welcome to lecture three history of evolutionary theory today what we're going to be doing is um building on that kind of quick introduction to the scientific method lecture that we had previously and start building the foundation of what evolutionary theory is what it isn't and who are some of the main early important individuals that helped establish this school of thought so why are we talking about this well before we can really talk about how evolution works and what it is it's important to understand exactly what science is and the relationship between facts hypotheses and theories and we laid all of that out in the previous lecture so just as a quick reminder a hypothesis is an explanation of observed facts a fact is a verifiable truth and a theory is a set of hypotheses that have been tested and not rejected and we use the scientific method where a problem is identified then we state the hypothesis and that hypothesis is tested through the collection or analysis of data and repeated testing of that hypothesis can lead to a theory so evolutionary theory developed from and also contributes to science as we know it today so when we're talking about evolutionary theorists what probably comes to your mind is big name darwin and while darwin's going to be a large part of what we're going to talk about moving forward we need to acknowledge and understand where the foundation of the previous scientific thinkers was that created the basis for darwin to be able to come up with the theory of evolution in the late 1800s so we're going to talk a little bit about some names you might have also heard of in other contexts aristotle newton galileo and we're going to touch on all of these in today's lecture as well as some this week and next week as well what is evolution evolution is put simply descent with modification what that means is that over time as we move from one generation of offspring to the next there are going to be slight more modifications in both form function or as we know today genetics so gradually over time as we get these selective pressures that we'll talk about in a few slides we can see if we look over hundreds or thousands or tens of thousands of years the gradual shift in species now the mechanism of evolution the thing that actually fuels and powers it is natural selection now you've probably heard this term before or you might have heard it referred to as survival of the fittest well natural selection is the mechanism of evolutionary change it refers to genetic change or changes in the frequencies of certain traits and populations due to differential reproductive success between individuals put in different terms whoever survives the best that has the most offspring that survive contributes larger portions to the gene pool and thus slowly over time we're able to see changes in species now to truly understand how and why darwin's contribution to science um and evolution in general is important and how we got to where we are today we have to first understand the even earlier scientific ideas like that i've been saying laid the foundation for his theory of evolution and natural selection so before darwin and wallace we get people like aristotle should be a name you're familiar with he's a philosopher from the 4th century bc and what he proposed well he proposed many things but in terms of evolution his contribution is something called the great chain of being which is this basic belief that all god's creations are arranged in a hierarchy that progressed from the simplest organisms to the most complex although positioning within this hierarchy was based on physical similarities between species no biological relationship was implied within this hierarchy the great chain of being last as a central tenant lasted for centuries without anyone really challenging it because you have to remember at the time science and religion are linked together during the middle ages uh the great chain of being kind of loses a little bit of its popularity and a new idea is proposed something called fixity of the species and this is a notion that species or the earth in general never changes never have and never will so basically everything that you see on the earth today exists in the form it currently is in and always has and always will with no change and questioning the assumptions proposed by the fixity of the species was seen as a direct challenge to god's perfection and would have been considered heresy remember this is also the time when we're looking at things like the spanish inquisition and some of the absolute power and control of um catholic church um and other religious denominations around the world and so all of this is kind of also mixed in with uh belief of the recent origin of earth um thinking that the earth is only several thousand years old so you can begin to understand why saying that nothing has changed when we're looking at that small of a scale of time made sense but we know now the earth is billions of years old and we've seen lots of change over those eons kind of following the middle ages we get into the major scientific revolution and the first guy we're going to talk about is copernicus copernicus is a mathematician it's around from about 1473 to 1543. just a little aside i i'm never going to ask you super specific dates with any of these individuals just know in general the century that they're from or that you know aristotle comes before copernicus so copernicus challenges aristotle's theory that the earth is the center of the universe and he argues that we are in fact a heliocentric universe with the sun at the center and the planets orbiting around it but he's mostly ignored until the 1600s when galileo comes along and he restates and substantiates copernicus's theory so the name galileo i hope is familiar he's a very well-known physicist and astronomer and what he's able to do is use those astronomical observations to use the scientific method to be able to track and catalog the movement of the planets to support this idea of a sun-centered or heliocentric universe now like i mentioned before unfortunately his idea of a heliocentric universe is in direct conflict with the catholic church and because of this galileo spends the last nine years of his life under house arrest now the 16th and 17th century is a time of immense scientific expansion and exploration and kind of pushing back against some of these previous notions that have been maintained for centuries it's at this time when we get people