Skip to main content
Social Sci LibreTexts

2.2: Evolutionary Theory (Part 1)

Don't go to a dictionary and look up the definition of "evolution". Most of the definitions are just going to reinforce your confusion. For this class we are using the biological definitions of evolution: the splitting of a lineage into two new species, or the change in allele frequency in a breeding population from one generation to the next. For this class an individual can never evolve in their lifetime, a cell phone operating system can never evolve, only a population or a species can evolve. Darwin understood the problem with the word "evolution" and preferred the phrase "descent with modification", but that obviously never caught on.

Understanding evolutionary theory is crucial for all the chapters that follow. For example, in the paleoanthropology section we will make arguments about how natural selection gave our ancestors advantages in different environments, and we will argue how gene flow kept our recent ancestors from becoming separate species. If you don't learn about the forces of evolution now you won't understand the arguments we're going to make later.

image024.gif

Figure \(\PageIndex{1}\)http://www.smbc-comics.com/index.php?db=comics&id=71

Evolutionary theory is a difficult concept. In the last section we discussed the ideological barriers that extremely dogmatic religious people have that might keep them from understanding evolutionary theory. Another common misconception of evolution is that there is inherently something good about it, that to evolve means to progress. The simple definition of evolution is just “change”. It doesn't mean change for the better, or change for the worse, just that a species is different that what it used to be. It's important to separate how a word is used on the street from the very specific definition we are using here in our biological context. The main reason people have problems with a neutral definition of evolution is that we've had thousands of years of cultural baggage that clouds our empiricism. The philosopher Aristotle stressed the importance of finding the essence of a thing, and from this we get the concept of essentialism. People often think of humans as diverging from or progressing towards some ideal form, but these are cultural constructs, not what we empirically see in biology. We carry baggage around that makes simple concepts seem counterintuitive. Understanding the incorrect ideas helps us accept the correct ones.

Exercise \(\PageIndex{1}\)

Read more about Darwin and design.

History of Evolutionary Theory, up to Darwin

It helps to understand evolutionary theory if you understand how it “evolved”. I put “evolved” in quotes because for this class I want to reserve the word evolution to mean “biological evolution” and not confuse it with historical and cultural changes. There are different ways to study history, and for this section we need to be careful not to fall into the trap of thinking of history as a series of Great Men – important people who change the world through their personal actions. This way of looking at history is very convenient for an introductory class, because you just need to make a handful of flashcards with the names on one side, and what they're famous for on the other. But, try to look beyond the individuals, and imagine the broader movements that were going on at the time these individuals lived.

It helps sometimes to put people and concepts into two columns: did they contribute to evolutionary theory or did they detract from the development of evolutionary theory? But, many historical figures can be put in both columns, depending on their effect on history, and what stage of their life you look at. For example, Linnaeus made amazing strides in biological taxonomy, but opposed evolutionary theory, at least until the end of his life; Lamarck created a great theory of evolution, but it was wrong; Cuvier contributed to our understand of extinction, but argued against evolution and fixity of species, Lyell argued against biological evolution until after Darwin convinced him; Wallace's evolutionary theory was mixed with quirky spiritualism; Darwin's theory of Natural Selection was revolutionary, but his emphasis on blending made it more likely to ignore important contributions from scientists like Mendel, and gradualism made it harder to accept punctuated equilibrium. Just realize that for an introductory class, we only have time to give you a cardboard cut-out of these fascinating and complex individuals and their historical milieux.

Exercise \(\PageIndex{2}\)

Read Dennis O'Neil's Intro

The Fixity of Species

In this modern world, we are so used to change that it's hard not be ethnocentric and imagine a time when things were pretty much the same as it was for your grandparents, and you expected things to be pretty much the same for your grandkids. Imagine growing up and liking the same music as your great-grandparents. Most religions around the world are conservative. God creates a world and some people to interact with it. And the reasoning often goes that if your deity is all-powerful, His creations would be perfect and He wouldn't need to keep tinkering with them. When people looked around at all the living creatures on the planet, they assumed that everything was stuck the way they saw it. This concept is called the fixity of species, and “fixity” in this case refers to being in a fixed position; unchanging.

Evolutionary theory is diametrically opposed to the fixity of species.

