TL;DR
A human being is not created by simply "reading off" a finished blueprint. Development is a dynamic process of cell division, signaling pathways, gene regulation, cell migration, and tissue remodeling. The 23 Carnegie stages help to morphologically organize these early developmental steps. Remarkably, the primitive heart tube begins to contract around day 22, while organ development and differentiation continue for many more weeks.
Modern stem cell research also shows how remarkably flexible cell identity can be: Shinya Yamanaka and John Gurdon received the Nobel Prize in 2012 for demonstrating that mature cells can be reprogrammed back into a pluripotent state under certain conditions. And a recent case from Greece shows another form of biological time: An embryo cryopreserved for more than 22 years led to a birth in 2026. The embryo did not simply get "older" during cryopreservation—its development was effectively paused and later resumed.
Perhaps the most surprising realization of modern developmental biology is that our bodies are not created by millions of independent decisions. Cells receive signals, activate specific genes, change their position, and take on specialized tasks step by step. An early cell population eventually becomes nerve cells, muscle cells, skin cells, blood vessels, and organs.
What are the Carnegie stages?
The scientific standard
The Carnegie stages are a standardized system for describing early human embryonic development. The first eight weeks of development are divided into 23 morphological stages. The crucial factor here is primarily which structures are already recognizable and formed—not just the age or size of the embryo.
This is important because two embryos do not always show the exact same morphological development on the same calendar day. Organizing the system by visible and anatomically defined features therefore makes comparisons between different developmental stages significantly more robust.
→ Source: UNSW Embryology – Carnegie Stages
| Range | What happens? |
|---|---|
| Carnegie 1–3 | Fertilization, cell divisions, formation of early embryonic structures and blastocyst. |
| Carnegie 7–13 | Gastrulation, germ layers, early organ primordia, neural development, and further folding of the embryo. |
| Carnegie 14–18 | Progressive development of the head, limbs, face, and internal organ structures. |
| Carnegie 19–23 | Increased external differentiation; fingers and toes become more recognizable, the head and body change their shape, and the embryonic period ends with Stage 23. |
The Carnegie stages describe the early morphology of the human embryo. Stage 23 corresponds to approximately days 56–60 and marks the end of the actual embryonic period.
→ Source: UNSW Embryology – Carnegie stage table
The three germ layers: How a body emerges from a few cell layers
A particularly fascinating step in development is gastrulation. During this process, the three primary germ layers—ectoderm, mesoderm, and endoderm—are formed. Practically all organs and tissues of the body subsequently arise from them.
Three layers – one body
- Ectoderm: Includes the nervous system and skin.
- Mesoderm: Includes muscles, bones, connective tissue, heart, and blood vessels.
- Endoderm: Includes large parts of the digestive and respiratory systems.
Development, therefore, does not just mean "growing bigger." Cells acquire new identities, migrate to specific positions, and react to signals from neighbors. It is the interplay of these processes that turns an early cell population into organized organs.
→ Source: NCBI Bookshelf / StatPearls – Embryology, Weeks 6–8
Day 22: The moment the primitive heart tube begins to beat
One of the best-known milestones in human embryology occurs around the 22nd day of development. At this point, the primitive heart tube begins to contract.
However, it is important to categorize this accurately: This is not yet the fully formed, four-chambered heart of a newborn. The early heart structure arises from cardiac progenitor cells that organize into a primitive heart tube. This is followed by, among other things, cardiac looping, formation of the outflow tract, and septation.
Why this is so remarkable
The heart is one of the organ systems that functions early on. Its initial contractions begin while numerous other organs are still far from their final structure.
→ Source: University of Minnesota – Development Timeline of Human Heart Embryology
The amazing 22-year pause: What cryopreservation truly shows
In September 2026, a birth was reported from Greece involving an embryo that had been cryopreserved for more than 22 years. Cristina Rapti-Tzelepi and Constantinos Raptis welcomed a daughter in Athens; the attending physician was Dr. Kostas Pantos.
What is biologically extraordinary about this
The long storage duration does not mean that the embryo continued to develop normally during that time and was subsequently "22 years younger." Cryopreservation is specifically designed to effectively halt biological processes. After thawing, development can be continued—provided the medical prerequisites are met.