like sir isaac newton coming up with the theory of gravity laws of motion we get newtonian physics coming in and so it's really laying the groundwork of being able to rationalize and explain the world around us and that's a really good segue to talk about these early naturalists people like copernicus and galileo and newton were concerned with these large universal constants things that apply everywhere and the naturalists were really busy looking at the biological life here on earth so the first guy we've got to talk about um is john ray and he and these other naturalists are really precursors to the theory of evolution they kind of set an a really important stage because before we can begin to understand the forms of organic life on earth it's first necessary to list and describe or classify all these forms so rey who's around from 1627 to 1705 was the first to recognize that groups of plants and animals could be distinguished from other groups by their ability to reproduce with one another and produce offspring so he kind of comes up with this idea of a species if they can reproduce he also recognizes that species frequently share similarities with other species and he groups um these similar species into something that he named the genus however rey still believed in fixity of the species and he stressed that nature was a deliberate outcome of the ultimate grand design carol linnaeus builds on ray's work he's around from about 1707 to 1778 once again his name might be familiar to you because he was one of the leading naturalists of the 18th century his goal was to categorize all known species so what he does is he standardizes rey's sporadic use of genus and species and establishes something that we call binomial nomenclature and so that's this concept of genus followed by species we are homo sapiens your dog is canis familiaris canis being the genus familiaris being the species and so he's able to start systematically organizing almost all of life on earth but he takes it a step further and he adds two more categories class and order which is the basis for modern taxonomy it's a system of classification that's still learned today you might have learned it in grade school with kingdom phylum order class genus species now linnaeus includes humans in his classification and he's the one who gives us the term homo sapiens now this is controversial at the time because it defined contemporary um as though humans were completely unique and should not be considered part of the animal kingdom so he kind of box those contemporary notions well keep in mind you know 18th century contemporary notions saying we're not super special um we're animals just like everything else on this planet and we deserve to be classified in the same manner however unfortunately linnaeus still believes in fixity of the species but later in life he does come to question this so continuing to move forward in time our next dude is competitive on he is the one that really gives the first big challenge to this idea of the fixity of species a buffon was from france and he was the keeper of the king's garden in paris he didn't believe that nature was perfect or served a specific purpose as was argued by the grand design he recognized the dynamic relationship between the external environment and living forms you know the kind of we're seeing the first inkling of this idea of natural selection so he publishes a book that stresses the importance of change in the universe and change in species he believes that when a group of organisms migrated to a new area that the local climate conditions would influence the group and result in gradually changing them as a result of the adaptation to the environment however he does not believe that one species can give rise to another species and finally for this era we're going to talk about erasmus darwin erasmus is charles darwin's grandfather and while he doesn't contribute to any of darwin's publications directly he has an important role to play he believes that all life originated in the sea and all species have descended from a common ancestor he stresses that vast expenses of time are needed for life to evolve that there is competition for resources and he harks on the importance of the environment in these evolutionary processes so you can imagine you've got darwin's grandfather chiming in his ear evolution takes a long time there's competition the environment is important and everything has a single common ancestor so next we're going to talk about jean baptiste lamarck lamarck is well known because he came up with a very popular idea at the time that at its heart tried to be the best it could but it got everything just a little bit wrong so lamarck is the first one to attempt to explain the process of evolution you know he's a well-trained biologist around from 1744 to 1829 and he proposes something called the theory of it the inheritance of acquired characteristics he proposes that there's a dynamic denied he proposes let's try that again that there is a dynamic interaction between organic life forms and the environment so as the environment changes the animal's activity patterns would result in a change in the body thus the theory of the inheritance of acquired characteristics so what he's basically saying is that a trait acquired by an animal during its lifetime can be passed on to its offspring lamarck is actually the one that coins the term biology and argues that it needs to be its own branch of science so let's take the classic example of these giraffes that we see here on the screen according to lamarck he argues that originally there was a short next draft ancestor but over time as they kept stretching their necks out to reach leaves higher up on the tree it stretches the necks out and eventually that action results in having offspring with longer necks like i said kind of right zip code wrong house we know that that isn't the case because we have to change our genetics in order to pass that on or offspring it would be like saying because your biological father was missing a leg that you would be born missing a leg if you had lost it in an accident or that because you are a bodybuilder that your children were automatically going to be born ripped so he's getting an inkling right knowing that the environment plays a role that it takes time that the um passing it on to offspring is important but like i said gets it just enough wrong that we talk about him but we no longer adhere to his theory our next guy's