Download natural selection

Charles Darwin
(Working off the information and data
collected from other scientists)
Species were not created in their present forms
but had evolved from ancestral species.
Darwin proposed a mechanism for evolution,
which he termed natural selection.
All species have such great fertility potential that
their population sizes would increase exponentially
if all individuals that are born reproduced
successfully.
Most populations are normally stable
in size, except for seasonal
fluctuations.
Natural resources are limited.
Production of more individuals than the environment can
support leads to a struggle for existence among individuals
of a population, with only a fraction of offspring surviving
each generation.
Individuals of a population vary extensively in their
characteristics; no two individuals are exactly alike.
Much of this variation is heritable.
Those individuals whose inherited characteristics fit them
best to their environment are likely to leave more
offspring than less fit individuals.
The unequal ability of individuals to survive and
reproduce will lead to a gradual change in a
population, with favorable characteristics to that
environment accumulating over generations.
A. Fossil evidence
helps to show how
different kinds of
organisms share
similar structures.
The forelimbs of a whale, bat, and a human
are homologous structures. Structures
which come from different organisms yet
have the same evolutionary origin are called
homologous structures…
b. Gill slits present in the embryos of fish, reptiles, birds, and
humans.
- Gill slits in fish embryos develop into gills but in human
embryos, gill slits develop into the tube that connects the
middle ear with the throat.
All organisms have DNA. All organisms are
composed of the same four bases, A,T,G, and C.
Closely related organisms have a nearly identical
order of bases.
Evidence of Micro-Evolution
(Natural Selection)
Industrial Melanism
A.Eskimos
B.Skin Color
A. The first cells developed on the Earth approximately 3.5-4.0 billion
years ago.
1. Prokaryotes vs. eukaryotes… Yeasts:
A.Prokaryotes: simple celled, no nuclear
membranes or other complex
organelles.
B.Eucaryotes: Complex cells…
C. The atmosphere consisted of a large quantity of carbon
dioxide. No oxygen was present during this time.
B. Eventually, these single celled organisms evolved into many
celled organisms in the ocean.
A. Examples would be sponges, starfish, and algae.
C. The ability to photosynthesize and create energy from the
sun brought about the release of oxygen into the atmosphere
from our first autotrophs.
D. As oxygen gradually became abundant, aerobic organisms could evolve
1. Aerobic respiration allowed organisms to extract more energy from
food molecules.
2. This increase in cellular energy allowed for a higher level of
organization and complexity in evolving primitive cells, (eucaryotic
cells).
1. Natural
Selection:
selection of
adaptive traits
in nature.
Natural Selection Cont’d
2.
There is variation among individuals in any population.
3.
Because of limited resources, not all individuals will
be able to fulfill their potential for reproduction.
4. Those individuals whose traits are better
adapted to their environment will reproduce
more than others.
5. Thus, the better-adapted traits tend to become
more prevalent in the population, and the
population as a whole tends to become better
adapted to its environment over time.
6. If two populations of the same species
evolve along different paths, eventually
they can become two separate species.