Chapter 25 (6)
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What does our study of macroevolution tell us about how evolution works?
Evolution is like tinkering- a process in which new forms arise by the slight modification of existing forms. Even large changes can result from the gradual modification of existing structures or the slight modification of existing developmental genes.
Francois Jacob's view of __ harkens back to Darwin's concept of __. As new species form, novel and complex structures can arise as gradual modification of ancestral structures. In many cases, complex structures have evolvod in increments from simpler versions that performed the same basic function.
- descent with modification
True or False:
Throughout their evolutionary history, eyes retained their basic function of vision. But evolutionary novelties can also arise when structures that originally played one role gradually acquire a different one.
As __ gave rise to early mammals, bones that formerly comprised the jaw hinge were incorperated into the ear region of mammals, where they eventually took on a new function: __.
- transmission of sound
Structures that evolve in one context but become co-opted for anothe rufnction are sometiems called __ to distinguish them fromt eh __ origin of the original structure. Note that the concept of __ does not imply that a structure somehow evolves in anticipation of future use. __ cannot predict the future; it can only improve a structure in the context of its current utility. Novel features, such as the new jaw hige and ear bones of early mammals, can arise gradualyl via a series of intermediate stages.
- natural selection
What else can we learn from patterns of macroevolution?
o Consider evolutionary "trends" observed int eh __. For instance, some evolutionary lineages exhibit a trend toward larger or smaller body sizes.
Extracting a single evolutionary progression from the __can be misleading; however; it is like describing a bush as growing toward a single point by tracing only the branches that lead to that twiig.
__ can result in a real evolutionary trend even if some species counter the trend. One model of long-term trends view species as analogous to individuals: __ is their birth, __ is their death, and new species that diverge from them are their __. In this model, Stanley suggests that just as individual organisms undergo __, species undergo __.
- Branching evolution
- natural selection
- species selection
The species that endure the longest and generate the most new offsprign species determine the direction o fmajor evolutionary trends. THe __ suggests that "__" plays a role in __ similar to the role of differential reproductive success in __.
- species selection model
- differential speciation success
Evolutionary trends can also result directly from __. Whatever itss cause, an evolutionary trend does not imply that there is some intrinsic drive toward a particular __. __ is the resutl of the interactions between organisms and their current environments; if environmental conditions change, an evolutionary trend may cease or even reverse itself. The cumulative effect of these ongoing interactions between organisms and their environments is enormous: It is through them that the staggering diversint of life - Darwin's "__"- has arisen.
- natural seleciton
- endless forms most beautiful
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