Natural Selection

Summary

In this Biology Essentials video, Mr. Andersen introduces Charles Darwin and the concept of natural selection. He clarifies that Darwin's fame lies in explaining the mechanism of evolution through adaptation. The video defines evolution as changes in the gene pool and discusses how natural selection, driven by differential reproductive success, leads to adaptations. Using the peppered moth example, Andersen illustrates how environmental changes can cause shifts in gene frequencies and result in new traits. The video also touches on the role of mutations and reproduction in creating variety within populations.

Takeaways

• 🧬 Charles Darwin is famous for providing the mechanism of natural selection, which explains how evolution and adaptation occur.
• 🌿 Evolution is defined as changes to the gene pool, which is the combination of all genes in a population, also known as alleles.
• 🔄 Hardy-Weinberg Equilibrium suggests that the gene pool should remain at equilibrium unless disturbed by factors like small population size, non-random mating, mutations, or migration.
• 🦠 Natural selection involves differential reproductive success, where organisms with certain traits are more likely to survive and reproduce based on their environment.
• 🦟 An example of natural selection is the development of antibiotic resistance in bacteria, where those with higher resistance are more likely to survive and reproduce.
• 🧬 Mutations introduce new characteristics into a population, such as antibiotic resistance, and are a source of variation for natural selection to act upon.
• 🌱 Reproduction, including sexual reproduction in humans, introduces variation in offspring, which can lead to new traits and adaptations.
• 🦋 The peppered moth example illustrates how natural selection can lead to changes in a population's phenotype in response to environmental changes, like the Industrial Revolution's impact on moth coloration.
• 🔢 The Hardy-Weinberg equation (P^2 + 2Pq + q^2) is used to calculate allele frequencies and understand changes in a gene pool over time.
• 🐠 Adaptations, like the cichlid fish's pharyngeal jaw, are the result of natural selection acting over time, allowing species to exploit different ecological niches.
• 🌱 Macroevolution, or large-scale evolutionary changes, can lead to the formation of new species when populations can no longer interbreed due to significant adaptations.

Q & A

Why is Charles Darwin famous in the context of biology?

Charles Darwin is famous because he provided the mechanism that explains how evolution, particularly adaptation, can occur through natural selection.

What is the definition of evolution as presented in the script?

In the script, evolution is defined as any changes to the gene pool, which is a combination of all the genes in a population, also referred to as alleles.

What are the five constraints of Hardy-Weinberg Equilibrium that, if violated, can cause evolution?

The five constraints of Hardy-Weinberg Equilibrium that can cause evolution if violated are: small population, non-random mating, mutations, migration, and natural selection.

What is meant by 'differential reproduction success' in the context of natural selection?

Differential reproduction success refers to the concept that an organism's ability to survive and reproduce is based on its physical appearance and how well it is adapted to its environment.

How does antibiotic resistance in bacteria illustrate natural selection?

Antibiotic resistance in bacteria illustrates natural selection by showing that bacteria with high resistance to antibiotics survive and reproduce, while those with low resistance die off, leading to a population with increased resistance over time.

What are the two ways through which variety can be introduced in a population according to the script?

The two ways through which variety can be introduced in a population are through mutation, which introduces new characteristics, and reproduction, which combines existing mutations to create a variety of types.

What is the significance of the peppered moth example in explaining natural selection?

The peppered moth example demonstrates how natural selection can lead to changes in a population's gene pool. The moths' coloration, which affects their camouflage and survival, changed as the environment became darker due to industrial pollution, leading to a higher survival rate for the darker moths.

How did the Industrial Revolution impact the peppered moth population according to the script?

The Industrial Revolution impacted the peppered moth population by causing environmental changes that favored the darker moths. As coal dust from industrial plants darkened the trees, the darker moths became better camouflaged, leading to a shift in the gene pool frequencies towards the dark phenotype.

What is an adaptation in the context of evolution as explained in the script?

An adaptation in the context of evolution is a characteristic or trait that has been selected for because it enhances an organism's survival and reproduction in a particular environment.

How does the script describe the process of natural selection leading to macroevolution?

The script describes the process of natural selection leading to macroevolution as a continuous process where random changes are selected by the environment over time, eventually leading to significant changes that result in new species that can no longer interbreed.