thomas malthus malthus is an english economist and he wrote an essay called on the principle of population and you might be asking yourself why the heck are we talking about a british economist economist man i can't get the words out today well this essay that he writes inspires darwin and wallace and in this essay malthus stressed that if not kept in check by limited food supplies human populations would double in size every 25 years as population size increases exponentially while food sizes remain stable humans ability to artificially increase food supplies reduces constraints on population growth but when we apply this to nature population increases are checked by resource availability so you can see why this how they're taking this economic principle and applying it to nature as we move on once again the environment is going to be acting as a stressor on population okay next we've got charles lyell he is a geologist starting at the end of the 1700s to about 1875 and lyell's considered the founder of modern geology and he was really good friends with charles darwin lyell wrote the principles of geology where he stressed this concept called uniformitarianism uniformitarianism is a theory that the earth's features are the result of long-term processes that continue to operate in the present as they did in the past this proposes an immense time scale for earth's history expanding it from the few thousands of years commonly held before to potentially millions of years so what lyell has done is given a term and a scientific explanation which gives the length of time needed for slow evolutionary change so now we're finally going to get to the big dude himself charles darwin so charles darwin um was around from 1809 to 1882 and following his graduation from university he was invited to accompany a scientific expedition that would circle the globe his voyage on the hms beagle lasts five years and changes not only darwin's life but the history of biological science darwin begins the journey believing in the fixity of the species but what he sees during his five-year long circumnavigation of the globe challenges that the most well-known is his time spent in the galapagos islands and what he notes there is that on every island the finches are all slightly different in the food that they eat in the size and shape of their beaks and their general overall body size as well now he recognizes that the finches have all descended from a common mainland ancestor but have become modified in response to the varying island habitats and alter dietary preferences he recognizes that it's the difference in the beak structure he recognizes how important biological variation within a species was critically important for survival now darwin kind of gets all the credit for coming up with the theory of evolution and natural selection but he has a contemporary that's not talked about as much and his name is alfred wallace wallace is a little bit younger than darwin not by much but was around from 1823 to 1913 and he's coming to some of these same conclusions that darwin is now darwin sat on his theory of evolution and this idea of natural selection for a long time you know he ends his voyage on the beagle in 1836 and he doesn't publish his kind of tome on the origin of species until 1859. so he bats around these ideas for 20-plus years because he's worried about what the backlash is going to do to him his friends his family his career because he would be trying to kind of rebuff the system at that point but wallace is a little bit more willing to do that and in 1858 he publishes on the tendency of varieties to depart indefinitely from the original type so wallace actually has the first publication that lays out natural selection and long-term evolution but because darwin was more well-known his publication a year later gets all of the scientific credit and merit even though darwin and wallace were corresponding with each other and wallace kind of gets left out of the spotlight so there's a really good quote from a letter that charles darwin wrote and he explains natural selection as it at once struck me that under these circumstances favorable variations would tend to be preserved and unfavorable ones to be destroyed the result of this would be the formation of a new species and i really like this quote because i think it lays out some kind of complicated processes in a very simple manner unfavorable traits are destroyed and favorable variations tend to be preserved now what's favorable and what's undesirable can change depending on how the environment changes so the theory of natural selection really comes down to six main points that there is biological variation that there is competition for limited resources that favorable traits mean favorable survival that there is a very important role of the environment which directly correlates with reproductive success and over time with all of these things working together we can get the formation of a new species so put in other terms time space and the appearance of a new species is the theory of natural selection now let's keep in mind as we move forward because we're going to be talking about this stuff all semester in one form or another that the unit of natural selection is the individual because the individual is the one that either lives or dies they're the one that survives to reproduce and it's their genes that are being passed on however we don't say that individuals evolve we say that populations evolve and that's because we're looking more at a species or a population level when we're looking at evolution so what are we going to talk about next well we're going to move more into the 19th and 20th century and then upcoming lectures when we talk about gregor or mendel and how we get to different sources of variation so in the 19th century they thought that inheritance was basically blending so it'd be like if you took a cup of sprite and a cup of coke and you mix them together you'd get a watered-down brown color um they thought that you just were an equal 50 50 blending of the mother and the father but gregor mendel he's an austrian monk alive from 1822 to 1884 so contemporary ish of darwin he does a lot of experiments talking about the inheritance of traits and genetics i'm gonna like i said we're gonna talk about him next and then we'll get more into actual molecular genetics talking about watson crick and franklin and um kind of the 20th and 21st century ideas of genetics and what evolution is