<p>This thesis outlined a novel operationalization and extension of the thrifty phenotype and fetal overnutrition hypotheses, two evolutionary developmental hypotheses stemming from the developmental origins of health and disease perspective, for developmental pathways from prenatal risk through child growth to early puberty. Support has accumulated for both, but previous studies have not clearly determined which hypothesis better predicts early puberty. Using the Fragile Families and Child Wellbeing Study (<i>n</i>=4898), the thrifty phenotype and fetal overnutrition pathways were tested against each other, separately by sex, and race/ethnicity for adrenal, and gonadal pubertal markers. Results indicated that in general, both hypotheses were supported. Contrary to hypotheses, the thrifty phenotype pathway did not predict perceived pubertal timing better in boys and the fetal overnutrition pathway did not predict perceived pubertal timing best in girls. Instead, both pathways predicted puberty equally well between girls and boys and the fetal overnutrition pathway stemming from maternal gestational weight gain was stronger than the pre-pregnancy BMI pathway. Individual paths of the hypothesized pathways were generally supported when analyzed by race/ethnicity group separately, but support for the entire pathways were sparse. Implications of this work are that pubertal timing may be similarly programmed by restrictive and overnutrition prenatal risks, both should be prioritized, and that interventions for maternal gestational weight should be prioritized over interventions for pre-pregnancy BMI for reducing rates of early puberty. </p>

Genetic and home chaos influences in early childhood have been independently associated with externalizing problems, characterized by inattentive, hyperactive, and aggressive behaviors. However, the Behavioral Genetics approach indicates that genetic and environmental influences, although independently effective, interact to produce behavior throughout development. Thus, this thesis uses two samples, the Early Growth and Development study (EGDS), n= 564, and the Avon Longitudinal Study of Parents and Children (ALSPAC), n= 8,952, and two genetically-sensitive approaches, a parent-child adoption approach and a polygenic scoring approach, to examine how genetic influences and home chaos interact in early childhood (age 3-4) to predict externalizing problems later in childhood (age 7). Results indicate that, although home chaos is correlated with later externalizing problems, the effect is reduced in the context of earlier externalizing, possibly suggesting that home chaos is most salient for concurrent, not later, externalizing problems. In addition, genetic influences were not predictive of externalizing problems in either study, nor was the interaction of home chaos and genetic influences. This pattern of results suggests that, although home chaos may be an important factor for concurrent externalizing problems, other factors, e.g., parenting style and prenatal risk, may be more salient than home chaos, especially in interaction with genetic effects. Further, failure to find genetic influence in this thesis suggest that accounting for the broad scope of genetic influences on complex traits like externalizing and the specific genetic risk for individual externalizing phenotypes is important in attempts to find genetic influence and interaction.

Adolescence is a time of great changes, a time where experimentation and exploration is expected and when the values of authority figures are examined and challenged. Adolescents will experiment and push the boundaries of all aspects of their life in order to find their own place and identity in a world that has changed its expectations of them. Use of drugs is one of the ways that they do this. Australian adolescents grow up in a society where alcohol and tobacco is an acceptable part of daily life. Their use of drugs is at least on par with and in some cases exceeds that of the general population. The overall goals of this research were to gain more information on drug use of Australian adolescents, using existing data sets. This research examined, using a number of different age groups, the differences in adolescent drug use between urban and rural Australia for lifetime use, use in the last year and use in the last month using the 2002 edition of the Australian School Student Alcohol and Drug (ASSAD) survey series in conjunction with the 2001 National Drug Strategy Household Survey (NDSHS). It also used these data sets to investigate differences between indigenous adolescents and non-Indigenous adolescents and whether there were any differences in adolescent drug use across socio-economic status groups. Four hypotheses were developed. The first was that rural adolescents are more likely than urban adolescents to use licit drugs and the second was that urban adolescents are more likely than rural adolescents to use illicit drugs. Thirdly, that Indigenous adolescents are more likely than non-Indigenous adolescents to use both licit and illicit drugs and the fourth was that adolescents from low socio-economic status (SES) groups are more likely than adolescents from high SES groups to use licit and illicit substances. The data offered little support for any of the hypotheses. The hypothesis on rural adolescents being more likely to use licit drugs was supported by the ASSAD surveydata but not the NDSHS. All other hypotheses were not supported by either of the data sets. While there are aspects of the information from the two data sets that are contradictory making it difficult to prove or disprove the hypotheses formulated for this research, they highlighted a number of aspects of adolescent drug use. The first of these is that this research supports the premise that rural adolescent drug use rates are converging with urban drug use rates for younger adolescents. It also highlighted that there are a large number of rural school students who are using alcohol and cannabis. The ASSAD data also confirmed other Australian research showing that Indigenous adolescents are less likely than their non-Indigenous counterparts to use alcohol. Both data sets confirmed previous research by indicating that adolescents from the high SES groups are more likely than their counterparts in the lower SES groups to consume alcohol. Further investigation is needed to find out why the data sets did not substantiate each other and to gain further insight into the consumption of alcohol by Indigenous adolescents and adolescents from the higher socio-economic status groups. Increasing the samples of Indigenous people in both of the data sets and lobbying the Australian Bureau of Statistics to increase their sample for the Indigenous Social Survey to include 12-14 year olds should give more information on Indigenous adolescents that could be used in research and prevention activities.

