This missing science of heredity, this unworked mine of knowledge on the borderland of biology and anthropology, which for all practical purposes is as unworked now as it was in the days of Plato, is, in simple truth, ten times more important to humanity than all the chemistry and physics, all the technical and industrial science that ever has been or ever will be discovered.Herbert G. Wells, Mankind in the Making, 1903
Humans, since the genesis of rational thought, must have wondered why like begets like. Why do we inherit genetic attributes from parents? We don’t know when it all started but it’s highly unlikely that neolithic or paleolithic humans ever came as close to hypothesizing about genetics as the philosophers of Ancient Greece. It is at this point in recorded history that we see glimpses of parochial humans start questioning about the nature of heredity. This is a story that spans nearly 2500 years but has a significance that amounts to the entirety of human existence.
The information on how to build, fix, and support bodies reside on chromosomes – long filamentous structures deep within every cell in your body that carry genes, usually tens of thousands, all linked together. Humans have fourty-six such chromosomes, twenty-three from each parent. Chromosomes contain the vast majority of the DNA. A sequence of four nucleobases along the two strands of the DNA encode the entire set of genetic instructions carried by an organism – the genome. The human genome contains about twenty-three thousand genes. Only about 2% of these are used in protein synthesis.
Of course, we know all this only because of 20th-century molecular biology. Nowadays, usage of the term ‘gene’ has invaded our daily discourse concerning heredity, race, culture, and politics that we seldom pause to think about how ancient humans, in a world without electron microscopes or specialized genetic laboratories, thought about heredity?
Pythagoras, who lived around 500BC, proposed the first known, widely accepted theory to explain the similarities between parents and children. According to him, hereditary information was primarily carried in male semen. It traveled all around the male body and absorbed genetic information. Once inside the womb, the semen matured into a fetus with nourishment from the mother. The father provided the data. The mother transformed the data into a child. This theory was termed spermism because it highlighted that only the male semen had any part in determining all the features of a fetus.
The so-called Pythagoreans, who were the first to take up mathematics, not only advanced this subject but saturated with it, they fancied that the principles of mathematics were the principles of all things.Aristotle
The Pythagoreans believed that nature was made of numbers. They were especially obsessed with the mystical geometry of triangles. They took to this symmetry – nature from the father, nurture from the mother – and argued that there existed a triangular harmony even in heredity. The Pythagoras’ theorem was applied with the father and mother’s individual contributions (the sides) resulting in the child (hypotenuse). They used this as proof that there were mathematical mysteries lurking everywhere in nature.
The obvious implication of this theory is that the mother exists only as a nutrition bag, dripping food through the umbilical cord into her child.
A century after Pythagoras, Plato was captivated by this metaphor. If heredity was a formula, in principle, it could be hacked. The perfect children could be produced by the perfect parents breeding at the perfect times – a twisted ‘law of births’. The elite ruling class in Plato’s republic deemed that only such propitious unions would occur in the future. This sowed the seed for a political utopia based on a perverted passion for the ‘perfect race’ that would disrupt the political order of modern Europe two millennia later.
Aristotle was the first to systematically tackle the merits and problems in Pythagoras’ theory of heredity using experimental data from the biological world. His text, “Generation of Animals” serves as the foundational text for human genetics. He pointed out the most obvious of the flaws in spermism i.e, children can inherit features only from the fathers. He observed physical traits such as skin color, the shape of the nose, marks, and growths inherited from the maternal side just as much as it is inherited from the paternal side. More acutely, he noted that even behavioral traits such as a manner of walking, talking, musing, or a state of mind could also be inherited.
He attacked Pythagoras’ theory with the easily discernible of evidence. How could the male semen absorb the instructions to produce the genitals of a female child?
Aristotle offered an alternate theory of heredity. Perhaps, along with the male, the female also contributes to the formation of a child through some form of female semen. To Aristotle, this exchange was not merely material but something rather mysterious. He argued that it was not matter that was exchanged through the male semen but a sort of a message. This message triggers the female semen – still unknown – into forming the physical body of the fetus. The male provides the message and the female provides the material. Although he was wrong about this partition of message and material, he captured one of the essential truths about heredity: the transmission of heredity was essentially the transmission of information. Information was then used to build the organism from scratch. Message became material.
This naturally leads to questions like: how is the message packaged, delivered, and interpreted? What does the message contain? Who is behind the transcription of the message?
Naturally, such questions have a religious interest. The most inventive form of an answer to these questions, proposed and used by religion, was preformation. It suggested that sperm contained a mini-human, fully formed and shrunken into a tiny package, waiting to be inflated into a baby. It refuted the message theory altogether, instead suggesting that the mini-human expanded into a fetus in the mother’s womb. There was no message. There was only miniaturization.
For medieval Christians, this theory provided a powerful way to explain original sin. Since, after birth, the once mini-human had to mature and in-turn produces its own children, it must have had more mini-humans lodged inside it. Naturally, this is infinitely recursive and can be traced back to Adam. All future humans had to have been ‘floating inside Adam’s loins’. All future humans bore a taint of the original sin because they had actually been there and tasted the fruit.
Variations of this theory existed in folklore. Paracelsus, a 16th-century alchemist, used the mini-human theory to suggest that human sperm, when heated with horse-dung and buried in mud for the forty weeks of natural conception, would grow into a baby.
The preformation theory was so powerful and seductive that it prevailed and even thrived, after the invention of the microscope. Seventeenth-century microscopists made pictures of mini beings with enlarged heads curled up inside the head of a sperm. At the end of the seventeenth century, preformation became the most widely accepted and the most logical explanation for human heredity.
“In nature there is no generation,” wrote a Dutch scientist, “but only propagation”
In 1768, the German embryologist Caspar Wolff envisioned that the embryo progressively matured from the fertilized egg into a human form. But apart from this vague idea, he couldn’t deal with any specifics. By the 1800s, the field of heredity had reached a dead-end.
A casual observer of today would dismiss such wild claims as non-sense but over the span of two millennia, the field of heredity had scarcely progressed from unfounded speculations by old Greek men who lived in faraway islands so long ago.
Gregor Johann Mendel, an Augustinian monk who lived in the 19th century, was the first to systematically study the nature of recessive and dominant genes in heredity and would pave way for a scientific progress in genetics. But that’s a story for another day.