Prejudice and stereotyping are biases that work together to create and maintain social inequality. Prejudice refers to the attitudes and feelings—whether positive or negative and whether conscious or non-conscious—that people have about members of other groups. In contrast, stereotypes have traditionally been defined as specific beliefs about a group, such as descriptions of what members of a particular group look like, how they behave, or their abilities. As such, stereotypes are cognitive representations of how members of a group are similar to one another and different from members of other groups. Importantly, people can be aware of cultural stereotypes and have cognitive representations of those beliefs without personally endorsing such stereotypes, without feelings of prejudice, and without awareness that such stereotypes could affect one’s judgment and behavior. Prejudice and stereotyping are generally considered to be the product of adaptive processes that simplify an otherwise complex world so that people can devote more cognitive resources to other tasks. However, despite any cognitively adaptive function they may serve, using these mental shortcuts when making decisions about other individuals can have serious negative ramifications. The horrible mistreatment of particular groups of people in recent history, such as that of Jews, African Americans, women, and homosexuals, has been the major impetus for the study of prejudice and stereotyping. Thus, the original conceptions and experiments were concerned almost entirely with conscious, negative attitudes and explicitly discriminatory actions. However, as the social acceptability of prejudice and stereotypes has changed, the manifestations of prejudice and stereotypes have also changed. In response to these changes, and given that people who reject prejudice and stereotyping can still unwittingly internalize stereotypic representations, the study of prejudice and stereotyping has recently moved to include beliefs, attitudes, and behaviors that could be considered positive and not obviously or overtly prejudiced. Importantly, even when prejudice and stereotypes are ostensibly positive (e.g., traditional women are wonderful and adored), they preserve the dominance of powerful groups: they not only limit the opportunities of stereotyped groups but also produce a litany of negative outcomes when those group members defy them. Because of these new conceptions of bias, there have also been methodological adaptations in the study of prejudice and stereotyping that move beyond the conscious attitudes and behaviors of individuals to measure their implicit prejudice and stereotypes as well. This article gives a quick tour through the social psychological study of prejudice and stereotyping to inform the reader about its theoretical background, measurement, and interventions aimed to reduce prejudice.
This collection takes a look back at Gordon Allport’s conceptualizations of prejudice and updates and extends his work with contemporary theories and evidence collected in the fifty years after the publication of On the Nature of Prejudice.
As oxygenic photosynthesis spread through the oceans, everything that could be oxidized by oxygen was, during what is called the (“GOE”), although there may have been multiple dramatic events. The event began as long as three bya and is . The ancient carbon cycle included volcanoes spewing a number of gases into the atmosphere, including hydrogen sulfide, sulfur dioxide, and hydrogen, but carbon dioxide was particularly important. When the continents began forming, carbon dioxide was removed from the atmosphere via water capturing it, , the carbon became combined into calcium carbonate, and plate tectonics subducted the calcium carbonate in the ocean sediments into the crust, which was again released as carbon dioxide in volcanoes.
About 2.7 bya, dissolved iron in anoxic oceans seems to have begun reacting with oxygen at the surface, generated by cyanobacteria. The dissolved iron was oxidized from a soluble form to an insoluble one, which then precipitated out of the oceans in those vivid red (the color of rust) layers that we see today and are called ("BIFs"), which became an oxygen sink and kept atmospheric oxygen low. The GOE is widely accepted to have created almost all of the BIFs, but it is not the only BIF-formation hypothesis and there is a great deal of controversy, but life processes are generally considered to be primarily responsible for forming the BIFs. Most iron in the crust is bound in silicates and carbonates, and it takes a great deal of energy to extract the iron from those minerals; the oxides that comprise BIFs are much less energy-intensive to refine, as the iron is so concentrated. Far less ore needs to be melted to get an equivalent amount of iron. BIFs are the source of virtually all iron ore that humans have mined. Life processes almost certainly performed the initial work of refining iron, and humans easily finished the job billions of years later. Copper was not refined by life processes, and copper ore takes twice as much energy to refine as iron ore does.