Despite executive function deficits now been examined in relation to the propensity to commit crimes in the general offending population, to date there has been little investigation of this within an intellectually disabled offending sample. The aim of the present study was to undertake a content analysis of the offending patterns and general behavior of Disabilities SA clients with a view to ascertaining whether such an assessment is justified for this offending group. The present study involved content analysis of five participants, currently clients of Disabilities SA. A coding schema was used to assess for evidence of four executive functions: Learning from previous experience; Engaging in logical reasoning; Impulse control; and Understanding the reactions of others. Findings suggest that offenders with intellectual disability have difficulties in all four areas. These findings are discussed in terms of the need for more comprehensive assessment and treatment implications.

<p>Infant exposure to the microbial and allergenic content of indoor floor dust has been shown to play a significant role in both the development of, and protection against, allergies and asthma later in life. Resuspension of floor dust during infant locomotion induces a vertical transport of particles to the breathing zone, leading to inhalation exposure to a concentrated cloud of coarse (> 1μm) and fine (≤ 1μm) particles. Resuspension, and subsequent exposure, during periods of active infant locomotion is likely influenced by gait parameters. This dependence has been little explored to date and may play a significant role in floor dust resuspension and exposure associated with forms of locomotion specific to infants. This study explores associations between infant locomotion dynamics and floor dust resuspension and exposure in the indoor environment. Infant gait parameters for walking and physiological characteristics expected to influence dust resuspension and exposure were identified, including: contact frequency (steps min^-1), contact area per step (m²), locomotion speed (m s^-1), breathing zone height (cm), and time-resolved locomotion profiles. Gait parameter datasets for standard gait experiments were collected for infants in three age groups: 12, 15, and 19 months-old (m/o). The gait parameters were integrated with an indoor dust resuspension model through a Monte Carlo framework to predict how age-dependent variations in locomotion affect the resuspension mass emission rate (mg h^-1) for five particle size fractions from 0.3 to 10 μm. Eddy diffusivity coefficients (m² s^-1) were estimated for each age group and used in a particle transport model to determine the vertical particle concentration profile above the floor.</p><p>Probability density functions of contact frequency, contact area, locomotion speed, breathing zone height, and size-resolved resuspension mass emission rates were determined for infants in each group. Infant standard gait contact frequencies were generally in the range of 100 to 300 steps min^-1and increased with age, with median values of 186 steps min^-1for 12 m/o, 207 steps min^-1 for 15 m/o, and 246.2 steps min^-1 for 19 m/o infants. Similarly, locomotion speed increased with age, from 67.3 cm s^-1at 12 m/o to 118.83 cm s^-1 at 19 m/o, as did the breathing zone height, which varied between 60 and 85 cm. Resuspension mass emission rates increased with both infant age and particle size. A 19 m/o infant will resuspend comparably more particles from the same indoor settled dust deposit compared to a 15 m/o or 12 m/o infant. Age-dependent variations in the resuspension mass emission rate and eddy diffusivity coefficient drove changes in the vertical particle concentration profile within the resuspended particle cloud. For all particle size fractions, there is an average of a 6% increase in the resuspended particle concentration at a height of 1 m from the floor for a 19 m/o compared to a 12 m/o infant. Time-resolved locomotion profiles were obtained for infants in natural gait during free play establish the transient nature of walking-induced particle resuspension and associated exposures for infants, with variable periods of active locomotion, no motion, and impulsive falls. This study demonstrates that floor dust resuspension and exposure can be influenced by the nature of infant locomotion patterns, which vary with age and are distinctly different from those for adults.</p>

