Chicken and the egg

Which came first, the chicken or the egg? This question often gets posed as an example of a question that is impossible to answer, since plainly chickens come from eggs and eggs come from chickens. In EDA, there are chicken and egg business issues: how do you get people to use synthesis when there are no libraries? So then how do you get people to create libraries when nobody uses synthesis? How do you get software engineers to use virtual platforms when the models are not created in advance? And get the component vendors to create the models when the user base is not large enough?

However, the answer to the actual chicken and egg problem seems obvious to me. Dinosaurs come from eggs. Reptiles come from eggs. All birds come from eggs. So if you take a chicken today and follow its ancestry back through egg and chicken all the way to primordial soup, then there is some point at which you have to decide that the creatures are sufficiently different from chickens that you no longer can call them chickens, you have identified the last chicken. For any reasonable definition of chicken, that creature came from an egg. So at that point you have a non-chicken laying an egg, and that egg hatching into a chicken. So the egg came first.

Going back up the line of ancestry has some interesting aspects. As you almost certainly know, only males have a Y-chromosome. So, if you are male, your Y-chromosome came from your father, not your mother. And his Y-chromosome came from your paternal grandfather. If you follow that line back thousands of generations, every one of those men has something atypical about them. They managed to avoid fatal childhood disease, avoid dying in war, find a mate and have a male child. In one sense that is really obvious, in another sense it is really deep. After all, the odds weren’t that great in the days with low life expectancy, high levels of violence in society and so on.

You may also know that the mitochondria in your cells come from your mother. So in the same way, they came from your maternal grandmother and so on all the way back. And all those women also managed to avoid dying young, less likely to die in war but more likely to die early in adulthood during childbirth, but they all managed to get through all that and have at least one daughter (who lived to adulthood and had a daughter of her own).

If you go back about 170,000 years (about 8,000 generations) you arrive at Mitochondrial Eve, the earliest ancestor (female, obviously) from which all humans today can trace their mitochondria. And about 60,000 years back (only about 3,000 generations) is Y-chromosomal Adam, the earliest ancestor from which all men inherit some of their Y-chromosome.

Firstly, note that these two lived in very different times, 100,000 years apart. There isn’t a single Adam and Eve from which everyone is descended in Biblical style. But we know, by definition, that all the other males in whatever group Y-chromosomal Adam lived failed to have an unbroken line of mail heirs, whereas he did. Similarly other female contemporaries of Mitochondrial Eve failed to have unbroken lines of female descendents, like she did.

The most recent common ancestor of all mankind is actually more recent than either of these two since that is a much less restrictive condition (the line of descent can pass through both males and females). Depending on which groups of people fail to make it in the future due to war, catastrophe or epidemic, the earliest common ancestor (and in a similar way the identity of Mitochondrial Eve and Y-chromosomal Adam) might get pushed back to different individuals as some lines of descent die out.

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