A Duel in Mid-Air
From Homo transformans: The Origin and Nature of the Species
Illustration by Epic Made
A Duel in Mid-Air
One afternoon, Ruwena [as a river otter] was visiting the otter family in a nearby stream. Suddenly, the female otter barked several warning calls to her pups and anyone else who would listen. She was looking up at the sky. Ruwena did the same and saw a strange creature, a lyvulfon, rising into the air with a pup in its claw.
Ruwena launched herself upwards out of the water, toward the lyvulfon, and in mid-air transformed into a Cooper’s hawk. The hawk immediately attacked the lyvulfon. The creature could not defend itself and still hold onto the pup. So, it dropped the pup and turned on the hawk. Then the aerial battle really began.
(Excerpt from Homo transformans: The Origin and Nature of the Species)
Metamorphosis is a change in the structure and function of an organism into an altogether different shape, form, and function (Aguirre, et al., 2014; Bishop, et al., 2006). It is the development of two different lifeforms from the same set of genes (genome). Caterpillars become butterflies or moths, tadpoles become frogs.
Metamorphosis is quite common. There are more species that undergo metamorphosis than there are those that do not. It occurs in several classes of animals: worms, aquatic invertebrates, arthropods, and amphibians. These species are considered to have complex life cycles (Aguirre, et al., 2014; Collet & Fellous, 2019).
Ontogenesis is the development of an organism from its earliest stage through maturity. It reflects the gradual growth and development of a single life form, from a simple or immature form to a more complex or mature form. Mammals, birds, reptiles, and most fish undergo ontogenesis and are considered to have simple life cycles.
Morphogenesis refers to the development (differentiation) of a life form’s shape and size. It applies to both ontogenesis and metamorphosis.
Metamorphosis in Nature
Metamorphosis is characterized by dramatic changes in form and function that reflect a major shift from one way of life to a categorically different way of life (Bishop, et al., 2006; Collet & Fellous, 2019). The following differences usually occur as a result of undergoing metamorphosis.
- Change in physical structure (morphology), organ systems (physiology), and function (life style) with two distinct life forms supported by the same genome.
- Change of habitat in which the two life forms have different niches: e.g., changing from land to air, water to land, fresh water to salt water, etc.
- Changes in feeding and food sources in which anatomy affects how food is acquired: g., from feeding on vegetation to feeding on nectar.
- Change of locomotion in which morphology alters the mode of transportation: g., from land based to flight, from swimming to hopping on land.
- Change in reproductive capability, typically from a nonreproductive state to the development of reproductive organs.
The process of metamorphosis is not the same in all species that undergo it. Different classes of animals may have developed metamorphosis independently along different evolutionary lines (Aguirre, et al., 2014; Collet & Fellous, 2019). For example, the biologic processes of metamorphosis in insects and amphibians are vastly different.
Insect metamorphosis is a radical change wherein the body of the caterpillar (the larval form of the insect) is virtually destroyed before a new form is generated. Genetically programmed cell death (apoptosis) triggers the release of enzymes that break down the original form and structure of the caterpillar (Buszczak & Segraves, 2000; Ureña, et al., 2016). Subsequently, the insect is completely redesigned, creating an altogether different insect in form and function: a butterfly.
In amphibians, the structure of the body (e.g., a tadpole) undergoes gradual changes. Cells and tissues are resorbed as others are being formed (Brown & Cai, 2007). The tadpole gradually changes its form and function as it develops into a frog.
Humans develop from a single cell into our final form without becoming two separate lifeforms. Initially, the human embryo undergoes remarkable changes before taking form as a human. From that point forward, however, it continues to undergo ontogenetic development, remaining in human form throughout life. Interestingly, frogs and humans use the same hormones ‒ cortisone and thyroid hormones ‒ for growth and development (Buchholz, 2015).
Ruwena was introduced to Madam Merena (mer-ā-nah) who would evaluate her swimming prowess. When asked if she could swim, Ruwena answered, “Yes.” Then Madam Merena asked Ruwena to swim across the indoor pool using her preferred swimming style. It suddenly dawned on Ruwena that her preferred swimming style was river otter, which she couldn’t demonstrate masquerading as H. sapiens. Nevertheless, swimming as an otter had come naturally to her. Surely, I ought to be able to swim as a human as well, she thought. So, Ruwena slipped off the side of the pool, into the water – and promptly sank like a rock. River otters have a thick, water-repellant coat of fur, an insulating layer of fat which provides buoyancy, and webbed feet. As a human, Ruwena had none of the above. (Excerpt from Homo transformans: The Origin and Nature of the Species)
Although pure fantasy, when an H. transformans changes into another species of animal, most of the criteria for metamorphosis apply.
- River otters and humans share some of the same features, albeit considerably rearranged. Humans can have webbed or fused fingers and toes (syndactyly), can develop excess hair growth over the body (hypertrichosis), and can develop excess body fat (all too common). Humans, however, do not develop a long muscular tail. River otters can stay submerged for about eight minutes. The average human can stay submerged for about two minutes.
- River otters are aquatic mammals that live both in rivers and on land. Although humans can swim in water, they cannot live in water without an artificial means to protect their skin.
- Feeding behaviors are quite similar – and, in some instances, almost identical – to that of humans. (Humans have been known to “wolf” down their food.)
- The otter’s webbed feet and muscular tail can propel it at about 7 miles per hour underwater. A trained athlete can swim about 5 to 6 miles per hour ‒ faster with flippers in lieu of webbed feet.
- Humans acquire reproductive capability at puberty; however, they develop reproductive organs from birth.
There is one other significant difference: size. The average river otter weighs between ten and thirty pounds and is about 2½ to 5 feet long, with males much larger than females. This raises the knotty problem of conservation of mass.
It would be lovely to become a river otter and race underwater, or a peregrine falcon and dive at 200 miles per hour, or perhaps become a brown bear with its strength and power. Alas, humans cannot. Our mammalian genome does not support it. Even if it did, metamorphosis is irreversible in those species that have the capability.
Aguirre, J. D., Blows, M. W., Marshall, D. J. (2014.) The genetic covariance between life cycle stages separated by metamorphosis. Proceed Royal Soc B Biol Sci, 281(1788). https://doi.org/10.1098/rspb.2014.1091.
Bishop, C. D., Erezyilmaz, D. F., Flatt, T., et al. (2006.) What is metamorphosis? Integrative and Comparative Biology, 46(6), 655-661. https://doi.org/10.1093/icb/icl004.
Brown, D. D., and Cai, L. (2007.) Amphibian metamorphosis. Dev Biol, 306(1), 20–33. doi: 10.1016/j.ydbio.2007.03.021.
Buchholz, D. R. (2015.) More similar than you think: Frog metamorphosis as a model of human perinatal endocrinology. Dev Biol, 408(2), 188-95. doi: 10.1016/j.ydbio.2015.02.018.
Buszczak. M., and Segraves, W. A. (2000.) Insect metamorphosis: Out with the old, in with the new. Current Biology, 10:R830–R833.
Collet, J., & Fellous, S. (2019). Do traits separated by metamorphosis evolve independently? Concepts and methods. Proceedings. Biological sciences, 286(1900), 20190445. doi:10.1098/rspb.2019.0445.
Ureña, E., Chafino, S., Manjón, C., et al. (2016.) The Occurrence of the Holometabolous Pupal Stage Requires the Interaction between E93, Krüppel-Homolog 1 and Broad-Complex. PLoS Genet, 12(5):e1006020. doi: 10.1371/journal.pgen.1006020.
Orig. 23 August 2019
Rev. 26 September 2019
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