Precursors of modern biology: from Hippocrates to the genome

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Human curiosity about life has accompanied our species long before the word "biology" existed. Philosophers, doctors, naturalists, and later, professional biologists, pieced together a huge puzzle: the workings of living beings, their origin, their diversity, and the laws governing heredity and evolution. Today we speak of modern biology, the genome, biotechnology, and gene editing, but all of this was only possible thanks to a long sequence of discoveries, debates, and even conflicts with religion and the dominant worldview of each era.

When someone tries to remember the name of a famous biologist, Darwin almost always comes up first, but the story is much broader than just one brilliant scientist. Alongside him we find naturalists from antiquity, monks counting peas in monastery gardens, doctors risking their reputations to dissect animals, philosophers attempting to classify everything that moved (and everything that didn't), as well as contemporary researchers who are unraveling DNA, the workings of cells, and the origin of life. This article takes a detailed tour of these precursors of modern biology, from their oldest roots to their most recent contributions.

Ancient Origins: Natural Philosophy and Primitive Medicine

Before biology existed as an independent science, the study of life was intertwined with philosophy, religion, and traditional medicine. Ancient civilizations wondered why people get sick, how plants grow, how animals reproduce, or how wounds heal. The answers to these questions often came from myths, but also from careful observations, which would later serve as the basis for more scientific thinking.

In ancient India, thinkers like Susruta, active around the 3rd century BC, were fundamental to the development of medicine and anatomy. In his classic work "Sushruta Samhita," he described surgical procedures, dissection techniques, and observations about the human body that reveal remarkable practical knowledge. Although his approach was embedded within its own philosophical and religious framework, his anatomical and surgical descriptions anticipate much of the systematic care of the body that would later become typical of biology and medicine.

In ancient China, physicians such as Zhang Zhong Jing (150-209 AD) also contributed to a more systematic understanding of health and disease. Embedded in a millennia-old tradition of medicine, he reinforced the importance of clinical observation and therapeutic experimentation. Even without separating physiology, pharmacology, and cell biology as we do today, these Asian schools created a body of knowledge that helped consolidate the idea that life can be studied through natural causes and not just spiritual ones.

In the Greek world, biology emerged as part of what was called "natural philosophy," in which nature was investigated using rational arguments and direct observation. It was in this context that two of the most emblematic names in the history of biology and medicine emerged: Hippocrates and Aristotle. They were not "biologists" in the modern sense, but literally philosophers of nature, concerned with understanding the workings of the body and the diversity of living beings.

Hippocrates of Kos: the body and the "medical crisis"

Hippocrates of Kos is traditionally remembered as the "father of medicine," but his legacy is also central to the history of biology. Living in Classical Greece, he distanced himself from supernatural explanations for diseases and began to emphasize natural factors such as environment, diet, and lifestyle habits. In the early phase of his career, he adopted the view of the Four Humors – blood, phlegm, yellow bile, and black bile – which should be in balance to maintain health.

Over time, Hippocrates began to abandon the rigid interpretation of humors and to place the overall well-being of the patient at the center of medical practice. Instead of limiting himself to diagnostic labels, he valued prognosis: monitoring the evolution of the disease and predicting its outcomes. From this arose the idea of ​​a "medical crisis," the decisive moment when the body's natural defenses either eliminate the attacking agent or lose the battle, allowing the disease to spread.

This focus on the evolution of the clinical picture led Hippocrates to record cases, compare patients, and look for patterns—an essentially biological approach. His proposal was not yet experimental in the modern sense, but it consolidated a way of thinking that viewed the organism as a system in constant struggle to maintain balance in the face of external threats, a concept that resonates, centuries later, in physiology and immunology.

Aristotle: classification of living beings and empirical observation

Aristotle, better known as a philosopher, was also one of the first great biologists in history. Orphaned in his teens, he had the intellectual freedom to study whatever he wanted and, at Plato's Academy in Athens, he immersed himself in all areas of knowledge. When he left the Academy, he spent a period on the island of Lesbos, where he dedicated himself intensely to the observation of plants, marine and terrestrial animals.