Outlines

00:00

🌿 Introduction to Natural Selection

Mr. Andersen introduces the concept of natural selection, emphasizing Charles Darwin's pivotal role in explaining the mechanism of evolution through adaptation. The video begins with a definition of evolution as changes in the gene pool, which is a collection of all genes within a population. The instructor explains that the gene pool is typically in equilibrium, but evolution can occur through factors such as small population size, non-random mating, mutations, and migration. The focus then shifts to natural selection, which is described as differential reproduction success based on physical appearance and how it affects survival. An example involving bacterial resistance to antibiotics illustrates how natural selection can lead to adaptations within a population. The instructor also touches on the importance of mutations and reproduction in creating genetic variety within populations.

05:04

🦋 The Peppered Moth and Industrial Melanism

This section delves into the famous example of the peppered moth to demonstrate natural selection in action. The moth's two phenotypes, light and dark, are explained in terms of genetic dominance. The light phenotype's advantage in camouflage is highlighted, showing how it confers higher fitness in certain environments. The instructor then discusses how the Industrial Revolution's environmental changes, particularly the darkening of trees due to coal dust, altered the moth population's gene pool. The shift from predominantly light to dark moths is quantified with historical data showing a significant change in allele frequencies over a 50-year period. The concept of adaptation is introduced as a process driven by natural selection, with the example of cichlids in the Rift Valley adapting to fill various ecological niches. The summary underscores how environmental pressures can lead to significant evolutionary changes.

10:08

🧬 The Essence of Natural Selection

In the concluding paragraph, Mr. Andersen summarizes the concept of natural selection as differential reproductive success, driven by random changes in the environment. He clarifies that natural selection does not aim for perfection but is a process where advantageous traits are selected for survival and reproduction. The paragraph reinforces Charles Darwin's significance in the field of biology for his explanation of this fundamental mechanism of evolution.

Keywords

💡Natural Selection

Natural selection is a key mechanism of evolution, first explained by Charles Darwin, which describes how organisms with traits that are better suited to their environment are more likely to survive and reproduce. In the video, natural selection is central to understanding how species adapt over time. For example, the peppered moth's coloration changed due to industrial pollution, favoring the darker moths as the lighter ones became more visible to predators.

💡Evolution

Evolution refers to any changes in the gene pool of a population over time. It is the overarching process that leads to the diversity of life on Earth. The video emphasizes that evolution is not just about physical changes but can also involve behavioral adaptations. It is a continuous process that occurs through mechanisms like natural selection.

💡Gene Pool

The gene pool is the total collection of all the genetic information in a population. It includes the different alleles, or varieties, of genes. The video explains that changes in the gene pool, such as through natural selection, lead to evolution. The Hardy-Weinberg Equilibrium is mentioned as a way to understand the frequencies of different alleles in a population.

💡Hardy-Weinberg Equilibrium

Hardy-Weinberg Equilibrium is a principle in population genetics that states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences. The video uses this principle to illustrate how allele frequencies can be calculated and how they change over time due to factors like natural selection.

💡Adaptation

Adaptation in biology refers to a trait that is advantageous for an organism's survival and reproduction in its environment. The video explains that adaptations can be physical, like the resistance of bacteria to antibiotics, or behavioral, and they result from natural selection acting on variations within a population.

💡Mutation

Mutation is a change in the DNA sequence that can lead to new traits or characteristics. The video emphasizes that mutations are the source of new genetic variation in a population. They are random events that can be beneficial, neutral, or harmful, and natural selection can act on these variations to favor certain traits over others.

💡Fitness

Fitness in an evolutionary context refers to an organism's ability to survive and reproduce. The video explains that organisms with high fitness are more likely to pass on their genes to the next generation. Fitness is a measure of an organism's success in its environment and is a key factor in natural selection.

💡Differential Reproductive Success

Differential reproductive success is the idea that some individuals in a population will have more offspring than others due to variations in traits that make them better suited to their environment. The video uses this concept to explain how natural selection works: individuals with traits that increase their chances of survival and reproduction will pass on those traits to future generations.

💡Phenotype

Phenotype refers to the observable physical or biochemical characteristics of an organism, which result from the interaction of its genotype with the environment. In the video, the peppered moth's coloration is an example of a phenotype that influences its survival and thus is subject to natural selection.

💡Allele

An allele is a variant form of a gene that arises by mutation and is found at the same place on a chromosome. The video discusses how different alleles can influence traits and how their frequencies in a population can change over time due to natural selection, as illustrated by the peppered moth example.

💡Reproduction

Reproduction is the biological process by which new individual organisms – 'offspring' – are produced from their 'parents'. The video explains that reproduction is essential for the process of natural selection because it allows for the passing on of genetic traits from one generation to the next, which can lead to changes in the gene pool over time.

Highlights

Charles Darwin is famous for explaining the mechanism of evolution through natural selection.

