My hypothesis to explain why today's adults look much younger than adults from decades ago

 Especially the "millennial" generation

Too many chronologically "youngest"??

The perception that today's adults, especially those between 30 and 50, look much younger than their parents and grandparents did at the same age has become quite popular. But if this isn't just an exaggerated impression, then what could be causing this change?

The "media" loves to list changes in habits or culture as the main causes. For example, the way we dress, eat, and other health-related habits would largely explain why today's adults look much younger than adults from 3 or 4 decades ago... Even if these factors have some influence, these differences begin with the very facial structure of today's adults compared to those of the past. An explanation limited to cultural generational differences may not be sufficient, as it could also be a biological phenomenon.

But what would that be?

I bet it's related to the demographic transition and also to cultural habits, but with intergenerational biological effects. I'll explain...

Over the last four or five decades, in many Western countries and some in the East, people have started having fewer children. So, firstly, there has been a reduction in the size of new generations. Secondly, which I consider the most important in my hypothesis, is that, in addition to having fewer children, people also started having them later, starting in their 30s. This is related to the increased mutational load in the human body, as we accumulate more mutations throughout our lives, that is, we age... And since older parents are more mutant, they would be more likely to experience a relative decline in the quality of their reproductive material, sperm, and eggs, resulting in more mutant children (??). But that's not the point, because it may be that youngest children tend to be more neotenic, retaining more childhood traits, both in terms of appearance and behavior. So, with people having fewer children and later, phenotypically "youngest" children, or children born to older parents, would have become more common demographically, including biological characteristics that are perhaps more common in this group. Which, on the one hand, could be a good thing: appearing younger than one's age, but on the other, it could be associated with certain behaviors considered common in new generations, especially adults aged 30 to 50, or "millennials," and not widely appreciated: such as "laziness," individualism, and a more deeply rooted attachment to childhood... a result of their (our?) own "underdeveloped" biologies?? As if we were human "tadpoles" that never quite reach "normal" or "complete" development??

It may also be related to an increase in disorders and diseases due to the increased accumulation of mutations over recent generations. This would explain why there have been more cases of young adults becoming ill and even dying (?).

In any case, unhealthy and assiduously practiced habits, such as smoking and drinking from an early age, having a poor diet, or constant exposure to the sun without any protection, may also have contributed to the premature aging (?) of young adults in previous generations, and new generations have only partially or predominantly reduced the practice of these habits...

Finally, in addition to the factors mentioned, as well as the one I considered the most important for my hypothesis, others could also be considered, such as the prevalence of assortative relationships, in which people are freer today to choose their mates according to their tastes. This, in turn, may have contributed to greater selective pressure for neotenic traits, perhaps associated with more robust sexual selection. (Not just a matter of appearing younger, but also of presenting a more "aesthetically pleasing" appearance.) If, in the past, arranged relationships were much more common and may have contributed to a greater randomness of biological makeup...

But is this supposed or possible phenomenon will it continue to manifest itself in younger generations?

Perhaps not so much, if according to my hypothesis, this tendency to appear younger among "millennials", besides being the effect of a period or demographic transition in which there was an abundance (more in the sense of relative proportion than absolute increase) of "chronologically youngest" children, is also a specific period in the dynamics of intergenerational mutation accumulation, in which the new generations, children of "millennials" and "zoomers" (Generation Z: born between 1994 and 2005ish), would be inheriting/an even greater mutational load, if they are already children of a majority who were born to older parents. So, this possible factor may be contributing to undoing this "spell" of "extended youth" (by appearance) among the youngest, although those who look younger for their age will continue to be relatively more common than in relation to generations much older than them.

3 pontos para explicar similaridades geracionais e diferenças intergeracionais de comportamento /3 points to explain generational similarities and intergenerational differences in behavior

 1. Gerações tendem a expressar aspectos estruturais ou socioeconômicos de suas épocas

Então, se os jovens, atualmente, estão em maior risco de ficarem desempregados do que nos tempos de juventude das gerações mais velhas, não é apenas porque tem mais preguiçosos entre os jovens atuais, mas também ou especialmente por causa de uma maior estagnação econômica (entre outros fatores, tal como o aumento da automação), resultando em um déficit entre a oferta e a demanda de emprego...

