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Charles Darwin
Carl Linnaeus (1700s)
classification
system
based on
similarities
among
organisms
Strange Fossils
(1800s)
Imagine you are a scientist in the
early 1800s. Fossils of some strange
animals have been found. Organisms that
did not look like anything on our planet.
And some familiar fossils have been found
where you least expect them. How did
seashells end up on the tops of
mountains? Remember, ideas about
Continental Drift and Plate Tectonics did
not exist yet.
In the 1800s geologists started to
realize the Earth is much older than
anyone had previously thought. Evidence
showed that gradual processes had
changed the Earth’s surface over millions
of years. Some scientists saw evidence of
evolution in the fossil record. However no
one had been able to explain how
evolution happens.
Jean Baptiste De Lamarck (early 1800s)
Theory of Acquired Characteristics –
incorrect because an organism
cannot acquire a trait during their life
and pass it to offspring
Young Charles Darwin & His Journey(1831-1836)
In 1831, 21 year-old Charles Darwin graduated from college. Like
many young people just out of college, Darwin didn’t know what he
wanted to do with his life. His father wanted him to become a doctor,
but seeing blood made him sick. Although he eventually earned a
degree in theology, Darwin was most interested in the study of plants
and animals.
So Darwin signed on for a 5-year voyage around the world to chart the coastline of
South America and some of the islands of the Pacific Ocean. He served as the
naturalist on the British ship the HMS Beagle. During his journey Darwin collected
thousands of plant and animal samples. He kept careful note of his observations
while traveling to some very interesting places.
Darwin’s Tree of Life
Darwin’s Book: The Origin of Species
(1859)
Provided an abundance of evidence and
the theory of Natural Selection which
explains how evolution happens.
Influences on Darwin
• Galapagos Islands & Darwin’s Finches
• Geology & Charles Lyell
• Selective Breeding (Artificial Selection)
• Population Control &Thomas Malthus
• Alfred Wallace & his Essay
Galapagos Islands &
Darwin’s Finches
One unique place Darwin visited on his HMS Beagle trip was the Galapagos
Islands. These islands are found 600 miles west of Ecuador in South America.
Darwin noticed that the animals and plants on the Galapagos were a lot like those
in Ecuador. However, they were not exactly the same. The finches of the
Galapagos Islands, for example, were a little different from the finches in Ecuador.
And the finches on each island differed from the finches on the other islands.
Darwin observed that each different group of finches had different size and shape
beaks and each group had their own unique feeding habits.
After returning to England, Darwin puzzled over the animals of the Galapagos
Islands. He tried to explain why the animals seemed so similar to each other yet
had so many different adaptations. For example, Darwin learned that the 13
different finches he had studied were each a separate species. Each species was
adapted to their own island habitat. Darwin hypothesized that the island finches
were descended from South American finches. The first finches on the islands may
have been blown from South America by a storm. Then a few individuals migrated
to neighboring islands where they became isolated and exposed to a new
environment. Over many generations, the finches may have adapted to different
ways of life on the different islands which included the types of food each species of
finch relied on for survival. Eventually they became a separate species from the
finches on neighboring islands.
Galapagos Islands
Galapagos Islands & Darwin’s Finches
Finches with different shape & size
beaks adapted from a common
ancestor
Charles Lyell &
Geology
During Darwin’s journey on the H.M.S. Beagle he had an opportunity
to read the first volume of his good friend, Charles Lyell’s newly published
book The Principles of Geology. Lyell proposed in his book that the earth
was very old, that it had been slowly changing for millions of years, and
that it was still changing. These changes were taking place from
weathering, erosion and deposition. Most of the geologists of the time did
not think the Earth was old enough to allow for slow changes.
After Darwin returned home from his voyage, he spent a great deal
of time studying his notes, reading, and conversing with colleagues. He
incorporated the ideas from Lyell’s book about the earth into his own
thoughts on how life changes on earth. Using Lyell’s hypothesis, Darwin
concluded that gradual geologic changes over long periods of time could
cause life to change over that same long period of time.
Charles Lyell (1797-1875)
If the earth is
extremely old
and can
change slowly
overtime, life
must change
with it.
Holstein
Jersey
Hereford
Selective Breeding
(Artificial Selection)
Darwin also studied the selective breeding of domestic animals and
crops. By selecting a parents with the most desirable traits, farmers and
animal breeders can raise more desirable offspring. Breeders, for instance,
select cattle for increased milk production (Holstein), for high-butterfat milk
(Jersey), or for meat (Hereford). Animal breeders and farmers determine
which members of the population shall reproduce and which shall not. Any
domesticated plant or animal bred to produce desirable characteristics is the
result of artificial selection. The striking changes produced over relatively
few generations are powerful proof that species can evolve. Darwin
suspected that a selection process also occurred in nature. If we can select
for useful traits in organisms through selective breeding; why can’t nature
select traits in organisms that make them more successful to survive.
Selective Breeding (animals)
Selective Breeding (plants)
If humans can select traits in species why can’t nature
Thomas Malthus &
Population Control
Shortly after Darwin returned to England, he read An Essay on the
Principles of Population by the economist Thomas Malthus. Malthus
stated in his essay that the human population was growing so fast that the
supply of resources could not keep up with demand. Malthus reasoned
that the human population tends to increase exponentially. For example,
if each pair of parents produced four children, the new generation would
have 4 individuals to replace the 2 that had produced them. The next
generation would have 8, the next 16, and so on. This type of population
growth will eventually exceed its available resources. According to
Malthus, when a population exceeds its resources, disasters such as war,
starvation, or widespread disease limit the population’s growth.
Darwin recognized that Malthus’s principles applied not only to
humans, but to all species. Any species can produce many offspring. He
also knew that the populations of all species are limited by starvation,
disease, competition, and predation. Only a limited number of individuals
survive to reproduce. Darwin reasoned that the offspring of the survivors
inherit traits that help the offspring survive in their environment.
Thomas Malthus (1766-1834)
If humans over
reproduce so do
animals in nature,
but competition
keeps populations
in check
Alfred Wallace &
His Essay
In 1858, Alfred Wallace, a young British naturalist and explorer, wrote Darwin
from Malaysia while he was on expedition. Wallace was seeking Darwin’s advice
about a theory he had. At the time Darwin was one of the leading naturalists of
England. However, Wallace had know idea of Darwin’s life work on his theory of
natural selection because Darwin had only shared his ideas with a few close
colleagues. Wallace sent Darwin an essay on his theory and it turned out that
Wallace had struck upon the theory of natural selection that Darwin had been
researching for 20 years. Wallace’s short sketch was far from the massive body of
evidence Darwin has collected, but its core ideas were similar.
Darwin and Wallace agreed that Wallace’s essay should be published along
with a summary of Darwin’s theory. A year later, in 1859, Darwin published his
book under the title The Origin of Species. Darwin’s book was fully supported by
examples and 20 years of research and influence. His theory on how evolution
works was eventually accepted around 1865 by most of the leading scientists of his
time. Without Wallace’s prompting, Darwin might never have published his theory
during his lifetime.
Alfred Wallace (1823-1913)
Also came up
with Natural
Selection, but
didn’t have as
much evidence.