Evolution part 3 Flashcards
What is a species?
“Species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups.”
How many species of living things exist?
Known to science – 1.8 million
Estimates – 5 million to 30 million
Based on the fossil record, it is estimated that 99% of all Earth’s biodiversity no longer exists (has gone extinct)
How are new species formed?
Geographic separation is one “popular” way
At first, two populations are genetically and phenotypically similar
Over time, the two populations evolve independently, so the more time they are separated, the more likely changes to prevent interbreeding will have occurred.
Define natural selection of individuals, populations and species
individuals are acted upon by selection regarding reproduction, but they do not evolve
populations evolve by selection because changes in trait frequency occurs over time when selection acts on individuals in the population
sometimes populations are separated causing different selection pressures to produce separate species
What is an example of Extrinsic isolating mechanism?
Geographic isolation -
Individuals of two populations cannot
interbreed if they live in different places
(the first step in allopatric speciation).
What are examples of Intrinsic isolating mechanisms
Ecological isolation
Even if they live in the same place, they
can’t mate if they don’t come in contact
with one another.
Temporal isolation
Even if they come in contact, they can’t
mate if they breed at different times.
Behavioral isolation
Even if they breed at the same time, they
will not mate if they are not attracted to
one another.
Mechanical isolation
Even if they attract one another, they
cannot mate if they are not physically
compatible.
Gametic isolation
Even if they are physically compatible, an
embryo will not form if the egg and sperm
do not fuse properly.
Hybrid invariability or infertility
Even if fertilization occurs successfully,
the offspring may not survive, or if it
survives, may not reproduce (e.g., mule).
Argument against evolution – missing links
The lack of fossil intermediates has been used as argument against the theory of evolution
There will always be missing links for some groups
However, as new fossils are discovered, the number of examples of fossil intermediates is diminishing
Homo neanderthalensis
Neanderthal-like traits appeared in Europe from 600 – 350 thousand years ago
Youngest Neanderthal are about 24 – 32 thousand years ago
What country had the most allele variation?
Sub-Saharan Africa
Modern Challenges to the Theory of Evolution (Intelligent Design or ID)
Certain features of living things (and the universe) are best explained by an intelligent cause (God) rather than a process such as natural selection
ID proposes that there are certain biochemical processes and structures that, being “irreducibly complex,” cannot have arisen through unguided natural processes
Most scientists argue that the unexplained is not necessarily unexplainable, and that “we don’t know yet” is a more appropriate response than invoking a cause outside of science
Understand How the Vertebrate Eye Works
Figure A: light entering the vertebrate retina (arrow) must pass through successive layers of blood vessels and nerves to reach the light-sensing cells on the far right. Signals from these cells then travel back (left) to the nerve cells nearer the surface of the retina, which travel along to the optic disk where they plunge into the retina, causing the blind spot (see eyeball above).
Is the vertebrate eye or the cephalopod eye a “better” design?
Both have a retina, lens, cornea and optic nerves, among many other structures.
In cephalopods, the light sensitive cells are in front of nervous tissue and blood vessels (opposite in vertebrates
In cephalopods, there is no blind spot
In cephalopods, the lens is moved backwards and forwards, whereas in vertebrate eyes the lens is stretched or relaxed to make it thicker or thinner
From an functional standpoint, cephalopod eyes are superior
Evolution does not operate as an engineer, it is more like a tinkerer
