Professor Dave here, let’s talk about Darwin.

For millennia, humans have wondered just how we got here.

Throughout most of human history, any answer to this question was the exclusive domain

of religion, but when modern science came about, it wasn’t bashful in having a go

at this question, too.

Remarkably, science came to answer it so well, that any discussion of the answer requires

many separate disciplines and years of study.

We need cosmology to discuss the origin of the universe.

Astrophysics is necessary to talk about the formation of the Milky Way galaxy, the solar

system, and our little earth.

We need chemistry and biochemistry to explain the assembly of self-replicating molecules

and the first living cell.

And finally, biology allows us to show how the first unicellular organisms eventually

gave rise to all the incredible species we see on earth today.

Many people remain understandably incredulous to all of this at face value, since they do

not personally possess this mountain of knowledge, but that’s why education is so important,

along with cultivating a societal attitude that values knowledge and growth, rather than

adherance to ancient dogma.

As far as biological evolution goes, the evidence for the descent of all life from a single

common ancestor is as firm and compelling as the evidence that the earth goes around

the sun, so let’s talk about the history of how this understanding came about, starting

with a man named Charles Darwin.

Charles Darwin was a biologist in the 19th century, and as a child he was fascinated

by nature and living things.

In his early twenties, he spent five years aboard the HMS Beagle, traveling all around

the world.

In his travels, he made some profound observations.

He noticed that organisms tend to be suited for their specific environments.

Whether ocean or land, jungle or desert, organisms have features and behaviors that make them

especially suited for their surroundings.

Also, he noticed that there is an incredible diversity of life on our planet, what he called

life’s “endless forms most beautiful”.

There are millions of different species, some of which are unrecognizably different from

one another.

Even so, there are characteristics that are shared by many forms of life.

A lot of animals have the same organs, similar appendages, brains, and behaviors.

Darwin wondered how this could be, and he published a hypothesis in his book, The Origin

of Species, in 1859.

This book almost single-handedly created the field of evolutionary biology, and it remains

one of the greatest accomplishments of scientific thought.

In it, he describes how descent with modification is responsible for the wide variety of species

as well as the similarities between them, as all life is descended from an ancient common

ancestor.

This kind of modification was later dubbed evolution, and the process of evolution can

now be discussed on the genetic level, with mutations that occur in the genome of a particular

organism that alter the products of gene expression, which can then be passed on to offspring.

The specifics of this require a modest understanding of biochemistry, so a viewing of that playlist

will offer a fuller appreciation of what will be discussed here.

But on a basic level, the end result is that if a mutation is favorable, increasing the

fitness of the organism, the organism is more likely to proliferate and pass on this mutation.

If the mutation decreases the fitness of the organism, the organism is more likely to die,

and that genome is never heard from again.

This is easily observable in bacterial cultures, where a chance mutation results in a bacterium

that is resistant to an antibiotic, which then divides while the others die, until the

whole culture has descended from that one mutant.

This concept, which we will discuss in greater detail later, is called natural selection.

We can also discuss evolution in a more historical context, by looking at fossils and other types

of data.

In this way, the theory of evolution by natural selection is a powerful model that correlates

an incredible array of observations.

In this case, as with all others, the word theory does not imply that we are not sure

about its validity.

In science, the word theory does not imply uncertainty at all; theories are not guesses.

They are models that correlate data.

If you like, click on this card to watch a clip with more information about exactly what

theories are.

As we just said, we can watch bacteria evolve in a Petri dish, so evolution itself is not

a theory.

It’s just something that happens.

Natural selection is the theory that explains how evolution has produced the vast array

of life on earth.

Now that we have a few basic concepts straightened out, let’s look at Darwin’s work in a

bit more detail.

The field of paleontology began to develop around the turn of the 19th century, and the

fossil record offered some peculiar data.

Fossils found deeper in the ground were understood to be older, and there was a distinct pattern

in how the older the organism, the less similar it was to current living organisms.

Some geologists of the time proposed that very gradual mechanisms like erosion from

wind and water could produce stunning geological features like canyons and valleys over huge

time spans, and this led the community to believe that the earth must be much older

than previously thought.

Indeed, prior conceptions of the age of the earth came only from a literal interpretation

of the bible, but this thinking came to be completely incompatible with the evidence

at hand.

Biologists of the time realized that if the earth is indeed billions of years old, changing

incredibly slowly through these subtle processes, then the same idea could be applied to biological life.

Miniscule changes to a species, propagated thousands or millions of times, could eventually

produce large-scale transformations in living organisms.

Jean-Baptiste de Lamarck was the first to suggest this kind of evolution, coincidentally

in 1809, the very year that Darwin was born.

However, he incorrectly proposed that these changes occurred in individual organisms,

where limbs and other features grew or atrophied according to their level of use in the lifetime

of that organism.

We now understand that no such change occurs within the lifetime of one organism, as individuals

do not evolve.

It is only over many generations that any such changes can occur.

But Lamarck did set the stage for Darwin to take the idea of evolution much further.

This accomplishment was catalyzed by his time on the HMS Beagle, which found Darwin exploring

South America and collecting thousands of plants and animals.

He gathered his most important evidence on the Galapagos Islands, studying several kinds

of mockingbirds and finches.

