Australian Aboriginal people have a lower intelligence
This is a very vague question. What is intelligence? And how do you measure it? Is this question about some sort of innate, genetic ability? Or is it about the intelligence of specific Aboriginal people in 1912? (In which case it will likely be difficult to find good sources, because of scientific racism).
Anyway, here are some studies about the subject:
Two tests of classificatory ability based on Piaget's theory of cognitive development, and the Peabody Picture Vocabulary Test (PPVT), were administered to 40 full-blood urban Aboriginal children in the Northern Territory of Australia. The PPVT was also given to 80 white urban children of similar low-socioeconomic status. A trend in an earlier study for high-contact Aboriginals to perform on classification tests at about the same level as white children in a similar environment was confirmed, despite the markedly lower verbal IQ scores of Aboriginal children. P. R. de Lacey, 1971.Classificatory Ability and Verbal Intelligence among High-Contact Aboriginal and Low Socioeconomic White Australian Children
Testing school readiness and language skills:
Using data on 4-5 year olds in the Longitudinal Survey of Australian Children, we focus on two cognitive tests: the Peabody Picture Vocabulary Test (PPVT) and the ‘Who Am I?’ test (WAI). We estimate the test score gap between Indigenous and non-Indigenous children to be about 0.3 to 0.4 standard deviations, suggesting that the typical Indigenous 5 year-old has a similar test score to the typical non-Indigenous 4 year-old. Between one-third and two-thirds of the Indigenous/non-Indigenous test score gap appears to be due to socio-economic differences, such as income and parental education. Leigh & Gong, 2008. Estimating cognitive gaps between Indigenous and non-Indigenous Australians (the APO doesn't seem to be peer reviewed)
"A history of Indigenous psychology" also gives a decent overview:
The Cambridge Anthropological Expedition took place in the late 19th century to study the people of the Torres Straits islands as a representation of ‘primitive man’. Test scores on a number of sensorimotor functions were compared between people from Murray Island and a small number of English people. Overall, few differences were found, making it hard to interpret the results from a social Darwinist perspective, particularly those that favoured the Murray Islanders’ performance.
Later, in the early 1900s, Porteus, a teacher at a special school, devised a series of maze tests to be used as a screening device for ‘mentally defective’ pupils. He used his test in a study of Aboriginal mission children and, later, with Aboriginal adults of the North Western and Central Australia (CA) regions.18 He found that Aboriginal adults in these regions performed at generally lower levels than the norming samples, although there were interesting variations.19The Aboriginal peoples with the most exposure to Western school experience, such as the Hermannsburg people of CA, achieved a higher ‘mental age’ than those with less exposure, suggesting that intelligence was not biologically determined but a result of experience.
Following Porteus, over the next two decades from the 1930s, a study was undertaken by psychologists at the University of Western Australia. They tested Aboriginal men and women on stations in the Gascoyne region of Western Australia (WA) and remarked on the wide range of scores, commenting that ‘some natives have intelligence of a high degree’.19p(41-2) The study indicated test score equivalence between Aboriginal and white Australian people, raising the question of the effects of differential experience on test performance.
From the late 1950s, McElwain conducted a series of investigations of cognitive ability using the Queensland Test (QT) with over 1,000 Aboriginal children and adults who had varying degrees of contact with white Australian culture. It was concluded that:
'the Aboriginal groups are inferior to Europeans, and in approximately the same degree as they have lacked contact with European groups ... It seems clear that test results are dependent to a considerable degree upon contact or some variable related to contact.'21(p47)
Despite concerted efforts to modify the QT to be non-verbal and culture-neutral, this research clearly demonstrated that it is not possible to create a culture-free test unaffected by Western cultural experience on the test performance of non-Western children.Dudgeon et al, 2014. A history of Indigenous psychology
Sanger first seems to talk about consensual sex, but then mentions rape, so I will focus on that part.
Most of the studies focus on the ethnicity of the victim, not the perpetrator of sexual violence. This is obviously important to consider when evaluating studies; A report by Carter from 1987 for example estimates that 42% of rapists of Aboriginal people were white (see here). Non-reporting is also always an issue with sexual assault, and more so when the victim has an indigenous background (see here).