His biological work brings together detailed descriptions of around 500 species, with an emphasis on zoology and marine life, but also with a keen eye on plants. Aristotle was not content with speculation; his writings show dissections and direct observations of organs and systems, with diagrams of the viscera so precise that they could hardly be the product of mere imagination. He investigated anatomy, reproduction, embryonic development, and behavior.

One of Aristotle's great legacies was his attempt to classify organisms into groups according to their similarities and differences. He created a hierarchy that separated, for example, animals with blood (approximately our vertebrates) from those without blood (invertebrates), and organized a kind of "natural scale" in which beings were arranged from the simplest to the most complex. Although today we know that many of his categories do not reflect evolution, his systematic approach influenced naturalists for centuries.

The Aristotelian view of an ordered nature, governed by causes and laws, shaped the thinking of physicians and naturalists from antiquity until well beyond the Middle Ages. Even when new evidence began to challenge his schemes, many scientists still looked to Aristotle as a reference, either to improve upon them or to criticize them. He is, without a doubt, one of the great forerunners of observational and classificatory biology.

Galen of Pergamon: anatomy, physiology, and experimentation on animals.

Galen of Pergamon, a Greek physician from late antiquity, is considered one of the most influential medical researchers of all time. His personality was described as difficult, arrogant, and confrontational with colleagues, leading him to fear reprisals and flee Rome to avoid a violent death. Despite this temperament, his scientific genius left a profound mark on biology and medicine.

In Galen's time, the dissection of human corpses was taboo in much of the Greco-Roman world, which forced him to study anatomy in animals. He performed numerous dissections on pigs, goats, and especially monkeys, imagining that their anatomy was very similar to that of humans. Knowing nothing about DNA or evolution, he started from external similarity to infer internal analogies between related species.

Galen stood out for his experimental boldness, even though he used techniques that are now considered extremely cruel. One of his famous experiments involved exposing the larynx of a live pig: while the animal screamed, he cut the vocal cords and observed that the sound ceased, even though the pig remained agitated. On other occasions, he severed motor nerves to study the relationship between these bundles and the sudden inability of a leg or other body part to move.

Galen's studies formed the basis for entire areas of medical biology, such as pharmacology, pathology, physiology, anatomy, and neurology. He described the role of various organs, discussed the partial circulation of blood, and suggested functional interpretations for nerves and muscles. Although many details of his theories were corrected centuries later, his work dominated European and Islamic medical teaching throughout the Middle Ages.

Contributions of the Islamic world to biology

While much of Western Europe was mired in religious conflict and cultural decline during the Early Middle Ages, the Islamic world was experiencing an intense scientific "Golden Age." Between the 8th and 9th centuries, Muslim scholars preserved Greek texts, engaged in dialogue with Persian and Indian traditions, and produced original works in astronomy, mathematics, medicine, and natural sciences, including the study of life.

One of the most interesting thinkers for biology was Al-Jahiz (781-869), who wrote about the relationships between organisms in food chains. His writings contain remarkable ideas about competition for resources, predation, and differential survival, anticipating by centuries certain concepts related to evolution and the "struggle for survival" that would later be associated with Darwin and natural selection.

Another key name is that of Al-Dinawari (828-896), often cited as one of the founders of scientific botany. He described around 637 plant species, discussing their forms, the environments in which they grew, and practical uses. His work helped create a more systematic view of the plant world, integrating field observation, classification, and medicinal or agricultural application.

Al-Biruni (973-1048), in turn, developed the concept of artificial selection, reflecting on how humans choose plants and animals with desirable characteristics for reproduction. This understanding of the effects of selection exerted by humans became, centuries later, a crucial argument for explaining natural selection in wild populations. In many respects, Al-Biruni can be seen as a precursor to evolutionary theories.

