Chapter 25, Macroevolution

macroevolution

the broad pattern of evolution above the species level.

four main stages of life

1. The abiotic (nonliving) synthesis of small organic mol- ecules, such as amino acids and nitrogenous bases

2. The joining of these small molecules into macromol- ecules, such as proteins and nucleic acids

3. The packaging of these molecules into protocells, droplets with membranes that maintained an internal chem- istry different from that of their surroundings

4. The origin of self-replicating molecules that eventually made inheritance possible

protocells

droplets with membranes that maintained an internal chemistry different from that of their surroundings

hydrothermal vents

areas on the seafloor where heated water and minerals gush from Earth’s interior
into the ocean.

hypotheiss for how organic molecules were produced

alkaline vents

other deep-sea vents that release water that has a high pH (9–11) and is warm (40–90°C) rather than hot, an environment that may have been more suitable for the origin of life

hypotheiss for how organic molecules were produced

Conditions on early Earth made the origin of life possible

• Experiments simulating possible early atmospheres have pro- duced organic molecules from inorganic precursors. Amino acids, lipids, sugars, and nitrogenous bases have also been found in meteorites.

• Amino acids and RNA nucleotides polymerize when dripped onto hot sand, clay, or rock. Organic compounds can spontaneously assemble into protocells, membrane-bounded droplets that have some properties of cells.

• The first genetic material may have self-replicating, catalytic RNA. Early protocells containing such RNA would have increased through natural selection.

fossils records

The fossil record, based largely on fossils found in sedimentary rocks, documents the rise and fall of different groups of organ- isms over time

• The fossil record shows how new groups of organisms can arise via the gradual modification of preexisting organisms.

sedimentary strata

Sedimentary strata are distinct, visible layers of rock or sediment formed by the accumulation, compaction, and cementation of mineral particles over time

reveal the relative ages of fossils. The ages of fossils can be estimated by radiometric dating and other methods.

radiometric dating

a technique used to date materials like rocks or organic remains by comparing the amount of a radioactive isotope to its stable decay product

Key events in life’s history

include the origins of unicellular and multicellular organisms and the colonization of land

unicellular organisms

a living thing that is made of only one cell either:

• Prokaryotes: Cells that do not have a true nucleus or membrane-bound parts. Bacteria are the most common example.

• Eukaryotes: Cells that have a clear nucleus holding their DNA and other specialized parts. Examples include amoebas and yeas

multicellular organisms

a living thing that is made up of more than one cell and has different cell types

moving of plate tectonics effect on speciation and extinction rates

continental plates move gradually over time, altering the physical geography and climate of Earth, leading to extinctions in some groups and speciation in others.

drive speciation (Increasing Diversity)by physically separating populations into isolated environments, while continental collisions increase extinction rates through heightened competition and habitat loss (decreasing diversity)

evolutionary histroy of mass extinctions

Evolutionary history has been punctuated by five mass extinctions that radically altered life’s history. Possible causes for these extinctions include continental drift, volcanic activity, and impacts from asteroids.

adaptive radiations

an evolutionary process where a single ancestral species rapidly diversifies into a multitude of new forms to exploit different ecological niches

this has caused large increases in the diversity of life after mass extinctions. Adaptive radiations have also occurred in groups of organisms that pos- sessed major evolutionary innovations or that colonized new re- gions in which there was little competition from other organisms

Major changes in body form

result from changes in the sequences and regulation of developmental genes

developmental genes

Developmental genes are the master regulatory instructions that guide how a single fertilized egg grows and transforms into a complex, multicellular organism

• Developmental genes affect morphological differences between species by influencing the rate, timing, and spatial patterns of change in an organism’s form as it develops into an adult.

• When nature designs a completely new body shape over millions of years, it usually happens in one of two ways:

  • Rewriting the code (Changes in nucleotide sequences): A permanent typo or mutation occurs inside the gene itself, forcing it to build a slightly different physical protein.

  • Flipping the switch (Changes in regulation): The gene stays exactly the same, but the "light switch" that turns it on or off gets altered. The gene might now turn on too early, stay on too late, or active in the wrong part of the body. [1, 2, 3]

what causes evolutionary trends

natural selection in a changing environment or species selection, resulting from inter- actions between organisms and their current environments.