Thus, reproductive medicine provides a real-world example that calendar time and developmental time are not the same. While an embryo is stored frozen, its normal development does not simply continue. It is only after thawing and successful implantation that development resumes.
→ Sources: Associated Press – After tragedy, a Greek couple welcomes a daughter born from an embryo frozen for 22 years; People – Report on the case from September 2026
Our body is not a static blueprint
The "blueprint" metaphor is useful—as long as we do not take it too literally. The genome contains the genetic information, but development arises from a network of gene regulation, signals, cell-to-cell communication, mechanical forces, and environmental conditions.
Modern developmental biology therefore depicts more of a dynamic operating system than a rigid blueprint. Genes are switched on or off in different cells at different times. Signaling pathways determine where cells are located, where they migrate to, and what identity they adopt.
This is exactly where the work of Shinya Yamanaka becomes relevant. The Nobel Prize-winning work of Yamanaka and John Gurdon showed that the identity of mature cells can be reprogrammed under specific experimental conditions. Induced pluripotent stem cells were successfully created from specialized cells.
Expert perspective: Shinya Yamanaka
Yamanaka's work changed the perception of how "fixed" an adult cell actually is. Cell identity is extraordinarily stable—but not irreversible under all conditions. This very discovery has opened up new fields of research regarding regeneration, disease models, and cell biology.
→ Source: Nobel Prize – Mature cells can be reprogrammed to become pluripotent
What does this have to do with aging?
This is where the transition from developmental biology to longevity research begins. If young cells build highly precise identities and organize tissues, the reverse question arises later: What changes when cells and tissues must be maintained over decades?
Geneticist David Sinclair has co-developed what is known as the Information Theory of Aging. In a perspective published in Nature Aging in 2023, his team describes aging partly as a progressive loss of epigenetic information—that is, changes in the regulation of gene expression, not simply changes in the DNA sequence itself.
Important: Theory is not therapy
The epigenetic information theory is an active area of research. It is not synonymous with the claim that today's nutritional supplements can "reverse" human aging. A clear distinction must be made between scientific hypothesis, experimental research, and clinically proven application.
→ Source: Lu, Tian & Sinclair – The Information Theory of Aging, Nature Aging (2023)
Expert perspective: Nir Barzilai and the difference between lifespan and healthspan
Gerontologist Nir Barzilai pursues a different, much more clinical perspective. His research focuses on the genetic and biological factors associated with better health in exceptionally long-lived individuals.
This is crucial for the public discussion about longevity: A long life alone is not the same as a long life with good physical and functional health. This is why modern aging research frequently discusses healthspan—the maintenance of function and health for as long as possible.
Expert perspective: Nir Barzilai
Barzilai's research approach focuses less on spectacular "anti-aging" promises and more on the mechanisms that could explain healthy aging and exceptional longevity. This shifts the central question: Not "How do I stop aging?" but "How do we maintain function and health for as long as possible?"
→ Source: Albert Einstein College of Medicine – Nir Barzilai, M.D.
And where does collagen fit in?
Here, one must cleanly distinguish between development, tissue structure, and supplementation. Collagen is not a "rejuvenation code." Rather, it is a vital structural protein of human connective tissue.
The development of the body makes this structural level particularly vivid: mesodermal tissues develop into, among other things, connective tissue, bones, muscles, and other structures. In adulthood, these tissues remain biologically active and are continuously built, remodeled, and repaired.
Focus nutrient: Vitamin C
According to approved EU nutritional claims, Vitamin C contributes to normal collagen formation for the normal function of skin, bones, cartilage, and other tissues. This is a much more precise scientific statement than blanket promises such as "anti-aging" or "cell rejuvenation."
180 capsules · 900 mg collagen hydrolysate + 100 mg hyaluronic acid per daily dose, supplemented with Vitamin C, zinc, Vitamin A, Vitamin B3, selenium, and Vitamin D3.
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According to the product label, the current Veyt formula provides 900 mg of collagen hydrolysate, 100 mg of hyaluronic acid, 24 mg of Vitamin C, 5 mg of zinc, 55 µg of selenium, and other micronutrients per daily dose of two capsules. Veyt also states that production and batches are laboratory-tested in Germany.