From natural philosophy to the Scientific Revolution

Throughout the Late Middle Ages, some European universities began to revive the study of nature, but biology remained overshadowed by fields such as physics and chemistry. Names like Hildegard of Bingen, Albertus Magnus, and the naturalist-emperor Frederick II of Hohenstaufen contributed observations on plants, animals, and the workings of the body, but the progress was relatively modest.

This changes more dramatically with the Renaissance and the transition to the Modern Age, when empiricism and reason gain new strength as ways of understanding the world. Interest in the natural sciences explodes, and botanists, anatomists, and naturalists begin producing herbaria, animal collections, illustrated bestiaries, and anatomical treatises based on human dissection. Modern medicine begins to consolidate, and with it, a more experimental view of physiology.

A decisive advance for biology came from physics and optics: the invention of the microscope at the end of the 16th century. With increasingly sophisticated lenses, it has become possible to see an entirely new dimension of life. Tiny details of insects, minuscule plant structures, and organisms invisible to the naked eye have become the subject of study, opening doors to microbiology and histology.

In 1665, Robert Hooke published "Micrographia," an illustrated book with observations made under a microscope that shocked and fascinated the European public. Looking at thin sheets of cork, Hooke described empty compartments he called "cells," coining a term that would become central to biology. He also recorded the structure of flies, ants, and other small creatures with unprecedented detail.

Anton van Leeuwenhoek: the microscopic world comes to life

Anton van Leeuwenhoek, a Dutch cloth merchant, was a passionate autodidact who took the microscope to a new level. Without formal university education, he started out working as a shopkeeper and accountant, but was fascinated when he saw a simple microscope for the first time. His curiosity led him to manufacture increasingly powerful lenses, surpassing the quality of many academic instruments.

Between work and family commitments, Van Leeuwenhoek dedicated hours to observing everything he could: drops of water, tooth clippings, blood, plant fibers, tissues, sperm, and much more. His goal was always to increase magnification power to reveal new details. This pursuit made him a great improver of microscopes, although many criticized him for his lack of "academic respectability."

Looking at seemingly clean water, Van Leeuwenhoek first described what we now call bacteria and protozoa, which he termed "animalcules." He also observed sperm, red blood cells, and a multitude of microscopic structures. These discoveries showed that life is not limited to what the human eye can see, forever revolutionizing how we understand disease, reproduction, and ecosystems.

Interestingly, his biography is marked by personal tragedies: he outlived four of his five children and both of his wives, which may have fueled his obsessive dedication to study. Viewed from a distance, however, this apparent "amateurism" was an advantage: he approached biology from a fresh perspective, less bound by academic dogma, which allowed him to make discoveries that many specialists, due to prejudice or lack of curiosity, missed.

Carl Linnaeus: Taxonomy as a Universal Language

Carl Linnaeus, a Swedish naturalist from a relatively wealthy family, was the great architect of the modern biological classification system. Educated in literature, science, and the arts, he developed an early interest in botany, something noticed by his teachers, who began to encourage him with books, plant samples, and study opportunities.

At the University of Lund and later in Uppsala, Linnaeus studied botany and medicine and delighted his teachers with his ability to observe and organize flora in a systematic way. He gained support for exploratory trips, such as a famous expedition to Lapland, and traveled through different regions of Europe collecting plants, describing species, and noting characteristics that he considered relevant for classification.

After many years of work and dozens of publications, Linnaeus refined the system that would make him one of the pillars of modern biology: binomial taxonomy. His proposal organizes living beings into hierarchical categories – such as kingdom, class, order, family, genus, and species – and establishes that each species receives a two-part scientific name in Latin, for example, Homo sapiens for the human species.

This system revolutionized Aristotle's legacy by offering a universal and standardized language for the diversity of life. Instead of relying on common names, which differed from region to region, botanists, zoologists, and naturalists worldwide began to understand each other using scientific names. This standardization was crucial for biology to become a comparative and global science, connecting observations made on distant continents.

Biology in the 19th century: evolution and genetics

From the late 18th century onward, biology entered a phase of explosive expansion, driven by technology, long-distance travel, and the Industrial Revolution. Physiology gradually separated from medicine, natural history gained more experimental rigor, and specialties such as morphology, embryology, bacteriology, geology, and biogeography emerged. Within this melting pot of ideas, the first theories of organic evolution were born.