The Great Chain of Being

The Great Chain of Being incorporates the concept of the fixity of species but ranks life into better or worse, noble animals like eagles and lions go towards the top, slimy animals like worms and eels go down to the bottom. Noah's Ark usually boards the same way, first-class passengers first. When applied to humans, the Great Chain of Being has always functioned to perpetuate political oppression such as racism, sexism, and classism. The dominance of the Great Chain of Being in Eurasian philosophy makes it hard at first for many students to accept the complete absence of any system of ranking or progress in evolutionary theory.

image026.gif

Figure \(\PageIndex{2}\) - Wikipedia;1579 drawing of the Great Chain of Being from Didacus Valades, Rhetorica Christiana.

John Ray

John Ray (1627-1705) is important to us because he invented the concept of the species (the word "species" is one of those Latin word that doesn't change between the singular and plural; "one species, two species"). Species are the most fundamental way of grouping life forms. You might ask how a book entitled "The Wisdom of God Manifested in the Works of Creation" could contribute to evolutionary theory but a common theme in all science is how scientists get some things right and some things wrong.

04138 John Ray- Wisdom of God manifested1000.jpg

Figure \(\PageIndex{3}\)John Ray

DrS.jpg

Figure \(\PageIndex{4}\) - The word "species" always has an "s" on the end

In Ray's book History of plants he grapples with how to group the varieties of life, and he comes up with a concept that is still useful today – individuals that can reproduce are from the same species:

no surer criterion for determining species has occurred to me than the distinguishing features that perpetuate themselves in propagation from seed. Thus, no matter what variations occur in the individuals or the species, if they spring from the seed of one and the same plant, they are accidental variations and not such as to distinguish a species… Animals likewise that differ specifically preserve their distinct species permanently; one species never springs from the seed of another nor vice versa *[Ray 1686Ray 1686]

A species is something that exists over time and is capable of perpetuating itself, and variations within a single species occur. The Notice at the end of the quote how he insists on the fixity of species, and denies speciation, but we still use Ray's species concept today.

Carolus Linnaeus

Linnaeus is the father of taxonomy. Taxonomy was different from the Great Chain of Being because instead of grouping animals into biblical categories, he grouped them by biological characteristics: how they give birth, what they eat, aging, exterior movement, internal propulsion of fluids, diseases, death, glands, skin, and the shape of the inner ear (Foucault 1970). This list is very arbitrary compared to how today we compare the DNA of a species to classify it, but Linnaeus' taxonomy was radically different from the more poetic groupings of his time. Linnaeus was able to distinguish bats from birds, and snakes from eels and worms. His taxonomy changed over his lifetime and has been an important concern of biology to this day.

His approach to classifying humans codified scientific blunders regarding race that have continued over two centuries.

Exercise \(\PageIndex{3}\)

Read this Introduction to Linnaeus

 image028.gif

Figure \(\PageIndex{5}\) - 1760 Hoppius based on Linnaeus, left to right: Troglodytes, Lucifer/Homo caudatus, Satyr, Pygmie

Exercise \(\PageIndex{4}\)

Briefly scan Linnaeus' system of nature 1740

Skim the pages on humans from this 1757 version

Buffon

George Louis Leclerc, Comte de Buffon wrote about how life changes according the environment but didn't explain how.

Erasmus Darwin

Erasmus Darwin was the grandfather of Charles Darwin and his poetic writing about about how life forms might change influenced his grandson, Charles.

* if you like prose, skim his chapter on generation

Jean-Baptiste Lamarck

Lamarck is known for his theory of Acquired Characteristics, also called the Use-Disuse theory. The theory goes that the physical traits you change during your lifetime get passed on to your kids. So if you believe in Lamarck's theory then you would expect Arnold Schwarzenegger's babies to be born with lots of muscles.

arnold-blueprint-mass-training-3-graphics.jpg

Figure \(\PageIndex{6}\)http://www.bodybuilding.com/fun/arnold-schwarzenegger-blueprint-trainer-mass-training.html

docubaby.jpg

Figure \(\PageIndex{7}\)Tobias Hellström 2008

Of course, Lamarck was wrong. Physical characteristics acquired during an individual's lifetime are not transferred to its offspring (with a few epigenetic counter examples). We'll show why he was wrong in the section on cellular biology. The reason Lamarck's theory sounds so plausible is because culture is transmitted this way; what you learn during your lifetime can be taught to your children. But biological inheritance has very specific mechanical processes that we can now see in a microscope. You have to give Lamarck credit for coming up with an elegant theory of evolution. It has been disproven, but it was still a great theory for its time. Understanding why Lamarck was wrong will help you understand natural selection.

