Evolution • Cladogram – a chart that shows an organism’s evolutionary history • Change in a population of organisms over time.
Theories of Evolution • Jean-Baptiste Lamarck – 1809 published his theory of evolution • Mechanism of Evolution = Inheritance of Acquired Characteristics
Theories of Evolution • Charles Darwin – 1859 published his theory of evolution in the major work, On the Origin of Species • Mechanism of Evolution = Natural Selection
Lamarck’s Ideas Organisms change over time Organisms are adapted to their environment All organisms are continually changing and acquiring features more suitable for their environment.
Larmarck’s Ideas Legless lizard: Note ear hole. Snakes do not have ears. During an organism's lifetime, there is selective use or disuse of its organs and traits. (Example: Lizard living in burrow…) These acquired traits can then be passed on to their offspring. Over time, this process leads evolution of the species.
Comparison of Lamarck’s and Darwin’s Ideas on Evolution Darwin • Same • Same • Same Lamarck • Short necked herbivore lives in savanna • Grasses are available to the animals. Trees leaves are out of reach of most of them • Animals are adapted to their environment.
Comparison of Lamarck’s and Darwin’s Ideas on Evolution Lamarck • The animals stretch their necks to reach the leaves on the trees. Continued stretching causes an elongation of necks. • The animals reproduce. The young have long necks. Darwin • Due to variation in the population there is a range of neck lengths. Some animals naturally have longer necks than others. • Those with longer necks can reach the tree leaves.
Comparison of Lamarck’s and Darwin’s Ideas on Evolution Darwin In the event of a shortage of grasses (drought), the animals are able to feed on leaves. The long necked animals are the most fit! These are the animals that survive and reproduce. Lamarck In the event of a shortage of grasses (drought), the animals are able to feed on leaves. The long necked animals are the most fit! These are the animals that survive and reproduce.
Comparison of Lamarck’s and Darwin’s Ideas on Evolution Darwin • Over the next generations, (due to mutations, new gene combinations, crossing over) there will again be variation in neck length • Those with the longest necks will be be most fit--with the greatest chance of survival. Lamarck • Over the next generations, the longer necked animals will continue to stretch and elongate their necks. • Each generation will pass on their longneck to their young
Macroevolution according to Darwin’s Ideas on Natural Selection Speciation = formation of new species
Variation and Natural Selection • Most phenotypes (traits) are polygenic. • A graph of these traits often shows a bell curve.
Types of Natural Selection Disruptive Stabilizing Directional
Stabilizing Selection If individuals near the center of the bell curve have higher fitness (= leave a greater amount of fertile offspring) then stabilizing selection occurs.
Directional Selection If individuals at one end of the bell curve have higher fitness then directional selection occurs. Example: long necks
Disruptive Selection If individuals at both ends of the curve have higher fitness than those in the middle then disruptive selection occurs.
Genetic Drift • If a small population is isolated from others of the same species, it is possible that just be “chance” one allele may become more common in a population.
Genetic Drift I’ I’m an Eastern Gray Squirrel For example: The Bronx, NY, becomes built up and trees are cut down. Few squirrels are able to survive. However, one section of the Bronx is set aside for the development of the Bronx Zoo. Trees are NOT cut down in this area. By chance, several of the gray squirrels in the area of the zoo have black fur (a variation in fur color). Over time, the allele for black fur becomes common in this population.
How do new species form?Example: Galapagos Finches A small group of a species of finch arrives on one of the Galapagos Islands These finches do not usually fly across open water—they may have gotten lost or were blown there by the wind.
Speciation continued! Over time these original finches may have ended up on other of the Galapagos Islands through some chance occurrence. USUALLY the finches do NOT fly from one island to another.
Speciation continued! • The Galapagos Islands had different environments. • Some had a low elevation and were dry with little plant material.
Speciation continued! Others had a higher elevation with greater rainfall and many plants.
Speciation continued! • Directional selection occurs: • One island may have seeds that are large and difficult to open. • Birds with a larger, thicker beak will have the highest survival rate on this island
Speciation continued! • Directional selection occurs: • Another island may have seeds that are small and easy to open • Birds with a small, thinner beak will have the highest survival rate on this island
Speciation continued! Reproductive Isolation: if the populations remain separate, and their gene pools continue to change, eventually they can no longer mate with each other—they are then TWO NEW SPECIES!!! On the Galapagos Islands this processes resulted in the evolution of 13 different finch species.
Cladograms – a diagram of evolutionary relationships • At the beginning of a cladogram is a single branch. This branch then splits several times into the several animals you have on a cladogram. • When you follow along a branch of the cladogram, it sometimes splits at nodes into two or more branches. • You can also tell how closely related animals are on the cladogram. If you want to know the closest relative of one animal you trace its branch back to the most recent node.
Which are more closely related: roundworms and annelids (earthworms) or arthropods and annelids?
Cladograms • Each node represents a new trait that has evolved and the common ancestor that evolved that trait. • As you follow an animal’s path in the cladogram from the beginning to the end, you can find out the animal’s adaptations through time. Each node it goes through is a trait that it evolved, in that order.
Cladograms • 100 million years go by …
Cladograms: Complete the table below! • Use the information in the table to construct a cladogram of these animals. Absent Absent Absent Present Absent Absent Present Present Absent Present Present Present
Making a Cladogram • Which organism is least like the others? Earthworm Absent Absent Absent Present Absent Absent Present Present Absent Present Present Present
Making a Cladogram • Use your worksheet on cladograms as your guide. • Develop a cladogram showing the evolutionary relationships between all 4 animals. Absent Absent Absent Present Absent Absent Present Present Absent Present Present Present
Making a Cladogram Earthworm Trout Lizard Human Hair Legs Backbone
Which animal is species X most closely related to on the cladogram? Earthworm Trout Lizard X Human Hair Legs Backbone