Definition of life: I can not define it, but Ill know it when I see it -Supreme Court Justice Stewart Maybe not so easy after all!
Symptoms of life: Order, reproduction, growth, development, energy utilization, response to environment But what distinguishes life from non-living chemical reactions?
The physical properties of living things can change, and these changes can be inherited by offspring
This is possible because the physical properties of life are determined by a program. This program can be copied, and when it is copied, it can be changed (mutated)
The physical properties of living things can change, and these changes can be inherited by offspring This is possible because the physical properties of life are determined by a program. This program can be copied, and when it is copied, it can be changed (mutated) Life is unique because it is a set of chemical reactions that can EVOLVE
So, we know what makes life unique But there are still many questions about how all the diversity of life came to be…
Life is different from non-living things because life can Evolve Evolution inevitably results in Natural Selection and Descent with Modification. Whats that, and whats the result?
Natural selection 1.The members of a population have heritable variations. 2.The population produces more offspring than the resources of an environment can support. 3.There is competition for resources; as a result, the better adapted individuals survive and reproduce more than the poorly adapted. 4.Across generations, a larger proportion of the population becomes adapted to the environment.
Natural Selection leads to Descent with Modification Once you have life, and competition for resources, natural selection will lead a population to change over time. Birds. Fig 1.11, page 9 Dogs (artificial selection) Descent with modification can lead to new species
How much of lifes diversity can be explained by descent with modification? How many different times was life created from non-life in order to get all this diversity?
All modern life on Earth is related by descent from a common ancestor (evolution). Why do we believe this? Because all life is descendent from one original life-form through an evolutionary process, we can work backward through time to modern lifes earlier and more simple form. Same 4 nucleotides in DNA Same central dogma Same 20 amino acids in protein
All life descended from one common ancestor Figure 1.4, page 6. Three main branches (Domains) When did this occur? And how do they know that?
Stromatolites: like microfossils of early life Modern stromatolitesAncient fossils (?)
How old is the oldest fossil? Tape measure: 25 feet = 2.5 billion years 1 foot = 0.1 billion = 100 million years 1 inch ~ 10 million years 1/8 of inch ~ 1 million years width of hair (~1/1000 inch) = 10,000 years
When did all this happen? today Time - billions of years ago Earth forms Period of heavy bombardment Carbon isotope (first evidence of life) First fossil microbes Oldest eukaryotic fossil dinosaurs hominids Animal diversity begins Oxygen accumulates in atmosphere And what does it mean?
When did all this happen? Geological timeline Billion years ago What was happening 15universe formed in Big Bang 4.5 Earth formed 4.0Heavy bombardment stops 3.85Fossils evidence of life (?) 2.0Fossils of eukaryotes (?) 0.5multi-cellular life becomes abundant 0.05dinosaurs go extinct 0.005chimp/human diverge firs modern humans humans colonize Americas (Indians) ancient Egypt, Greece, Rome, etc dark ages of Europe your parents were born Life started quickly (~200 my), but intelligent life came so late it might have missed the party all-together (human intelligence arrived after 4 by of evolution, with only another 1 or 2 by left before all life on Earth ends)