7.2: History of Life - Biology

7.2: History of Life - Biology

We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.

How do we learn about the past?

We study the remains of things that existed many years ago. The Ruins of Pompeii have given archeologists, historians, and other scholars a tremendous amount of information about life two thousand years ago. This section discusses studying things that are many thousands of years older than these remains.

Earth in a Day

It’s hard to grasp the vast amounts of time since Earth formed and life first appeared on its surface. It may help to think of Earth’s history as a 24-hour day, as shown in Figure below. Humans would have appeared only during the last minute of that day. If we are such newcomers on planet Earth, how do we know about the vast period of time that went before us? How have we learned about the distant past?

History of Earth in a Day. In this model of Earth’s history, the planet formed at midnight. What time was it when the first prokaryotes evolved?

Learning About the Past

Much of what we know about the history of life on Earth is based on the fossil record. Detailed knowledge of modern organisms also helps us understand how life evolved.

The Fossil Record

Fossils are the preserved remains or traces of organisms that lived in the past. The soft parts of organisms almost always decompose quickly after death. On occasion, the hard parts—mainly bones, teeth, or shells—remain long enough to mineralize and form fossils. An example of a complete fossil skeleton is shown in Figure below. The fossil record is the record of life that unfolded over four billion years and pieced back together through the analysis of fossils.

Extinct Lion Fossil. This fossilized skeleton represents an extinct lion species. It is rare for fossils to be so complete and well preserved as this one.

To be preserved as fossils, remains must be covered quickly by sediments or preserved in some other way. For example, they may be frozen in glaciers or trapped in tree resin, like the frog in Figure below. Sometimes traces of organisms—such as footprints or burrows—are preserved (see the fossil footprints in Figure below). The conditions required for fossils to form rarely occur. Therefore, the chance of an organism being preserved as a fossil is very low. You can watch a video at the following link to see in more detail how fossils form:

The photo on the left shows an ancient frog trapped in hardened tree resin, or amber. The photo on the right shows the fossil footprints of a dinosaur.

In order for fossils to “tell” us the story of life, they must be dated. Then they can help scientists reconstruct how life changed over time. Fossils can be dated in two different ways: relative dating and absolute dating. Both are described below. You can also learn more about dating methods in the video at this link:

  • Relative dating determines which of two fossils is older or younger than the other, but not their age in years. Relative dating is based on the positions of fossils in rock layers. Lower layers were laid down earlier, so they are assumed to contain older fossils. This is illustrated in Figure below.
  • Absolute dating determines about how long ago a fossil organism lived. This gives the fossil an approximate age in years. Absolute dating is often based on the amount of carbon-14 or other radioactive element that remains in a fossil. You can learn more about carbon-14 dating by watching the animation at this link:

Relative Dating Using Rock Layers. Relative dating establishes which of two fossils is older than the other. It is based on the rock layers in which the fossils formed.

Molecular Clocks

Evidence from the fossil record can be combined with data from molecular clocks. A molecular clock uses DNA sequences (or the proteins they encode) to estimate relatedness among species. Molecular clocks estimate the time in geologic history when related species diverged from a common ancestor. Molecular clocks are based on the assumption that mutations accumulate through time at a steady average rate for a given region of DNA. Species that have accumulated greater differences in their DNA sequences are assumed to have diverged from their common ancestor in the more distant past. Molecular clocks based on different regions of DNA may be used together for more accuracy.

Consider the example in Table below. The table shows how similar the DNA of several animal species is to human DNA. Based on these data, which organism do you think shared the most recent common ancestor with humans?

OrganismSimilarity with Human DNA (percent)
Fruit Fly44

Geologic Time Scale

Another tool for understanding the history of Earth and its life is the geologic time scale, shown in Figure below. The geologic time scale divides Earth’s history into divisions (such as eons, eras, and periods) that are based on major changes in geology, climate, and the evolution of life. It organizes Earth’s history and the evolution of life on the basis of important events instead of time alone. It also allows more focus to be placed on recent events, about which we know the most.

