Flashcards in adaption Deck (49):
a change or the process of change by which an organism or species becomes better suited to its environment
when does adaption occur
hone an organism displays traits that allow it to live in a particular environment--> all organisms are
all organisms are..
adapted to their environment
Lamarck and Erasmus Darwin emphasised the role of inheritance in explaining similarities between organisms. Both argued that modifications were gradual and not random, but arose in response to an organisms environment i.e. they adapted
what idea of charles Darwin brought the idea of adaption to the forefront of evolutionary biology
Neo-Darwinists theory- led by RA fisher, tied the concept of fitness (reproductive success) to those of adaption and natural selection
role of natural selection in adaption
if the rate of mutation or drift balances selective pressure then it might appear that the population is not under selection
explores possibilites, NS defines traits that a re adaptive
accumulation of deleterious mutations (which can be removed by sexual reproduction and recombination
over time pop. move toward local peaks or optima- the process is dynamic and promoted by mutations and is counteracted by drift and introgression
what promotes adaption
-moderate mutation rate
-a small amount of gene flow
what prevents adaption
-large amounts of gene flow
Therefore small populations have less potential for adaption
the fundamental niche includes
the total range of environmental conditions that are suitable for existence without the influence of interspecific competition or predation from other species
the realised niche
describes the part of the fundamental niche occupied by the species
local adaption and NS
any widespread population is likely to experience diff environmental conditions
-as a consequence it will soon consist of a number of sub-population that differs slightly, even considerably
e.g. rat snake, has geographic 'race', that still share a common gene pool
example of adaption: moths
Evolution of moths has been studied greatly over the past 200 years. Originally the vast majority had light coloration for camouflage (light colored trees). However due to widespread pollution during the industrial revolution, many of the lichens died out and the trees which peppered moth rested on became blackened by soot, causing most of the light-colored moths to die off. Dark colored moths flourished.
¬ Light colored moths (typica) vs. Dark colored, or melanic moths (carbonaria) flourished.
¬ The first cabronaria moth was recorded by Edleston in Manchester 1848, and over the subsequent years it increased in frequency.
any change in the environment is likely to..
lead to local adaption
populations consistent of sub-populations because..
any widespread pop. is likely to experience diff environmental conditions in diff parts of its range
a sudden change from one generation to the next, this is large or very large, in comparison with eh usual variation of an organism.
Darwin sad that the evolutionary process must occur gradually, not in salutation, since saltation are not presently obsessed and extreme deviation from the usual would be more likely to be selected against
who disagreed with the theory of saltationism
Darwin, since saltation are not presently observed and extreme deviations from the usual phenotypic variation would be more likely to be selected against
most major animal group appear for the first time in fossil record some 545million years ago (on the geologic sale this is a relatively short time period)--> a time known as the cambrian explosion
There was once many more body plans
- 545mya a sudden diversity of body plans took place
evidence for cambrian explosion
many strange fossils have been found and can be dated to around 545 mya
what leads to macro evolution
advocates of salvationism deny the
Darwinian idea of slowly and gradually growing divergence of character as being the only source of the evolutionary process
sudden discontinuous ad crucial changes -macro mutations
macro evolutions are said to be responsible for the appearance
if new higher taxi including class and order
microevolution is thought to be responsible for
the fine adaption below the species level
hopeful monster hypothesis
suggests that major evolutionary transformation have occurred in large leaps between species due to macromutation
micro/macroevolution is characterised by two extremes
1. gradualism- evolution generally occurs uniformly and by steady and gradual transformations
2. punctuated equilibrium- evolution is marked by isolated episodes of rapid speciation between long period of little or no change
evolution generally occurs uniformly and by steady and gradual transformations
evolution is marked by isolated episodes of rapid speciation between long periods of little or no change
we can look at homologous structures found in the fossils of extinct species and
infer their function by looking at homologues structures in species that do exist eg. claws of dogs and cats have similar functions and structures
why must we take great care in establishing function of traits found in extinct species
analogous structures in unrelated species e.g. fns on fish, whales and cuttle fish where there is no common descent
similarity by common descent, similar function and form, similar development trajectory
diff ancestry, same function, diff developmental trajectory
adaptation that involves new uses for existing traits
e.g. malleus and incus wer originally part of the lower jaw of reptiles required for chewing
co-opted traits are the same as
traits may be selected for because they are linked to something else. e.g. a certain unuseful gene may be linked to a very useful gene
e.g. genetic hitchhiking occurs when an allele changes frequency not because itself is under NS, but because it is near another gene that is undergoing nS
believed evolutionary solutions are not optimal
example of an imperfect design (Dr Pangloss)
te male urogenital system.
during the evolution of mammals, testes moved from an internal position to a specialised structure outside the body, the scrotum
o Whilst the sperm duct passes ventral to the ureter, the testis migrates dorsal to the ureter during development, requiring a lengthening, not a shortening of the sperm duct
o A more efficient design would be migration of the testis on the same side of the ureters the sperm duct
once a pathway of progressive adaptations begins
reversals may become competitively disadvantageous or diff to achieve
evolution is not reversible i.e. structures or function discarded during the course of evolution do not reappear in a given line of that organism
criticism of the 'adaptionist adgenda'
adaptationists seek to find adaptive explanation for every characteristic of an organism, however some things ar not 'for' the 'purpose' etc they seem to be filling.
Somethings that exist are not adaptive- selectively neutral e.g. ear lobe
more harmful than helpful, in contrast with an adaptation, which is more helpful than harmful.
sickle cell and maladaptations
o Heterozygosity (HA/HS) or sickle trait leads to some resistance to malaria infection. fitness advantage
o Homozygosity (HS/HS) however leads to premature death
In one setting the trait is advantageous, in another its deleterious and maladaptive.
summary of adaption
occurs when an organism displays traits that allow it to live in a particular environment - all organisms are adapted.
-adaptation is a by-product of NS
-requires a balance between mutation , genetic drift and introgression
-there has previously been much greater diversity
-evolutnitonary solutions ar imperfect, not optimal
-we have to be wary of speculation and just so stories
there are many ideas about adaption since
there are many evolutionary biologists
evolution of the Eye-Eye
Some scientists think this is how the eye has evolved:
o Simple light sensitive spot on the skin of some ancestral creature gave it some tiny survival advantage, perhaps allowing it to evade a predator. Random changes then created a depression in the light sensitive patch, a deepening pit that made “vision” a little sharper. At the same time, the pits opening gradually narrowed, so light entered through a small aperture, like a pinhole camera.
o Every change gave a survival advantage, no matter how slight. Eventually the light sensitive spot evolved into a retina, the layer of cells and pigment at the back of the human eye. Over time a lens formed at the front of the eye
o In fact, eyes corresponding to every stage in this sequence have been found in existing living species. The existence of this range of less complex light-sensitive structures supports scientist hypotheses about how complex eyes like our could evolve.
o The evolution of the eye is estimated to have taken 364,000 years.