Life History Theory In Depth

What is life history theory?

The framework in evolutionary biology that explains how organisms allocate their limited resources

What does the life history theory hypothesise?

That trade-offs between competing processes arise

Why do organisms face trade-offs?

Because they cannot invest maximally in all functions at once

What is the selfish brain hypothesis?

The simultaneous challenge of both cognitive and physical functions resulted in relative preservation of cognitive function over physical power output, showing that the body will prioritise encephalization over the muscular system. This may be an evolved trait as if we can think better we can make smarter decisions leading to survival

What does the life history theory involve?

The allocation of finite resources: energy, time, effort. These are key to biological activities such as growth, maintenance, reproduction, and parental care

What happens since resources are limited?

Organisms can't maximise everything at once so they evolve strategies that are shaped by natural selection to optimise timing and intensity of various life events

What are the different life strategies?

• Fast strategy

• Slow strategy

• Altricial

• Precocial

What does the fast strategy involve?

• Early reproduction

• More offspring

• Less investment per child

• Common in high-risk or unstable environments

• r-selected species such as rats, mice, frogs

• Generally small animals

What does the slow strategy involve?

• Delayed reproduction

• Fewer offspring

• More investment per child

• Favoured in stable, resource-rich environments

• k-selected species such as humans, apes, elephants

• Generally large animals such as mammals

What does the altricial life strategy involve?

• Eg. human infants

• Born underdeveloped

• Require intense care

• Such as humans that cannot walk and escape from predators so need to be carried by the parent

• Eg. Dogs and cats are born blind, deaf, and immobile and therefore need urgent care and attention from the parent

What does the precocial life strategy involve?

• Eg. horses

• More developed at birth

• Nedd less care

Are life history strategies fixed?

No, life history strategies are not fixed

What can life history strategies be shaped by?

• Environmental harshness (eg. high mortality risk can favour faster strategies)

• Predictability (unpredictable environments can often lead to riskier, fast strategies)

What are the different trade-offs?

Since resources are finite, organisms must make trade-offs

• Current vs future reproduction (eg. Having offspring now vs investing in survival to reproduce later)

• Quantity vs quality of offspring (eg. Many low-investment offspring vs few high-investment ones)

• Growth vs reproduction (investing energy into getting bigger vs reproducing sooner)

What are key life history traits?

• Age at first reproduction

• Number and size of offspring

• Frequency of reproduction

• Lifespan

• Parental investment