Some types were unique to a particular island, some lived on two or more islands, and most

of these were not found anywhere on earth but here.

He reasoned that ancestors of these birds must have arrived from the mainland and then

slowly diversified over time, giving rise to these new species.

He also reasoned that these species showed examples of adaptation, whereby they possessed

characteristics that made them well suited for their environments.

Each species had a beak shape that was adapted to the food source available on their particular island.

He understood that a small change in an organism’s characteristics may impact its chances of

survival, and this is how he arrived at the notion of natural selection.

If a longer beak helps a bird eat more food, then the birds with the longest beaks will

be more likely to eat enough to survive, and thus pass on their genes to new offspring.

Gradually, over many generations, the beak length of a species will grow until it has

become differentiated enough from its ancestors that it merits the distinction of being a

completely new species.

We must understand that in this way, evolution is completely blind, and has no particular

trait or form in mind.

It is simply that any physical change that results in enhanced fitness for the organism

will result in a higher likelihood of survival and therefore reproduction, and thus those

traits are more likely to be passed down, whether this is the ability to better evade

predators, eat more food, or survive the elements.

Over millions of years, a time span now understood to be feasible thanks to advancements in geology,

one can see how this process could result in the emergence of dramatically different

species all over the world, as organisms responded to the completely different sets of stimuli

present in various earthly environments.

Darwin was reluctant to publish these findings because he knew that they would cause a huge

backlash.

Evolution is still strongly contested by religious communities today, so imagine back then, when

the science was brand new.

He delayed publication, and another naturalist named Alfred Russel Wallace put forth a paper

presenting conclusions very similar to Darwin’s.

But then the following

year, Darwin published his masterpiece, The Origin Of Species.

Its logic, evidence, and mechanism were undeniable, and the scientific community quickly accepted

that the diversity of life on earth is indeed the product of evolution by natural selection

over millions of years.

There are those who find this hard to grasp, arguing that species are too dissimilar for

one to have evolved from the other, but they neglect to realize that when two species have

a common ancestor, there are so many organisms that have been lost to extinction in between

the two species being compared.

Tiny gradations of change over a huge time span eventually result in visibly different

species, so if we take away everything in the middle, the gap becomes highly pronounced.

But this is just the way that one color gradually turns into another on a color wheel.

If we see the whole wheel, it makes sense how one color turns into the other.

But if we take away all the shades in between, all we see is these two distinct and seemingly

unrelated colors.

The perils of nature have taken away the vast majority of all species, over 99 percent of

them in fact, and we must keep this in mind so that we can allow ourselves to use the

fossil record to fill in the gaps when understanding exactly how animals like the elephant and

the manatee really did evolve from a common ancestor.

It’s not that an animal gave birth to sibling manatees and elephants, nor did a chimpanzee

ever give birth to a human, as is popularly suggested by critics of evolution.

Instead, an animal gave birth to two nearly identical organisms that initiated divergent

paths of evolution, which over millions of years and many thousands of generations, produced

completely divergent sets of characteristics, due to differing environmental stimuli.

Natural selection is quite easily demonstrable in an analogous but accelerated version, which

we call artificial selection.

Dogs used to all look kind of like wolves, but once we started selectively breeding specific

dogs with other specific dogs to deliberately get the tiniest dogs possible, or fastest,

or most colorful, or any other arbitrary characteristic, we eventually produced an incredible variety

of dog breeds, which are now so numerous only because of human intervention.

If a future biologist were to study fossils of all these breeds, they would undoubtedly

label them as separate species.

We have done this extensively with plants as well.

Kale, Brussels sprouts, cabbage, and broccoli are all direct descendants of the wild mustard

plant, resulting from artificial selection based on certain traits of the plant.

A similar process has produced modern corn, which once looked very different from this

familiar image.

Darwin realized that this happens in nature at a much slower rate, since there is no sentience

to guide it.

As inherited traits must vary slightly, and many offspring fail to survive, nature rewards

the individuals best suited for survival with a higher chance of reproducing and thus passing

on their traits.

This results in the gradual accumulation of favorable traits within a population, which

is what creates the illusion that an organism was somehow designed for its surroundings.

It’s incredible to think that so much evidence was compiled in favor of evolution by natural

selection even before we had any understanding of the chromosomal theory of inheritance or

gene expression.

Now we understand how the genome can be altered through routine errors in the cellular machinery

or exogenous mutagens, and how this can act as a source of novel phenotypes.

These mutations can be subtle, but some can be significant, as there are individual mutations

observed in fruit flies that cause the fly to grow legs where antennas should be.

So we now have a firm understanding of the genetic basis with which variation comes to pass.

When we combine this with natural selection, and an understanding of how characteristics

that enhance chances for survival will slowly mold life into new forms over time, just like

water slowly erodes rock to form a canyon, we arrive at a powerful comprehension of the

origin of all life on earth.

Over the century and a half since Darwin’s work, the entire field of biology has become

inextricably intertwined with evolution, such that biology makes no sense whatsoever without

evolution for contextual basis.

So let’s move forward and look at some of the evidence that has cropped up to make evolutionary

biology consistent far beyond reasonable doubt.