Ehrlich was born in Philadelphia, Pennsylvania, the son of William Ehrlich and Ruth (Rosenberg) Ehrlich. His father was a shirt salesman, his mother a Greek and Latin scholar.
Ehrlich earned a bachelor's degree in zoology from the University of Pennsylvania in 1953, an M.A. from the University of Kansas in 1955, and a Ph.D. from the University of Kansas in 1957, supervised by the prominent bee researcher Charles Duncan Michener. During his studies he participated with surveys of insects in the areas of the Bering Sea and Canadian Arctic, and then with a National Institutes of Health fellowship, investigated the genetics and behavior of parasitic mites. In 1959 he joined the faculty at Stanford University, being promoted to professor of biology in 1966. By training he is an entomologist specializing in Lepidoptera (butterflies); he published a major paper about the evolution of plants and insects. He was appointed to the Bing Professorship in 1977.
He is president of the Center for Conservation Biology at Stanford University. He is a fellow of the American Association for the Advancement of Science, the United States National Academy of Sciences, the American Academy of Arts and Sciences and the American Philosophical Society.
A lecture that Ehrlich gave on the topic of overpopulation at the Commonwealth Club of California was broadcast by radio in April 1967. The success of the lecture caused further publicity, and the suggestion from David Brower the executive director of the environmentalist Sierra Club, and Ian Ballantine of Ballantine Books to write a book concerning the topic. Ehrlich and his wife, Anne Ehrlich, collaborated on the book, The Population Bomb, but the publisher insisted that a single author be credited.
Although Ehrlich was not the first to warn about population issues – concern had been widespread during the 1950s and 1960s – his charismatic and media-savvy methods helped publicize the topic.
The original edition of The Population Bomb began with this statement: "The battle to feed all of humanity is over. In the 1970s hundreds of millions of people will starve to death in spite of any crash programs embarked upon now. At this late date nothing can prevent a substantial increase in the world death rate ..." Ehrlich argued that the human population was too great, and that while the extent of disaster could be mitigated, humanity could not prevent severe famines, the spread of disease, social unrest, and other negative consequences of overpopulation. By the end of the 1970s, this prediction proved to be incorrect. However, he continued to argue that societies must take strong action to decrease population growth in order to mitigate future disasters, both ecological and social.
In the book Ehrlich presented a number of "scenarios" detailing possible future events, some of which have been used as examples of errors in the years since. Of these scenarios, Ehrlich has said that although, "we clearly stated that they were not predictions and that 'we can be sure that none of them will come true as stated,’ (p. 72) – their failure to occur is often cited as a failure of prediction. In honesty, the scenarios were way off, especially in their timing (we underestimated the resilience of the world system). But they did deal with future issues that people in 1968 should have been thinking about." Ehrlich further states that he still endorses the main thesis of the book, and that its message is as apt now as it was in 1968.
Ehrlich's opinions have evolved over time, and he has proposed different solutions to the problem of overpopulation. In Population Bomb he wrote, "We must have population control at home, hopefully through a system of incentives and penalties, but by compulsion if voluntary methods fail. We must use our political power to push other countries into programs which combine agricultural development and population control." Voluntary measures he has endorsed include the easiest possible availability of birth control and abortion. In 1967 he had expressed his belief that aid should only be given to those countries that were not considered to be "hopeless" to feed their own populations.
In their sequel to The Population Bomb, the Ehrlichs wrote about how the world's growing population dwarfs the Earth's capacity to sustain current living standards. The book calls for action to confront population growth and the ensuing crisis:
When is an area overpopulated? When its population can't be maintained without rapidly depleting nonrenewable resources  (or converting renewable resources into nonrenewable ones) and without degrading the capacity of the environment to support the population. In short, if the long-term carrying capacity of an area is clearly being degraded by its current human occupants, that area is overpopulated.
In this paper, the Ehrlichs discuss the 'optimal size' for human population, given current technological realities. They refer to establishing "social policies to influence fertility rates."
During a 2004 interview, Ehrlich answered questions about the predictions he made in The Population Bomb. He acknowledged that some of what he had published had not occurred, but reaffirmed his basic opinion that overpopulation is a major problem. He noted that, "Fifty-eight academies of science said that same thing in 1994, as did the world scientists' warning to humanity in the same year. My view has become depressingly mainline!" Ehrlich also stated that 600 million people were very hungry, billions were under-nourished, and that his predictions about disease and climate change were essentially correct. Retrospectively, Ehrlich believes that The Population Bomb was "way too optimistic".
