UPI Study › Courses › Criminology › Free lessons › Lesson 6.4 Free with a free account
Biological Theories of Crime and Somatotype Theory: Definitions and Applications
Criminology · Chapter 6: Choice, Trait, Biological, and Psychological TheoriesSection 6.4 · lesson 17 of 91video coming soon
← Individual Trait Theory: Factors, Biases, and Leadership ApplicationsNext lesson: Psychological Theories of Crime: Assumptions, Criticisms, and Policy Impact →
In this lesson
Somatotype theory, heredity designs, and contemporary biosocial research.
- Describe the principal biological explanations of offending.
- State the empirical standing of somatotype and hereditary claims.
- Compare what family, twin, and adoption designs can separate.
- Explain what a contemporary biosocial claim does and does not assert.
Transcript
Everything said in the video, section by section (1,706 words). Read along, or search it.
Opening Question
Born Criminal? A Policy Board Weighs In
Few ideas in criminology have done more damage than the claim that criminals are born, not made. Picture a policy board weighing a proposal: screen young people for a biological marker associated with later offending. Before anyone votes, their adviser, Amara, a criminologist, walks them through the evidence. This lesson does the same. You'll describe the principal biological explanations of offending, organized into three distinct waves, and state the empirical standing of somatotype theory and hereditary-criminality claims. You'll compare what family, twin, and adoption studies can and can't separate, and explain exactly what a contemporary biosocial claim asserts, and what it doesn't. Throughout, the lesson applies the methodological cautions from subchapter six point three. They matter most here, because this is where criminology has been most badly wrong.
Historical Overview
Three Waves of Biological Explanation
Amara starts with history. Biological explanations of offending have moved through three broad waves. The first was nineteenth-century constitutional claims, reviewed in subchapter six point two: fixed physical characteristics marked a criminal type. The second wave, in the mid-twentieth century, focused on body type and heredity specifically. The third is contemporary biosocial research, which studies how biological and environmental factors interact. It uses far more cautious methods, and reaches far more modest conclusions. The first two waves failed the empirical tests later applied to them. The third operates under a different, more disciplined standard of evidence. It also helps to read the waves as a sequence of responses to failure. Body-type theorists presented themselves as a more systematic alternative to crude physical measurement. Biosocial research arose largely because both earlier waves failed properly controlled comparison. Its emphasis on interaction, replication, and modest claims is a direct response.
Second Wave
Somatotype Theory and Its Confounded Evidence
In her university classroom, Amara teaches the second wave's best-known example: somatotype theory. It claimed that body build corresponds to a characteristic temperament, and that temperament, in turn, predicts a likelihood of delinquency. The theory sorted people into a small number of physical categories, then linked each category to a proposed personality type. This is presented strictly as a historical position. When later researchers used properly controlled comparisons, the association didn't survive. In the populations studied, body build was heavily confounded with nutrition, occupation, and social class. Each of those independently affects both physical build and the likelihood of contact with the justice system. So the original studies couldn't separate any effect of build from the effects of those circumstances. Somatotype theory has no standing in contemporary science; it's discussed only as part of the discipline's history.
Research Designs
Family, Twin, and Adoption Study Limits
Any claim about heredity and behavior depends on research design, so it pays to know three designs well. Picture three families on one street. A family study compares rates of an outcome among biological relatives, like Rosa and her son. But relatives usually share both genes and environment. So if an outcome runs in a family, a family study can't say whether biology, environment, or both explain it. A twin study compares identical and fraternal twins, using their difference in genetic similarity to produce a genetic estimate. It still assumes both kinds of twins experience comparably similar environments. That doesn't always hold, since identical twins may share more similar environments: the shared-environment confound. An adoption study compares adopted children, like Eli, with both their biological and their adoptive relatives. It offers the strongest separation of genetic and environmental contribution among the three designs. Even so, adoptive placement is rarely random with respect to the biological family's circumstances. And prenatal environment is shared with the biological mother, regardless of later adoption.