Geologic Time Scale. The geologic time scale divides Earth’s history into units that reflect major changes in Earth and its life forms. During which eon did Earth form? What is the present era?


  • Much of what we know about the history of life on Earth is based on the fossil record.
  • Molecular clocks are used to estimate how long it has been since two species diverged from a common ancestor.
  • The geologic time scale is another important tool for understanding the history of life on Earth.

Explore More

Use the time slider in this resource to answer the questions that follow.

  • Evolution at
  1. When did the Big Bang occur?
  2. When did the sun ignite?
  3. When did the Earth form? What was the form of this Earth?
  4. What was lacking in the Earth's early atmosphere?
  5. When did the first cells appear?


1. What are fossils?

2. Describe how fossils form.

3. Distinguish relative dating from absolute dating.

4. This table shows DNA sequence comparisons for some hypothetical species. Based on the data, describe evolutionary relationships between Species A and the other four species. Explain your answer.

SpeciesDNA Similarity with Species A
Species B42%
Species C85%
Species D67%
Species E91%

5. Describe the geologic time scale.


The goal of NASA ’s Exobiology program (formerly Exobiology and Evolutionary Biology) is to understand the origin, evolution, distribution, and future of life in the Universe. Research is centered on the origin and early evolution of life, the potential of life to adapt to different environments, and the implications for life elsewhere. This research is conducted in the context of NASA’s ongoing exploration of our stellar neighborhood and the identification of biosignatures for in situ and remote sensing applications.

Exobiology is now a program with No Due Dates (NoDD). For more information about NoDD in PSD , visit:

Click here for information on the Research Opportunities in Space and Earth Sciences ( ROSES )-2021 call for Exobiology.

Click here to view the Research Opportunities in Space and Earth Sciences ( ROSES )-2021 Blog.

Planetary Conditions for Life:
Research in this area seeks to delineate the galactic and planetary conditions conducive to the origin of life. Topics of interest include the formation and stability of habitable planets, the formation of complex organic molecules in space and their delivery to planetary surfaces, models of early environments in which organic chemical synthesis could occur, the forms in which prebiotic organic matter has been preserved in planetary materials, and the range of planetary environments amenable to life.

Prebiotic Evolution:
Research in the area of prebiotic evolution seeks to understand the pathways and processes leading from the origin of planetary bodies to the origin of life. The strategy is to investigate the planetary and molecular processes that set the physical and chemical conditions within which living systems may have arisen. A major objective is determining what chemical systems could have served as precursors of metabolic and replicating systems on Earth and elsewhere, including alternatives to the current DNA – RNA – protein basis for life.

Early Evolution of Life and the Biosphere:
The goal of research into the early evolution of life is to determine the nature of the most primitive organisms and the environment in which they evolved. The opportunity is taken to investigate two natural repositories of evolutionary history available on Earth: the molecular record in living organisms and the geological record. These paired records are used to: (i) determine when and in what setting life first appeared and the characteristics of the first successful living organisms (ii) understand the phylogeny and physiology of microorganisms, including extremophiles, whose characteristics may reflect the nature of primitive environments (iii) determine the original nature of biological energy transduction, membrane function, and information processing, including the construction of artificial chemical systems to test hypotheses regarding the original nature of key biological processes iv) investigate the development of key biological processes and their environmental impact v) examine the response of Earth’s biosphere to extraterrestrial events vi) investigate the evolution of genes, pathways, and microbial species subject to long – term environmental change relevant to the origin of life on Earth and the search for life elsewhere and vii) study the coevolution of microbial communities, and the interactions within such communities, that drive major geochemical cycles, including the processes through which new species are added to extant communities.