In a 2008 discussion hosted by the website Salon, Paul Ehrlich has become more critical of the United States specifically, claiming that it should control its population and consumption as an example to the rest of the world. He has disavowed some of what he said in The Population Bomb. He still thinks that governments should discourage people from having more than two children, suggesting, for example a greater tax rate for larger families.
In 2011, as the world's population passed the seven billion mark Ehrlich has argued that the next two billion people on Earth would cause more damage than the previous two billion because we are now increasingly having to resort to using more marginal and environmentally damaging resources. As of 2013, Ehrlich continues to perform policy research concerning population and resource issues, with an emphasis upon endangered species, cultural evolution, environmental ethics, and the preservation of genetic resources. Along with Dr. Gretchen Daily, he has performed work in countryside biogeography; that is, the study of making human-disturbed areas hospitable to biodiversity. His research group at Stanford University examines extensively natural populations of the Bay checkerspot butterfly (Euphydryas editha bayensis). The population-related disasters Ehrlich predicted have largely failed to materialize, with population growth rates slowing and new food production technologies increasing the food supply faster than the population. Ehrlich endorses his general thesis that the human population is too large, posing a direct threat to human survival and the environment of the planet.
Critics have disputed Ehrlich's main thesis about overpopulation and its effects on the environment and human society, and his solutions, as well as some of his specific predictions made since the late 1960s. One criticism concerns Ehrlich's allegedly alarmist and sensational statements and inaccurate "predictions". Ronald Bailey of Reason Magazine has termed him an "irrepressible doomster ... who, as far as I can tell, has never been right in any of his forecasts of imminent catastrophe." On the first Earth Day in 1970, he warned that "[i]n ten years all important animal life in the sea will be extinct. Large areas of coastline will have to be evacuated because of the stench of dead fish." In a 1971 speech, he predicted that: "By the year 2000 the United Kingdom will be simply a small group of impoverished islands, inhabited by some 70 million hungry people." "If I were a gambler," Professor Ehrlich concluded before boarding an airplane, " I would take even money that England will not exist in the year 2000." When this scenario did not occur, he responded that "When you predict the future, you get things wrong. How wrong is another question. I would have lost if I had had taken the bet. However, if you look closely at England, what can I tell you? They're having all kinds of problems, just like everybody else." Ehrlich wrote in The Population Bomb that, "India couldn't possibly feed two hundred million more people by 1980."
Carl Haub of the Population Reference Bureau has replied that it was precisely the alarmist rhetoric that prevented the catastrophes of which Ehrlich warned. "It makes no sense that Ehrlich is now criticized as being alarmist because his dire warnings did not, in the main, come true. But it was because of such warnings from Ehrlich and others that countries took action to avoid potential disaster." During the 1960s and 70s when Ehrlich made his most alarming warnings, there was a widespread belief among experts that population growth presented an extremely serious threat to the future of human civilization, although differences existed regarding the severity of the situation, and how to decrease it.
Dan Gardner argues that Ehrlich has been insufficiently forthright in acknowledging errors he made, while being intellectually dishonest or evasive in taking credit for things he claims he got "right". For example, he rarely acknowledges the mistakes he made in predicting material shortages, massive death tolls from starvation (as many as one billion in the publication Age of Affluence) or regarding the disastrous effects on specific countries. Meanwhile, he is happy to claim credit for "predicting" the increase of AIDS or global warming. However, in the case of disease, Ehrlich had predicted the increase of a disease based on overcrowding, or the weakened immune systems of starving people, so it is "a stretch to see this as forecasting the emergence of AIDS in the 1980s." Similarly, global warming was one of the scenarios that Ehrlich described, so claiming credit for it, while disavowing responsibility for failed scenarios is a double standard. Gardner believes that Ehrlich is displaying classical signs of cognitive dissonance, and that his failure to acknowledge obvious errors of his own judgement render his current thinking suspect.
Barry Commoner has criticized Ehrlich's 1970 statement that "When you reach a point where you realize further efforts will be futile, you may as well look after yourself and your friends and enjoy what little time you have left. That point for me is 1972." Gardner has criticized Ehrlich for endorsing the strategies proposed by William and Paul Paddock in their book Famine 1975!. They had proposed a system of "triage" that would end food aid to "hopeless" countries such as India and Egypt. In Population Bomb, Ehrlich suggests that "there is no rational choice except to adopt some form of the Paddocks' strategy as far as food distribution is concerned." Had this strategy been implemented for countries such as India and Egypt, which were reliant on food aid at that time, they would almost certainly have suffered famines. Instead, both Egypt and India have greatly increased their food production and now feed much larger populations without reliance on food aid.
