How many people is it possible to know

By , however, the world population passed the 1 billion mark and has since continued to grow to its current 7. This growth is driven in large part by advances in public health, medicine, and nutrition that have lowered death rates, allowing more people to live far into their reproductive years. Guesstimating the number of people ever born requires determining population sizes for different points in human prehistory and history and applying assumed birth rates to each period.

We start at the very, very beginning—with just two people a minimalist approach! Although it is unlikely that humans descended from two people, this approach simplifies our estimation. One complicating factor is the pattern of population growth. Did it rise to some level and then fluctuate wildly in response to famines and changes in climate?

Or did it grow at a constant rate? We cannot know the answers to these questions, although paleontologists have produced a variety of theories. For the purposes of this exercise, we assumed a constant growth rate applied to each period up to modern times. Birth rates were set at 80 per 1, population annually through 1 C. Rates then declined to below the 20s by the modern period see Table 1. This semi-scientific approach yields an estimate of about billion births since the dawn of modern humankind.

Clearly, the period , B. If we were to challenge our conclusion at all, it might be that our method underestimates the number of births to some degree. The assumption of constant rather than highly fluctuating population growth in the earlier period may underestimate the average population size at the time. When we adjusted the date of the first Homo sapiens on Earth from 50, B.

But perhaps these two sets of estimates form some sort of boundary as to the possible highs and lows of this slippery issue. As new archaeological discoveries are made and analyzed using increasingly innovative methods, expanding our understanding of human population history, we look forward to yet again tackling this ever-intriguing proposition! Toshiko Kaneda is a technical director, demographic research at PRB; Carl Haub is a former senior demographer at PRB and is also the author of the original version of this article in Project Details Date May 18, However, there are some major problems with relying on community infection to create herd immunity to the virus that causes COVID :.

Herd immunity also can be reached when enough people have been vaccinated against a disease and have developed protective antibodies against future infection. Unlike the natural infection method, vaccines create immunity without causing illness or resulting complications. Using the concept of herd immunity, vaccines have successfully controlled contagious diseases such as smallpox, polio, diphtheria, rubella and many others.

Herd immunity makes it possible to protect the population from a disease, including those who can't be vaccinated, such as newborns or those who have compromised immune systems. The U. For example:. The number of fully vaccinated adults continues to rise. In addition, more than 31 million people in the U. However, if you are in an area with a high number of new COVID cases in the last week, the CDC recommends wearing a mask indoors in public and outdoors in crowded areas or when you are in close contact with unvaccinated people.

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This content does not have an English version. This content does not have an Arabic version. See more conditions. Show references Poland GA. Preserving civility in vaccine policy discourse: A way forward. Poland GA. The Lancet. Metcalf CJE, et al. Understanding herd immunity. Trends in Immunology.

Scale may be one of the issues with the massive social networking sites that now dominate our lives. And for certain Facebook users, the smaller and more secret the groups , the better. Thus far, the research of Dunbar and colleagues on online relationships suggests that these are similar to offline relationships in terms of numerical restrictions. Dunbar and colleagues also have performed research on Facebook, using factors like the number of groups in common and private messages sent to map the number of ties against the strength of those ties.

When people have more than friends on Facebook or followers on Twitter, Dunbar argues, these represent the normal outer layers of contacts or the low-stakes connections : the and For most people, intimacy may just not be possible beyond connections.

There is a balance between the amount of connections you have and the intimacy of those connections Credit: Emmanuel Lafont. He compares anonymous internet interactions to the use of confessionals in the Catholic church. Face-to-face relationships, with all the non-verbal information that is so critical to communication, remain paramount. Those aged 18—24 have much larger online social networks than those aged 55 and above. And the primacy of physical contact in the social brain hypothesis may apply less to young people who have never known life without the internet , for whom digital relationships may be just as meaningful as analogue ones.

Without the pressure for longevity, ideal community size may be less relevant. Curious about the hidden forces shaping the world? So are we. This article is part of our Invisible Numbers series, where we explore the digits, percentages and equations that govern our everyday lives in dramatic ways, often without us realising it.

Join one million Future fans by liking us on Facebook , or follow us on Twitter or Instagram. If you liked this story, sign up for the weekly bbc. Invisible Numbers Psychology. Dunbar's number: Why we can only maintain relationships.