Transcript of Natural Selection - Survival of the Fittest

Panama Central America as dawn breaks the forest comes alive this is one of the richest environments on earth here more than anywhere you cannot avoid one inescapable fact life is varied biologist David Rubik of the Smithsonian Tropical Research Institute has spent 30 years studying the wildlife here even after all that time he's still amazed at the diversity of life in this small patch of jungle here if we looked around here we would find almost 500 different kinds of butterflies that live just in this one acre of tropical forests even in the tiny area the crane covers at full reach scientists have found 240 species of plants over 4000 species of insects and nearly 50 species of mammals and they're still counting but what created this dazzling diversity and how did the Earth's myriad of species come to be some think they must be the work of a divine creator Darwin on the other hand claimed that they evolved naturally through a process he called natural selection it's one of the most breathtaking ideas ever conceived but what is natural selection and how does it work how can a blind undirected force of nature create new species Darwin saw the answer in an unlikely place the relentless slaughter of the natural world nature is brutal most creatures that are born on this earth die before they can reproduce and it's not just animals most plants die young too [Music] but according to Darwin out of this ghastly slaughter something beautiful emerges [Music] some individuals have characteristics which make them more likely to survive perhaps they have sharper eyes or quicker hooves to help them escape a predator either way these individuals are more likely to live long enough to produce young this is survival of the fittest and it's mainly the fittest who passed their characteristics on to the next generation in natural history there's a future in the future belongs to the fit Darwin said that over many generations these small differences can grow into large differences eyes get sharper legs go faster eventually the changes become so great they lead to new species this explains how life gets more complex but how does it get more diverse how does one species become 2 according to Darwin the answer lies in the environment imagine that a group of brown bears leaves its natural home and heads north to the Arctic in this new environment a bear with light colored fur will find it easier to hunt seals making it more likely to survive more light-colored bears reproduce and eventually the color of the bear population changes according to the scientists that's what happened [Music] step-by-step a population of brown bears became polar bears one species became - this is Darwin's big idea evolution by natural selection species can branch off like limbs of a tree and over time evolved into new species it's an extraordinary idea that tiny changes each offering some small advantage can build up into a new species but is it true Darwin's opponents say not they argue that many animals have features so complex that they can't possibly have evolved the aerodynamics of a hummingbird's wings the pumping action of a beating heart the firing of neurons in an active brain but are these the work of a supreme designer or did they evolved by natural selection critics of Darwin's theory focus their attacks on one organ in particular the eye they argue only works when it's fully formed like a camera the eye needs a lens to focus the image an iris to control the amount of light that enters and photoreceptors to detect that light what use they ask is a half-built eye to show that natural selection works scientists have to demonstrate that an eye could evolve in small steps each step offering an advantage over the one before at Lund University in Sweden dan Eric Nielsen researches animal vision he's convinced that eyes evolved by natural selection not just once but several times though they saw ice of box jellyfish each animal has four of these structures each carries one large lens eye a smaller lens on one pair of slit eyes and one pair of pit eyes they've got 24 eyes altogether they have got a brain our eye is very sophisticated but could it have evolved from simple eyes like these Nielsen has built models to show how natural selection can turn a simple patch of light-sensitive cells like these into a complex eye step by tiny step [Music] the first shows the earliest stages of AI evolution it demonstrates how a flat piece of light-sensitive skin could deepen over thousands of generations to form a depression and if you hold this model up against the light you can see that the flat piece of skin it gives you no information but where the lamp is but if step-by-step the eye socket got deeper and the opening at the front smaller represented here by the ping-pong balls the direction of the lamp becomes clearer each step offers an advantage over the one before pit eyes like this are used by some flatworms detecting the direction of light helps them avoid predators but the biggest improvement came when natural selection found a way to focus light and waken focus light gradually by this little device which is water inflatable lens [Music] by injecting water into the lens we can gradually form the lens so the image gradually becomes sharper until we eventually have a pretty nice and crisp image at the bottom of the retina the combination of an iris and a lens created a defined image on the retina in nature the most likely way the lens formed was when part of the transparent liquid that fills the eye became denser little by little this focused the light and vision became sharper once again each step is an improvement on the last the demonstration shows that the eye could have evolved by natural selection just as Darwin said it did in the Cambrian period of Earth history 543 million years ago the competition to hunt food escape predators and find a mate drove the eyes rapid evolution and the same is true of other complex organs from beating wings to pumping hearts Nielsen's demonstration shows that Darwin's big idea natural selection is theoretically possible but is it true in practice what evidence is there that evolution happened in these small step-by-step changes evolutionists claim that all large creatures living on land today including us came from fish that walked out of the water but if some fish did become land animals where is the evidence you