Regarding sexual child abuse:
Indigenous children were the subject of proportionately fewer substantiations for sexual abuse than non-Indigenous children and proportionately higher substantiations for neglect than non-Indigenous children.
Other indicators suggest that these departmental figures may under-estimate child abuse and neglect more among Indigenous children than among non-Indigenous children (for example, Gordon, Hallahan and Henry 2002; Memmott et al. 2001).
Statistics from the Western Australian criminal justice system reveal that in 2000, the rate of reports to police of sexual assault of Indigenous girls was approximately double that of non-Indigenous girls (Ferrante and Fernandez 2002, reported in Gordon, Hallahan and Henry 2002). Yet it is estimated that less than 30 per cent of sexual assaults on children are actually reported to police and that this reporting rate is lower in Indigenous communities than non-Indigenous communities. Further, it was noted in the Robertson Report (2000) that 88 per cent of all rapes in Indigenous communities go unreported. Thus, it would appear that the documented extent of assault in Indigenous communities is just the tip of the iceberg.Stanley et al, 2003. Child abuse and neglect in Indigenous Australian communities
Regarding sexual assault:
[E]vidence suggests that sexual assault of Indigenous women by both Aboriginal and non-Aboriginal men is endemic.
[T]he incidence of sexual offences was 1,070 per 100,000 persons for Aboriginal women, compared to 290 per 100,000 for non-Aboriginal women (Loh & Ferrante 2000);Lievore, 2003.Non-reporting and Hidden Recording of Sexual Assault: An International Literature Review
Intelligence and Sexual Crime
A study comparing convicted sex and non-sex offenders found a difference in IQ:
The results from the current study indicate that sex offenders differ from non-sexual violent criminals in terms of IQ. Differences between sex offenders and NSV criminals are particularly significant on total and performance IQ scores. When compared with NSV criminals, sex offenders showed significantly lower results on performance scales.Guay et al, 2005. On intelligence and crime: a comparison of incarcerated sex offenders and serious non-sexual violent criminals.
Richard Lynns Research
Richard Lynn is the editor of a journal that has been called white supremacist, and his work is often described as promoting scientific racism, so I would be a bit skeptical on what he has to say about the topic. His book "Race Differences in Intelligence" - which is used as a source here - has been criticized for using faulty data:
There are reasons for being concerned about this data set. Lynn and Vanhanen did not actually have IQ data for all of their 185 nations, they only had data for 81. The other 104 “data points” were estimated from the 81 actual data points, using a rather unclearly specified method of estimating an unknown point by averaging over actual values from nearby countries that Lynn and Vanhanen felt were appropriate comparisons. In addition, the age and quality of the original data varied widely. Some of the data points provided by Lynn and Vanhanen do, indeed, represent reasonably large, reasonably representative samples of the populations in question. Others do not. The estimate for Belgium was based on a study about 50 years earlier. The majority of the data points were based upon convenience rather than representative samples. Some points were not even based on residents of the country. For instance, the “data point” for Suriname was based on tests given to Surinamese who had migrated to the Netherlands, and the “data point” for Ethiopia was based on the IQ scores of a highly selected group that had emigrated to Israel and, for cultural and historical reasons, was hardly representative of the Ethiopian population. The data point for Mexico was based upon a weighted averaging of the results of a study of “Native American and Mestizo children in southern Mexico” with result of a study of residents of Argentina. Upon reading the original reference, we found that the “data point” that Lynn and Vanhanen used for the lowest IQ estimate, Equatorial Guinea, was actually the mean IQ of a group of Spanish children in a home for the developmentally disabled in Spain.
Whetzel and McDaniel (2006) pointed out that several criticisms of the Lynn and Vanhanen data set raised questions about some of their very low estimates, on the grounds that it is illogical to believe that citizens of functioning countries are, on the average, at an intelligence level approximating that of marginally functional individuals in an industrially developed country. Hunt & Wittmann, 2008. National intelligence and national prosperity
The paper then goes on to show that the stated correlation between IQ and GDP may be accurate if a clean data set is used, but that doesn't seem relevant to this question.