An American fuel pump that dispensed gasoline with tetraethyllead additives. The<unk>  is the association between elevated blood<unk>  levels in children and increased rates of<unk> , delinquency, and recidivism later in life.<unk>  is widely understood to be highly toxic to multiple organs of the body, particularly the brain. Individuals exposed to<unk>  at young ages are more vulnerable to learning disabilities, decreased I.Q., attention deficit hyperactivity disorder, and problems with impulse control, all of which may be negatively impacting decision making and<unk> ing to the commission of more<unk> s as these children reach adulthood, especially violent<unk> s. Proponents of the<unk>  argue that the removal of<unk>  additives from motor fuel, and the consequent decline in children's<unk>  exposure, explains the fall in<unk>  rates in the United States beginning in the 1990s. This hypothesis also offers an explanation of the earlier rise in<unk>  in the preceding decades as the result of increased<unk>  exposure throughout the mid-20th century. The<unk>  is not mutually exclusive with other explanations of the drop in US<unk>  rates such as the legalized abortion and<unk>  effect.<unk>  exposure during the years in question correlated with exposure to urban poverty, due to close residential or primary school proximity with high-density motor vehicle traffic burning<unk> ed gasoline or from residing in older, poorly maintained housing stock, much of which contained high levels of<unk>  in the form of<unk>  paint,<unk>  solder, or other<unk> -based building materials; additionally, municipalities with a low taxation base often continued to receive drinking water via degraded<unk>  pipes rather than upgrading to modern infrastructure. The difficulty in measuring the effect of<unk>  exposure on<unk>  rates lies in separating the effect from other indicators of low socioeconomic status such as poorer schools, nutrition, and medical care, exposure to other pollutants, and other variables that are predictive of<unk> nal behavior.
Lead–crime hypothesis
Protein leverage hypothesis
Functional matrix hypothesis
Timing hypothesis 
Conformation–activity relationship
Weathering hypothesis
Antagonistic pleiotropy hypothesis
Thrifty gene hypothesis