The scientifically sound connection between this product and the topic of this article is therefore not that a supplement "recaptures" the embryonic development process. The connection lies in the maintenance of normal tissue structures and in the role of certain nutrients in normal physiological processes.
→ Source: Veyt – Hyaluron Kollagen Plus
Why early embryos of different vertebrates look similar
The well-known similarity of early vertebrate embryos is real, but often exaggerated. Early developmental programs share many fundamental mechanisms, which is why certain structures in related animal groups may initially appear similar.
However, this does not mean that a human embryo is "first a fish, then a pig, and then a human." The old formula "ontogeny recapitulates phylogeny" is now considered outdated in this simplified form. Common developmental patterns are instead understood as the expression of shared evolutionary developmental programs.
→ Source: PBS – Comparative Embryology: The Vertebrate Body as well as the modern classification of Carnegie stages by UNSW Embryology.
When development becomes mechanical: folding, rotation, and organ positioning
Another surprise of embryology: not everything is a matter of "which gene makes which organ?". The body must also organize itself spatially.
During embryonic development, therefore, complex folding and rotation processes occur. Organs change their position, tissues grow at different rates, and structures must arrange themselves correctly in three dimensions.
Development is thus simultaneously genetic, chemical, and mechanical. An organ does not arise just because a gene has been activated, but because cells react to one another and move within an emerging spatial system.
→ Source: NCBI Bookshelf – Embryology, Weeks 6–8
What this research tells us about our body
The big picture
From embryo to adult, the body remains a dynamic system. Cells communicate, tissues are remodeled, structures are maintained, and repair processes continue constantly. Science therefore does not speak of a rigid blueprint, but of a complex development and regulation system.
The 23 Carnegie stages show how precisely early development can be described. The heartbeat around day 22 shows how early functional systems can emerge. Yamanaka's reprogramming research shows that cell identity can be surprisingly flexible biologically. Sinclair investigates how regulatory information changes with age. And Barzilai focuses on the question that is ultimately more decisive for humans: how can health and function be maintained for as long as possible?
The perhaps most important finding is therefore not that we have discovered a secret "code of eternal life." Much more interesting is that our body remains a living, regulated, and constantly renewed system, even in adulthood.
Frequently asked questions about embryonic development
What are the Carnegie stages?
The Carnegie stages are 23 standardized developmental stages of the human embryonic period. They are based primarily on morphological features and cover approximately the first eight weeks of embryonic development.
When does the embryonic heart begin to beat?
The primitive heart tube begins to contract around day 22, according to the University of Minnesota's developmental schedule. However, this is not yet a fully developed four-chambered heart.
Can an embryo remain frozen for 20 or 30 years?
Long-term cryopreservation can pause embryonic development for long periods. The current case from Greece documents a birth after the use of an embryo that had been cryopreserved for more than 22 years.
What does Yamanaka's research have to do with cell aging?
Yamanaka's Nobel Prize-winning work showed that mature cells can be reprogrammed into pluripotent cells under certain conditions. This has fundamentally changed modern research into cell identity and reprogramming.
Is collagen an anti-aging agent?
This phrasing would be scientifically too broad. Collagen is an important structural protein. When considering a dietary supplement, one should distinguish between proven nutritional functions, research into collagen peptides, and unproven anti-aging promises.
Why does Veyt Hyaluron Kollagen Plus fit this topic?
The product provides collagen hydrolysate and hyaluronic acid as well as vitamin C and other micronutrients. Vitamin C contributes to normal collagen formation. The product should therefore be understood as a component of a nutritional routine—not as a means to "turn back" biological age.
References & Scientific Citations
- UNSW Embryology. Carnegie Stages
- UNSW Embryology. Carnegie Stage Table
- Donovan MF, Cascella M. Embryology, Weeks 6–8. StatPearls / NCBI Bookshelf.
- University of Minnesota. Development Timeline of Human Heart Embryology
- Associated Press. After tragedy, a Greek couple welcomes a daughter born from an embryo frozen for 22 years (September 2026).
- Nobel Prize. Mature cells can be reprogrammed to become pluripotent.
- Lu YR, Tian X, Sinclair DA. The Information Theory of Aging. Nature Aging. 2023.
- Albert Einstein College of Medicine. Nir Barzilai, M.D. – Institute for Geroscience.
- Veyt. Hyaluron Kollagen Plus.