Exercise \(\PageIndex{5}\)

Look at the classic example of Giraffes 

Skim this Biography of Lamark

Georges Cuvier

Cuvier is important to evolutionary theory in promoting the concept of extinction. He saw fossils of animals no longer on the planet, such as giant elephants, and he correctly explained their disapearance as extinction, the big elephants just died out.

CuvierMammothJaws2.jpg

Figure \(\PageIndex{8}\)http://evolution.berkeley.edu/evolibrary/article/history_08

His views on extinction contributed to evolutionary theory but his attempts to reconcile geology with The Bible did not. Cuvier is also known for his theory of Catastrophism: extinctions in the fossil record are only because of sudden changes in the environment, such as world wide floods, like Noah's flood.

Geologists: James Hutton and Charles Lyell

Geology has always had a profound impact on evolutionary theory. Most of the scientists of the 18th and 19th Centuries called themselves "naturalists" and didn't distinguish between fields such as geology and biology. James Hutton and Charles Lyell were two of the most important scientists to use empirical observations to guide theories of how the Earth arose and became what we see today. Their two main contributions to evolutionary theory are the concept of geological time and the principle of uniformitarianism.

Geology is important to biological anthropology in many ways, such as dating and environmental context in paleoanthropology. In archaeology, Lyell's Law of Superposition is crucial – the deeper you dig, the older things are.

Geological Time

How long are you going to live? 50 years? 100 years? The length of time that you can perceive is limited by your own biological expiration date. The neat thing about geology is you start thinking like a rock. Imagine 1,000 years passing, 10,000 years, 100,000 years, 1,000,000 (a million) years, 1,000,000,000 (a billion) years… Lyell proved that the Earth is old, that rocks have been around for a long time. This was important to biologists and paleontologists because it showed that fossils are very old too. If life has been around for billions of years we can more easily accept that drastic changes could happen over that long a time span. Geological and astronomical time is sometimes called Deep time, and it is one of those very disturbing nonhuman concepts that science often forces us to think about.

The Principle of Uniformitarianism

What happened in the past continues to happen today. Most cosmologies around the world have some concept of a mythical past, where different laws of nature applied. Lyell demonstrated that huge geological formations can be explained by the same simple forces that we see today, such as erosion, wind, earth moved by earthquakes. We can explain something as awesome as the Grand Canyon with two simple processes that can be seen today: uplifting and erosion.

In biology, we can find simple processes that differentiate me from a banana slug. Both, the biological and the geological require huge quantities of time.

Exercise \(\PageIndex{6}\)

Skim the 1830-3 Table of Contents of Lyell's Principle of Geology (10 pages)

Thomas Malthus

Malthus studied demography, how populations change. Overpopulation creates competition for limited resources. This idea of competition within a population is similar to the idea of competition within a species, and creates change. According to Malthus, humans can increase their population faster than they can increase their food supply. Having more people than food leads to starvation and competition for limited resources.

For example, imagine that Octamom has 8 daughters who each have 8 daughters who each have 8 daughters who each have 8 daughters, and in 5 generations you have a population of around 32,000. When Octamom works a plot of land she can produce one bushel of food per month, with her daughters helping she can produce 2 bushels, with her grandkids helping, 3 bushels, but by the time her great-great-grandkids have exhausted the nutrients in the soil, and run out of fertilizer made from non-renewable resources, her descendants are back to producing about 3 bushels a month, except it's like a Mad Max dystopia with thousands fighting over those few bushels, and most starving to death.

Darwin took Malthus' very specific observations of how humans compete for limited resources and generalized them to the broader field of biology.

Mary Anning

Mary Anning was the most famous fossilists of 19th century. A fossilist is someone who gathers fossils. A fossil is the imprint of a biological form, and we will come back to fossil in the sections on paleontology and paleoanthropology. Fossils represent biological data. If we go back to section 1.1 and consider the scientific method, it's important to remember that hypotheses are based on empirical observations, things we can see with our own senses. With a phenomenon like gravity you see the apple falling from the tree, but seeing evolution is more difficult. What many of the evolutionary thinkers of the 19th century got to see were the fossils collected by Mary Anning.

* Watch this puppet show of Mary Anning's life

Imagination Questions

  • How big is life?
  • How old is life?
  • The line "same as it ever was", from the Talking Heads song "Once in a Lifetime" always reminds me of uniformitarianism and the song makes make think of deep time. Do you ever freak out about how short your lifespan is compared to how long the planet has been around?