Lecture 2025 01 20: Adolescence and Adulthood
When and How Does Puberty Start?
First, watch this video: https://www.youtube.com/watch?v=1Sx_gI2zTnU
And then, look up this research report for the term 'kisspeptin'
https://www.jneurosci.org/content/25/49/11349.short
or you can download the full document:
https://www.jneurosci.org/content/jneuro/25/49/11349.full.pdf
We only need the conclusion from the Abstract:
These observations suggest that activation of GnRH (gonadotropin releasing hormones) neurons by kisspeptin at puberty reflects a dual process involving an increase in kisspeptin input from the AVPV ( anteroventral periventricular nucleus)and a post-transcriptional change in GPR54 (kisspeptin receptor) signaling within the GnRH neuron.
So where is the anteroventral periventricular nucleus? It is located in the hypothalamus, and is key, sexually dimorphic (its shape and size are different in males and females) brain region crucial for reproductive functions, particularly regulating hormone release like GnRH (gonadotrophin releasing hormone).
What is meant by post-transcriptional?
In genetics, post-transcriptional refers to after it's transcribed from DNA but before it's translated into a protein, controlling gene expression by altering the RNA's stability, localization, and readiness for translation.
And then the production of the sex hormones--estrogen in females, testosterone in males--begins, initiating puberty.
Puberty manifests in humans in primary sex characteristics--the ability to reproduce--and secondary sex characteristics--breasts in females, pubic hair growth in both sexes.
Paus et al. (2005) have demonstrated that the two regions essential for language function--Broca's in the left frontal lobe, and Wernicke's in the left parietal lobe--become stronger and denser between ages 4 and 17. The most significant changes occur in the prefrontal cortex, the part of the brain associated with the ability to regulate emotions and to control attention and behaviour.
Giedd et al. (1999) reported that the prefrontal cortex undergoes a second wave of proliferation just before puberty and a second wave of pruning during adolescence.
In industrialized countries like Canada, female puberty--known as menses, the beginning of menstruation--happening at earlier and earlier ages. Ellis & Garber (2000) hypothesize the reason is diet. Young females have more bodyfat than ever before, and adipose tissue (bodyfat) secretes estrogen. Belsky (2019) hypothesizes that young females growing up households with high levels of conflict
Adolescent Behaviour
According to Epstein (2007) adolescents in the United States and Canada are often subjected to a lot of restrictions, even more than people on active military duty or incarcerted felons. Buchanan et al. (1992) are no moodier than children and flucuations in their hormone levels have a very small impact on their moods.
Emerging Sexuality: Neurology
Androphilic: sexual attraction to males, whether in heterosexual females or gay men.
Gynophilic: sexual attraction to females, whether in heterosexual males or lesbians.
Psychoanalytic theories stressed upbringing; research however has failed to
identify any aspect of parenting that has a significant impact on a child's ultimate
sexual orientation. (Bell, Weinbery & Hammersmith, 1981).
Children raised by homosexual couples or heterosexual couples are equally likely
to become heterosexual adults. (Patterson 1995).
There is little support for the idea that a person's early sexual encounters have a
lasting impact on their sexual orientation. (Bohan, 1996).
Biology appears to play the major role. Gays have a larger proportion of gay
siblings than do heterosexuals (Bailey et al., 1999). An identical twin of a gay man
has a 50% chance of being gay; a fraternal twin has a 15% chance. A similar
pattern has emerged in the studies of lesbians.
Fetal environments also play a role. High levels of androgens in the womb
predispose a person to be attracted to women, whether they are hetero males, or
lesbians. (Meyer-Bahlberg et al., 1995).
For example, Congenital Adrenal Hyperplasia (CAH): Females with CAH, a condition resulting in high androgen exposure in the womb, are more likely to exhibit homosexual or bisexual attraction as adults.
