Imagine yourself standing at the top of a giant pyramid made up of your ancestors. This pyramid stretches far back into the past, with each layer representing a generation of your family. Let’s explore how many ancestors you have and what this means for our understanding of human history.
You have two parents, four grandparents, and eight great-grandparents. If you go back four generations, you have 30 direct ancestors. If we keep doubling the number of ancestors with each generation, just 40 generations ago, you would have a trillion ancestors! That’s more than the number of stars in the Milky Way and more than the total number of people who have ever lived.
Humans have been around for about 200,000 years, which means there have been around 7,000 to 8,000 generations leading up to you. So, where are all these missing ancestors? The answer lies in the fact that our family trees have branches that often overlap. In the past, people usually chose partners from nearby, which means many people share common ancestors. This reduces the actual number of unique ancestors we have.
When we consider factors like migration and historical events, we find something fascinating: every person alive today shares a common ancestor who lived about 3,000 years ago. This means that even if you argue with someone online, you both share a distant ancestor! Although we don’t know who this ancestor was, the math shows they existed.
Our DNA carries the story of our ancestors. As DNA is passed down through generations, small changes, or mutations, occur. Scientists can read these changes like a clock to estimate how closely related people are. Interestingly, humans are genetically very similar. In fact, chimpanzees living close together have more genetic differences than all humans combined. This suggests that humans are a relatively young species and that our population was once very small, possibly as few as 10,000 individuals.
Today, DNA testing can reveal your genetic ancestry by examining thousands of small changes in your DNA. These changes, known as SNPs (single nucleotide polymorphisms), can indicate the geographic origins of your ancestors. For example, my DNA shows that my ancestry is primarily from Northern Europe and Scandinavia.
While most of our genetic material is mixed over generations, there is one part that remains unchanged: the mitochondrial DNA. This DNA is passed down from mother to child and traces back to a single woman who lived about 150,000 years ago in Africa. Known as mitochondrial Eve, she is the ancestor of all humans alive today.
Our ancestry is not just a story of the past; it also shapes our future. With modern technology, we have the power to influence our genetic future. What will our species look like in the years to come? The possibilities are endless, so stay curious and keep exploring.
This article is part of a series exploring the story of our species, where we came from, how we are all connected, and where we are headed. Be sure to check out other parts of the series to learn more about the fascinating history of humanity.
Imagine your family tree as a pyramid. Create a visual representation of your own ancestral pyramid by drawing or using a digital tool. Start with yourself at the top and work your way down through your parents, grandparents, and great-grandparents. Reflect on how quickly the number of ancestors grows with each generation.
Research and discuss with your classmates how family trees overlap. Interview family members to find out if there are any known shared ancestors or connections with other families. Share your findings with the class and discuss how this overlap affects the number of unique ancestors.
Engage in a classroom debate about the concept of a common ancestor. Divide into groups and argue for or against the idea that everyone alive today shares a common ancestor from 3,000 years ago. Use historical events and migration patterns to support your arguments.
Create a timeline that illustrates how DNA mutations have occurred over generations. Use this timeline to explain how scientists estimate the relatedness of individuals and the age of our species. Present your timeline to the class and discuss the implications of these genetic findings.
Research mitochondrial DNA and its significance in tracing ancestry. Create a presentation or poster that explains how mitochondrial DNA is passed down and what it reveals about our common ancestor, mitochondrial Eve. Share your work with the class and discuss the importance of this unbroken lineage.
Here’s a sanitized version of the transcript:
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This is you. And these are your ancestors, forming a vast pyramid stretching into the past and balancing on your head. How many ancestors do you have? You have two parents, four grandparents, and eight great-grandparents. Four generations back, your direct ancestors total 30. If we continue this pattern, doubling at each step, just 40 generations ago, we would find a trillion ancestors, all living at the same time. This is an astonishing number—more than the total number of people who have ever lived, and even more than the stars in the Milky Way.
Since our species emerged around 200,000 years ago, there have been perhaps 7 or 8 thousand generations of humans leading up to you. So, where are all your missing ancestors? Clearly, there has been some interbreeding. We’re not referring to extreme cases, but every family tree inevitably has branches. Before modern dating apps, choices for partners were often limited to those within walking distance. Even notable figures like Charles Darwin and Albert Einstein married their first cousins. Because many people with shared ancestors have reproduced, the actual number of our ancestors is much smaller than simple calculations suggest.