Evolution of Advanced Life:
Research associated with the study of the evolution of advanced life seeks to determine the biological and environmental factors leading to the development of multicellularity on Earth and the potential distribution of complex life in the Universe. This research includes studies of the origin and early evolution of those biological factors that are essential to multicellular life, such as developmental programs, intercellular signaling, programmed cell death, the cytoskeleton, cellular adhesion control and differentiation, in the context of the origin of advanced life. This research area also includes an evaluation of environmental factors such as the influence of extraterrestrial (e.g., bolide impacts, orbital and solar variations, gamma-ray bursts, etc.) and planetary processes (“Snowball Earth” events, rapid climate change, etc.) on the appearance and evolution of multicellular life. Of particular interest are mass extinction events.

Exobiology for Solar System Exploration:
Research in this area focuses on relating what is known about life on Earth to conditions prevailing on other planetary bodies. This research includes assessments of the survivability of various types of Earth microorganisms and the formation and retention of biosignatures under non-Earth conditions (e.g., Mars, Europa). Also included under this research area are efforts to assess the potential habitability of planetary environments other than those found on the Earth.

Sign-up to get the latest in news, events, and opportunities from the NASA Astrobiology Program.


Nest Placement

Common Ravens build their nests on cliffs, in trees, and on structures such as power-line towers, telephone poles, billboards, and bridges. Cliff nests are usually under a rock overhang. Tree nests tend to be in a crotch high in the tree, but below the canopy and typically farther down in a tree than a crow’s nest would be.

Nest Description

Males bring some sticks to the nest, but most of the building is done by females. Ravens break off sticks around 3 feet long and up to an inch thick from live plants to make up the nest base, or scavenge sticks from old nests. These sticks, and sometimes bones or wire as well, are piled on the nest platform or wedged into a tree crotch, then woven together into a basket. The female then makes a cup from small branches and twigs. The cup bottom is sometimes lined with mud, sheep’s wool, fur, bark strips, grasses, and sometimes trash. The whole process takes around 9 days, resulting in an often uneven nest that can be 5 feet across and 2 feet high. The inner cup is 9-12 inches across and 5-6 inches deep. Nests are often reused, although not necessarily by the same birds, from year to year.

Nesting Facts

Clutch Size:3-7 eggs
Number of Broods:1 brood
Egg Length:1.7-2.0 in (4.4-5.2 cm)
Egg Width:1.2-1.4 in (3.1-3.6 cm)
Incubation Period:20-25 days
Nestling Period:28-50 days
Egg Description:Green, olive, or blue, often mottled with dark greenish, olive, or purplish brown.
Condition at Hatching:Naked except for sparse tufts of grayish down, eyes closed, clumsy, and looking like “grotesque gargoyles” according to a 1945 description.

Section Summary

Nearly all eukaryotes undergo sexual reproduction. The variation introduced into the reproductive cells by meiosis appears to be one of the advantages of sexual reproduction that has made it so successful. Meiosis and fertilization alternate in sexual life cycles. The process of meiosis produces genetically unique reproductive cells called gametes, which have half the number of chromosomes as the parent cell. Fertilization, the fusion of haploid gametes from two individuals, restores the diploid condition. Thus, sexually reproducing organisms alternate between haploid and diploid stages. However, the ways in which reproductive cells are produced and the timing between meiosis and fertilization vary greatly. There are three main categories of life cycles: diploid-dominant, demonstrated by most animals haploid-dominant, demonstrated by all fungi and some algae and alternation of generations, demonstrated by plants and some algae.



alternation of generations: a life-cycle type in which the diploid and haploid stages alternate

diploid-dominant: a life-cycle type in which the multicellular diploid stage is prevalent

haploid-dominant: a life-cycle type in which the multicellular haploid stage is prevalent

gametophyte: a multicellular haploid life-cycle stage that produces gametes

germ cell: a specialized cell that produces gametes, such as eggs or sperm

life cycle: the sequence of events in the development of an organism and the production of cells that produce offspring

meiosis: a nuclear division process that results in four haploid cells

sporophyte: a multicellular diploid life-cycle stage that produces spores

Возникновение жизни

How did life emerge on Earth? How have life and Earth co-evolved through geological time? Is life elsewhere in the universe? Take a look through the 4-billion-year history of life on Earth through the lens of the modern Tree of Life!

