hazards of being both a trained scientist and a Christian is being asked how I can be both. When the question comes from Christians, what the person usually means is “How do you reconcile mainstream scientific ideas with the biblical account of creation?” When the question comes from non-Christians, the person is usually asking not so much “Why Christianity?” but “How can you believe in any kind of Creator God?” After all, can’t science explain everything, eliminating the need for God? The idea that science has replaced God is a common misconception, and one I once held. But the more I studied science, the more I realized how every living thing is perfectly suited to function in the environment in which it lives, so much so that it seems almost impossible this could have happened by chance. 

Sophisticated Oxygen Transport Systems

Take, for example, red blood cells (RBCs). The job of RBCs is to carry oxygen to tissues throughout the body and to retrieve carbon dioxide so it can be transported back out. RBCs are packed with hemoglobin, a protein that binds to both oxygen and carbon dioxide. Except for icefish, all vertebrates use hemoglobin-containing RBCs to transport both gases.1 This sounds simple enough, but different animals have different oxygen requirements and live under different conditions.

Red Blood Cells in Mammals

Endotherms––birds and mammals—generate their own body heat and use more oxygen than ectotherms—fish, amphibians, and birds.2 Mammals are able to carry more oxygen in their RBCs than other animals can. This is because RBCs in mammals, unlike those in other animals, lack the nucleus and other organelles found in other cells. In all vertebrates (including mammals), newly formed RBCs contain a nucleus and other organelles, but during development the nucleus becomes inactive and either shrinks in size (in nonmammals) or disappears altogether (in mammals). In mammals, the other organelles disappear as well.3 The process of mammalian RBCs losing their nucleus is a complex, multistep process that is not fully understood. Not having a nucleus creates space to pack in more hemoglobin. This not only increases oxygen-carrying ability, but it also changes the size, shape, and flexibility of the cell.4 On average, mammalian RBCs are about one-fifth the size of nonmammalian RBCs.5 The reduced size is important because mammals have smaller capillaries than nonmammals and the smaller RBCs can fit through them more easily. 

But even with their reduced size, mammalian RBCs are still larger than the capillaries and must bend to fit through them. This is why flexibility is important. Without a nucleus or organelles, most mammalian RBCs are shaped like flattened round discs which can easily bend to squeeze through the smaller capillaries.6 The flattened shape also yields a greater surface area to volume ratio, which provides more surface area for diffusion of gases across the cell membrane.

A Beneficial Anomaly in Camels

One interesting exception to the usual shape of mammalian RBCs is found in camels.7 While camel RBCs still lack a nucleus and organelles, they are ellipsoid in shape and their cell membrane has a uniform thickness. This shape reduces the surface area to volume ratio and may seem like a disadvantage, but it turns out to be very beneficial to camels. During dehydration, blood becomes more viscous. In most mammals, viscous blood doesn’t flow well and the disc-shaped RBCs are prone to shearing. In camels, however, the ellipsoid-shaped cells are better able to withstand mechanical stress of viscous blood, so they do not shear. Their movement changes as well. When the blood becomes viscous, the cells begin to rotate and “tumble,” which allows them to continue to flow.8 Further, upon rehydration, camel RBCs can expand 240% without bursting (tantamount to 1.6 times the amount other mammalian RBCs can).This physical feature could be one reason why camels can endure long trips across deserts.

Birds’ Efficient Respiration

Birds meet their greater demand for oxygen in a different way—by having highly efficient respiratory systems. Mammals breathe bidirectionally, moving air back and forth, into and out of the lungs. In birds, air flows through the lungs in a single direction. The higher-oxygen “fresh” air is not diluted with lower-oxygen “stale” air as in mammalian lungs. Additionally, the walls of pulmonary capillaries in birds are thinner and more uniform than in mammals, meaning it’s easier for oxygen to diffuse into the bloodstream. Finally, birds have an extensive network of air capillaries extending throughout their bodies, which provides a larger surface for gas exchange and more opportunities for oxygen to enter the bloodstream.

