Textbook Notes (362,796)
Canada (158,054)
Environment (154)
ENV100Y5 (125)
Chapter 4

Chapter 4.docx

5 Pages
Unlock Document

University of Toronto Mississauga
Monika Havelka

Chapter 4: Evolution: in broad sense means change over time, but scientist most often use the term to refer specifically to biological evolution, which consists of genetic change in populations of organisms across generations Natural Selection: traits that enhance survival and reproduction persist in population • Natural selection shapes organisms and diversity • A trait promotes success is called an adaptive trait or an adaption – a trait that reduces success is said to be maladaptive • Only natural selection produces adaption • Natural selection is powerful • individuals vary (different genotypes) • not all individuals will survive to reproduce • success is usually not random • parents pass traits on to offspring Darwin’s dangerous ideas: • Evolutionary change by descent with modification • Natural selection produces adaptations Genetic Variation: • Mutations = accidental changes in DNA that may be passed on to offspring; provide the genetic variation on which selection acts • mutation in myostatin gene produced “double muscling” in Belgian blue cattle • sexual reproduction also generates variation • recombination produces novel combinations of genes, generating variation among individuals • Natural selection can act on genetic variation and alter the characteristics of organism thought time in three main ways: • Directional selection: fast to slow, large to small (one direction) • Stabilizing selection: produces intermediate traits (selection against extremes) • Disruptive selection: diverge from their starting condition in two or more directions • Random drift • Migration Evolution: change in the genetic composition of a population • Closely related species that live in different environments and thus experience different selective pressures tend to diverge in their traits as the differing pressures drive the evolution of different adaptations – divergent evolution • Sometimes very unrelated species may have similar traits as a result of adapting to selective pressures from similar environments – convergent evolution Evidence of natural selection: • Artifical selection: process of selection conducted under humans Biological diversity or biodiversity: • Total variety of all organisms in an area, taking into account the diversity of species, their genes, their populations, their habitats, their communities Species: • Is a particular type of organism or more precisely, a population or group of populations whose members share certain characteristics and can freely breed with one another and produce fertile offspring • Speciation: the process by which new species are generated • Allopatric speciation: o Single population o Geographically isolated populations o Divergence due to long-term geographical isolation o Isolated populations come together; the two populations can no longer interbreed and are now two species Excinction: • Extinction = the disappearance of a species from Earth • most species are extinct! • most extinction from interactions with other species • mass extinctions due to environmental change • there have been 5 mass extinctions in ~ 600 million years • mass extinction: 50 – 95% of all life gone
More Less

Related notes for ENV100Y5

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.