A Very Brief and Incomplete History of Developmental Biology.
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Transcript of A Very Brief and Incomplete History of Developmental Biology.
The past is full of ideas about how organisms developed and where they came from.
These range from pure magic
Questions?Where are the plans or instructions for development?
How are they interpreted and used?
Where are the raw materials for development?
How did those raw materials get to the embryo?
How are they used?
How do different cells and tissues know what to become?
How do cells migrate? How do they know where to go?
How is neural circuitry established?
How do axons find their targets?
Etc., etc, etc.
One important thing to keep in mind,
Information and mechanisms at the cellular and/or molecular
levels are needed to accomplish development.
Development DOES NOT happen by magic.
Aristotle considered two basic developmental questions:
Do all parts of a developing organism come into existence together and simply grow larger?
or
Is development a stepwise process characterized by progressive organization and an increase in complexity?
Preformation versus Epigenesis
Preformation - The organism is preformed as a complete miniature structure in the sperm or the egg and simply grows larger as it develops. This means that the first reproducing human would have had to have all succeeding generations within itself. Sort of like Russian dolls.
Aristotle believed that the embryo was formed from the menstrual blood as a result of that blood’s interaction with a male factor, called the male dynamic, that was present in the semen.
His observations supported the concept of epigenesis, though this term would not be used until the mid to late 17th century.
Mid 17th century - 18th century
Epigenesis vs Preformation - a matter for debate
Spermists vs ovists
Jan Swammerdam ~ 1672
Marcello Malpighi ~ 1672
Nicholas Malebranche ~1673
Nicolas Hartsoeker ~ 1694
Charles Bonnet ~ 1762
Preformationists
William Harvey ~ 1651
Rene Descartes ~ 1664
Pierre Maupertuis ~ 1745
Epigeneticists
Jan Swammerdam, ~1672
17th century Dutch microscopist
Debunked “Spontaneous generation” using meticulous dissections and careful experimentation.
Preformationists
Recipe for bees:
Kill a young bull, and bury it in an upright position so that its horns protrude from the ground. After a month, a swarm of bees will fly out of the corpse.
Jan Baptista van Helmont’s recipe for mice:
Place a dirty shirt or some rags in an open pot or barrel containing a few grains of wheat or some wheat bran, and in 21 days, mice will appear. There will be adult males and females present, and they will be capable of mating and reproducing more mice.
SPONTANEOUS GENERATION
LOUISE PASTEUR’S EXPERIMENT
Jan Swammerdam
17th century Dutch microscopist
Debunked “Spontaneous generation” using meticulous dissections and careful experimentation.
Preformationists
Thought to have originated the idea of Preformation
Greatest contribution to science - demonstrated that in insect development, the same organism persists through various stages, i.e. larva, pupa, juvenile, adult.
Marcelo Malpighi, ~1672Professor of medicine and personal physician to Pope Innocent XII
Early microscopist
One of the first scientists to study structures such as the lungs, kidneys, spleen, brain, and skin
Because of the importance of his early work a number of anatomical structures still bear his name - Malpighian corpucles (renal corpuscle) in kidney,Malpighian layer in epidermis of skinMalpighian tubules in insects
Marcello Malpighi - did not believe what was right before his eyes when examining chicken development with the microscope.
Preformationists
Nicholas Malebranche, ~1673
A priest and philosopher
Most original and influential of the Cartesian philosophers
Preformationists
The Cartesians tried to develop a comprehensive science of nature and to resolve the problems about mind-body interaction.
Nicolas Hartsoeker, ~1694
Dutch mathematician and physicist
Invented the screw-barrel microscope
Co-discoverer of sperm.
Preformationists
Swiss lawyer, naturalist, philosopher
Ovist - from studies of parthenogenesis in Daphnia - felt that the theory of preformation was “…one of the greatest triumphs of rational thought over sensual conviction.”
In Philosophical Palingests, or Ideas on the Past and Future - argued that females carry within them all future generations in miniature form.
Comment on the preformation paradox:
“…it is always possible, by adding zeros, to crush the imagination under the weight of numbers.”
PreformationistsCharles Bonnet, ~1762
Epigeneticists
Physician to King Charles I of England
In 1628 Harvey published An Anatomical Study of the Motion of the Heart and of the Blood in Animals which explained how blood was pumped from the heart throughout the body, then returned to the heart - recirculation of blood.
Also published Essays on the Generation of Animals - considered the foundation for modern embryology
William Harvey, ~1651
Philosopher, physicist, physiologist and mathematician – famous in all.
Considered one of the most important and influential thinkers in human history.
Cogito ergo sum - “I think, therefore I am.”
“If you would be a real seeker after truth, it is necessary that at least once in your life you doubt, as far as possible, all things.”
Rene Descartes, ~1664
Epigeneticists
Pierre Maupertuis, ~1745
French mathematician and biologist
In Essai de cosmologie - introduced the theory of survival of the fittest.
Argued that preformation could not account for hybrids or “congenital monsters”
Proposed that the embryo goes through a number of distinct developmental stages.
Epigeneticists
What’s the correct answer, epigenesis or preformation?
Neither is totally correct as originally stated; however, there’s some truth to both, though not in the context of 17th and 18th century thought.
Epigenesis - in that development does occur gradually in a stepwise progression moving from a single cell to a multicellular organism of increasing complexity (however, development does not start out from an unorganized state, the zygote
is highly organized at the cellular and molecular level).
Preformation - in that the instructions for development are present “preformed” in the zygote - genes (DNA).