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How closely related are we? - The Ralph and Coop Theory
- Healthasion
- Oct 17, 2020
- 3 min read
Is it true that everyone in the world is related to each other? This mind-boggling concept has kept humanity eagerly on their toes for an answer. Scientists across the globe have conducted innumerable studies and presented theories. One prominent answer to this question has been presented by scientists Peter Ralph and Graham Cooper, who theorized that everyone in the world is related to each other.
Each of us have two parents, four grandparents and eight great grandparents. Four generations back, your direct ancestors comprised 30 people. If we continue down this pattern by doubling every step, we can find that just over 20 generations ago, we would have around 1 million ancestors – all living at the same time! However, as we extend this pattern, we can discover something astounding. When we get to 40 generations, our ancestors would total over 1 trillion people – which is greater than the number of people who have ever lived (Stephenson, 2012). According to Peter Ralph of USC Dornsife, he deduced that having over a trillion ancestors is a “problem”, mainly due to the fact that we now would have more ancestors than there were people (Bell, 2013). Thus, it can be understood that many of those ancestors must be the same person (Bell, 2013).
To envision this concept, Ralph suggested drawing an imaginary family tree. Based on his findings, he describes that it looks like a tree at first – with the branches doubling every generation. Although, as the branches start intersecting one another, Ralph depicts it as a “web-like tapestry,” as distant cousins marry each other and share a set of distant grandparents (Bell, 2013).
Additionally, a paper written by Joseph Chang was published in 1999. Chang, who was a statistician at Yale University, investigated the ‘tapestry’ numerically and confirmed that everybody is bonded by a mutual ancestor. As we go back in time, the number of mutual ancestors of the current population would rise, “until all people who have descendants amid the existing population are actually ancestors of all present-day individuals,” (Bell, 2013) as stated by Chang.
Since the publishing of Chang’s paper, there has been tremendous progress in collecting genetic information. This has enabled scientists to accumulate vast DNA databases. Ralph joined hands with his previous postdoctoral advisor Coop, who is also a geneticist at UC
Davis (Brown, 2013). They concentrated on the ancestry of Europe by using the ‘Population Reference Data Sample’. This provides the entire genome sequencing information on 2,257 people, residing in more than 40 European populations (Brown, 2013). This specific sample was chosen for one reason alone - in terms of geography, it provided a good match to the genetic data set. The data set also explored 500,000 locations on the genome, which can denote individual variations from each person.
Following this in 2013, Coop and Ralph used a computer program to find either matching, or nearly matching DNA sequences, enabling them to figure out relations between individuals (Ralph & Coop, 2013). They were able to identify 1.9 million shared DNA segments that were millions of base pairs in length, proving their owners were relatives. By viewing the length of the segment, this allowed them to approximate how long ago their common ancestor lived. According to the scientists, “the length of the shared DNA sequence shows how closely, or distantly, two people are related” (Bell, 2013). It was observed by Ralph and Coop that the DNA sequences shared with parents are the longest – the sequences with grandparents are half as long and so on, which means that “the longer ago an ancestor is, the shorter the chunk is likely to be” (Bell, 2013).
Ralph and Coop’s research confirmed Professor Chang’s theory of everyone’s link with a mutual ancestor. They claimed that everyone who was alive in Europe 1000 years ago and had offspring is an ancestor of everyone who is currently alive today with some European ancestry. These scientists continued their research to show that the shared segments are from ancestors who lived 3000 years ago or 100 generations.
Overall, the research done by scientists Ralph and Coop presented a convincing answer and supported Professor Chang’s theory. This revolutionary exploration can potentially aid in solving age-old questions in various subjects: archaeology, linguistics, ecology, and history, bringing forth new theories for humanity to anticipate.
References:
Bell, S. (2013). Researcher uses DNA to demonstrate just how closely everyone on Earth is related to everyone else. Phys.org. https://phys.org/news/2013-08-dna-earth.html
Brown, E. (2013). Everyone on Earth is related to everyone else, DNA shows. Los Angeles Times. https://www.latimes.com/science/la-xpm-2013-may-07-la-sci-european-dna-20130508-story.html
Ralph, P., & Coop, G. (2013). The geography of recent genetic ancestry across Europe. PLOS Biology, 11(5), e1001555. https://doi.org/10.1371/journal.pbio.1001555
Stephenson, W. (2012). Do the dead outnumber the living? BBC news. https://www.bbc.com/news/magazine-16870579
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