This course will evaluate the entire history of life on Earth within the context of our cutting-edge understanding of the Tree of Life. This includes the pioneering work of Professor Carl Woese on the University of Illinois Urbana-Champaign campus which revolutionized our understanding with a new "Tree of Life." Other themes include: -Reconnaissance of ancient primordial life before the first cell evolved -The entire

4-billion-year development of single- and multi-celled life through the lens of the Tree of Life -The influence of Earth system processes (meteor impacts, volcanoes, ice sheets) on shaping and structuring the Tree of Life This synthesis emphasizes the universality of the emergence of life as a prelude for the search for extraterrestrial life.

7.2-million-year-old pre-human remains found in the Balkans

The common lineage of great apes and humans split several hundred thousand earlier than hitherto assumed, according to an international research team headed by Professor Madelaine Böhme from the Senckenberg Centre for Human Evolution and Palaeoenvironment at the University of Tübingen and Professor Nikolai Spassov from the Bulgarian Academy of Sciences. The researchers investigated two fossils of Graecopithecus freybergi with state-of-the-art methods and came to the conclusion that they belong to pre-humans. Their findings, published today in two papers in the journal PLOS ONE, further indicate that the split of the human lineage occurred in the Eastern Mediterranean and not -- as customarily assumed -- in Africa.

Present-day chimpanzees are humans' nearest living relatives. Where the last chimp-human common ancestor lived is a central and highly debated issue in palaeoanthropology. Researchers have assumed up to now that the lineages diverged five to seven million years ago and that the first pre-humans developed in Africa. According to the 1994 theory of French palaeoanthropologist Yves Coppens, climate change in Eastern Africa could have played a crucial role. The two studies of the research team from Germany, Bulgaria, Greece, Canada, France and Australia now outline a new scenario for the beginning of human history.

Dental roots give new evidence

The team analyzed the two known specimens of the fossil hominid Graecopithecus freybergi: a lower jaw from Greece and an upper premolar from Bulgaria. Using computer tomography, they visualized the internal structures of the fossils and demonstrated that the roots of premolars are widely fused.

"While great apes typically have two or three separate and diverging roots, the roots of Graecopithecus converge and are partially fused -- a feature that is characteristic of modern humans, early humans and several pre-humans including Ardipithecus and Australopithecus," said Böhme.

The lower jaw, nicknamed 'El Graeco' by the scientists, has additional dental root features, suggesting that the species Graecopithecus freybergi might belong to the pre-human lineage. "We were surprised by our results, as pre-humans were previously known only from sub-Saharan Africa," said Jochen Fuss, a Tübingen PhD student who conducted this part of the study.

Furthermore, Graecopithecus is several hundred thousand years older than the oldest potential pre-human from Africa, the six to seven million year old Sahelanthropus from Chad. The research team dated the sedimentary sequence of the Graecopithecus fossil sites in Greece and Bulgaria with physical methods and got a nearly synchronous age for both fossils -- 7.24 and 7.175 million years before present. "It is at the beginning of the Messinian, an age that ends with the complete desiccation of the Mediterranean Sea," Böhme said.

Professor David Begun, a University of Toronto paleoanthropologist and co-author of this study, added, "This dating allows us to move the human-chimpanzee split into the Mediterranean area."

Environmental changes as the driving force for divergence

As with the out-of-East-Africa theory, the evolution of pre-humans may have been driven by dramatic environmental changes. The team led by Böhme demonstrated that the North African Sahara desert originated more than seven million years ago. The team concluded this based on geological analyses of the sediments in which the two fossils were found. Although geographically distant from the Sahara, the red-colored silts are very fine-grained and could be classified as desert dust. An analysis of uranium, thorium, and lead isotopes in individual dust particles yields an age between 0.6 and 3 billion years and infers an origin in Northern Africa.

