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335 BCE
Aristotle
Aristotle grouped animals with similar characteristics together into “genera” and then categorized them within the genera. This classification system was the very first of its kind and opened the door for other scientists to build on this idea. -
1545
Human Anatomy
Charles Estienne is known to have been the first to find valves in the orifice of the hepatic veins as well as discovering a canal through the entire length of the spinal cord. He also put out an anatomy textbook with well-drawn woodcuts in 1545. This was the very beginning of studying humans and it is still developing daily. -
1546
Diseases
Italian scholar and physician, Girolamo Fracastoro, introduced germ theory in 1546. He noted that epidemic diseases are caused by transferable seed-like entities that transmit infection by direct or indirect contact. Diseases were assigned based on how they were transmitted and how long they could lie dormant which is similar to modern day classification. -
Cells
Robert Hooke discovered the first cell in 1665 by examining cork under a microscope. Hooke thought it resembled the small rooms that monks live in (cells) and named it accordingly. Soon after this, many cell discoveries followed. -
Blood
A French physician, Jean-Baptiste Denys, administered the first thoroughly documented blood transfusion. Sheep blood was transfused into a 15-year old boy, which appeared to help aid in his recovery. Transfusions from animals to humans were later banned in 1670 as additional attempts resulted in patients dying and therefore lead to using same-species blood only. -
Redi
Francesco Redi set up an experiment with flasks containing different meats, half sealed and half open. On attempt two, instead of sealing the flasks, he covered half of them with gauze so that air could enter. The meat in all of the flasks putrefied and he found that the meat in the opened and uncovered flasks contained maggots, indicating that flies were able to enter and lay eggs, proving spontaneous generation to be impossible. -
Microscopy
Anton van Leeuwenhoek was the first person to discover bacteria. He built a simple microscope with only one lens (examining things such as blood, yeast, and insects) which has ended up becoming much more powerful over the years and we can now see things that were previously invisible to the naked eye. -
Classification
Similar to Aristotle, Carl Linnaeus created a system of naming plants and animals where each species of plant or animal is given a genus name followed by a specific name (species). He named over 12,000 species of plants and animals. -
Needham
John Needham conducted an experiment, similar to Redi's, where he placed broth in a bottle, heated the bottle to kill anything inside, and then sealed it. He reported the presence of life in the broth a few days later, claiming that life had been created from nonlife. -
Spallanzani
Lazzaro Spallanzani assumed that John Needham's heated bottle did not kill everything inside, so he carried out his own experiment by placing some broth in two separate bottles, boiling both, and then sealing one bottle while leaving the other one open. The unsealed bottle was full of living things while the sealed bottle showed no signs of life. Scientists later noted that Spallanzani deprived the closed bottle of air, which was thought to be necessary for spontaneous generation. -
Immunization
Edward Jenner injected cowpox into an eight-year-old boy. The child developed symptoms of cowpox for nine days but then felt better the following day. Jenner then injected him again, except this time it was smallpox, and nothing changed. This opened the door for vaccinations. -
Dinosaurs
Iguanodon was the second dinosaur to be identified and named, suggesting that there were very large animals on earth prior to humans. The teeth that were unearthed closely resembled those of an iguana. -
Cellular Biology
Theodor Schwann proposed that all living things are made of cells and that all animal tissues are built up from a basic cell structure the same way as plants are. He also indicated that animal cells contain nuclei. -
Cellular Biology
Rudolf Virchow published Cellular Pathology, confirming that all diseases could be traced to cells. Diseases attack normal cells and cause them to malfunction. A whole organism will not get sick as each disease affects a certain set or sets of cells. -
Evolution
Charles Darwin created Theory of Evolution, which is the idea that all life descended from common ancestors. Beneficial mutations are maintained because they aid survival, which is known as "natural selection." The mutations are then passed on to the next generation and can result in an entirely different organism. -
Biogenesis (Pasteur)
Louis Pasteur filled J-shaped glass flasks with broth and then heated them to sterilize the broth. The glass necks were not sealed so air could enter freely and microbes ended up being trapped in the curve and held by gravity, so no microbes were found in the broth. To show that the broth was not contaminated, Pasteur broke the neck of one flask and the broth then became polluted. Once again, this experiment showed that spontaneous generation was not plausible. -
Genetics
Gregor Mendel discovered fundamental laws of inheritance from pea plants. Genes come in pairs and are inherited as distinct units, one from each parent. Mendel's Laws of Heredity include law of segregation, law of independent assortment, and law of dominance. -
Doggy Slobber
Ivan Pavlov trained a dog to salivate at the sound of a bell instead of just at the sight of food. This was named Pavlovian conditioning or classical conditioning -
Genetics