The glymphatic system (GS) is primarily a neural waste clearance system that relies on cerebrospinal fluid (CSF) to transport neuronal byproducts and nutrients. Studies demonstrate that sleep facilitates movement within the GS to clear metabolites and maintain cerebral homeostasis. However, functions of the GS during sleep and its implications have predominantly been examined in animals, clinical/at-risk, and ageing populations. Our understanding of the neural mechanisms underlying GS during sleep in typically developing human infants is limited. The objective of this study was to investigate the relationship between GS imbalance (characterized by extra-axial CSF [EA-CSF] from MRI structural images) and sleep problems in early development. Data from 75 infants were obtained from the Baby Connectome Project. Sleep was indexed with the Brief Infant Sleep Questionnaire. Multilevel models were utilized to explore the associations of EA-CSF volumes and EA-CSF/total cerebral volume (TCV) ratios with age and sleep. We replicated previous findings on lower TCV and overall CSF volumes in infants with dysregulated sleep compared to infants with regulated sleep. Results also demonstrated a decline in EA-CSF/TCV ratios from 9 to 34 months of age (b = -0.0005, <i>t</i> = -2.19, <i>p</i> = .032). Sleep problems were not associated with differential developmental trajectories of EA-CSF volumes or EA-CSF/TCV ratios. Findings from the present study do not support sleep problems as a mechanism through which CSF disbursement within the GS is altered. Although elevated EA-CSF is associated with developmental and neurodegenerative pathology, in early typical development, its links with sleep dysregulation are not robust.

<p>The manifestations of early sleep disturbances on cerebrospinal fluid and their relations with early developmental competencies are understudied. Recent studies highlight cerebrospinal fluid disbursement as a potential factor associated with dysfunctions in brain development. With two studies, we explored sleep and extra-axial cerebrospinal fluid (EA-CSF) connection as a potential mechanistic pathway by which sleep dysregulation influences brain and behavior development. Specifically, we evaluated associations between (1) EA-CSF to total cerebral volume (EA-CSF/TCV) ratios, (2) parent-report of child sleep problems, and (3) social communication development in typical (Study 1) and atypical populations (Study 2). In typical infants, early sleep problems did not precede later elevated EA-CSF/TCV ratios or social-communicative competence. Elevated EA-CSF/TCV ratios were associated with impaired social communication skills, suggesting that a relationship between elevated EA-CSF/TCV ratios and social communication impairments exists regardless of neurological or sleep problems. In an atypical population with autism spectrum disorder (ASD), older children with ASD had similar EA-CSF/TCV ratios to a group of their typically developing peers. Sleep problems were negatively associated with EA-CSF/TCV ratios but positively associated with social-communicative impairments for children with ASD, highlighting the influence of sleep problems on both brain and behavioral outcomes in an atypical population. In both studies, EA-CSF volumes continue to increase during early development in the typically developing populations (but not later in the atypical sample), underlining its relevance as a marker of atypical processing. Recognizing the potential roles of EA-CSF in influencing several biosocial and behavioral aspects of development, we encourage researchers to continue to explore EA-CSF growth, especially during developmental periods of flux and transition. Future work with longitudinal data can also serve to explore sleep-related developmental changes in EA-CSF, in association with behavioral and phenotypic changes. </p>