Moreover, the dusty sediment has a high content of different salts. "These data document for the first time a spreading Sahara 7.2 million years ago, whose desert storms transported red, salty dusts to the north coast of the Mediterranean Sea in its then form," the Tübingen researchers said. This process is also observable today. However, the researchers' modelling shows that, with up to 250 grams per square meter and year, the amount of dust in the past considerably exceeds recent dust loadings in Southern Europe more than tenfold, comparable to the situation in the present-day Sahel zone in Africa.

Fire, grass, and water stress

The researchers further showed that, contemporary to the development of the Sahara in North Africa, a savannah biome formed in Europe. Using a combination of new methodologies, they studied microscopic fragments of charcoal and plant silicate particles, called phytoliths. Many of the phytoliths identified derive from grasses and particularly from those that use the metabolic pathway of C4-photosynthesis, which is common in today's tropical grasslands and savannahs. The global spread of C4-grasses began eight million years ago on the Indian subcontinent -- their presence in Europe was previously unknown.

"The phytolith record provides evidence of severe droughts, and the charcoal analysis indicates recurring vegetation fires," said Böhme. "In summary, we reconstruct a savannah, which fits with the giraffes, gazelles, antelopes, and rhinoceroses that were found together with Graecopithecus," Spassov added

"The incipient formation of a desert in North Africa more than seven million years ago and the spread of savannahs in Southern Europe may have played a central role in the splitting of the human and chimpanzee lineages," said Böhme. She calls this hypothesis the North Side Story, recalling the thesis of Yves Coppens, known as East Side Story.

The findings are described in two studies pubished in PLOS ONE titled "Potential hominin affinities of Graecopithecus from the late Miocene of Europe" and "Messinian age and savannah environment of the possible hominin Graecopithecus from Europe."

Northern Illinois University Department of Biological Sciences College of Liberal Arts and Sciences

The health and safety of our students, faculty and staff is our priority. Please visit the NIU coronavirus (COVID-19) website for current updates and information. See details about available services and hours and frequently asked questions.

Biology is a diverse and rapidly expanding field of study that addresses issues relevant to health, agriculture, industry and the environment. Biologists are responsible for new discoveries in medicine and molecular biology, increasing crop yields and pest resistance, defining the ecological relationships that maintain our planet, and examining the origins and evolution of species, to name just a few.

You will learn and conduct research alongside our faculty, who are highly-regarded and internationally known for their discoveries. Beyond the classroom, we encourage students to seek out faculty mentors and to conduct research very early in their college careers. Not only does this provide you the opportunity to apply knowledge learned in the classroom, but it also establishes you in the field and paves the way for future success.

Our program is highly regarded by both employers and educational institutions, allowing our graduates to pursue careers in government, education, and industry. Many students go onto graduate or professional schools, such as medical, dental, podiatric medicine, optometry, veterinary medicine and pharmacy.

Diversity Statement

The Department of Biological Sciences at NIU stands against oppression in all its forms. We stand for social and racial justice and are working to improve diversity, equity and inclusion (DEI) in our department. We recognize that biological sciences has a long history of colonialism, racism and white supremacy and has participated in oppressive endeavors, including biological racism, eugenics and inhumane treatment of and experimentation on Black, Indigenous and People of Color (BIPOC). That history and that of our society mean institutionalized, systemic racism is still a part of biology today.

We have recently formed a DEI committee that has helped to remove the GRE from consideration in our graduate application process, instituted DEI discussions as part of regular faculty meetings, and edited our bylaws to ensure search committees have student representation and that tenure/promotion criteria are clear and equitable. We commit to further amending our policies, practices and curricula, to continue to make our department a better, more welcoming place for all faculty, students and staff.

There are several recipes to prepare PBS solution. The essential solution contains water, sodium hydrogen phosphate, and sodium chloride. Some preparations contain potassium chloride and potassium dihydrogen phosphate. EDTA may also be added in cellular preparation to prevent clumping.

