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\b[There is no general basis for assigning behaviour a smaller causal role in macroevolution. Its immediate effects are usually easier to measure within populations, but those effects can alter lineage formation and persistence.] The comparison needs a definition of “contribution”: the proportion of evolutionary changes initiated by behaviour, their magnitude, their necessity, or the strength of available evidence would give different answers. <Microevolution> concerns change within <biological populations>; <macroevolution> concerns patterns at and above the level of <species>, including <speciation>, <adaptive radiation> and <extinction>. They are connected processes with different objects of measurement.
At the population scale, <animal behaviour> changes who encounters which resources, survives, mates and reproduces. <Habitat preference> changes exposure to ecological <natural selection>; <mate choice> changes reproductive success; <dispersal> changes the spatial distribution of <alleles>. Behaviour can therefore affect the evolution of other traits even if the behaviour itself does not evolve. Conversely, an environmentally induced change in behaviour is not automatically evolutionary change. <Learning> and <phenotypic plasticity> can occur within one lifetime, whereas an evolutionary claim requires persistence through inherited differences or an explicitly specified process of <cultural inheritance>.
A simple <population genetics> calculation makes the distinction concrete. Let $x_i$ be an individual's number of copies of a focal <allele>, $w_i$ its contribution to reproduction, and $p=\mathbb E(x)/2$. With unbiased <Mendelian segregation> and no other transmission change, the expected <allele frequency> after selection satisfies:
$$
p'-p=\frac{\operatorname{Cov}(w,x)}{2\mathbb E(w)}.
$$
Behaviour can change $w$ and thereby change the <covariance>, whether selection acts directly on a behavioural difference or on another trait whose consequences depend on behaviour. The equation does not imply that every correlation between a behaviour and reproductive success is genetic: common environment, age and condition can generate such correlations. A <common garden experiment>, a <pedigree> and measurements across environments help identify the inherited component.
Behaviour may expose a previously uncommon <phenotype> to selection. Foraging in a new habitat can make a different resource profitable, after which selection can refine feeding structures or behavioural response thresholds. Laboratory competitions between spadefoot tadpoles from populations differing in expression of a carnivore ecomorph found differences in resource capture and morphology consistent with adaptive refinement of a formerly plastic response. Expression without the inducing cue also supported <genetic assimilation>. <Plasticity-led evolution: evaluating the key prediction of frequency-dependent adaptation by Nicholas A. Levis and David W. Pfennig>[laboratory competition and expression of the carnivore ecomorph in spadefoot tadpoles]{ref} This is a combination of behaviour and development, not proof that behaviour universally comes first. <Genetic accommodation> requires evolution of the response, rather than assuming that an acquired habit is copied directly into <DNA>.
The opposite effect is also possible. Through <phenotypic buffering>, movement or flexible foraging may keep individuals in suitable conditions and reduce selection on physiological or morphological differences. Thus flexibility can promote occupation of a new environment, delay genetic divergence, or prevent local <extinction>. The sign depends on whether behaviour changes exposure to selection or allows animals to avoid it. A short-term adaptive response is consequently not evidence for a universal acceleration of evolutionary change.
At the boundary between populations and species, the behavioural effects are particularly direct. <Assortative mating>, host choice and learned signals can reduce <gene flow>. In the Big Bird lineage of <Darwin's finches>, field observations and genomic ancestry documented an immigrant <Geospiza conirostris> breeding with a resident <Geospiza fortis> and the formation of an endogamous descendant lineage. Song and distinctive morphology contributed to mating within that lineage. <Rapid hybrid speciation in Darwin's finches by Sangeet Lamichhaney and others>[Science 359, pp. 224–228; immigrant ancestry, endogamy and the Big Bird lineage]{ref} The evidence links immigration, <hybridization> and mate recognition to rapid reproductive separation; it does not show that song alone caused isolation or establish the lineage's indefinite future persistence. Nevertheless, behaviour participates in an event conventionally classified as <macroevolution>.
Over longer periods, these mechanisms can influence the rates of lineage origination and disappearance. Behaviour that permits colonization can expose populations to ecological opportunity and eventual <adaptive radiation>. Specialization in host use or mating signals can strengthen reproductive barriers. Conversely, costly reproductive competition or inflexible resource use can increase vulnerability. In fossil <ostracods>, greater sexual dimorphism was associated with greater estimated <extinction> risk, using carapace differences as a proxy for male reproductive investment. <High male sexual investment as a driver of extinction in fossil ostracods by Maria João Fernandes Martins and others>[Nature 556, pp. 366–369; dimorphism as a proxy and fossil extinction estimates]{ref} This is unusually direct evidence about actual lineage loss, but an anatomical proxy does not preserve courtship or experimentally isolate <sexual selection> from every correlated attribute. It supports a possible connection rather than a general law that strong <sexual selection> causes <extinction>.
Evaluating a claim about relative importance also requires correcting unequal evidence. Contemporary behavioural experiments can manipulate cues and follow reproduction, whereas most ancient behaviour must be inferred from traces, anatomy or living relatives. Living-only comparative studies omit extinct lineages and can confuse a trait associated with diversification with a trait that evolved after diversification. Comparisons should allow for shared ancestry, environmental opportunity and incomplete sampling, and distinguish an increased <speciation> rate from a reduced <extinction> rate. Counting observed behavioural changes over years against anatomical changes over millions of years is not a meaningful common denominator.
\b[Behaviour has demonstrable population-level effects and plausible, sometimes well-documented effects on <speciation> and <extinction>. The stronger conclusion is that its evolutionary influence is context-dependent and transmitted across scales, while the evidence becomes harder to identify over deep time.] A qualified statement about evidential accessibility is defensible; a general ranking of causal importance is not.
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