Chapters 16 and 17: Evolution – part I

Evolution – the process by which species change over time People in the 1800’s did not believe in evolution Thought the Earth was a few thousand years old and did not change Thought all life was created by a divine creator in the span of 1 week – very religious!! Thought that life did not evolve

Charles Darwin 1831, set sail on HMS Beagle Ship’s naturalist -observer/collector of plants, animals, & fossils Left from England, sailed around South America, across Pacific, around Africa, and back to England Most famous for observations made at Galapagos Islands

Darwin was influenced by: Charles Lyell – geologist Suggested the Earth was several million years old Suggested that Earth changed over time due to geologic forces (volcanoes, earthquakes, wind, erosion, etc.) Darwin reasoned that if Earth changed, those who lived on it would have to adapt/change to survive.

Thomas Malthus – an economist Wrote an essay on overpopulation of humans – food supply not increasing as rapidly as population growth. Number of people could not keep growing this way and growth would be limited by factors such as disease, war, and famine. Darwin reasoned that the same limits could apply to organisms in nature.

Jean-Baptiste de Lamarck French scientist in 1809 Noticed organisms are usually well-adapted to their environments Suggested that organisms acquired traits during their lifetime to adapt to their environment and passed those acquired traits onto their offspring. WRONG – only traits found on genes can be passed onto offspring!! (Remember – it wasn’t until the 1860’s that Mendel suggested how inheritance works) Example – webbed feet from stretching digits, long neck by stretching

Darwin also took interest in the practice of breeding, particularly exotic pigeons Studied breeding of dogs, orchids, and food crops as well Breeders selected individuals with desired traits to breed the next generation – artificial selection This can contribute to changes in the genetic make-up of a population

Darwin published his findings in 1859 in a book entitled The Origin of Species by Means of Natural Selection. He was motivated to publish his book in 1859 because Alfred Wallace had independently come up with the same conclusions and was ready to publish his findings. Darwin is credited with the theory of natural selection due to the volume of evidence to support his theory.

Populations become modified through natural selection Natural selection - the process by which individuals that are better adapted to their environment survive and reproduce more successfully than less well-adapted individuals do Fitness – reproductive success

Natural selection involves the following: Overproduction – more offspring are produced than can possibly survive Variation – differences within a population Selection – having a particular trait may make an individual more likely to survive Adaptation – those “selected” traits improve survival and become more common in a population

Patterns of natural selection: Stabilizing selection – average form of a trait is favored; extreme forms of a trait are eliminated. Directional selection – one extreme form of a trait is favored. Disruptive selection – both extremes of a trait are favored over an average form of a trait.

Stabilizing selection

Directional selection

Disruptive selection

Adaptations vs. Variations Variations – differences that exist within a population that may have no effect on fitness Ex: length of your thumb Adaptations – a variation that all members of a population have inherited because that trait improves fitness Ex: an opposable thumb

Examples of adaptations: Physical features of an organism Ex: long tongue to get food, sharp teeth Actions an organism takes Ex: migration, tracking prey, storing nuts, growing towards light Chemicals produced/biochemical processes Ex: venom, ink of octopus, protein in web, respiration rate, digestive enzyme, blood clotting