Studied by 0 people
Looks like no one added any tags here yet for you.
biological species concept
a group of organisms that can interbreed and produce fertile offspring in natural conditions
limitations: asexual reproduction, and hybridization (some species can interbreed and produce viable offspring (eg. canids), which complicates the definition)
morphological species concept
a species is defined based on physical characteristics and structural features
limitations: convergent evolution (organisms that are not closely related may appear similar (mimicry) leading to misclassification), variation within species ( there can be significant variability within a species that may lead to misidentification)
reproductive isolating factors
mechanisms that prevent species from interbreeding, thus maintaining species boundaries
prezygotic factor
prevent mating or fertilization from occurring
habitat isolation- species live in different habitats and don't meet
temporal isolation- species breed at different times of the day or year
behavioral isolation- differences in mating behaviors or rituals prevent species from mating
mechanical isolation- incompatible reproductive organs prevent successful mating
gametic isolation- even if mating occurs, the sperm and egg are incompatible
postzygotic factors
these occur after fertilization and affect the viability or reproductive capability of the offspring
hybrid inviability- hybrids don't develop properly or die early
hybrid stability- hybrids are sterile (eg mules)
hybrid breakdown- first-gen hybrids are viable and fertile, but their offspring are inviable or sterile
3 key steps to speciation
isolation, divergence (via natural selection, mutation, genetic drift, etc.), reproductive isolation
allopatric speciation
when a population becomes isolated from the rest of its species and eventually evolves into a new species
sympatric speciation
when a new species evolves from an ancestral species while both continue to live in the same geographic area
vicariance
occurs when a physical barrier (like a mountain range or river) arises and divides a population into 2 or more isolated groups
dispersal
when species form new species through movement and expansion into new areas
why is allopatric speciation more common than sympatric speciation?
geographic barriers- physical barriers are prevalent in nature and can easily separate pops, leading to isolation and divergence
reduced gene flow- isolation minimizes gene flow between populations, allowing for more significant genetic differentiation without the mixing that can occur in sympatric settings
strong selective pressures- isolated populations often face different environmental pressures, driving divergent evolution more effectively than in overlapping habitats where species interact closely
stable environments- in many cases, stable geographic regions promote sustained evolutionary changes over time
how does sympatric speciation generally occur in animals?
disruptive selection- environmental factors or changes lead to differing selective pressures on individuals within a pop (eg darwins finches, individuals with larger beaks favored)
behavioral isolation- differences in mating behaviors, preferences, or timing can arise as certain individuals prefer to mate with others that exhibit specific traits.
genetic divergence- over time, the populations accumulate genetic differences, leading to reproductive isolating mechanisms
reproductive isolation- eventually, even if individuals from the diverged groups come into contact, they can no longer interbreed successfully
how does sympatric speciation generally occur in plants?
hybridization- two different species interbreed, producing hybrid offspring that may have advantages in certain environments
polyploidy- if the hybrid offspring undergo chromosome duplication (eg become tetraploid) they may be reproductively isolated from both parent species
disruptive selection- hybrid plants may occupy different ecological niches, leading to further divergence and the establishment of new species
instantaneous speciation by hybridization
occurs when 2 distinct species produce offspring with unique genetic compositions that are reproductively isolated from both parent species
what is the ploidy of gametes made by plants?
diploid (2N) plant: produces haploid (N) gametes
tetraploid (4N) plant: produces diploid (2N) gametes
octoploid (8N) plant: produces tetraploid (4N) gametes
autopolyploidy
occurs when an individual has multiple sets of chromosomes derived from the same species (eg a diploid plant undergoes chromosome duplication to become tetraploid)
allopolyploidy
involves hybridization between 2 different species, followed by chromosome duplication. the resultant individual had sets of chromosomes from both parent species (eg a hybrid between a diploid species and another species, resulting in a polyploid)
why would an autotetraploid be reproductively isolated from its diploid ancestor?
