It is only in relatively recent times that the mysteries of life have been unlocked. Indeed, the 18th to the 20th centuries are regarded as the ‘golden era’ of biology. Here is our list of what, in our opinion, are the ten greatest discoveries in biology.
1 – Microorganisms
In the latter half of the 1600’s, A Dutch cloth merchant, Anton van Leeuwenhoek, became fascinated by microscopy. The compound microscope had been around since the end of the 16th century but the lenses were of poor quality meaning that they could only magnify 20 – 30 times. Leeuwenhoek started to make his own microscope lenses and became so adept at it that he was able to really push the boundaries – his best microscopes were able to magnify by about 200 times.
He had an incredible natural curiosity and was a skilful observer so he could see natural wonders that had never been seen or even suspected before. Amongst his discoveries of micoorganisms were spirogyra, vorticella, bacteria found in plaque taken from teeth, foraminifera, nematodes and rotifera.
Although he only spoke Dutch, his letters to the Royal Society in London were translated and published as the quality of his observations and discoveries were both of great interest and important for the time. He was made a full member of the Society in 1680 and continued his work almost to the day he died in 1723.
2 – Cell Nucleus
Over a century after the death of Leeuwenhoek, the former army surgeon and botanist, Robert Brown (of brownian motion fame), was studying the plants that he had brought back with him from a five year trip to Australia. He was looking at the plant cells when he noticed that there was a similar structure to be seen in each and every cell he examined. This opaque structure appeared circular to oval in shape. It had in fact been observed before but it was Brown who named it ‘the nucleus’ and realised that it was an important feature as every plant cell had one.
During a conversation about the growth of new plant cells with fellow scientist (Matthias Schleiden), physiologist Theodor Schwann realised that the nucleii in the notochord (embryonic spinal cord) played the same role in animal cells, thus making the momentous discovery that all life on Earth was linked in some way. From this beginning, he went on to develop the cell theory of life that underpins all of biology today.
3 – Archaea
Eventually, it was realised that the single celled bacteria had no nucleus so the established theory was that life was divided into two main groups. The prokaryotes had cells without a nucleus and contained the DNA within the cell whilst the eukaryotes had a nucleus which contained the DNA.
But in 1977, a third form of life was discovered on Earth, the archaea. This discovery was made by Carl Woese who was studying a methane producing bacterium. He realised that the cell processes were unlike anything that had been seen before. He was regarded as a bit of a renegade in his field and it wasn’t until a decade later that this discovery was generally accepted by the scientific community.
In some ways, they are more like the eukaryotes – they share several metabolic pathways and some genetic similarities.
There are, however, plenty of differences – they reproduce asexually by budding, binary fission or fragmentation and can use a much wider range of chemicals as energy sources which enables them to live in extreme conditions such as around the ‘black smokers’ of the deepest ocean beds and the hot springs of volcanic regions as shown in the image above.
4 – Cell Division
As with many of these ten greatest discoveries in Biology, cell division had already been seen before its significance was realised. It had been described as early as 1842 by Carl Nageli, but he thought that he had simply witnessed a random event. It fell to Walther Flemming, working at the University of Prague and later the University of Kiev, to realise that it was fundamental to the development of life.
He was the first to study in detail the chromosomal movements during the process of mitosis. He found that certain aniline dyes revealed the threadlike structures in the nucleus which we now call chromosomes. Through his staining techniques, he was able to see what happened to the chromosomes as cells divided, publishing his work in 1882.
What we know today about mitosis stems from Flemming’s work. He saw that the chromosomes were ‘doubled’ but didn’t quite get to the bottom of the whole process. His pioneering observations were significant for later work in meiosis and helped to unravel the details of the chromosomal theory of inheritance.
5 – Sex Cells (Gametes)
Biologists knew of the existence of sex cells in both plants and animals but they had no idea of how or why they were the only cells cabable of creating new life when they fused together. Piecing together the whole story took around 30 years and involved biologists from both sides of the Atlantic.
At the heart of the formation of a sex cell lies the process of meiosis.
Meiosis was first spotted in sea urchin eggs in 1876 by the German biologist Oscar Hertwig. Then, in 1883 the Belgian zoologist Edouard Van Beneden made the next contribution from his studies of Ascaris worms’ eggs. He spotted that the worms eggs only had two chromosomes instead of the usual four and crucially noticed that the mother’s and the father’s chromosomes came together in the fertilised egg. He saw this as a contradiction and took his studies no further.
That was left to German biologist August Weismann. Using Van Beneden’s observations plus work of his own, he came up with a theory that gametes were formed in a different way to other cells, in a process that was named meiosis (from the Greek word for lessening) some years later.
Cells normally divide to form new cells through a process called mitosis. Essentially, in mitosis, the chromosomes double and split so that the new nucleus has a full set of chromosomes identical to the original cell.
However, during meiosis, the chromosomes do not double, they split, leaving only half of the chromosomes in the nucleus of the new cell. When the male and female sex cells fuse, they form a cell called a zygote which contains a full set of chromosomes, half from the father and half from the mother.
