Week 7 Flashcards
Describe the Savannah hypothesis
The genus Homo emerged at a time of climate change and expansion of open Savannah habitats
According to the Savannah hypothesis, traits that are considered “human” are…
Adaptive solutions to life in the savannah = hot and dry climates
Define a niche
Every selective pressure to which a population is exposed
Are there genes for inheritance of chronic disease?
Yes, but they are negligible compared to how much chronic disease is actually prevalent in society
Are there genes for life history traits?
Yes, and they are substantial!
Give examples of life history traits we know are controlled by genes (5)
- birth weight
- infant growth rate
- pubertal timing
- adult height
- adult weight
Describe a major goal of the human genome project
Pre 1990s, the human niche was considered to be relatively unchanging and experts thought the main selective pressures on humans would be genetic
Looked for genes which could be the basis of chronic disease!
In the long term, climate appears to be relatively (stable/unstable), but in the short term, it is actually (stable/unstable)
Stable, unstable
Describe the changing temperature of the planet over the last 60 kya
Rapid shifts in temperature
What would the main selective pressure have been against hominins in a changing climate?
No conditions to truly adapt to; need to adapt to instability
How did natural selection alter the human risk management system?
Shaped the capacity for generating risk-management systems: increased capacity for risk-management
What is bet-hedging?
Adapting based on odds, not necessarily based on the environment
What are the 2 main kinds of bet-hedging?
Diversifying and conservative
Describe diversifying bet-hedging
Offspring will have different phenotypes in the hopes that some will be well-suited for the environment. The population doesn’t converge on one pheotype
Describe conservative bet-hedging
Pick one average phenotype and stick to it. The offspring might not be the best adapted to the environment but they probably won’t be the worse either
Describe reversibility in regards to a strategy for risk-management
Reduced life-course commitment to any one phenotype = phenotypic plasticity
A periodic fast-onset warming event is called…
El Nino: causes severe floods
A periodic fast-onset cooling event is called…
La Nina: can cause severe drought
After El Nino periods, why does disease burden increase?
Stress might cause switch to faster life histories, and flooding will cause spread of disease from disease vectors such as mice or rats
What are 2 huge drivers of ecological instability which affect human life history strategies?
Infectious disease and food availability
When do homo sapiens appear in the fossil record, roughly?
2 million years ago, ish
What (generally) was happening to other species 2 million years ago, and what does this reflect?
Shorter body size (diverted investments), flexible behaviour, specialists tend to go extinct around then = fast life history! environmental volatility
Describe the specialist/generalist behaviour of Paranthropus
Specialized in what they eat - similar to gorillas now. They also die out around 2 million years ago (remember, specialists die at this time)
El nino and la nina events are referred to as…
Enso cycles
Give five examples of adaptive responses to enso cycles in more generalist species
- Long lifespan: can miss a breeding season if conditions are suboptimal
- rapid reproduction when things are good
- Cooperative breeding (makes reproduction more viable in poor years)
- Slow and plastic early life growth (to tolerate unexpected ecological deterioration)
- The capacity to store energy
Describe how sociality can be an energy store in primates
Social loans: lending and returning favours, social relationships - safety nets for if you fall on hard times
Describe how cooperative breeding can be an energy store in primates
If you die, your genes live on through your offspring and someone else will take care of them to ensure the genes are passed on to the next generation
Describe how the human life history strategy compares to other primates. What species is its similar to?
Generally different than other primates, tends to be more similar to species which are adapted to changing environments
What 3 traits of the human life history strategy are unusual compared to other primates?
- slow growth and ageing, but fast reproduction
- high adiposity and large brain
- sensitive insulin metabolism
What are the 4 levels of adaptation?
- environment
- culture and technology
- physiology and development
- genetic adaptation
The dogma of evolution of brain size states that in relation to life history strategy…
Brain size evolved first
Why would it make sense for life history to evolve prior to our increase in brain size?
Big brain was a biologically favoured trait, and life history reorganization could be reorganized to provide the energy for this huge advantage, then brain size increase could have evolved
What is happening to the climate that homo sapiens evolved in in the short term?
Large and frequent climatic fluctuations
Evolution of this important trait coincides with the start of fluctuating global climate
Brain size: growth after the onset of these fluctuations is exponential
In a map of genetic distance, humans are (close/different) in genome
Extremely close despite intense phenotypic variations!
One (of many) possible explanations for the human phenotypic variation present in the global population is…
Our flexibility in life history to adapt to different environments
What life history strategy does an organism use if the environment is constantly changing?
Strategy of no strategy: favour metabolic adaptability
If glucose homeostasis is so important, why isn’t it more canalized?
It is the strategy to which we have adapted: metabolic adaptability - glucose/insulin is the mechanism of diverting resources to different organs
What could be an explanation for why chronic disease doesn’t have much of a genetic basis?
Chronic disease is a response to plasticity in insulin metabolism - particularly when it is being overloaded
Describe the obesogenic niche
Prevailing economic policies subject individuals to invasive cues favouring fat accumulation
Genetic variability may affect susceptibility to chronic disease, but what other key element is required for a diseased phenotype?
The obesogenic niche - lifestyle!
Define the factors which make up the obesogenic niche (do not list factors)
The total sum of modern selection pressures: diet, activity, pressure to consume, physical and social factors
Is the obesogenic niche exclusive to humans?
It is possible in other animals (re: fat dogs, cattle) but it is unnatural for them due to their lack of industrialization