Archibald Garrod was the first to connect a human disorder with Mendel's laws of inheritance. He also suggested the idea that diseases occur through metabolic means leading to molecular basis of inheritance. -
Cancer
Coal tar was painted on the inside of rabbit ears and ended up producing a true malignant carcinoma in 1915. The following year, metastases in the local lymph glands in two of cases were also reported. -
Microscopy
Frits Zernike invented the phase-contrast microscope that allowed for the study of colorless and transparent biological materials. His design was based on finely tuned rays of light that could be separated as they passed through materials. When using this microscope, the light is focused at an angle to enhance the structure of the cells in tissue without staining or killing them as was required in earlier microscopes. -
Cellular Processes
Instead of just watching living cells from the outside, phase-contrast microscopes let scientists see the organelles inside. Kurt Michel of the Carl Zeiss Microscope Company was able to bring this technique to time-lapse imaging which enhanced the ability to focus on harder images. -
Genetics
Three researchers, Oswald Avery, Maclyn McCarty, and Colin MacLeod, identified Griffith's transforming principle. With large cultures of heat-killed S cells, they purified the transforming principle by washing away, separating out, or enzymatically destroying other cellular components and obtaining small amounts of highly purified transforming principle which could be analyzed through other tests to determine its identity which was likely DNA. -
Miller-Urey
To try and recreate how life on earth began, Stanley Miller and Harold Urey sealed a mixture of water, ammonia, methane, and hydrogen in a sterile flask and heated it to produce water vapor. Simulated lightning (sparks) was passed through the mixture of water vapor and gases. A week later, the contents were analyzed and amino acids were found. -
DNA
James Watson and Francis Crick determined DNA’s structure to be a double helix polymer, both sides containing a long chain of monomer nucleotides wound around each other. DNA replicated by separating into individual strands with both strands becoming templates for a new double helix. Watson and Crick also figured out how it was possible for genetics to be passed from generation to generation. -
Endosymbiosis
Dr. Lynn Margulis proposed the Endosymbiotic Theory. This belief suggests that cells originally combined with organelles to live together in a mutually benefitting relationship, as they may not be able to survive on their own. -
Classification
Like Aristotle and Linnaeus, R.H. Whittaker proposed the five-kingdom classification in 1969 which is still commonly used today. All living organisms are divided into five kingdoms: Monera (small, single celled), Protista (single-celled eukaryotes and mostly aquatic), Mycota (also known as Kingdom Fungi, thread-like structures called as mycelium), Metaphyta (Kingdom Plantae, eukaryotic multicellular plants), Metazoa (Kingdom Animalia, heterotrophic, eukaryotic multicellular). -
Anthropology/Evolution of Humans
A paleoanthropologist, Don Johanson, and his colleagues unearthed around 40% of a hominid skeleton (nicknamed “Lucy”) dating back roughly 3.2 million years ago. With the help of another paleoanthropologist, Tim White, they were able to figure out what this was, Australopithecus afarensis, and her place in the family tree. -
Extinction
A theory brought forth claims that an asteroid the size of San Francisco slammed into Earth 65 million years ago, setting off earthquakes greater than 11 in magnitude and widespread tsunamis, and shrouding the globe for years in dust and debris. This ended the reign of the dinosaurs. -
Genetics
The first approved gene therapy procedure was performed on four-year-old girl who was born with a rare genetic disease. She was immunocompromised and vulnerable to every infection. In the gene therapy procedure, doctors removed white blood cells from her body, inserted the missing gene, and then replaced the modified blood cells back into her bloodstream. -
Genetics
A microbe found in 1982 had its genome sequenced and many genes were found that no one had ever seen before. Methanococcus jannaschii is a type of archaea, a family of microbes thought to have evolved separately from plants and animals and also from bacteria. This was the first member of archaea to be sequenced as well as the first extremophile (lives in very severe climates) to be sequenced. -
Genetics
The Human Genome Project published the draft sequence, which covers more than 90% of the human genome, and initial analysis of the human genome. The sequence shows the exact order of DNA's four bases (A, T, C, and G) along the human chromosomes and includes everything such as eye colour, height, and disease. -
Stem Cells
President Obama lifted Bush administration’s limits on human embryonic stem cell research and issued an executive order intended for advancement. Obama followed up with a statement prompting that this would not open doors to cloning for human reproduction. This was a huge win for scientists as it increases research opportunities with the potential of new discoveries. -
Genetics (Birds & Dinosaurs)
Scientists created a chick embryo with a dinosaur-like snout and palate, similar to Velociraptor. Birds have been found to have a unique cluster of genes related to facial development, which non-beak creatures lack, and when these genes are silenced, the beak and palatal bone in the roof of the mouth reverts back to its original state. -
Dinosaurs in the Mesozoic Era
Researchers analyzed dinosaur bones for their chemical composition. The study identified clear structures in the fossils consistent with preservation of bone collagen, the protein in all vertebrate bones.
