Lec 2 slides and reading Flashcards
evolutionary change
-relies on mutations of organisms
-caused by stable changes in genetic material, transmitted from parent to offspring
-other processes (natural selection and genetic drift) cause mutations to increase in frequency within the pop
-combined effects of mutation, natural selection and genetic drift cause changes in the composition of a population
-over a long period of time, they alter the pop. genetic makeup and can change species’ characteristics from its ancestors
genetic drift
random changes resulting from selectively neutral variability
Biological evolution involves changes over time in the characteristics of populations of living organisms
-Evolution can be studied during a human lifetime, when changes occur in a single character (increase in freq. of strains of bacteria resistant to penicillin)
-On the extreme side, evolution involves events such as the emergence of a major new design of organisms, which may take millions of years and require changes in different characteristics (transition from reptiles to mammals)
what does evolutionary change rely on?
relies on the appearance of new variant forms of organisms
-Caused by stable changes in the genetic material that can be transmitted from parent to offspring
effects of mutations on characteristics of an organism
(some have no detectable effects- exist only to study the genetic material directly, some have small effects - eye colour change, some have drastic changes - a leg grows on a fly’s head)
An altered state of a character as a result of a mutation, such as antibiotic resistance, occurs in one individual and is restricted to a small part of a pop. for many generations
how can a mutation result in evolutionary change
other processes must cause it to increase in frequency within the population
natural selection
process that leads to evolutionary changes in structure, functioning and behaviour of organisms
theory of evolution by natural selection
-Many more individuals of a species are born than can normally live to maturity and breed successfully, so that there is a struggle for existence
-There is individual variation in innumerable characteristics of the pop., some of which may affect an individual’s ability to survive and reproduce. The successful parents of a given gen. may therefore differ from the pop.
-There is likely to be a hereditary component to much of this variation, so that the characteristics of the offspring of the successful parents will differ from the characteristics of the previous gen. in a similar way to their parents
effects of NS over long periods of time
-If this process continues from gen to gen, there will be a gradual transformation of the pop. such that the frequencies of characteristics associated with greater survival ability or reproductive success increases over time
-These altered characteristics originated by mutation, but mutations affecting a trait appears all the time regardless of whether or not they are favoured by selection
-Most mutations either have no effects on the organism or reduce its ability to survive or reproduce and are removed from pop. by NS against them
-It’s the process of increase in frequency of variants that improve survival or reproductive success that explains the evolution of adaptive characteristics, since better performance of their body or behaviour contributes to greater survival or reproductive success
where is NS more likely to occur
more likely if a pop. is exposed to a changed environment, where a different set of characteristics is favoured from those already established by selection
genetic drift (explanation)
-how species come to differ with respect to traits with little or no influence on the survival or reproductive success of their possessors, and which are therefore NOTsubject to NS
-This is true for the large category of changes in the genetic material which have little or no effect on the organism’s structure or functioning
-If there’s selectively neutral variability, so that on avg there are no differences in survival or fertility among diff individuals, it is still possible for the offspring gen. to DIFFER slightly from the parent gen.
This is due to the absence of selection, the genes in the pop. of offspring are a random sample of the genes present in the parental pop.
Real pop. are finite in size and so the composition of the offspring pop. will differ somewhat from the parents gen
Even the biggest biological pop, such as bacteria are finite, so that genetic drift will ALWAYS operate
how do the processes of evolution cause changes in the composition of a population
-Over a long period of time, these cumulative effects alter the pop genetic make-up and can greatly change the species’ characteristics from its ancestors
-In thinking about evolution, it makes sense to consider 2 pop. of sexually reproducing organisms as different species if they cannot interbreed with each other, so that their evolutionary fates are independent
-Migration tends to prevent the genetic make-up of different pop. of the same species from diverging very much
what must the formation of a new species involve?
Once such barriers form, the pop can diverge under mutation, selection and genetic drift
This process of divergence ultimately leads to the diversity of life
If we understand how barriers to
interbreeding evolve, and how populations subsequently diverge, we will understand the origin of species
Paley’s argument from design
universe is intricate and complex (like the watch) and couldn’t have been created by chance
-thus, universe implies an intelligent designer
-must look at purpose of intricate things in universe as evidence for a designer
-appearance of “design” in nature can be explained by existence of “designer”
Lamarck
-first to offer a mechanism for evolution of species
-explained evolution as a process of adaptation
-came up with hypothesis of ‘inheritance of acquired traits”
