Lec 4 slides and reading notes Flashcards
fossil record
only direct source of info on the history of life and provides strong evidence for evolution
Follows same principle of uniformitarianism that’s applied by geologists to the history of the structure of the Earth
uniformitarianism
Uniformitarianism associated with James Hutton and Charles Lyell
- The application to the history of the structure of the Earth
Geological change over time reflects the operation of the law of physics, which are unchanging
Uniformitarianism assumption in geology implies that the present-day constitution of the Earth’s surface reflects the cumulative action of processes of formation of new rocks by volcanic action and deposition of sediments
Darwin found the Chilean earthquake resulted in the permanent elevation of the land
impact of geology on evolution
Geology helps interpret the structure of Earth and the events that led to the shaping of the Earth
-Order of these events can be established by the principle of stratigraphy
-Fossils represent the preserved remains of long-dead plants and animals
-Types of fossils found in sedimentary rock layer provides evidence about environment that prevailed when it was laid down
-Using the principle that older rocks must normally lie below younger ones, the comparison of the succession of strata enabled geologists to reconstruct sequences of strata that were laid down through immense periods of time
-Helps determine the major divisions of geological time
fossil record and soft parts of fossils
To interpret it correctly, necessary to understand how fossils are formed, and how scientists study them
When a plant, animal or microbe dies, soft parts usually decay rapidly
Only in unusual environments(arid atmospheres of desert or preservative chemicals in amber) are the microbes responsible for decay unable to break down soft parts
fossil record and underwater fossils
Fossilization more likely to happen under water, where the deposition of sediment and precipitation of minerals occur at bottom of seas, lakes, etc
Remains that sink to bottom can turn into fossils although chance that this happens is small
Marine organisms in shallow seas (sediments continuously formed) have best fossil record and flying creatures have the worst
how can the fossil record be incomplete
Fossil record can be incomplete sometimes due to some species leaving no fossil record because of their low abundance and great depth where they live (e.g. coelacanth fish)
Gaps in fossil record mean that it’s rare to have a long-continued series of remains showing the more or less continuous changes which are expected under the hypothesis of evolution
In most cases, new groups of animals or plants make their first appearance in the fossil record without any obvious links to earlier forms
E.g. Cambrian explosion → most major groups of animals appear for the first time as fossils in the Cambrian period
darwin and the fossil record
Fossil record helps us find links between fossils and animals now
E.g. fossils link birds and dinosaurs together, fossil mammals found with forelimbs and reduced hindlimbs adapted to swimming
Darwin argued on the basis of anatomical similarities that humans were most closely related to gorillas and chimps, and therefore probably originated in Africa from an ancestor that also gave rise to apes
Species closely related to us, Homo and Homo neanderthalensis
Possible now to extract DNA for sequencing from bones or teeth of Neanderthals and Denisovans, which revealed that their sequences differ slightly more from ours than do the sequences of two different Homo sapiens individuals
End of Cambrian era
(evidence of major animal groups)
Devonian era
(evidence of freshwater life and primitive species, 1st land vertebrates)
Carboniferous era
(evidence of coral deposits, trees, vertebrates fully independent of water)
Permian era
(evidence of reptiles, insects, dinosaurs, extinction occurs)
Jurassic era
(evidence of mostly dinosaurs, and reptiles)
Cretaceous era
(evidence of flowering plants, extinction that took out dinosaurs occurs)
what does fossil record suggest about life before humans
Fossil record suggests that life started in the sea over 3 billion years ago and only single-celled organisms existed before that
Understandable from evolutionary perspective
Back then, evidence showed there was little oxygen in atmosphere
Consequent lack of protection from UV radiation by atmospheric ozone(formed from oxygen) would have prevented life on land or freshwater
Once oxygen built up (due to photosynthetic activities of early bacteria and algae), possibility of life on land grew
Evidence for increase in atmospheric oxygen levels during the period leading up to the Cambrian → allowed for the evolution of bigger and more complex animals
The rapid diversification of groups after the colonization of a new habitat (land invasion) or after extinction of a dominant rival group (dinosaurs) is expected on evolutionary principles
evolution on galapagos
flora and fauna of oceanic islands, such as Galapagos and Hawaiian islands, which geological evidence shows were formed by volcanic action and were never connected to a continent
According to evolution, the current inhabitants of those islands must be the descendants of individuals who were able to cross the vast distances separating the newly formed islands from nearest inhabited land
restrictions on evolution in oceanic islands
The difficulty of colonization of a remote piece of newly formed land means that few species will be able to establish themselves
Only types of organism that have characteristics that enable them to cross the ocean can become established
Even in the groups that are represented, there will be a highly random element to which species are present, because of the small number of species that arrive on the islands
Therefore evolution on such remote islands produces many forms of animals found nowhere else
Rampant evolution found on these groups of oceanic islands
darwin’s explanation for cause of evolution on islands
These observations can be explained if the colonist ancestors of these island species found themselves in environments free from established competitor species
This situation would permit the evolution of traits that adapted the colonists to new ways of life and allowed diversification of an ancestral species into several descendant species
E.g. evidence found that Darwin’s finches are closely related to species on mainland South America
The theory of evolution provides the answer to questions and research on island life has confirmed Darwin’s insights
genotype
genetic constitution of an organism
phenotype
-morphological, behavioural, biochemical traits
-feature of organism as observed
differential fitness
some forms are more successful at (surviving and) reproducing than others in a given environment
-heritable variants need to have differential fitness
sources of genetic variation
mutation, independent assortment, recombination (genetic variation modified)
mutation
stable change in the DNA sequence (any change at nucleotide level)
-occurs at low rate
characteristics of mutation
-mutation not directed toward an outcome by organism or by the environ.