Brains structures of gays and lesbians tend to look like the structures of members
of the opposite sex. The two hemispheres are unequal in size in hetero males and
lesbians, but equally sized among straight women and gay men. (Lindstrom, 2008)
Gender Fluidity
Research suggests links between the hypothalamus, a brain region governing hormones, and gender identity, with studies finding structural and functional differences in hypothalamic areas like the
INAH-3 and BSTc that align more with a person's experienced gender than their assigned sex at birth, pointing to a biological basis for gender fluidity and dysphoria, though it's complex and involves prenatal factors. These studies often show that transgender individuals' brains in these regions resemble those of their identified gender, suggesting early brain differentiation influenced by hormones plays a role, not just social factors.
https://pmc.ncbi.nlm.nih.gov/articles/PMC7415463/
Key Findings & Concepts:
Structural Differences: Specific hypothalamic nuclei, like the interstitial nucleus of the anterior hypothalamus (INAH-3) and bed nucleus of the stria terminalis (BSTc), show size and neuron patterns similar to those of the individual's experienced gender, not their birth sex, in transgender people.
Functional Alignment: Even before hormone therapy, the hypothalamus in transgender individuals can show functional responses (like to certain scents) similar to those of their identified gender, suggesting a biological underpinning for gender identity.
Prenatal Influences: Differences in brain structures and functions, including those in the hypothalamus, are thought to stem from prenatal hormonal environments, influencing the brain's sexual differentiation.
Not Solely Biology: While biology provides strong evidence, gender identity is multifactorial, and research continues to explore the interplay of genetics, hormones, and other mechanisms.
Gender-Based Behaviour
Baily & Zucker (1995) reported that a child's behaviour is a surprisingly good indicator of their adult sexual orientation.
Halim et al. (2014) reported that most child go through a period where they will adamantly refuse to do anything that is stereotypically associated with the opposite gender.
Li et al (2017) reports that children who engage in gender nonconforming behaviour are more likely to become gay, lesbian, or bisexual adults.
Women's sexual orientation is not a good predictor of their physiological arousal to erotic stimuli. Straight women are equally aroused by erotic pictures of women or men, and lesbians are only slightly more aroused by erotic pictures of women than of men. (Chivers et al., 2004, 2007).
What do we know about teenage sexual experience? It is difficult to tell if related behavioural problems are the causes or the effects of early sexual debut, but Golden et al. (2106) reports that teenagers who have sex before the age of 15 have a lower sense of self-worth and higher rates of anxiety, depression, aggressiveness, and substance abuse.
Is There a Possible Future For a New Kind of Sexual Brain Architecture?
The answer is yes. I asked Google Gemini this question:
Would it be possible to create a neural link between the prefrontal cortex and the HPA axis?
Creating a neural link between the prefrontal cortex (PFC) and the hypothalamic-pituitary-adrenal (HPA) axis is scientifically possible, as these systems are already biologically connected through complex, indirect neural pathways. As of 2026, researchers are actively using neuromodulation to "strengthen" these links to treat stress-related disorders
https://pmc.ncbi.nlm.nih.gov/articles/PMC12090024/
When and How Did Menopause Emerge in the Human Genome?
Human menopause is defined as menstrual cycle cessation and usually is recognized 1 year after the final menses (Col et al., 2009).
Anatomically Modern Humans (~50,000 Years Ago): Some research posits a recent evolution, potentially within the last 50,000 years, coinciding with the dispersal of modern Homo sapiens. This timeline allows for the accumulation of the fertility-diminishing mutations that define the phenotype.
https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2016.00222/full
The Grandmother Hypothesis (Adaptive Selection): This theory suggests that natural selection favored females who ceased reproduction early. By doing so, they could provide vital care and food to their grandchildren, increasing the survival of their own genetic line through "inclusive fitness".
An Idea that has Persisted: Erikson's Stages of Psychosocial Development.