Evolution is defined as changes in the gene pool of a population.

Gene pool equilibrium can be disrupted by factors like small population size, non-random mating, mutations, and migration.

Natural selection is based on differential reproduction success determined by an organism's appearance.

Adaptation occurs when a population evolves to better suit its environment.

Mutations introduce new characteristics into a population, such as antibiotic resistance.

Reproduction, including sexual reproduction in humans, creates variety in a population.

The peppered moth example illustrates how natural selection can lead to changes in a population's physical characteristics.

The Industrial Revolution's impact on the environment caused a shift in the peppered moth's gene pool.

Hardy-Weinberg Equilibrium is a fundamental concept for understanding allele frequencies in a population.

The peppered moth's gene pool frequencies changed dramatically over fifty years due to natural selection.

Adaptations can be physical characteristics or behaviors that are selected for by the environment.

Cichlids in the Rift Valley have adapted to fill various ecological niches through natural selection.

Natural selection leads to macroevolution, where species can no longer interbreed.

Charles Darwin's theory of natural selection explains how random changes are selected by the environment.

Transcripts

Hello. It's Mr. Andersen and welcome to Biology Essentials - video 1. This

is on natural selection so I've included a picture here of Charles Darwin. Most people

think that Charles Darwin is famous because he somehow invented evolution. That's not

totally accurate. Why Charles Darwin is famous is that he's the first scientist that really

gave us the mechanism that explains how evolution, especially adaptation can occur. And so if

you are trying to learn biology the best place to start is with Charles Darwin and a better

understanding of natural selection. Before we can talk about natural selection, however,

we should define what evolution is. And so in this class in evolution, evolution is simply

going to be changes, biological evolution is any changes to the gene pool. So a gene

pool is a combination of all the genes in a population or we call those different varieties

alleles in a population. And so according to scientists the gene pool should remain

at equilibrium. In other words, the frequency of the different alleles will never change

unless you violate one of these five constraints of Hardy-Weinberg Equilibrium. And it happens

all the time, so evolution is constantly occurring and it can occur if you have a small population,

non-random mating, mutations, migration. So these five things can cause evolution but

we are going to talk about those later. Today I want to talk about selection. Because selection

is when you live or die, it's called differential reproduction success, when you live or die

based on the appearance that you have. In other words you're made the way you are and

as the environment changes you're selected. Either you have high fitness and you're able

to survive and pass your genes on or you have low fitness and you die. And if you have enough

fitness over time, that can eventually lead to adaptions in a population. So the smallest

unit that can actually evolve is a population and it's simply changes in the gene pool.

Why do we start with natural selection? Well of these five things here, it's the only one

that can lead to adaptation or organisms that are better adapted to their environment. And

so let me give you an example of that. Let's say you have a bacterial infection. Let's

say you are infected by a number of bacteria, let's call them seven and you decide to treat

the bacteria. So let's say you take some antibiotics, penicillin for example. And they have different

varieties of resistance to that antibiotic. And so when you take the antibiotic on day

one it destroys or lysis or pops all of these bacteria, those that have low resistance.

So these ones are selected, in other words the ones that have a high resistance are selected

for. The ones that have a low resistance are actually going to die. These ones then will

reproduce through binary fission and we're going to have a new population of organisms

that have a better resistance to antibiotics. Now there are two ways that we can actually

get variety in a population. The only was we can get new novel characteristics in other

words like the ability to be resistant to antibiotics is through mutation. Everything

that's been added to the first strand of DNA in that first living thing has been added

through a mistake or a change in the DNA and that's called a mutation. The other thing

that can actually create variety is reproduction. And so in bacteria they use asexual reproduction

but they have mechanisms by which they can change those mutations or vary those mutations

or pass them on. In us its just sex and sex is going to take those mutations and then

in our offspring create a variety of different types. And so this is just theoretically how

natural selection occurs. But let me give you maybe the most famous example of how natural

selection occurs in the wild. And right here is a picture of a peppered moth. A peppered

moth has two different varieties, it has the dark phenotype or physical characteristic

and the light phenotype. Now we know this about moths, that the light phenotype is actually

homozygous recessive (dd). In other words that is a recessive trait. And the dark appearance

you can be either homozygous dominant (DD) or you can be heterozygous dominant (Dd) for

that and you're going to have the dark appearance. And so if you look at this wood right here

where it appears today you can see that this one, the light phenotype or the light physical

characteristic is camouflaged. In other words it fits in. If you are a bird flying over

and you are looking for moths to eat you're not going to see that light appearance. You're