Phosphate-buffered saline is not ideal for use in solutions that contain divalent cations (Fe 2+ , Zn 2+ ) because precipitation may occur. However, some PBS solutions do contain calcium or magnesium. Also, keep in mind phosphate may inhibit enzymatic reactions. Be particularly aware of this potential disadvantage when working with DNA. While PBS is excellent for physiological science, be aware the phosphate in a PBS-buffered sample may precipitate if the sample is mixed with ethanol.

A typical chemical composition of 1X PBS has a final concentration of 10 mM PO4 3− , 137 mM NaCl, and 2.7 mM KCl. Here's the final concentration of reagents in the solution:

Salt Concentration (mmol/L) Concentration (g/L)
NaCl 137 8.0
KCl 2.7 0.2
Na 2HPO 4 10 1.42
KH 2PO 4 1.8 0.24


Ascaris species are very large (adult females: 20 to 35 cm adult males: 15 to 30 cm) nematodes (roundworms) that parasitize the human intestine. A. lumbricoides is the primary species involved in human infections globally, but Ascaris derived from pigs (often referred to as A. suum) may also infect humans. These two parasites are very closely related, and hybrids have been identified thus, their status as distinct, reproductively isolated species is a contentious topic.

Life Cycle:

Adult worms live in the lumen of the small intestine. A female may produce approximately 200,000 eggs per day, which are passed with the feces . Unfertilized eggs may be ingested but are not infective. Larvae develop to infectivity within fertile eggs after 18 days to several weeks , depending on the environmental conditions (optimum: moist, warm, shaded soil). After infective eggs are swallowed , the larvae hatch , invade the intestinal mucosa, and are carried via the portal, then systemic circulation to the lungs . The larvae mature further in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed . Upon reaching the small intestine, they develop into adult worms. Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the adult female. Adult worms can live 1 to 2 years.


Humans and swine are the major hosts for Ascaris see Causal Agents for discussion on species status of Ascaris from both hosts. Natural infections with A. lumbricoides sometimes occur in monkeys and apes.

Occasionally, Ascaris sp. eggs may be found in dog feces. This does not indicate true infection but instead spurious passage of eggs following coprophagy.

Geographic Distribution

Ascariasis is the most common human helminthic infection globally. The burden is highest in tropical and subtropical regions, especially in areas with inadequate sanitation. This infection is generally rare to absent in developed countries, but sporadic cases may occur in rural, impoverished regions of those countries. Some cases in these areas where human transmission is negligible have direct epidemiologic associations to pig farms.

Clinical Presentation

Although heavy infections in children may cause stunted growth via malnutrition, adult worms usually cause no acute symptoms. High worm burdens may cause abdominal pain and intestinal obstruction and potentially perforation in very high intensity infections. Migrating adult worms may cause symptomatic occlusion of the biliary tract, appendicitis, or nasopharyngeal expulsion, particularly in infections involving a single female worm.

Becoming Disabled

Not long ago, a good friend of mine said something revealing to me: “I don’t think of you as disabled,” she confessed.

I knew exactly what she meant I didn’t think of myself as disabled until a few decades ago, either, even though my two arms have been pretty significantly asymmetrical and different from most everybody else’s my whole life.

My friend’s comment was meant as a compliment, but followed a familiar logic — one that African-Americans have noted when their well-meaning white friends have tried to erase the complications of racial identity by saying, “I don’t think of you as black,” or when a man compliments a woman by saying that he thinks of her as “just one of the guys.”

This impulse to rescue people with disabilities from a discredited identity, while usually well meaning, is decidedly at odds with the various pride movements we’ve come to know in recent decades. Slogans like “Black Is Beautiful” and “We’re Here, We’re Queer, Get Used to It!” became transformative taunts for generations of people schooled in the self-loathing of racism, sexism and heterosexism. Pride movements were the psycho-emotional equivalents of the anti-discrimination and desegregation laws that asserted the rights of full citizenship to women, gay people, racial minorities and other groups. More recently, the Black Lives Matter and the L.G.B.T. rights movement have also taken hold.

