Charles Darwin as ships naturalist
observed unusual animals and their fossilized ancestors.
armadillos, rhea (flightless bird)
from South America
life differ greatly from that found off the Pacific coast.
that the only native species were bats. All other were introduced by
Still other observations came from the Galapagos
- Islands off the S.A. coast (3000 miles away)
From the Galapagos Islands
- tortoise populations showed distinctive features
unique to three local islands.
- Three species of finch show most similarity to
finches found on the S.A. mainland
Each new species had a common ancestor that responded
to new island conditions producing new species.
beak to crush seeds
beak to catch insects
using a cactus needle to catch insects
evidence for common ancestry
scientists note difficulty distinguishing between embryo’s of a
mammal, bird or reptile. Biologists
today still recognize many similar embryonic features gill slits,
Evidence of Common Ancestry
features found in different species that have different function. These
features are said to be homologous
Bats have wing bones very similar to those bone of
animals with walking feet or whale fins
organs no longer function in one species are still used in others.
that move ears in cats no longer function in many humans.
Breeding and Natural Selection
Darwin observed that human beings were able to produce
new breeds of dog by selective breeding. Mate only those dog that
possess a desired trait.
Horticulturalists develop new species of flowers by
So why can’t nature impose environmental constraints
Natural Selection as Darwin described was a process
whereby species that withstood environmental pressure would live to
reproduce and pass on those successful traits.
for Darwin’s Evolution: Natural Selection
He wrote in an abstract to the Linnean Society in
As many more individuals of each species are born than can possibly
survive; and as consequently, there is a frequently reoccurring struggle
for existence, it follows that any being, if it vary however slightly in
any manner profitable to itself, under the complex and sometimes varying
conditions of live, will have a better chance of surviving, and thus be naturally
selected. From the strong principle of inheritance, any selected
variety will tend to propagate it’s new and modified form"
Discoveries after Darwin
In Darwin's time there was not explanation for how
inheritance worked. Gregor Mendel’s Particulate
factors are passed in pairs – one from each parent while maintaining
their individual characteristics. See Pea Plant Flower experiment
These factors are now know as genes segments of DNA
stored as chromosomes in the nucleus of each cell.
Darwin believed a organic evolution occurred
gradually. New species are derived by slowly by selective pressures like
Ammonites gradual change from straight shell to complexly sutured
& curled shell.
Evidence for this gradualistic evolution is lacking in
the fossil record. Intermediate species do not always appear.
Radiation: Punctuated Equilibrium
Some groups may change little for most of their history
but, then a rapid change and production of new species can occur.
is disappearance of species as a result of extreme limiting
factors: Fossil record not longer contains evidence of their
restrictions like drastic climate change, meteorite impact or
geographic isolation – mountain building or faulting due to plate
is a form of extinction by evolving into a different species.
many species are lost over a very short period of time
Extinction vary greatly