So what exactly did Erikson's theory of psychosocial development entail? The stages that make up his theory are as follows:
Stage 1: Trust vs. Mistrust (Infancy from birth to 18 months)
Stage 2: Autonomy vs. Shame and Doubt (Toddler years from 18 months to three years)
Stage 3: Initiative vs. Guilt (Preschool years from three to five)
Stage 4: Industry vs. Inferiority (Middle school years from six to 11)
Stage 5: Identity vs. Confusion (Teen years from 12 to 18)
Stage 6: Intimacy vs. Isolation (Young adult years from 18 to 40)
Stage 7: Generativity vs. Stagnation (Middle age from 40 to 65)
Stage 8: Integrity vs. Despair (Older adulthood from 65 to death)
Much like Sigmund Freud, Erikson believed that personality developed in a series of stages. Unlike Freud's theory of psychosexual stages, however, Erikson's theory described the impact of social experience across the whole lifespan. Erikson was interested in how social interaction and relationships played a role in the development and growth of human beings.
Adulthood
The stage of development that begins around 18 to 21 and ends in death. From an
evolutionary psychology point of view, however, an adult is an infant's way of
making another infant.
Adulthood is a period of life that is characterized by unanticipated change. Change slows but never stops, and its pace is faster than we expect.
The physical peak occurs in the early 20s, and the slow decline begins between 26 and 30. After this age, you will lose one pound of muscle, to be replaced with fat.
Sensory abilities will decline, and brain cells die off faster.
It is important to note (from an evolutionary perspective) that the normal human
life span, up until the last 100 years was 32 for men, and 28 for women.
On the positive side, there is greater resistance to colds and flu. In Canada, 84% of
men and woman will reach age 65.
Prefrontal cortex and subcortical connections deteriorate with age. Episodic memory declines, but not semantic memory; working memory, but not long-term memory.
Older adults, however, improve their strategies to maintain performance. (Blackman & Dixon, 1992).
Division of Labour
As the brain ages, it becomes dediffentiated. (Lindenberge & Baltes, 1994).
When young adults try to keep verbal information in working memory, the left prefrontal cortex becomes more strongly activated than the right; the opposite happens for spatial memory. (Smith & Jonides, 1997).
Bilateral asymmetry largely disappears in older adults; it suggests that older brain is compensating for declining abilities in each neural structure by calling in other neural structures to help. (Cabeza, 2002).
Changing Goals & Roles
Socioemotional selectivity: young adults are largely motivated toward the acquisition of information that will be useful to them in the future; older adults are oriented towards information that is emotionally satisfying. (Carstensen et al.,2000).
Memory generally declines with age, but the ability to remember negative information—declines much more quickly than the ability to remember positive information. (Carstensen et al., 2000).
Older adults are better at sustaining positive emotions and curtailing negative ones.
(Isaacowitz, 2012); they also express fewer negative ones.
Does marriage make one happier, or do happier people get married? (Lucas et al.,2003).
Children do not increase parental happiness (Senior, 2014) ; they may decrease it.
What is Aging, Anyway? A Look at Human Telomeres
Human telomeres, protective caps on chromosome ends, shorten with each cell division, acting as a biological clock that signals cellular aging, leading to senescence, increased disease risk (like heart disease, fibrosis), and reduced lifespan, though lifestyle and genetics influence this rate, and longer telomeres aren't always better, sometimes promoting cancer by allowing mutated cells to persist.
Life Extension by Genetic Engineering: What is the Human Maximum?
Can nanotechnology be used to protect human telomeres?
In 2026, research into nanotechnology for protecting human telomeres has advanced from theoretical concepts to promising in vitro studies and preclinical development.
Scientists are utilizing nanomaterials both as therapeutic agents themselves and as delivery vehicles for telomere-restoring molecules.
https://www.sciencedirect.com/science/article/pii/S0024320525005399
We explore current therapeutic strategies ranging from telomerase modulation to senolytic approaches, highlighting emerging technologies in drug discovery, including CRISPR-based interventions, nanomedicine, mRNA-based therapies, partial cellular reprogramming, and artificial intelligence applications. The convergence of mechanistic understanding with innovative therapeutic approaches positions telomere biology as a promising frontier for addressing multiple age-related conditions simultaneously, potentially shifting medicine from reactive disease treatment toward proactive aging-focused prevention