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Who saw the importance of biological variation within a species.
The Struggle for Existence
- The idea that in each generation more offspring are born than survive to adulthood, coupled with the notions of competition for resources and biological diversity led to the theory
- of evolution.
He wrote,“ It at once struck me that under these circumstances favourable variations would tend to be preserved, and unfavourable ones to be destroyed.”
What is “the key” to understanding evolution
Processes of Natural Selection
Natural Selection, the basic processes
1.All species are capable of producing offspring at a faster rate than food supplies increase. So, there is a tendency towards overproduction.
2.There is biological variation within all species.
- 3.Since in each generation, more individuals can be produced than can survive, and because of limited resources, there is
- competition (not necessarily the same thing as fighting, however) among individuals.
- 4.Individuals possessing favorable variations or traits (i.e. speed, resistance to disease, protective coloration) have an advantage
- over those who do not. In other words, have greater fitness because favorable traits
- increase the likelihood of survival and reproduction.
5.The environmental context determines whether or not a trait is beneficial. Hence, favorable traits become most advantageous are the results of a natural process.
- 6.Traits are inherited and passed on to the next
- generation. Individuals who produce more offspring are said to have a greater reproductive success, or fitness.
7.Variations accumulate over long periods of time, so later generations may be distinct from ancestral ones.
8.As populations respond to pressures over time, they may become distinct species, descended from a common ancestor.
Geographical isolation (distance, natural barriers such as oceans) contributes to the ?
formation of new species as individuals begin to adapt to different environments.
- (differential ecological circumstances) cause distinct species
- to develop
Describe Evolutionary Change Through Natural Selection
1.A trait must be inherited if natural selection is to act on it.
2.Natural selection can’t occur without population variation in inherited characteristics.
3.Fitness is a relative measure that changes as the environment changes.
4.Natural selection can only act on traits that affect reproduction.
Pertaining to natural selection, a measure of relative reproductive success of individuals.
Fitness can be measured by an individual’s genetic contribution to the next generation compared to that of other individuals.
The ability to conceive and produce healthy offspring.
- An animal that gives
- birth to more young passes its genes on a faster rate than one that bears few
An important element, however, is also the number of young raised successfully to the point where they reproduce, or differential net reproductive success.
With the discovery of the structure of DNA came the understanding of the entire genetic makeup of an individual or species.
Human and chimpanzee genomes were sequenced in 2003 and 2005, respectively.
Refers to a biological continuum.
When expressions of a phenomenon continuously grade into one another so that there are no discrete categories, they exist on a continuum.
Color is one such phenomenon, and life-forms are another.
Most people hold to belief systems that do not emphasize this or offer scientific explanations.
Why It Matters
Understanding evolution makes a difference.
Example: HINI Flu viruses are the result of viruses “evolving” or changing in form.
- Medical researchers try to predict which of several strains
- will pose the most serious threat and try to develop a vaccine that targets
- that specific “evolving” strain.
If future physicians and researchers don’t understand evolution, there is little hope they can forestall potential medical crises as the pace of change in pathogens exceeds that of the antibiotics designed to defeat them.
Contemporary Health Challenges
- The inevitable outcome of our more aggressive methods to fight microbes (disease causing micro-organisms such as bacteria and viruses) will lead to modified micro-organisms that have
- evolved to resist therapies such as antibiotics. More use of antibiotics to treat bacterial infections weed out vulnerable microbes, but leave less vulnerable to reproduce. Less vulnerable cause more serious forms of disease
- than the organisms that were eliminated.