Case Review
Three Historical Claims That Collapsed
Back in class, Amara tests three historical biological claims, and records each outcome. Somatotype theory compared body-build categories to delinquency, and failed because build was confounded with nutrition, occupation, and social class. The hereditary-criminality claim traced institutional records across multiple generations. It failed because those records were confounded entirely with shared poverty and shared environment. The early XYY chromosome claim relied on chromosome surveys of institutionalized populations, and its finding wasn't replicated in general-population samples. Notice the pattern: each claim drew on a narrow or confounded sample, and each collapsed under controlled comparison. None of the three has any standing in contemporary science.
Historical Record
Hereditary Claims and Forced Sterilization
Hereditary-criminality claims held that criminality passes down biologically, across generations, and they were central to the twentieth-century eugenic movement. That movement sought to reduce reproduction among people classified as hereditarily criminal, or otherwise unfit. As documented history, not live science, it produced involuntary sterilization programs authorized by state statute, and early court decisions upheld those programs. They were applied to people confined in state institutions, on the basis of now-discredited hereditary claims. The programs were later repudiated. The scientific claims behind them collapsed under scrutiny, and their human costs became impossible to justify by any standard. This history is stated plainly because it's part of the discipline's record. Hereditary-criminality claims of this kind retain no scientific support.
Third Wave
Gene-Environment Interaction Explained Modestly
Contemporary biosocial research deserves an accurate and modest description. Its central concept is gene-environment interaction. An individual difference and an environmental exposure combine to produce an effect that neither would produce alone. Neither factor determines the outcome by itself. Picture a pediatric checkup. Related research examines the documented neurological consequences of severe childhood adversity, and of exposure to environmental toxins. Both can affect brain development relevant to impulse control and decision-making. The general finding across this literature is clear, and it shouldn't be overstated: no single biological factor explains offending. Biological factors that show any association are one modest influence among many, alongside the situational, developmental, and social factors examined throughout this course.
Scope
Narrow Claims, Not Genetic Determinism
Back at the board, Amara gets specific, because vague descriptions invite overreach. A typical study might ask whether documented early adversity is linked to differences in brain regions, specifically those for impulse regulation. Another might ask whether a developmental toxin exposure is linked to later behavioral outcomes, at the population level. These are narrow, mechanism-specific claims about documented exposures and their measurable physiological correlates. They're not claims that any individual's behavior is fixed by biology. Nor do they apply to any social group defined by ancestry, rather than by documented exposure. That narrowness is part of what makes this research defensible, where earlier waves weren't. Interaction is also explicitly not genetic determinism, the view that genes fix an outcome regardless of environment. The whole point is that one genetic difference can lead to very different outcomes, depending on the environment a person experiences. So environment remains a live, and often more actionable, point of intervention.
Common Misuse
Why Research Cannot Support Racial Claims
Someone on the board asks about race. Amara is direct: none of this research supports any claim about racial or ethnic groups. There are two specific reasons, and each one works independently. The first comes from population genetics. Human genetic variation doesn't sort neatly into the racial categories a society uses in ordinary language. So a genetic finding can't be assumed, in the first place, to track a socially defined racial group. The second concerns unequal exposures, such as childhood adversity and toxins. These are unequally distributed because of structural factors like housing policy, occupational segregation, and concentrated disadvantage. A group difference in exposure explains a group difference in outcome, without any reference to biology at all. Either reason alone rules out the group-level biological claims that earlier waves attempted. The field's history of being badly wrong about exactly this claim is reason for particular caution.
Applying It
Screening Proposal and Its Policy Risks
Now the proposal itself: screen young people for a biological marker, to direct additional support to those identified. Omar points out that even a genuine, replicated association is typically modest. Recall the base rate problem from subchapter six point three: most people the marker flags will never go on to offend. So the program must get the intervention right. It can't harm, stigmatize, or restrict people who were never at risk. This connects to a standing policy risk. Locating a cause inside a person invites intervention aimed at that person. Locating a cause in conditions invites intervention aimed at those conditions, as subchapter six point seven develops. Even accurate biosocial findings can be misused to justify screening, labeling, or restricting individuals. Yet the same research points to environmental conditions as the more clearly modifiable half of the interaction.
