Evolution Notes Darwin and His Ideas

Transcription

1 Evolution Notes Darwin and His Ideas

2 Charles Darwin Charles Darwin was born in 1809 (on the same day as Abraham Lincoln) In Darwin s day, scientists were just starting to come around to the idea the Earth was old, and that the Earth and living things have changed over time This change over time is referred to as evolution

3 Darwin s Contribution to Science Darwin developed the scientific theory of biological evolution that explains how modern organisms evolved over long periods of time through descent from common ancestors. This has been hailed as one of the single best ideas that anyone has ever had. Darwin s work helps us understand how the living world is constantly changing, even now!

4 Darwin s Voyage of discovery In 1831, Darwin joined the crew of the British survey ship, the HMS Beagle, as the ship s naturalist. Darwin spent the next 5 years aboard the Beagle as it circumnavigated the globe. Darwin made many observations during this time that would shape his hypothesis about how life has evolved over time

5 Darwin s Observations Darwin was surprised by the variety and number of different organisms that he encountered on his journey. Darwin filled his notebooks with observations of these different species Darwin noticed three distinctive patterns of biological diversity; Species vary globally Species vary locally Species vary over time

6 Darwin s Observations Species Vary Globally Darwin noticed that different, yet ecologically similar, animal species inhabited separated, but ecologically similar habitats around the globe. Unrelated animals living in similar habitats appeared to have similar traits! Rheas in South America similar to ostriches in Africa

7 Darwin s Observations - Species Vary Locally Darwin noticed that different, yet related, animal species often occupied different habitats within a local area Darwin noticed that tortoises from the different islands of the Galapagos varied in their neck length and shell type Darwin rode these giant tortoises and wrote of his experience: I frequently got on their backs, and then giving a few raps on the hinder part of their shells, they would rise up and walk away; but I found it very difficult to keep my balance.

8 Darwin s Observations - Species Vary Locally (2) Isabella Island Tortoise Dome shaped shells and short necks Vegetation on island is abundant and close to the ground Hood Island Tortoise Curved shells that open around neck, and long necks and legs Vegetation on island is sparse and high up

9 Species Vary Over Time In addition to collecting specimens of living species, Darwin collected fossils the preserved remains or traces of ancient organisms Darwin noticed that some fossils of extinct animals were similar to living species Glyptodon and armadillo Some fossils didn t look anything like living organisms Giant sloth

10 Darwin Had Help Darwin wasn t alone in his observations of the Earth and living things. Many scientists were beginning to look at the Earth and the life on it as dynamic, and changing It had been believed previously that the Earth was young and unchanging Darwin was influenced by scientists studying Geology, Biology, human population growth, and even animal breeding

11 Ideas that Shaped Darwin s Thinking Hutton and Lyell James Hutton, a geologist, looked at the processes of rock formation and erosion and concluded that in order for things like mountains and canyons to form, the Earth must be really old Deep time Charles Lyell, another Geologist concluded that the processes that are shaping Earth today take a long time, then they must have taken a long time in the past so, again, Earth is older than previously thought

12 Ideas that Shaped Darwin - Lamarck French naturalist Jean-Baptise Lamarck was one of the first scientists to propose a mechanism for how life changed over time Lamarck suggested that organisms could change during their lifetimes by selectively using or not using various parts of their bodies. He also suggested that individuals could pass these acquired traits on to their offspring, enabling species to change over time This is NOT Correct

13 Ideas that Shaped Darwin - Lamarck

14 Ideas that Shaped Darwin Malthus and Population Growth Thomas Malthus was an English economist in the late 1700 s. Malthus observed that humans were being born faster than people were dying, causing overcrowding. Malthus reasoned that if the human population continued to grow unchecked, there wouldn t be enough living space and food for everyone Darwin saw this in nature organisms reproduced far more offspring than can survive on a limited resource base

15 Malthus Theory

16 Ideas that Shaped Darwin -Artificial Selection Breeding Plants and Animals Plant and Animal breeders had known for centuries that individuals of the same species can vary from each other Some plants bear larger or smaller fruit than average for their species Some cows give more or less milk than others in their herd These variations or differences in traits can be passed on to offspring!