-random with respect to effects on fitness
-change in genetic code has nothing to do with environ or fitness
-environ can affect mutation rate (mutagens, high temp)
-replication process increases in high temps
true or false: some (gene) mutations can cause an advantage in fitness
true
-in G6PD deficiency, causes severe anemia but also protects against malaria
how does recombination in meiosis further contribute to variation
synapsis of bivalents–>crossing over at chiasmata–> recombinant chromosomes
=new gene combo in some chromatids
preformationism theory (1700s)
spermists/ovists believed only one parent contributed to inheritance
theory of blending inheritance (1800s)
postulated that factors from both parents mix together irreversibly
what happens to a new mutation across generations
no way for it to be increased in frequency unless through inheritance
key conclusions from Mendel’s pea experiments
1) inheritance is determined by discrete particles (genes)
2) each diploid organism carries 2 copies (alleles) of each gene
-alleles can exhibit dominance/recessivity
-gametes contain only one allele per gene
3) gametes fuse to make offspring
-sperm/pollen fuses with egg/ovule
4) offspring inherit one gamete from each parent at random
-one allele per gene at random from each parent
quantitative traits affected by many factors
-complex polygenic inheritance
-environmental interactions
discrete variation
-mendelian genetics
-genes of major effect, dominance and recessiveness
-spread of alleles, change in allele frequency
continuous variation
-quantitative genetics (major environ. effects)
-many genes each with alleles of small effect, important environ. effect
-selection response as change in average trait value
particulate inheritance
Particulate inheritance is a concept in genetics that explains how traits are passed from parents to offspring. This theory, proposed by Gregor Mendel in the 19th century, suggests that inheritance is controlled by discrete units or “particles” (now known as genes). These particles retain their identity across generations, rather than blending together.
Key points of particulate inheritance:
Genes come in different versions called alleles, which can be dominant or recessive.
Each individual has two alleles for each gene, one inherited from each parent.
The combination of alleles determines the trait expressed, but the alleles themselves do not blend; they remain distinct.
This theory contrasts with the earlier idea of blending inheritance, which held that offspring traits were a smooth mix of the parents’ traits. Mendel’s experiments with pea plants demonstrated that traits could reappear in later generations, supporting the particulate theory of inheritance.
what problem does particulate inheritance solve for evolutionary biology?
Particulate inheritance solves a major problem in evolutionary biology by preserving genetic variation across generations, which is crucial for evolution by natural selection. Here’s how:
Problem with Blending Inheritance:
Before Gregor Mendel’s theory of particulate inheritance, the dominant idea was blending inheritance, which suggested that offspring traits were a mix or average of the parents’ traits. This posed a problem for evolutionary theory, specifically Darwin’s theory of natural selection. In a blending model:
Genetic variation would decrease over time, as offspring traits would continually blend.
Favorable traits that provided a survival advantage could eventually be diluted or lost as they mixed with less favorable traits in subsequent generations.
This would limit the capacity of populations to evolve new traits, which would hinder the process of natural selection and adaptation.
Solution by Particulate Inheritance:
Mendel’s concept of particulate inheritance solved this issue by showing that genes (discrete units of inheritance) do not blend but remain intact across generations. This preserves variation and allows for evolutionary processes like natural selection to work more effectively. Specifically:
Preservation of Variation: In particulate inheritance, even if a trait is not expressed in one generation (due to dominance or recessiveness), the genetic material is still present and can reappear in future generations. This maintains a pool of variation within a population.
Selection and Evolution: Favorable traits are passed down intact and can accumulate in a population without being diluted. As selection pressures act on these traits, populations can adapt to changing environments over time.
Recombination and Novel Traits: Sexual reproduction shuffles genes through recombination, which creates new combinations of traits while still keeping the individual genes intact. This process fuels genetic diversity, another key factor for evolution.
In short, particulate inheritance provides a mechanism by which genetic variation can be preserved, passed on, and acted upon by natural selection, thereby facilitating adaptive evolution.