Another group of critics, generally of the political left, argues that Ehrlich emphasizes overpopulation too much as a problem in itself, instead of distribution of resources. Barry Commoner argued that Ehrlich emphasized overpopulation too much as the source of environmental problems, and that his proposed solutions were politically unacceptable because of the coercion that they implied, and because they would cost poor people disproportionately. He argued that technological, and above all social development would result in a natural decrease of both population growth and environmental damage. Ehrlich denies any type of racism, and has argued that if his policy ideas were implemented properly they would not be repressive.
Julian Simon, a cornucopian economist, argued that overpopulation is not a problem in itself, and that humanity will adapt to changing conditions. Simon argued that eventually human creativity will improve living standards, and that most resources were replaceable. Simon stated that over hundreds of years, the prices of virtually all commodities have decreased significantly and persistently. Ehrlich termed Simon the proponent of a "space-age cargo cult" of economists convinced that human creativity and ingenuity would create substitutes for scarce resources and reasserted the idea that population growth was outstripping the earth's supplies of food, fresh water and minerals. This exchange resulted in the Simon–Ehrlich wager, a bet about the trend of prices for resources during a ten-year period that was made with Simon in 1980. Ehrlich was allowed to choose ten commodities that he predicted would become scarce and thus increase in price. Ehrlich chose mostly metals, and lost the bet, as their average price decreased by about 30% in the next 10 years. Simon and Erlich could not agree about the terms of a second bet.
Ehrlich has argued that humanity has simply deferred the disaster by the use of more intensive agricultural techniques, such as those introduced during the so-called Green Revolution. Ehrlich claims that increasing populations and affluence are increasingly stressing the global environment, due to such factors as loss of biodiversity, overfishing, global warming, urbanization, chemical pollution and competition for raw materials. He maintains that due to growing global incomes, reducing consumption and human population is critical to protecting the environment and maintaining living standards, and that current rates of growth are still too great for a sustainable future.
Ehrlich was one of the initiators of the group Zero Population Growth (renamed Population Connection) in 1968, along with Richard Bowers and Charles Remington. He and his wife Anne were part of the board of advisers of the Federation for American Immigration Reform until 2003. He is currently a patron of Population Matters, (formerly known as the Optimum Population Trust).
Ehrlich has spoken at conferences in Israel on the issue of desertification. He has argued that "True Zionists should have small families".
Ehrlich has been married to Anne H. Ehrlich (born Anne Fitzhugh Howland, 1933) since 1954; he and Anne are parents to one child, Lisa Marie.
Ehrlich has said he has had a vasectomy.The John Muir Award of the Sierra Club
The Gold Medal Award of the World Wildlife Fund International
A MacArthur Prize Fellowship
The Crafoord Prize, awarded by the Royal Swedish Academy of Sciences and considered the highest award given in the field of ecology
ECI Prize winner in terrestrial ecology, 1993
A World Ecology Award from the International Center for Tropical Ecology, University of Missouri, 1993
The Volvo Environmental Prize, 1993
The United Nations Sasakawa Environment Prize, 1994
The 1st Annual Heinz Award in the Environment (with Anne Ehrlich), 1995
The Tyler Prize for Environmental Achievement, 1998
The Dr A.H. Heineken Prize for Environmental Sciences, 1998
The Blue Planet Prize, 1999
The Eminent Ecologist Award of the Ecological Society of America, 2001
The Distinguished Scientist Award of the American Institute of Biological Sciences, 2001
Ramon Margalef Prize in Ecology and Environmental Sciences of the Generalitat of Catalonia, 2009.
Fellow of the Royal Society of London 2012
2013 BBVA Foundation Frontiers of Knowledge Award in Ecology and Conservation Biology
Ehrlich, P. R. (2010). "The MAHB, the Culture Gap, and Some Really Inconvenient Truths". PLoS Biology. 8 (4): e1000330. PMC 2850377 . PMID 20386722. doi:10.1371/journal.pbio.1000330.
Ceballos, Gerardo; Ehrlich, Paul R.; Barnosky, Anthony D.; García, Andrés; Pringle, Robert M.; Palmer, Todd M. (2015). "Accelerated modern human–induced species losses: Entering the sixth mass extinction". Science Advances. 1 (5): e1400253. doi:10.1126/sciadv.1400253.
Ceballos, Gerardo; Ehrlich, Paul R.; Dirzo, Rodolfo (23 May 2017). "Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines". PNAS. doi:10.1073/pnas.1704949114.