When we apply more complex mathematics, taking into account factors like migration, life expectancy, and historical events, we discover something intriguing: every human alive today shares a common ancestor who lived only about 3,000 years ago. So, the next time you find yourself in a disagreement with a stranger online, remember that you share a distant ancestor. However, we don’t know who this person was. The math indicates they existed, but they left no fossils or artifacts.
We all carry a record of our ancestors in our DNA. As DNA is copied through generations, occasional mistakes occur. Just like making a copy of a copy can lead to a less clear image, these mutations can accumulate over time. Scientists can read these changes like a molecular clock, estimating how much time has passed and determining how closely related individuals are.
Humans may appear very different, but on a genetic level, we are remarkably similar. Groups of chimpanzees living in close proximity show more genetic variation than the entire human population. This genetic similarity indicates that our species is relatively new and that at one point, our population may have been as small as 10,000 individuals.
To put that in perspective, that’s only about a third of the average concert crowd. Today, any two humans differ by about 1 out of 1,000 DNA base pairs. However, given the size of our genome, that still amounts to millions of single-letter differences, known as SNPs (single nucleotide polymorphisms). We often see combinations of these changes associated with different geographic locations. Companies that analyze DNA ancestry examine thousands of these single-letter changes to create a unique genetic signature for individuals. They then compare this signature to thousands of reference individuals from various regions to determine the likely geographic origins of your genetic makeup.
In my case, my ancestry is primarily from Northern Europe and Scandinavia, which explains certain traits I have. Some people discover unexpected aspects of their ancestry through DNA testing. While our external appearances may not reveal our origins, DNA provides an accurate account.
Previously, we identified a common ancestor from not too long ago who is related to all of us. However, the genetic influence of that individual has been so mixed over time that it’s no longer visible in our DNA. Is there someone whose genes have been passed down unbroken to the present day? Yes, there is. You have a 47th chromosome that resides in mitochondria, the powerhouse of the cell. Mitochondria used to be free-swimming and have their own genetic material. Unlike your other chromosomes, there is no shuffling of this DNA when it is passed down through generations. Moreover, all your mitochondria come from your mother’s egg, not your father’s sperm, creating an unbroken lineage through every female in your family tree.
By comparing the changes that have accumulated over millennia, we find that the most ancient human mitochondrial DNA traces back to Africa, where our species originated. We can even trace it back to one woman who lived about 150,000 years ago. Other Homo sapiens females lived alongside her, but only her lineage continues today; all other lineages have become extinct. This woman is referred to as mitochondrial Eve, and every one of us is a descendant of her lineage. In a true sense, we are all family, even if distantly related.
Our ancestry is not just a tree reaching into the past; it also extends into the future. Today, we have unprecedented power to shape that future, even at the genetic level. What might our species’ future look like? Stay curious.
This video is part of a special series about the story of our species: where we came from, how we are all connected, and where we are going. If you haven’t already, check out parts 1 and 2 to explore the fossils in our family tree and learn why we are the only humans left. Be sure to subscribe so you don’t miss any of our upcoming videos.
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This version maintains the original content while removing any informal language and potentially sensitive references.
Ancestors – Organisms from which others have descended – Scientists study fossils to learn more about the ancestors of modern animals.
Generations – Groups of organisms born and living around the same time – Over many generations, the traits of a species can change due to natural selection.
DNA – The molecule that carries genetic information in living organisms – DNA contains the instructions needed for an organism to develop, survive, and reproduce.
Mutations – Changes in the DNA sequence that can lead to variations in traits – Some mutations can be beneficial and help an organism adapt to its environment.
Migration – The movement of organisms from one place to another, often seasonally – The migration of birds is a fascinating phenomenon that scientists study to understand animal behavior.
Species – A group of similar organisms capable of interbreeding and producing fertile offspring – The cheetah is a species known for its incredible speed and agility.
Common – Shared by two or more organisms or groups – Humans and chimpanzees have a common ancestor, which is why they share many genetic similarities.
History – The study of past events, particularly in relation to organisms and their development – The history of life on Earth is recorded in the fossil record, showing how species have evolved over time.
Genetic – Relating to genes or heredity – Genetic research helps scientists understand how traits are passed from parents to offspring.
Ancestry – The lineage or descent of an organism – By studying ancestry, scientists can trace the evolutionary path of a species.
