One of the most well-known philosophical questions is what came first: the chicken or the egg? A chicken is born from an egg, and an egg is birthed by a chicken. This means that the cause and effect are intertwined in a never-ending cycle. This kind of problem is known as circular cause and consequence or circular reference.
In some ways, this question is extremely easy to answer. In biology, many different creatures lay eggs to give birth to their young, but there are no examples of a chicken being born without an egg being involved. The chicken is most likely a product of a lineage of evolving species that ultimately resulted in the genetic makeup of a chicken. That “proto-chicken” would have laid an egg, which had enough mutations in its genome to be sufficiently different from the proto-chicken to be called a “chicken”. Therefore, the egg must have come before the chicken. Even if we use the strict rule of defining “egg” by as a “chicken egg”, the egg that birthed the first chicken contained the original genetic makeup for chickens; ergo the chicken egg came before the chicken.
Science and philosophy aside, a completely unrelated point about chickens and eggs is that there is a Japanese dish called oyakodon, which is made with chicken and egg over a bowl of rice and vegetables. The name comes from the Japanese for parent (“oya”, 親) and child (“ko”, 子), giving away the cruel nature of the relationship between the main ingredients in the dish.
We were all born from our parents. Our parents were all born from our grandparents. Everyone has a family tree and a root. If so, is it possible to find the beginning of mankind – our true “root”?
Our cells have an organelle (a part of the cell) called mitochondria. Mitochondria act as the cell’s engine and allow the cell to generate energy through respiration. An interesting fact about them is that they are not originally “ours”. About 1.5 billion years ago, there was an event where a prokaryote (cells without a nucleus, like a bacteria) invaded (or was eaten by) a eukaryote (cells with nuclei, like our cells). The prokaryote and the cell began a symbiosis and the prokaryote became a part of the cell.
Due to the external origin of mitochondria, they have a different genome to us. This is called mitochondrial DNA, shortened to mtDNA, which allows mitochondria to divide and synthesise proteins without the help of the host cell. It used to be a completely independent organism, but it has lost some of its functions to the cell.
mtDNA is inherited in a different way to normal DNA. Normally we receive half of our mother’s and half of our father’s genes, but we only inherit our mother’s mtDNA. This is because sperm keeps mitochondria in the tail which is lost during fertilisation, meaning our father’s mitochondria cannot be inherited. The only way to gain mitochondria is from those in the cytoplasm (the material that fills cells) of our mother’s egg. This is known as maternal inheritance.
Using this information, scientists compared a large sample of people’s mtDNA to turn back the clock. Knowing that a child and its mother share the same mtDNA and the mother and grandmother share the same mtDNA, we can analyse mtDNA to find the origin of mankind, or our first common female ancestor – also called Mitochondrial Eve.
Mitochondrial Eve is estimated to have lived 200,000 years ago in Africa, thus she is also known as African Eve. Her mtDNA is an ancient heirloom passed along generation after generation to us, as evidence of evolution. Every living person on the face of the Earth is a descendant of her. So in some ways, it could be said that we truly are one big family.