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Course: Middle school biology - NGSS > Unit 8
Lesson 1: Evolution and common ancestryEvolution
Evolution is the process where heritable traits in a group of organisms change over many generations. This process is made possible by genetic variation. This variation, often resulting from sexual reproduction, leads to a range of traits within a population. Over time, small differences between organisms in a population can accumulate, leading to the evolution of new species. Created by Khan Academy.
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- How did the world begin?(10 votes)
- Your answer depends on what you mean by "world". If you meant the universe: The universe (space, time, matter, energy, etc.) all began with the Big Bang. I suggest searching for Khan Academy's "Big bang introduction" video!
If you meant the Earth, it formed when a lot of debris accreted around the sun. Basically, gravity attracted rocks together to form one big planet. You could search for Khan's video "Earth formation" to learn more.
Since you asked this on the "Evolution" video, I wanted to add that the theory of evolution describes how life changes over time, but it doesn't say how the first life came into being.
Does that help?(9 votes)
- What is the weirdest theory of how the universe was made?(6 votes)
- There are some weird theories out there, but the one I think seems to be the most implausible yet very fascinating is the big bounce. It explains how the universe ends and also its beginning.
I don't believe it but it goes like this: There were multiple Big Bangs. The big bang was the "start" of the universe and the expanded for some time, but eventually, gravity was stronger than dark energy, and the universe collapsed and fell back into the dense point it was. This is called the Big Crunch Theory. However, the Big Bounce goes even further. It says that from that extremely dense point sprung another big bang. It shows that this could happen over and over again.
Again, I don't believe this theory and science also finds this more unfavorable.(6 votes)
- So, what about asexual reproduction?
Can't it cause the evolution because every offspring is the exact copy of its parents?(5 votes)- Actually, asexual reproduction does result in offspring that differ from their parents. These are just mutations that happen during mitosis instead of recombinations and mutations occurring in meiosis and sexual reproduction.(3 votes)
- Also, are all traits heritable?(3 votes)
- Now, if you have an Apple iPhone, right now, you would have noticed a button at the bottom of the screen. [But I think this is only for older versions], that button is Fingerprint.
So, you cannot place your fingerprint and download apps from the App Store because it has 'your parent's fingerprint'. Even if it has your people who are genetically related, it still isn't accepted because it has a 'different fingerprint'. That is an example of a trait.
I hope this answers your question!(4 votes)
- how did the world begin ?(3 votes)
- I think it’s something called The Big Bang theory.(4 votes)
- So if all animals have genes and human too and scientists can make human genes change what will happen when you mix a animals gene with a human (Siderman?)?...(4 votes)
- that's a creepy thought -_- :((1 vote)
- What or who is at the top of the world’s family tree(4 votes)
- A single called organism named Luca. This is a probable theory but we don’t have any definitive proof.(1 vote)
- What caused the asteroids to crash into earth and kill the dinosaurs?(3 votes)
- Basically gravity. Earth's gravitational pull captured a huge asteroid, causing it to fall down on the dinosaurs(1 vote)
- At3:10, the speaker is telling that when there is a change in the heritable trait, the organism has evolved. Does that mean when an organism gets a mutation(brown to blue eye colour, etc.), it evolves?(3 votes)
- When you mention the ancestors of birds, below you put an image of a pterosaur (4:05) that is neither a dinosaur nor an ancestor of current birds(2 votes)
- I'm pretty sure that the pterosaur is an ancestor of current bird species. I'm not sure whether it's a dinosaur or not, but if scientists put "-saur" after it's name, they probably classified it as a dinosaur.(1 vote)
Video transcript
- [Speaker] How many different species or kinds of birds are there? Take a guess. 100, 1,000, more? Well, biologists have estimated that there are at least 10,000
different species of birds all around the world,
and some biologists think that there are even more, up
to 18,000 different species. Birds are incredibly diverse. Think about the differences
between an eagle, a parrot, a hummingbird, a duck, and a penguin. Some of them are small and some are big, and take a look at the differences in their beaks or bills
and their feathers. And not all of these
birds can fly, either. Penguins use their wings like
flippers to swim underwater. Collectively, these 10,000
plus different species of birds are a product of evolution, which is the change in heritable traits that occurs in a group of
organisms over many generations. But what are these
heritable traits exactly? Heritable traits are those that are passed from parents to offspring via genes, and they include things like the colorful patterns and plumage or the webbing or toes
and claws of bird feet. And even though offspring
inherit traits from their parents and look pretty similar to them, over many, many generations, these heritable traits can change. Evolution is made possible
by genetic variation or differences in genes
within a population. Genes are passed from parents to offspring and they affect how an organism
develops, how it functions, and even how it looks. Genes can come in
different forms or alleles, which can lead to different
versions of a trait. For example, in city pigeons,
also called rock doves, which you might see flying around, different alleles cause
different eye colors such as orange, black, and white. Genetic variation causes
organisms within a population to have a range of traits like differences in plumage or eye color. Genetic variation can come
from lots of different sources, one of which is through
sexual reproduction. This type of reproduction causes offspring to have different sets of
traits compared to their parents because they receive genetic material from both of their parents. In other words, the offspring aren't an exact genetic
copy of either parent. In this example of rock doves, parents carry different alleles
that affect their plumage, and, in turn, their offspring can inherit different sets of traits and may look quite different
from their parents. Now, let's take a look
at that dove example with the plumage differences and think about it at the population level with lots of doves. You could imagine that
those plumage traits can change over many, many generations of parents and offspring
in a large population. You might see new traits appear like different colors or
different patterns and feathers, or existing traits like dark colors may become more or less common. When this type of change occurs or any change in heritable traits, that group of organisms has evolved. Over many generations,
small differences in traits between generations can
add up, and over time, over thousands to millions of years, evolution can give rise
to new types of organisms. For example, over many generations, one population can evolve
into two different species, like the rock dove and the hill pigeon. Even though these two types of birds look pretty similar to one another, they are a distinct species that have been changing along
independent evolutionary paths for about a million years. Over the billions of years
that life has existed on Earth, evolution has given rise
to the amazing diversity of organisms on our planet. We have over 10,000 species
of birds alive today, and there are even more bird ancestors species that once existed. Ancestors that were literally dinosaurs, but, that's a topic for another video.