It wasn’t until the 20th century, 1911 in fact, that the American geneticist Thomas Hunt Morgan observed the full process in Drosophila and provided the first genetic evidence that genes are transmitted on chromosomes.
Meiosis is therefore the driving force behind evolution as it is the point at which variation is achieved. Natural selection then filters out the bad combinations and keeps the gene pool viable.
6 – Cell Differentiation
OK, once the zygote is formed you have a single cell from which a new organism will grow. You have probably seen video clips of a zygote dividing into two cells, then four, eight and so on. But therin lies a bit of a mystery, when and how do cells differentiate to become limbs, muscles, eyes, the heart etc?
Prior to the 1890’s, there were two theories of how a new embryo became a complete organism – preformation and epigenesis. The former stated that the zygote contained a ready-made miniature of the adult which grew larger. Epigenesis suggests that development becomes more complex as the embryo grows.
In the 1890s, the first evidence for epigenesis was seen. Hans Driesch separated sea urchin embryo cells, expecting to ultimately get ‘half embryos’. This was not the case and he ended up with full embryos but smaller than the originals.
So it seemed that all cells of an embryo could still become any cell, these cells are now known as ‘stem cells’ and are the subject of much research. It seems possible that stem cells could be used to grow new organs to eliminate the possibility of rejection following transplants. There is evidence that the formation of a specific type of cell could be reversible and research is currently underway in the USA to find out more.
Hans Spemann was awarded the Nobel Prize in 1935 for his discovery of the ‘organiser’ – a region of the developing embryo which influences the cells around it, directing what the stem cells become.
7 – Krebs Cycle
Hans Krebs fled from Nazi Germany to the UK in the 1930s where he researched the energy release in cells. Whilst working at the University of Sheffield, he broke open cells and collected the fluids from within, identifying the chemical reactions from the reactants and products that he found.
In 1937, building on work by a Hungarian physiologist (Albert Szent-Györgyi) from several years earlier, Krebs identified a cyclic pattern of chemical reactions that appeared to release energy within the cell. The Krebs cycle is also known as the citric acid cycle and the tricarboxylic acid (TCA) cycle.
During the Krebs Cycle, glucose molecules are used to create several chemicals including adenosine triphosphate (ATP) and carbon dioxide. ATP is the chemical that carries energy in a format that is usable by other cell processes whilst the carbon dioxide is the waste product.
8 – Mitochondria
During the 19th century, microscopes revealed increasing detail within plant and animal cells. One of the structures were the mitochondria which appeared to be made from 2 membranes that could change shape. At the time, that was all they knew.
Looking at the organelles in a cell has always been tricky as the cell is transclucent so things are always a little ‘fuzzy’. Enter Britton Chance, an American researcher. He designed and built a ‘dual wavelength spectrometer’ in order to cut through the fuzziness and view the inside of cells with greater clarity.
Whilst viewing the mitochondria, he discovered two components that linked it to the Krebs Cycle, tying it in to the release of energy within the body.
9 – Neurotransmitters
At the end of the 19th century, the workings of the nervous system was still largely a mystery. It was known that nerve impulses were electrical and it was assumed that it was also electricity that passed impulses from one nerve to the next.
Early in the 20th century, Thomas Elliott had noted that chemicals in the blood (hormones) could produce a reaction in the body that were very similar to stimulating certain nerves. He suggested that when nerves were stimulated, they released adrenaline which then stimulated the next nerve cell. The idea of chemical neurotransmitters was born but went no further for 3 decades.
Henry Dale discovered acetylcholine, now known as a neurotransmitter, in 1914 and speculated what effect it might have in the body. His friend and former co-researcher at UCL, Otto Loewi, had devised an experiment using frog’s hearts showing that stimulated nerves released a chemical that could affect other nerves. It turned out that this was acetylcholine.
Throughout the 1930s Dale and his colleagues discovered that chemical neurotransmission took place throughout the nervous system. He developed a new way of classifying nerve fibres and redefined the understanding of how nerves affect the body. Dale and Loewi were duly awarded the Nobel Prize in 1936.
In the 1940s, Dale became involved in a heated debate about neurotransmission, a group of biologists believed that his findings were wrong and that neurotransmission was electrical. It turned out they were both right, some signalling is electrical but the bulk is chemical.
10 – Hormones
The final of our ten greatest discoveries of biology is that of hormones. Around the turn of the 20th century, William Bayliss and Ernest Starling were studying digestion to try to establish what made digestive juices flow at just the right time.
They took a sample of blood from a dog that had just been fed and injected it into a hungry dog. The dog started to secrete digestive juices even though it had not eaten. Further investigation showed that on eating, the small intestine secretes a chemical into the blood. As the blood passes through the pancreas, the chemical stimulates the pancreas to release digestive juices.
They called the substance ‘secretin’ and it represented the first of a never-before-seen group of chemicals that we now call hormones. Currently over 50 are known and like neurotransmitters, they carry messages round the body.
That rounds off our top ten. Perhaps you agree that these are the greatest discoveries in Biology, perhaps not. But what they do have in common is that very often, when the initial discovery was made, the immediate importance was often not recognised until years or even decades later.