17 Artificial Selection - continued Farmers may select for breeding only the cows that produced the most milk. Over time, this selective breeding would produce more cows that gave even more milk. Darwin called this process Artificial Selection In artificial selection, nature provides the variations, and humans select those they find useful

18 Darwin Writes it Down And Waits After Darwin thought about Malthus ideas, and Artificial Selection, he worked out the main points about his argument for what he called Natural Selection He wrote a draft of his work, and didn t publish it for another 20 years He wanted to gather more evidence for his ideas His idea was radical for the time, he didn t want to cause a lot of controversy

19 Wallace, and The Origin of Species Darwin received a letter from another English naturalist, Alfred Russell Wallace, describing his ideas. Wallace had independently come to the same conclusion as Darwin had about how organisms evolve Darwin HAD to publish his work, or else he wouldn t get the credit! In 1859, Darwin published his book On the Origin of Species In his book he outlined the process of Natural Selection as the mechanism (the how) of evolution.

20 Natural Selection - The Struggle for Existence Darwin (with the help of Malthus) came up with the idea of the struggle for existence to describe the situation in which more individuals are produced than can survive (due to limits on resources) This means that members of a population must compete to obtain food, living space, and other necessities of life Which individuals come out on top in this struggle?

21 Natural Selection Variation Darwin knew that individuals have natural variations (or differences) in their heritable traits. Some of these variations make an individual better suited to life in their environment than others. Faster predators of a species catch more prey Faster members of prey species avoid getting eaten (they survive)

22 Natural Selection - Adaptation Any heritable characteristic that increases an organism s ability to survive and reproduce in its environment is called an adaptation. Adaptations can be; Structural: body parts (claws, camouflage) Physiological: processes, like the way a plant carries out photosynthesis, or a bacteria is resistant to antibiotics Behavioral: avoiding being eaten, mating rituals to increase reproduction chances, etc.

23 Examples of Adaptation - The Cuttlefish

24 Examples of Adaptations Vampire Finches t=pltxf78zn40cixsks3mkqyd8jpywdwqsyu

25 Natural Selection Survival of the Fittest Darwin realized that there is a connection between how an organism makes its living and its environment Fitness describes how well an organism can survive and reproduce in its environment Individuals with adaptations that are well suited to their environment can survive and reproduce more successfully high level of fitness Individuals with characteristics that are not well suited to their environment die without reproducing or leave few offspring low fitness Darwin called this Survival of the fittest

26 Natural Selection Darwin named his mechanism for evolution Natural Selection because of its similarities to Artificial Selection Natural Selection is the process by which organisms with variations most suited to their local environment survive and leave more offspring.

27 Natural Selection - Continued Natural Selection occurs in any situation in which more individuals are born than can survive (the struggle for existence), there is natural heritable variation (variation and adaptation), the there is variable fitness among individuals (survival of the fittest)

28 Importance of Environment to Natural Selection The conditions in the local environment, or habitat, of an organism can change. If conditions change, some traits that were once adaptive may no longer be useful, and different traits may become adaptive. Ex. Webbed digits (fingers and toes) would be useful in an aquatic environment, but if the area dried out, webbed digits may no longer be useful

29 Descent with Modification Darwin s mechanism for evolution (Natural Selection) suggests something about living and extinct species Darwin proposed that, over many generations, adaptation could cause successful species to evolve into new species. He also proposed that living species are descended, with modification (changes), from common ancestors this is called Descent with Modification. This is how Darwin explained the great diversity of life

30 Common Descent Darwin s Tree of Life According to the principle of common descent, all species living and extinct are descended from ancient common ancestors. That means at some level, all life is related. Darwin used the idea of a tree of life to illustrate this principle. Each branch is a species, and where two branches separate is the common ancestor of both species

31 Crash Course Biology Natural Selection video _M