Jean-Baptiste Lamarck, at the beginning of the 19th century, proposed that organisms change over generations in response to the use or disuse of organs. According to him, frequently used structures would develop and be passed on to descendants, while rarely used parts would tend to atrophy. Although it is now known that this mechanism does not explain evolution, Lamarck deserves recognition for placing species change at the center of scientific debate.

The major turning point, however, came with Charles Darwin, an English naturalist, biologist, zoologist, and geologist whose life could have been much more peaceful. Pressured by his family to pursue a career in medicine or the clergy, Darwin did not adapt to surgical practice and ended up becoming involved in natural history discussion groups. In one of these circles, he met the zoologist Robert Edmund Grant, a proponent of evolutionary ideas in 19th-century Christian England, a time when openly admitting evolution was to risk prestige and even job security.

Aboard the ship Beagle, on a long circumnavigation voyage, Darwin accumulated observations and collections of animals, fossils, and plants which, combined with the demographic theories of Thomas Malthus, led him to the formulation of natural selection. He realized that in any population, more individuals are born than the environment can sustain; as a consequence, there is a "struggle for survival" in which advantageous variations increase the chances of leaving descendants. In popular language, this has been summarized in the expression "survival of the fittest".

In 1859, Darwin published "On the Origin of Species by Means of Natural Selection," a work that sold out on its first day and shocked conservative British society. The book, written with great clarity and didacticism, discussed fossil evidence, comparative anatomy, geographic distribution, and the breeding of domestic animals to support the thesis that species transform over time. It is no exaggeration to say that it is one of the most widely read and influential scientific books of all time.

While Darwin was laying the foundations for understanding the diversity of life, another precursor was working almost silently on the basis of modern genetics: Gregor Mendel. The son of a poor farmer, Mendel excelled in physics and mathematics, but his frail health and the cost of his studies hindered his education. Entering a monastery and becoming a friar was the solution he found to ensure both his education and livelihood.

At the University of Olomouc, Mendel took classes with Johann Karl Nestler, a professor of Natural History who researched hereditary characteristics in animals. This sparked his interest in biological inheritance. In the monastery garden, Mendel spent years crossing different pea plants, noting flower colors, seed shapes, and other characteristics in successive generations. From this scientific patience were born Mendel's laws, which explain how hereditary factors (now called genes) combine and segregate in the formation of gametes.

Although his work was undervalued during his lifetime, the rediscovery of Mendel's laws in the early 20th century solidified the link between Mendelian genetics and Darwinian evolution. This conceptual encounter generated what is known as the modern synthesis of evolution, which views natural selection as acting on heritable genetic variations, completing the picture begun by the first precursors of biology.

From cell to DNA: consolidating modern biology.

Between the late 19th and early 20th centuries, a series of discoveries brought biology ever closer to chemistry and physics. Scientists like Matthias Schleiden and Theodor Schwann showed that all living things are made up of cells, establishing cell theory. Robert Koch identified the causative agent of tuberculosis and helped found bacteriology, while Louis Pasteur developed pasteurization and pioneered the creation of vaccines.

In genetics, the work of Thomas Hunt Morgan revealed that genes are organized along chromosomes, paving the way for the study of inheritance at the chromosomal level. Aleksandr Oparin, in turn, proposed plausible chemical scenarios for the origin of life on primordial Earth, discussing how organic molecules could arise under ancestral conditions. These advances paved the way for the greatest molecular revolution of the 20th century: the discovery of the structure of DNA.

James Watson and Francis Crick, based on X-ray diffraction data produced by Rosalind Franklin and Maurice Wilkins, described the DNA double helix in 1953. By understanding how genetic information is stored, copied, and transmitted, biology gained a new language: that of the genetic code. From there, genetics, biochemistry, and molecular biology integrated into an extremely powerful field for unraveling vital processes.