Quick Check
Birth Parents Resemblance: Other Explanations
Quick check. A study finds that adopted children's outcomes resemble their birth parents' more than their adoptive parents'. Before calling that genetic, what else could explain it? Pause, and decide. Prenatal life: before any adoption, the child shared the birth mother's prenatal environment. Selective placement could matter too, if agencies matched homes to the birth family's circumstances. The adoptive home itself would pull outcomes toward the adoptive parents, not the birth parents.
Evidence Standard
Four Requirements for Biological Claims
Given this history, Amara closes with a standard of evidence. A biological claim earns a hearing in contemporary criminology only by meeting it. First, it must use a design capable of separating genetic from environmental contribution; the three families on that street showed which designs come closest. Second, it must be replicated across independent samples, not rest on a single study. Third, it must state its effect size honestly. Reporting only that an association is statistically detectable isn't enough. Fourth, it must never be extended to a socially defined group without independently meeting both objections: population genetics, and unequal exposure. A claim that falls short hasn't earned the confidence earlier biological waves received. As this history shows, that unearned confidence was itself the problem.
Practice
Sorting Claims and Spotting Misapplications
Now practice. Sort these claims into refuted historical claims and cautiously supported findings. Body build determining temperament, heredity alone, and the chromosome claim are refuted. Childhood adversity, toxin exposure, interaction effects, and the finding that no single factor explains offending are cautious findings. Then ask what each design can and can't establish; for instance, a family pattern can't separate genes from shared environment. Finally, spot the misapplications. Restricting flagged youth, surveilling a family, and explaining racial differences genetically all misapply the research. So does targeting individuals when the evidence points at the toxin exposure itself.
Key Takeaways
Failed Waves, Modest Findings, Modifiable Conditions
Let's recap. Biological explanation moved through three waves, and the first two failed empirical testing. Somatotype theory was confounded with nutrition, occupation, and social class. Adoption designs separate genes from environment best, though not perfectly. Biosocial research makes modest, interaction-based claims about documented exposures, never about groups defined by ancestry. And conditions are the more clearly modifiable half of the interaction.
About Criminology at UPI Study
Criminology (Criminology 150) is a self-paced online course of 91 video lessons in 21 chapters, from classical criminology and crime data to theories of crime, victims, policing, courts and corrections. It carries a NCCRS credit recommendation for 3 semester credits.
Every lesson transcript is free on pages like this one, and the videos are free with a free UPI Study account. Enrolling adds a practice quiz after each lesson, the graded work and final exam that earn the credit, lifetime access, and an official transcript on completion. UPI Study has helped over 130,000 students with college credits. ACE and NCCRS have over 2,100 cooperating colleges that will consider accepting credits; the final decision is with the universities.
Enroll now → Course details Download the syllabus Every course with PRO →
Why take it here
Why students take Criminology with UPI Study
Where the credit goes
Universities that work with NCCRS
Criminology carries a NCCRS credit recommendation. These universities work with NCCRS; some are UPI Study's signed partners. ACE and NCCRS have over 2,100 cooperating colleges that will consider accepting credits; the final decision is with the universities.
Thomas Edison State UniversitySigned partner
University of the PeopleSigned partner
Charter Oak State CollegeSigned partner
Strayer UniversitySigned partner
Columbia Southern UniversitySigned partner
Indiana TechSigned partner
Penn StateWorks with NCCRS
Southern New Hampshire UniversityWorks with NCCRS
SUNYWorks with NCCRS
+many more cooperating universitiesFind my college →Find my college → Not listed? Ask Athena in the corner of this page, or book a 15-minute call.
FAQ
Questions students ask us
About Biological Theories of Crime and Somatotype Theory: Definitions and Applications
What is somatotype theory, and why is it rejected today?
What can family, twin, and adoption studies separate when studying heredity and crime?
What does a contemporary biosocial claim say about crime, and what does it not say?
Why can't biological research on offending be used to explain racial differences in crime?
About the Criminology course
How many college credits is Criminology?
How much does Criminology cost and what is included?
Which universities accept UPI Study credits?
How long does Criminology take?
How are the exams done?
How do my credits reach my college?
Ready for the full course? Earn 3 credits in Criminology.
91 video lessons, a quiz after each one, and the graded work that earns the credit. Recommended for credit by NCCRS.
3 credits · NCCRSEnroll →