Yet pride movements for people with disabilities — like Crip Power or Mad Pride — have not gained the same sort of traction in the American consciousness. Why? One answer is that we have a much clearer collective notion of what it means to be a woman or an African-American, gay or transgender person than we do of what it means to be disabled.

A person without a disability may recognize someone using a wheelchair, a guide dog or a prosthetic limb, or someone with Down syndrome, but most don’t conceptualize these people as having a shared social identity and a political status. “They” merely seem to be people to whom something unfortunate has happened, for whom something has gone terribly wrong. The one thing most people do know about being disabled is that they don’t want to be that.

Yet disability is everywhere once you start noticing it. A simple awareness of who we are sharing our public spaces with can be revelatory. Wheelchair users or people with walkers, hearing aids, canes, service animals, prosthetic limbs or breathing devices may seem to appear out of nowhere, when they were in fact there all the time.

A mother of a 2-year-old boy with dwarfism who had begun attending Little People of America events summed this up when she said to me with stunned wonder, “There are a lot of them!” Until this beloved child unexpectedly entered her family, she had no idea that achondroplasia is the most common form of short stature or that most people with the condition have average-size parents. More important, she probably did not know how to request the accommodations, access the services, enter the communities or use the laws that he needs to make his way through life. But because he is hers and she loves him, she will learn a lot about disability.

The fact is, most of us will move in and out of disability in our lifetimes, whether we do so through illness, an injury or merely the process of aging.

The World Health Organization defines disability as an umbrella term that encompasses impairments, activity limitations and participation restrictions that reflect the complex interaction between “features of a person’s body and features of the society in which he or she lives.” The Americans With Disabilities Act tells us that disability is “a physical or mental impairment that substantially limits one or more major life activities.”

Obviously, this category is broad and constantly shifting, so exact statistics are hard to come by, but the data from our most reliable sources is surprising. The Centers for Disease Control and Prevention estimates that one in five adults in the United States is living with a disability. The National Organization on Disability says there are 56 million disabled people. Indeed, people with disabilities are the largest minority group in the United States, and as new disability categories such as neurodiversity, psychiatric disabilities, disabilities of aging and learning disabilities emerge and grow, so does that percentage.

Disability growth areas — if you will — include diagnostic categories such as depression, anxiety disorders, anorexia, cancers, traumatic brain injuries, attention-deficit disorder, autoimmune disease, spinal cord injuries, autistic spectrum disabilities and dementia. Meanwhile, whole categories of disability and populations of people with certain disabilities have vanished or diminished significantly in the 20th century with improved public health measures, disease prevention and increased public safety.


Because almost all of us will experience disability sometime in our lives, having to navigate one early in life can be a great advantage. Because I was born with six fingers altogether and one quite short arm, I learned to get through the world with the body I had from the beginning. Such a misfit between body and world can be an occasion for resourcefulness. Although I certainly recognized that the world was built for what I call the fully fingered, not for my body, I never experienced a sense of losing capacity, and adapted quite readily, engaging with the world in my preferred way and developing practical workarounds for the life demands my body did not meet. (I used talk-to-text technology to write this essay, for example.)

Still, most Americans don’t know how to be disabled. Few of us can imagine living with a disability or using the technologies that disabled people often need. Since most of us are not born into disability but enter into it as we travel through life, we don’t get acculturated the way most of us do in our race or gender. Yet disability, like any challenge or limitation, is fundamental to being human — a part of every life. Clearly, the border between “us” and “them” is fragile. We just might be better off preparing for disability than fleeing from it.

Yet even talking about disability can be a fraught experience. The vocabulary of this status is highly charged, and for even the most well-meaning person, a conversation can feel like stepping into a maze of courtesy, correctness and possible offense. When I lecture about disability, someone always wants to know — either defensively, earnestly or cluelessly — the “correct” way to refer to this new politicized identity.

What we call ourselves can also be controversial. Different constituencies have vibrant debates about the politics of self-naming. “People first” language asserts that if we call ourselves “people with disabilities,” we put our humanity first and consider our impairment a modification. Others claim disability pride by getting our identity right up front, making us “disabled people.” Others, like many sign language users, reject the term “disability.”