Precursors of contemporary biology

In the 20th and early 21st centuries, new pioneers expanded the frontiers of biology, particularly in molecular genetics, developmental biology, systems biology, and ecology. They drew upon the legacy of Darwin, Mendel, and so many others to explore questions such as embryonic development, gene expression, the workings of gene networks, the origin of life, and ecological diversity.

Leroy Hood, for example, is an American biologist who revolutionized systems biology and genomics by developing crucial instruments for the study of DNA and proteins. Among his contributions is the elucidation of how the immune system generates a huge diversity of antibodies from combinations of DNA segments, explaining the molecular basis of the immune response. In his work on antibody diversity, he showed that functional variety depends on variations in the amino acid sequences that make up these molecules.

Hood also led the development of the first automated DNA sequencer, a fundamental tool for the Human Genome Project and for high-throughput genomics. In interviews, he emphasizes that this innovation not only made it possible to read the human genome in record time, but also ushered in an era in which biology began to deal with large volumes of data, favoring the emergence of systems biology and personalized medicine.

Christiane Nüsslein-Volhard, a German developmental biologist and laureate of the Nobel Prize in Physiology or Medicine in 1995, is another key figure in modern biology. She investigated how genes control embryonic development, starting with the fruit fly Drosophila melanogaster. In her studies, she identified maternal and zygotic genes that establish the embryo's axes, such as the bicoid gene, whose messenger RNA is concentrated in the anterior region of the egg and determines the formation of the insect's head.

Nüsslein-Volhard extended this approach to zebrafish, helping to transform it into a model organism for the study of vertebrate development. By analyzing mutations that affect pigmentation, organ formation, and body pattern, she helped to reveal general principles of how genomes direct the construction of complex organisms from a single fertilized egg.

J. Craig Venter is another protagonist of the genomic era, known for leading one of the first drafts of the human genome sequencing and for transfecting cells with synthetic chromosomes. He pioneered the creation of expressed sequence tags (ESTs), a technique that involved sequencing parts of cDNA to rapidly identify and catalog genes. This accelerated the discovery of new genes and reorganized the way the genome was mapped.

In partnership with Hamilton Smith, Venter also sequenced the complete genome of the bacterium Haemophilus influenzae, making it the first free-living organism with a fully deciphered genome. This achievement, accomplished in less than a year, demonstrated the potential of new sequencing technologies to transform microbiology, medicine, and evolutionary biology.

Ronald M. Evans, an American biologist, made decisive contributions to molecular genetics by characterizing nuclear hormone receptors. He showed that these proteins form a "superfamily" of receptors that respond to steroid hormones, thyroid hormones, vitamins A and D, and dietary lipids, regulating gene networks that extend from embryonic development to adult metabolism.

Evans also uncovered molecular pathways involved in cancer and diabetes that can be modulated by drugs that activate these receptors. In his studies, he highlighted, for example, the central role of the MYC proto-oncogene in multiple cell signaling pathways, including in pancreatic cancer. More recently, he helped develop so-called "exercise mimetics," substances capable of activating in muscles some of the same genetic programs triggered by physical activity, with the potential to treat metabolic and muscular disorders.

Jack W. Szostak, Nobel laureate in Physiology or Medicine, is among the leading names in modern genetics. He was responsible for creating the first artificial yeast chromosome, constructed with cloned genes, replicators, centromeres, and telomeres, reproducing essential properties of natural chromosomes. This innovation made it possible to map genes in mammals and improve genetic manipulation techniques.

In the 1990s, Szostak's laboratory turned to the study of RNA enzymes and the origin of life. He developed the in vitro RNA evolution technique, which allows the selection of molecules with desired functions through cycles of mutation, amplification, and selection, and isolated the first aptamers, RNAs with high affinity for specific targets. Currently, his research explores how RNA chains could have replicated on early Earth, using imidazole-activated ribonucleotides as building blocks, and seeks to create protocells in the laboratory to better understand the emergence of life.