gamete incompatibility- the autotetraploid produces diploid gametes, while the diploid ancestor produces haploid gametes. When they mate, the resulting offspring would be triploid (3N), which is typically sterile due to irregularities in chromosome pairing during meiosis
different chromosome numbers- the difference in chromosome numbers leads to difficulties in pairing and segregation during reproduction, creating a barrier to successful interbreeding
phylogenetic trees
diagrams that depict the evolutionary relationships among various biological species or entities based on their genetic or morphological characteristics
determining relatedness- to assess how closely taxa are related, look at the nodes. the more recent the common ancestor (the node) shared between two taxa, the more closely related they are. For example, if two taxa share a node that is more recent than that of another taxon, they are more closely related to each other than to that other taxon.
monophyletic group
includes a common ancestor and all its descendants (e.g., birds and their ancestors). this is the ideal group in phylogenetics
paraphyletic group
includes a common ancestor and some, but not all, of its descendants (e.g., reptiles, excluding birds)
polyphyletic group
does not include the common ancestor but includes descendants from different lineages (e.g., warm-blooded animals like birds and mammals without their common ancestor)
what types of characters should you use when constructing phylogenetic trees?
homologous characters, which are traits inherited from a common ancestor
morphological traits- physical characteristics like bone structure or leaf shape
molecular data- DNA, RNA, or protein sequences that reflect genetic relationships
ancestral characters
traits that were present in the common ancestor of a group (e.g., vertebrae in vertebrates)
derived characters
traits that evolved after the common ancestor and are specific to certain lineages (e.g., feathers in birds)
outgroup
a species or group that is outside the group of interest (the ingroup)
Establish polarity: Help determine which traits are ancestral and which are derived by providing a point of comparison.
Root the tree: Allow for the identification of the direction of evolution among characters, helping to clarify relationships within the ingroup.
background extinction
the normal rate of species extinction that occurs over geological time due to natural processes such as competition, predation, and environmental changes
caused by
ecological interactions (competition, predation)
habitat loss due to gradual environmental changes
climate fluctuation
mass extinction
relatively rapid event that results in the widespread and significant loss of biodiversity, with a substantial number of species going extinct in a relatively short geological time frame (less than 2 million years)
catastrophic events (eg asteroids, volcanos)
major climate changes (eg ice ages)
ocean anoxia (depletion of oxygen in oceans)
habitat destruction on a global scale
how many mass extinctions have there been? which was largest in terms of species that went extinct?
there have been 5 major mass extinctions. the largest was the permian-triassic extinction event
permian-triassic extinction
252 million years ago, marking the boundary between the permian and triassic periods of the paleozoic and mesozoic eras
what do experts believe to be the main cause of the end-Cretaceous extinction?
asteroid impact- asteroid struck the yucatan peninsula, creating the shicxulub crater- led to firestorms, tsunamis, and ash that blocked sunlight, reducing photosynthesis
volcanic activity- volcanos in india released vast amounts of volcanic gases. led to
acid rain
climate cooling and prolonged warning
environmental changes- the combination of the impact and volcanic activity led to severe disruptions in climate and ecosystems, ultimately causing food chain collapses and widespread extinctions
what do experts believe to be the main cause of the permian extinction?
volcanism- the siberian traps produce massive volcanic eruptions that release volcanic gasses
carbon dioxide- lead to global warming
sulfur dioxide- lead to acid rain and decrease in temps
ocean anoxia- depletion of oxygen levels in deep oceans, making environments inhospitable for marine life
methane release- the warming may have triggered the release of methane hydrates from ocean sediments, further exacerbating climate change
loss of biodiversity- as habitats changed and conditions became inhospitable, many species could not adapt quickly enough, leading to widespread extinctions across marine and terrestrial environments
what is adaptive radiation? how does adaptive radiation come into play after mass extinctions?
organisms diversify rapidly into a wide variety of forms to adapt to different environments or ecological niches
after mass extinctions, surviving species often undergo adaptive radiation because
the extinction event creates vacant ecological niches
reduced competition allows the survivors to exploit new resources
rapid evolutionary changes occur as species adapt to new environments
when did primates evolve?