The high oxygen levels may have turned pyrite on the continents into acid, which increased erosion, flooded essential nutrients, particularly phosphorus, into the oceans, and would have facilitated a huge bloom in the oceans. But this also happened in the midst of Earth's first ice age, so increased glacial erosion may have been primarily responsible, as we will see with a . The two largest carbon-isotope excursions () in Earth's history are related to ice ages. The first was a positive excursion (more carbon-13 than expected), and the second was negative. Scientists are still trying to determine what caused them. Beginning a little less than 2.3 bya and lasting for more than 200 million years is the Lomagundi excursion, in which there was great carbon burial. When the Lomagundi excursion finished, oxygen levels seem to have crashed back down to almost nothing and may have stayed that way for 200 million years, before rebounding to a few percent, at most, of Earth's atmosphere, and it stayed around that low level for more than a billion years.
Many people are familiar with the term , which was all of today’s continents merged into a supercontinent. Pangaea formed about 300 mya, but it was not the only supercontinent; it was just the only one existing during the eon of complex life. One called may have existed one bya and did not break up until 750 mya (and reformed into another supercontinent, , 600 mya, which did not break up until 550 mya), and there is a hypothesized earlier one called that existed two bya. There is also a hypothesis that all continental mass was contained in one supercontinent that lasted from . The continental land masses of two bya may have been only about 60% the size of today’s. Supercontinents .
About the time that the continents began to grow and began, Earth produced its first known glaciers, between 3.0 and 2.9 bya, although the full extent is unknown. It might have been an ice age or merely some mountain glaciation. The , and numerous competing hypotheses try to explain what produced them. Because the evidence is relatively thin, there is also controversy about the extent of Earth's ice ages. About 2.5 bya, the Sun was probably a little smaller and only about as bright as it is today, and Earth would have been a block of ice if not for the atmosphere’s carbon dioxide and methane that absorbed electromagnetic radiation, particularly in the . But life may well have been involved, particularly oxygenic photosynthesis, and it was almost certainly involved in Earth's first great ice age, which may have been a episode, and some pertinent dynamics follow.
When the total continental land mass was small or combined into a supercontinent, there was no land to divert that diffusion of warm water toward the poles, which results in currents. During those times, the global ocean became one big, calm lake, with no currents of significance. Those oceans are called today, and they would have been anoxic; the oxygenated surface waters would not have been drawn by currents to the ocean floor, and the oceans were certainly anoxic before the GOE. The interplay of those can be incredibly complex and lead to the multitude of hypotheses posited to explain those ancient events, but a leading hypothesis today is that a combination of factors, including supercontinents, variations in volcanic output, Canfield Oceans, and ice ages prevented life from gaining ecosystem dominance until the waning of the second Snowball Earth event, which was the greatest series of glaciations that Earth has yet experienced. It is known today as the , which ended about 635 mya. The study of the Cryogenian Period, which is the subject of , resulted in the term “.”
This chapter will provide a somewhat detailed review of the Cryogenian Ice Age and its aftermath, including some of the hypotheses regarding it, evidence for it, and its outcomes, as the eon of complex life arose after it. The ran from about 850 mya to 635 mya. This review will sketch the complex interactions of life and geophysical processes, and the increasingly multidisciplinary methods being used to investigate such events, which are yielding new and important insights.
The of an ice age is only a few hundred years old, and was , who got his first ideas from and others. There had also been . By the 1860s, most geologists accepted the idea that there had been a cold period in Earth’s recent past, attended by advancing and retreating ice sheets, but nobody really knew why. Hypotheses began to proliferate, and in the 1870s, proposed the idea that variations in Earth’s orientation to the Sun caused the continental ice sheets. Because of problems in matching his hypothesis with dates adduced for ice age events, it fell out of favor and was considered dead by 1900. Croll’s work regained its relevance with the publication of a paper by (usually spelled Milankovitch in the West) in 1913, and by 1924, Milankovitch was widely known for explaining the timing of advancing and retreating ice sheets during the current ice age.
The book that made Milankovitch famous (Croll’s work is still obscure, even though Milankovitch gave full credit to Croll in his work) was co-authored by Alfred Wegener, who a decade earlier first published his hypothesis that . As is often the case with radical new hypotheses, , but Wegener was the first to propose a comprehensive hypothesis to explain an array of detailed evidence. Wegener was a meteorologist working outside of his specialty when he proposed his “continental drift” hypothesis. His hypothesis was , and . His continental drift hypothesis quickly sank into obscurity. It was not until my lifetime, when , that Wegener’s work returned from exile and became a cornerstone of geological theory. Ice age data and theory does not pose an immediate threat to the or "," so the history of developing the data and theories has been publicly available.