Sydney Brenner, another prominent Nobel laureate, used the tiny worm Caenorhabditis elegans to unravel principles of genetics and development. He helped decipher how cells read DNA to produce proteins, showing that triplets of nucleotide bases code for specific amino acids. He also studied how mutations in genes shape complex structures in higher organisms.

Brenner transformed C. elegans into a reference animal model for studying aging, programmed cell death, and neural development. Researchers like Heidi Tissenbaum report that this transparent worm has allowed the identification of hundreds of genes and mechanisms that modulate lifespan, revealing conserved pathways between invertebrates and mammals. Recognition of this work earned Brenner and colleagues the Nobel Prize in 2002.

Edward O. Wilson ultimately brought an ecological and behavioral perspective to modern biology, specializing in the study of ants (myrmecology). His meticulous work on the social behavior of these insects led him to be called the "father of sociobiology" and the "father of biodiversity." He showed how seemingly altruistic behaviors in ants—such as the sacrifice of individuals in defense of the colony—can be explained by shared genetic interests, since the worker ants are highly related to each other.

Wilson also defended the idea of ​​"consilience," the union of knowledge from different areas—natural sciences and humanities—into an integrated vision. For him, human nature is shaped by epigenetic rules, genetic patterns that influence mental development, while culture and rituals are products, not foundations, of this nature. His environmental activism contributed to placing biodiversity conservation at the center of the scientific and public agenda.

Biology in the 21st century

The 20th and 21st centuries have witnessed a veritable explosion of new biological subfields, especially those related to molecular genetics, biotechnology, and biophysics. The sequencing of the human genome, completed at the beginning of this century, opened up the possibility of studying diseases, kinship, and evolution at a level of detail unimaginable to Darwin or Mendel.

Tools like the CRISPR gene-editing technique have transformed DNA into a highly precise, manipulable target, allowing for the correction of mutations, the creation of modified organisms, and the investigation of the role of specific genes. At the same time, there has been growing interest in understanding complex biological systems – such as microbiomes, neural networks, and entire ecosystems – using systems biology approaches, which integrate large-scale data with computational modeling.

At the interface with physics, biophysics, a field in which researchers like Tikvah Alper have excelled, studies how radiation, forces, and energy interact with cells, tissues, and biological molecules. Alper investigated the effects of radiation on cells and physiological and chemical processes, making a decisive contribution to understanding diseases such as transmissible spongiform encephalopathies, including the famous "mad cow disease." His research had a direct impact on epidemic containment strategies.

Alper's trajectory also highlights the weight of social barriers in a scientific career: as a married woman and a critic of apartheid in South Africa, she had to seek opportunities in hospitals and universities in the United Kingdom to continue her research. There, he produced high-level work in radiobiology and molecular biology, reinforcing the importance of more inclusive academic environments for the advancement of science.

Kristine Bonnevie, a Norwegian biologist, is another example of a researcher who combined intense scientific production with political activism. The daughter of a professor and politician, she inherited a love of study and public life. A biology graduate, she dedicated her thesis to germ cells and excelled in human cytology and embryology, focusing on genetic inheritance. She participated in committees and scientific associations and even served as an adjunct representative in the Norwegian parliament, advocating for science and education.

Today, with technologies such as virtual reality and digital laboratories, teaching and research in biology are reaching increasingly larger audiences. Simulation platforms allow students and teachers to virtually experiment with laboratory techniques, explore microscopic structures, and test hypotheses without the physical limitations of a single laboratory. This democratizes access to knowledge and helps train new generations of scientists and problem solvers.

The thread that connects Hippocrates, Aristotle, Galen, Asian and Islamic sages, Darwin, Mendel, Linnaeus, Van Leeuwenhoek, and contemporary molecular biologists is the same essential curiosity about life. Over the centuries, each person has added a new piece: from basic anatomy to the cell, from the organism to the species, from the gene to the genome, from the individual to the global ecosystem. Thanks to this collective effort, today we are able to treat diseases, conserve species, improve agriculture, and better understand humanity's place in the web of life, while new ethical and scientific challenges continue to emerge with each discovery.