65 million years ago during the late cretaceous or early paleogene periods
which primate are humans most closely related to? When did we diverge from this group?
chimpanzees and bonobos. our divergence from the common ancestor occurred around 5-7 million years ago
how similar are we genetically to this group of primates (at the chromosome level; this is the same as the other great apes)?
humans share around 98-99% of their DNA with chimpanzees at the genetic level. the high similarity extends to chromosome structure, with both species having the same number of chromosomes (46) but differing in specific arrangements and sequences
what is the oldest known hominin genus?
sahelanthropus, dating to about 7 mil years ago
which evolved first in human evolution, large brains or bipedalism?
bipedalism evolved first, established by the time of early hominins like australopithecus
members of which hominin genus showed the first clear evidence of bipedalism as a primary mode of locomotion?
the genus australopithecus showed the first clear evidence of bipedalism as a primary mode of locomotion, particularly with fossils such as Australopithecus afarensis (e.g., "Lucy").
which hominin species was the first to show body proportions like modern humans?
homo erectus, with a more elongated limb structure suitable fo efficient bipedalism
which hominin species was the first to migrate out of Africa?
homo erectus, spreading into asia and europe around 1.8 million years ago
when and where did the first Homo sapiens evolve?
in africa around 200,000-300,000 years ago
what is the relationship between H. sapiens and H. neanderthalensis?
they share a common ancestor and coexisted for a period. genetic studies indicate that modern-day non-african populations carry around 1-2% neanderthal DNA, suggesting interbreeding
which hominin species could H. sapiens have coexisted with?
homo neanderthalensis, homo erectus, and denisovans
“out of africa” model
modern humans migrated from africa in several waves, replacing or interbreeding with local hominin populations
supporting evidence
fossil evidence of early homo sapiens in africa
genetic studies show lower diversity in non-African populations compared to African populations
Archaeological findings of early human tools and sites outside Africa dating to around the same period of migration.
which hominin species hybridized with H. sapiens?
homo neanderthalensis and denisovans both hybridized with homo sapiens, contributing to the genetic diversity of modern non-african populations
how does the relative amount of genetic variation between individuals within a conventionally defined racial group compare to that between groups?
the relative amount of genetic variation among individuals within a conventionally defined racial group is genetically greater than that between groups. studies have shown that about 85-90% of genetic variation exists within populations, while only 10-15% is attributable to differences between groups. This indicates that traditional racial categories do not reflect significant genetic distinctions.
why are there no genetically unique/discrete lineages within H. sapiens (i.e., no biological races)?
Gene Flow: Throughout human history, populations have migrated and interbred, leading to genetic mixing that blurs the lines between groups.
Clinal Variation: Genetic traits tend to vary gradually across geographic areas rather than being distinctly grouped, resulting in continuous variation rather than discrete categories.
Recent Common Ancestry: All modern humans share a relatively recent common ancestry, which diminishes the potential for distinct biological races.
are complex traits, such as hypertension, more common in certain “races” than others?
Complex traits such as hypertension can appear more common in certain populations, but this is often influenced by a combination of genetic, environmental, and socio-economic factors rather than race itself. The higher prevalence of such traits in certain groups can often be traced to shared environments, lifestyles, and historical factors (e.g., diet, access to healthcare) rather than intrinsic genetic differences.
why do you think there more genetic variation within sub-Saharan African human populations than human populations from other places?
sub-Saharan Africa exhibits more genetic variation than other regions primarily due to:
Origin of Modern Humans: Modern humans originated in Africa, and as populations migrated out, they carried only a subset of the genetic diversity present in the continent.
Longer Duration of Human Presence: Populations in Africa have had more time to accumulate genetic diversity due to longer evolutionary history and larger population sizes.
Environmental Diversity: The wide range of environments and ecological niches within Africa has led to diverse adaptations and consequently greater genetic variation.
which hominin species that we discussed in lecture evolved outside of Africa?
homo neanderthalensis
