EvolutionChapters 13, 14, & 15

Earth has millions of other kinds of organisms of every imaginable shape, size, and habitat.

The variety of living things is called biological diversity.

How did all these different organisms arise?How are they all related?

Evolution= The Tree of Life

All living things share a common ancestor.

We can draw a Tree of Life to show how every species is related.

Evolution: Change over time; the process by which modern species have descended from ancient species (common ancestors).

Evolution… theory or fact? It’s both!

The theory of evolution is an explanation of HOW evolution happens. Our understanding of this process is always changing.

Evolution is also a fact due to the huge amount of indisputable evidence for its occurrence.

HistoryLamarck believed genes were

determined by the environment, and the use or disuse of body parts.

He thought that if an animal acquired a characteristic during its lifetime, it could pass it onto its offspring (Inheritance of acquired characteristics).

Hence giraffes got their long necks through generations of straining to reach high branches.

Jean Baptiste de Lamarck

Charles DarwinA young, British naturalist interested in

biological diversity and how it occurred.

Toured the world from 1831-1836 on board the HMS Beagle.

Took lengthy observations of the different species found on the Galapagos Islands. Mainly of the different beaks of finches, and shapes of tortoise shells found on various islands.

Published a book on his findings in 1859: The Origin of Species by means of Natural Selection.

Natural SelectionThe best adapted to the environment survives to

reproduce.

Proposed by Charles Darwin as the driving force behind the theory of evolution.

Evolution by Natural Selection

Natural selection occurs under 5 main conditions

(1) Variation: Natural differences within a species caused by mutations, and sexual reproduction.

Adaptation: A variation that increases an organism’s ability to survive and reproduce.

Ex: Organisms of the same species that are faster, have bigger claws, or are better camouflaged are likely to survive longer.

Natural selection continued…

(2) The struggle for existence- Members of a population must compete for food, space, and other limited necessities of life; (3) competition.

(4) Overproduction: Too many offspring, must compete, some survive.

(5) Survival of the fittest- Those most genetically “fit” survive.

Caused by variation + overproduction + competition + the struggle for existence

Darwin’s Conclusions:1. The diverse forms of life have arisen by

descent with modification from ancestral species.

2. The mechanism of modification has been natural selection working over enormous spans of time.

A summary of Natural Selection

Only well-adapted individuals survive and reproduce. From generation to generation, populations continue to change as they become better adapted, or as their environment changes.

Darwin also proposed that, over many generations, adaptations could cause successful species to evolve into a new species.Speciation: The formation of a new species.