Icefish Are Suited for Cold Environments

Icefish are the only known vertebrates to lack both hemoglobin and RBCs. They are able to survive in extremely cold environments, typically near Antarctica, thanks to features including much larger hearts than would be expected for their body size, an extensive network of blood vessels, and plasma proteins that act as an antifreeze to prevent their blood from freezing.10 Gases dissolve better in cold liquids than in warmer ones—that’s why soda goes flat when it gets warm. The increased solubility of oxygen in blood at cold temperatures, coupled with the icefishes’ low oxygen requirements, means that icefish are able to rely on oxygen dissolved in their blood and thus do not need RBCs.

How Red Blood Cells Produce Energy

In addition to oxygen, all cells need energy. This energy comes in the form of adenosine triphosphate (ATP), which is produced in mitochondria—the powerhouse of the cell! RBCs lack mitochondria, so they must produce ATP in a different way. They do this anaerobically, using a multistep process that requires many enzymes.11 Although the primary reason for utilizing these anaerbobic reactions is RBCs’ lack of mitochondria, there are advantages to producing ATP this way. Since the process doesn’t use oxygen, all of the oxygen within the RBC is delivered to tissues. Further, the reactions appear to generate fewer harmful reactive oxygen species (ROS) than when ATP is produced in mitochondria, reducing oxidative stress on the cell.12

Preponderance of Evidence

There is no doubt that RBCs are impressive and that they reveal the intricate processes at work in every living thing. The question is, How did this all come about? Evolutionary scientists have offered possible explanations of how each structure or process in a cell may have arisen on its own through evolution and natural selection. However, as I studied science, I started adding up all of the examples of times we had to be really, really lucky for life to exist. One or two I might be able to accept, but there were way too many examples where if things hadn’t gone exactly the way they did, we wouldn’t be here. A prosecuting attorney would call this a “preponderance of the evidence,” and it’s why I came to believe that life had to be designed by a Divine Creator. RBCs serve as yet one more piece of evidence that life couldn’t have happened by chance.


1. Bo-Mi Kim et al., “Antarctic Blackfin Icefish Genome Reveals Adaptations to Extreme Environments,” Nature Ecology and Evolution 3 (February 5, 2019): 469–478, doi:10.1038/s41559-019-0812-7.

2. James F. Gillooly, Juan Pablo Gomez, and Evgeny V. Mavrodiev, “A Broad-Scale Comparison of Aerobic Activity Levels in Vertebrates: Endotherms versus Ectotherms,” Proceedings of the Royal Society B 284, no. 1849 (February 22, 2017): 284, doi:10.1098/rspb.2016.2328.

3. Peng Ji, Maki Murata-Hori, and Harvey F. Lodish, “Formation of Mammalian Erythrocytes: Chromatin Condensation and Enuclueation,” Trends in Cell Biology 21, no. 7 (July 1, 2011): 409–415, doi:10.1016/j.tcb.2011.04.003.

4. Ji, Murata-Hori, and Lodish, “Formation of Mammalian Erythrocytes,” 409-415.

5. Juan A. Claver and Agustin I. E. Quaglia, “Comparative Morphology, Development, and Function of Blood Cells in Nonmammalian Vertebrates,” Journal of Exotic Pet Medicine 18, no. 2 (April 2009): 87–97, doi:10.1053/j.jepm.2009.04.006.

6. Claver and Quaglia, “Comparative Morphology,” 87-97.

7. Ursula Windberger et al., “Near-Newtonian Blood Behavior—Is It Good to Be a Camel?,” Frontiers in Physiology 10 (July 17, 2019): 10:906, doi:10.3389/fphys.2019.00906.

8. R. C. Schroter et al,, “Influence of Dehydration and Watering on Camel Red Cell Size: A Scanning Electron Microscopic Study,” Respiration Physiology 81, no. 3 (September 1990): 381–390, doi:10.1016/0034-5687(90)90118-1

9. J. B. West, R. R. Watson, Z. Fu, “The Human Lung: Did Evolution Get It Wrong?” European Respiratory Journal 29 (April 1, 2007): 11–17, doi:10.1183/09031936.00133306

10. Kim et al., “Antarctic Blackfin Icefish,” 469-478.

11. Wouter W. van Solinge and Richard van Wijk, “Enzymes of the Red Blood Cell,” Basicmedical Key (November 27, 2016), ch. 23.

12. Zhong-Wei Zhang et al., “Red Blood Cell Extrudes Nucleus and Mitochondria against Oxidative Stress,” IUBMB Life 63, no. 7 (July 2011): 560–565, doi:https://doi.org/10.1002/iub.490.