Mesmo diferenças físicas, como de estatura e peso entre as gerações, também podem ser reflexos (nesse caso, cumulativos) de mudanças nas estruturas socioeconômicas, de quando tinha mais pobreza e desnutrição até quando passou a ter mais fartura.

2. Gerações expressam aspectos genéticos e fenotípicos correntes de suas populações 

Diferenças nos padrões seletivos e reprodutivos podem gerar mudanças na paisagem genética entre as gerações e mais notadamente entre as gerações mais distantes. Por exemplo, décadas com baixas taxas de fecundidade, grande aumento da natalidade tardia e da reprodução assortativa* (com base em similaridades fenotípicas do casal) podem causar um acúmulo progressivo de mutações de uma geração para a outra.

* Parcial e possivelmente associada a uma maior incidência de casos de autismo, por exemplo, no vale do Silício, região do estado da Califórnia, nos EUA, com grande concentração de engenheiros, cientistas e técnicos da computação mais propensos a estarem "dentro do espectro"

E como citado acima como parte reflexiva do estado dominante das estruturas socioeconômicas de uma geração, diferenças físicas também expressam o estado corrente de características fenotípicas da mesma, tal como a estatura e o peso. 

3. Gerações tendem a expressar aspectos culturais e psicológicos específicos às suas primeiras décadas de existência

A partir de suas tendências reativas mais comuns a esses aspectos, tal como por diferenças culturais de criação, por exemplo, das gerações mais antigas, em que o modelo era mais "tradicional" ou autoritário, e das gerações mais novas (atualmente, nesse início de século XXI), em que tem havido uma maior atenuação desse autoritarismo dos pais em relação aos seus filhos. 

Além disso, o que é universal à toda geração é uma ligação emotiva à cultura dominante de sua época, especialmente de seus "anos formativos', de infância e juventude, ainda que a força dessa ligação também dependa de outros fatores, tal como a compatibilidade de características intrínsecas, como a personalidade, com a cultura ou, subculturas de influência, no caso das tribos urbanas.  

1. Generations tend to express structural or socioeconomic aspects of their times

So, if young people today are at greater risk of becoming unemployed than in the youth in older times, it is not only because there are more lazy people among today's young people, but also or especially because of greater economic stagnation ( among other factors, such as increased automation), resulting in a deficit between job supply and demand...

Even physical differences, such as height and weight between generations, can also be reflections (in this case, cumulative) of changes in socioeconomic structures, from when there was more poverty and malnutrition to when there was more affluence.

2. Generations express current genetic and phenotypic aspects of their populations

Differences in selective and reproductive patterns can generate changes in the genetic landscape between generations and more notably between more distant generations. For example, decades with low fertility rates, a large increase in late births and assortative reproduction* (based on the couple's phenotypic similarities) can cause a progressive accumulation of mutations from one generation to the next.

* Partially and possibly associated with a higher incidence of autism cases, for example, in the Silicon Valley region of the state of California, in the USA, with a large concentration of engineers, scientists and computer technicians more likely to be "within the spectrum "

And as mentioned above as a reflective part of the dominant state of the socioeconomic structures of a generation, physical differences also express the current state of its phenotypic characteristics, such as height and weight.

3. Generations tend to express cultural and psychological aspects specific to their first decades of existence

Based on their more common reactive tendencies towards these aspects, such as cultural differences in upbringing, for example, of the older generations, in which the model was more "traditional" or authoritarian, and of the younger generations (currently, at the beginning 21st century), in which there has been a greater attenuation of this authoritarianism of parents towards their children.

Furthermore, what is universal to every generation is an emotional connection to the dominant culture of their time, especially their "formative years" of childhood and youth, although the strength of this connection also depends on other factors, such as compatibility of intrinsic characteristics, such as personality, with culture or, subcultures of influence, in the case of urban tribes.