going to see that dark appearance and you are going to go eat that moth. And so you

are going to select that dark appearance. You are going to kill that dark appearance

and its genes are going to die with it. And so at this point the light moth is going to

have a higher fitness. It's more likely to survive, reproduce and pass its genes on generation

after generation. So natural selection has created this appearance. Now why would we

even have the dark moth. Well maybe they can fit in on some of these dark splotches or

maybe they can help them and that's actually what happened. And so in the Industrial Revolution

in the 1800s coal powered plants started to push coal dust out into the environment and

so the environment started to get darker. In other words as that coal dust started to

accumulate on the trees the trees got darker and darker and darker. When they got darker

these moths that were light in appearance, now they started to pop out and those are

the ones that were going to be preyed on by the birds themselves. And so what happened

was a change in the gene pool and natural selection or evolution occurred. So let's

look at some actual numbers. In 1848, 98% of the individuals were light in appearance

and only 2% were the dark. And so we an actually figure out what the gene pool frequencies

were. And so over here I have 100 genes and all of them are light right now. So let's

figure out how many of them were light. And so right here to understand this you have

to have an understanding of Hardy-Weinberg equilibrium. And so here's our famous equation.

If you don't know this you should probably look at the video on Hardy-Weinberg Equilibrium.

P squared stands for the individuals that are homozygous dominant. 2pq stands for the

individuals that are heterozygous and q squared tells us what individuals are, the frequency

of the individuals that are homozygous recessive. And so we can actually use this whenever we

are doing these problems. We usually start with the recessive and we can figure out the

allele frequency. And so 98% of the individuals we know that they are little d little d. That

they're light in appearance. And so I can set q squared equal to 0.98. I can take the

square root of both of those, and I've done this earlier so I know that q is roughly .99.

In other words q tells us the allele frequency. And so that means that back in the day, in

1848, 99 out of 100 were of the light allele frequency and only 1 out 100 were of the dark

frequency. And so that's a simple Hardy Weinberg problem. Now let's see what happens over the

next fifty years. Well if we check back in the next 50 years we find that the population

has changed quite a bit or it has evolved quite a bit. And so it's almost reverse. So

now we have 5% of those that are the light appearance because they are being prey on

birds. And 95% of those are on the dark appearance. Let's see what happened to the actual allele

frequency. And so we know that q squared at this point is not 0.98 it is .05. And so if

I take the square root of that, q now equals roughly 0.22. In other words the gene pool

has changed. The gene pool has changed dramatically. We used to have 99% or 0.99 as our q value

but now it is only 0.22. And so we still have a lot of those dark around. We still have

a lot of those light around but it's changed over time. And the reason it's changed over

time is due to selection. In other words the environment changed and when the environment

changed then they adapted, or the population adapted. What can that lead to? Well it eventually

can lead to something called an adaptation. So an adaptation, if we talk about an adaptation,

is the best example or the best word for that is a process. We tend to think lots of times

that an adaptation has to be a physical characteristic, but it could be your behavior that you have.

And so what is an adaptation? It is a process that is selected for. In other words let me

give you an example of that. In the Rift Valley, it is a great place to study evolution right

now, in the Rift Valley we have these lakes and the lakes are inhabited by a type of fish

called a cichlid. What's unique about a cichlid is that they have this jaw out here that we

can see. It's not quite that big, but the have another jaw back here. It's called a

pharyngeal jaw. And what that allows them to do is to use that for different processes

for feeding, for feeding on different foods and by doing that they are able to, they are

able to exploit a number of different niches in that environment. And so what we have seen

is an explosion of cichlid populations in these lakes in Africa. It started with just

probablyone or a few different types of cichlids and they have adapted to fill all of these

different roles. And so they're perfectly adapted for that environment. How did they

become perfectly adapted? It's just through a process of natural selection. As that environment

starts to change, and they are starting to change, as we get invasive species or fish

that weren't there to begin with, then we're going to have pressure, change in the environment

and those species are going to have to adapt. And so this is how we get species. It's just

evolution taken to its extreme where we get macro evolution or big changes so species

can't interbreed anymore. And so that's a lot, but we're just getting started. And so

what's natural selection? Natural selection, if I could give you one example, the best

definition for what natural selection is, natural selection is simply differential reproductive

success. In other words, we're each made a little bit different. If that allows us to

survive and pass those genes on, we have high fitness, that eventually can lead to adaptations.

But again there's no goal towards this perfection. It's simply random changes that are selected

by the environment. And that's why Charles Darwin is famous. So thanks.