Do aging human phenotypes recapitulate ancestry?
I previously posted about this idea; please read it here. However, revisiting it is not only useful for newer readers, but every iteration of the idea expands and extends the analysis, allows for more ideas to come forth, more hypotheses to be tested, and more possibilities to be discussed and evaluated.
Read this about recapitulation theory:
The theory of recapitulation, also called the biogenetic law or embryological parallelism—often expressed using Ernst Haeckel’s phrase “ontogeny recapitulates phylogeny”—is a historical hypothesis that the development of the embryo of an animal, from fertilization to gestation or hatching (ontogeny), goes through stages resembling or representing successive adult stages in the evolution of the animal’s remote ancestors (phylogeny).
The idea of this post is this: Aging human phenotypes recapitulate ancestry. In other words, as people age, their physical appearance (and perhaps other phenotypic markers including behavior) tend to reflect to greater or lesser degrees certain aspects of their ethnoracial ancestry.
Imagine a Greek-Danish hybrid. Perhaps they look (and act?) “more Greek” when younger and “more Danish” when older.
Mono-ethnic individuals can display such trends; after all, modern ethnies are derived from mixtures of older stocks.
We can compare that to pictures of the Duce taken in later years:
Mussolini obviously looked more typically European as he aged.
This phenomenon may be restricted to just physical appearance, or, more interestingly, behavioral changes may track with appearance over time (see below), associated with phenotypes reflecting ancestral stocks. An individual may be a greasy, undisciplined southerner as a youth and a restrained, more gracile northerner in older age.
Does this tracking of ancestral phenotypes with aging follow a specific direction as does the ontology-phylogeny association (in that case toward greater evolved complexity and toward the final form of the organism)?
In Mussolini’s case you can say that the direction was toward a more gracile and “northern” phenotype (but not by much, truth be told), although the coarseness of aging to a large extent counteracts any racial gracilization that occurs (perhaps this is why it is “not by much”), or from Mediterranid to Alpinid, or, perhaps more properly speaking, from East Mediterranean/Levantine toward a more West Mediterranean/Central European focus.
That may be a specific case and not generalizable, or it may reflect some underlying trends, at least for some Europeans, as well as for people of part European descent (such as Ted Williams). Here we see a young Ted Williams, who looks ready for a zoot suit riot; on the other hand, a John Wayne-esque older Ted Williams reflects more of his paternal heritage. Williams was of mixed British Isles (Welsh, Irish) and (diverse) Mexican ancestry.
Getting back to Europeans – Mussolini was Northern Italian. What about a Southern Italian? A young Joe DiMaggio (Sicilian ancestry) looks like a S. Italian zip; an older Joe DiMaggio looks like a N. Italian banker. All anecdotal evidence to be sure; but provocative nevertheless. A wholly Northern European celebrity? Perhaps Sean Connery would be instructive here?
Does the same hold for unmixed non-Europeans? Who knows? Does it require some threshold level of different underlying ancestries and, if so, how far back? Racial purity in the absolute sense it a myth, and, once again considering Europe, if you can far back enough all Europeans are mixes of different tribes or proportions of Hunter-Gatherer, Neolithic Farmer, Steppe, and other elements. In a case of someone of perhaps less “recent” “admixture” would they recapitulate their proportions of those ancient ancestral source populations? These are all fruitful questions for more study.
Individuals of mixed race, crosses of different continental population groups, would be expected to show similar patterns of phenotypic change with age.
What could be possible mechanisms for this phenomenon? Epigenetic changes with age? Hormonal changes with age, affecting gene expression (including by epigenetic effects)? Are there timed sequences of gene expression “cassettes” activated by some mechanism (including those just mentioned) that activate different phenotypic profiles at different ages.
Also, we can ask whether this phenomenon is just an emergent property of the complexities of gene expression from mixed ancestry, or whether there is some sort of selective pressure at work. Is reproductive success at younger ages emphasized by a less gracile, more “southern,” more r-selected type phenotype, and then, with increasing age, and the need to provide for family, to be a stable provider, to increase fitness of grandchildren and the extended family, and/or group selective mechanisms for prudent group activity, older people expresses a more k-selected, gracile, restrained, “northern” phenotype?
Does this imply that behavioral changes accompany the changes in physical appearance? The impetuous energetic youth looking more like a greasy swarthoid, and the same individual in a more prudent old age, looking more like the centroid of the European phenotypic range (for Europeans)?
No doubt, we can find pictures of people who look less racially gracile with age. So, for the theory in its broadest sense, phenotypic change with age is key, not necessarily becoming more racially gracile with age. It may not even be a matter of a unidirectional trend – toward either greater or lesser racial gracility with age. One could imagine a situation where a person, at different stages of their life, reflects different aspects of their ancestry in their phenotype, possibly fluctuating back and forth between different degrees of racial gracility.
How long does it take for these changes to occur? Decades would certainly be enough time. But less than a decade? Years? I would think that changes may not be so noticeable for periods less than ten years.