Chapter 18 : Evolution

Linnaeus ( 1760s ) : biologist. He invented the modern system of biological classification.

Hutton ( 1795 ) geologist. He proposed that slow, gradual changes altered the landscape eg rivers eroding mountains. Later Darwin applied this idea of slow, gradual change to living species.

Malthus ( 1800 ) minister. Malthus Malthus said that the human population will grow until limited by disease, starvation.

Lamarck ( 1810 ) biologist. He said that evolution was caused by passing on characteristics acquired during life. For example people who work out a lot will have babies born with large muscles!

Lyell ( 1830 ) geologist. He calculated that the earth was millions of years old, at least, rather than the 6,000 years that creationists believed.

The theory of evolution was jointly developed by Charles Darwin and Alfred Wallace.

Darwin and Wallace's theory of Evolution.

1) All species can rapidly increase in population, if all their young survive.

2) Most wild populations are stable over time.

3) The reason popultions do not normally increase is that resources ( food, water, nesting sites ) are limited, so there is a struggle for survival.

4) Individuals in a population vary.

5) Most of this variation is inherited.

Conclusion : Individuals who are the best adapted will survive and reproduce, ones who are less adapted will die. Darwin and Wallace called this process "Natural selection". Later the term "survival of the fittest" was used.

Evidence for evolution.

1) Fossils show how species have changed over time:
A) The oldest fossils show no modern species.

B) Particular groups can be studied: eg modern horses evolved from Hyracotherium a small, leaf eating mammal with 4 toes.

C) Intermediate fossils connect different groups. Fig 17-7. eg Archaeopteryx links birds to reptiles. Drawing

2) Biogeography : particular species are only found in certain areas. Islands often have unique species:
eg Hawaii - over 300 unique species. Madagascar - lemurs are only found here. Florida - Key deer in Florida keys.

3) Comparative anatomy : all vertebrates ( reptiles, birds, mammals etc ) have the same arm bones. Fig 17-10.

4) Comparative embryology : vertebrate embryos are all similar, with gill slits and a tail. Fig 17-14.

5) Molecular biology : closely related species have similar DNA and proteins. Fig 17-15.

6) Vestigial organs : have no function but are inherited from an ancestor where they did have a function:
eg pelvic bones in snakes. Also the appendix, third eyelid, muscles to move ears in humans.

7) Atavisms : genes from ancestors that are usually switched off can be switched on.
eg horses with 3 toes. Or humans with dense hair all over the face "werewolf gene".

8) Imperfect "design" : an organism just needs to survive long enough to reproduce, it is not a perfect design.
eg legs longer than neck in a giraffe. The human skull is made of several bones joined together.The human eye has nerves infront of the retina.

9) New species have evolved recently: eg Spartina cordgrass in Europe. Spartina Primula kewensis in 1920s. HIV evolved in about 1940. Scientists see new species born Butterfly evolution

Human evolution

The oldest human fossils are roughly 6 to 7 million years ago. Fossil. Later (roughly 4 million to 2 million years ago) the genus Australopithecus evolved. It was only found in Africa, slightly larger than a modern chimp, but walked on two legs.

The genus Homo evolved about 2 million years ago. Homo habilis : used stone tools, was about 5ft tall, had a small brain, only found in Africa. Homo habilis

Homo erectus : used tools and fire, roughly 6 ft tall, larger brain, spread from Africa to Asia and Europe. Homo erectus. Modern humans and Homo erectus may have come into contact in Asia. Louse study

Homo neanderthalensis : largest brain of any human, buried their dead. They were hunters, living mainly on large mammals. They cooked their food. DNA studies show that Neanderthals and Homo sapiens did not interbreed, even though they lived in the same areas.

In 2004 skeletons of a new species of human were found on Flores, Indonesia. They were smaller than pygmies, but hunted large mammals and cooked their food. Homo floresiensis

Homo sapiens : spread worldwide, the only surviving human species. skull Modern humans all come from a small population who moved out of Africa less than 100,000 years ago: When humans faced extinction Early humans were "hunter-gatherers" - in other words they hunted animals and collected fruit, berries and shellfish. Humans did not start growing crops until about 10,000 years ago.

Summary of Human evolution

Age of fossils
(Years ago)		GenusSpeciesLocationComments
4 million to 2 millionAustralopithecusafarensisAfricaSmall brain, no tools, bipedal
2.5 million to 1.5 millionHomohabilisAfricaLarger brain, tools, 4.5ft tall
2.3 million to 30,000HomoerectusAfrica, Asia, EuropeUsed fire, 6ft tall
130,000 to 30,000HomoneanderthalensisAfrica, Asia, EuropeLargest brain, buried their dead
100,000 to 12,000HomofloresiensisFlores island, IndonesiaHeight 3ft, hunted, used fire
150,000 to PresentHomosapiensWorldwideOnly human to reach America

Note that from about 100,000 years ago to 30,000 years ago, there were four different species of human on the planet.

Last edited November 2008 by David Byres, dbyres@fccj.edu