The old way of talking about disability as a curse, tragedy, misfortune or individual failing is no longer appropriate, but we are unsure about what more progressive, more polite, language to use. “Crippled,” “handicapped” and “feebleminded” are outdated and derogatory. Many pre-Holocaust eugenic categories that were indicators for state-sponsored sterilization or extermination policies — “idiot,” “moron,” “imbecile” and even “mentally retarded” — have been discarded in favor of terms such as “developmentally delayed” or “intellectually disabled.” In 2010, President Obama signed Rosa’s Law, which replaced references to “mental retardation” with “intellectual disability” in federal statutes.

The author and scholar Simi Linton writes about learning to be disabled in a hospital after a spinal cord injury — not by way of her rehabilitation but rather by bonding with other young people new to disability. She calls this entering into community “claiming disability.” In “Sight Unseen,” an elegant explication of blindness and sight as cultural metaphors, Georgina Kleege wryly suggests the difference between medical low vision and blindness as a cultural identity by observing that, “Writing this book made me blind,” a process she calls gaining blindness rather than losing sight.

Like them, I had no idea until the 1980s what it meant to be disabled, that there was a history, culture and politics of disability. Without a disability consciousness, I was in the closet.

Since that time, other people with disabilities have entered the worlds in which I live and work, and I have found community and developed a sturdy disability identity. I have changed the way I see and treat myself and others. I have taken up the job of teaching disability studies and bioethics as part of my work. I have learned to be disabled.

What has been transformed is not my body, but my consciousness.

As we manage our bodies in environments not built for them, the social barriers can sometimes be more awkward than the physical ones. Confused responses to racial or gender categories can provoke the question “What are you?” Whereas disability interrogations are “What’s wrong with you?” Before I learned about disability rights and disability pride, which I came to by way of the women’s movement, I always squirmed out a shame-filled, “I was born this way.” Now I’m likely to begin one of these uncomfortable encounters with, “I have a disability,” and to complete it with, “And these are the accommodations I need.” This is a claim to inclusion and right to access resources.

This coming out has made possible what a young graduate student with a disability said to me after I gave a lecture at her university. She said that she understood now that she had a right to be in the world.

We owe much of this progress to the Americans With Disabilities Act of 1990 and the laws that led up to it. Starting in the 1960s, a broad disability rights movement encouraged legislation and policy that gradually desegregated the institutions and spaces that had kept disabled people out and barred them from exercising the privileges and obligations of full citizenship. Education, transportation, public spaces and work spaces steadily transformed so that people with disabilities came out of hospitals, asylums, private homes and special schools into an increasingly rebuilt and reorganized world.

That changed landscape is being reflected politically, too, so much so that when Donald Trump mocked the movement of a disabled reporter, most of the country reacted with shock and outrage at his blatant discrimination, and that by the time the Democratic National Convention rolled round, it seemed natural to find the rights and dignity of people with disabilities placed front and center. Hillary Clinton’s efforts early in her career to secure the right to an education for all disabled children was celebrated Tom Harkin, the former Iowa senator and an author of the Americans With Disabilities Act, marked the law’s 26th anniversary and called for improvements to it. People with disabilities were featured speakers, including Anastasia Somoza, who received an ovation for her powerful speech. President Obama, in his address, referred to “black, white, Latino, Asian, Native American young, old gay, straight men, women, folks with disabilities, all pledging allegiance, under the same proud flag.”

Becoming disabled demands learning how to live effectively as a person with disabilities, not just living as a disabled person trying to become nondisabled. It also demands the awareness and cooperation of others who don’t experience these challenges. Becoming disabled means moving from isolation to community, from ignorance to knowledge about who we are, from exclusion to access, and from shame to pride.

This is the first essay in a weekly series by and about people living with disabilities.

Watch the video: Aot react to our worldpart urban legends that turned out to be true7k special (December 2022).