Hominin life history: reconstruction and evolution.

Note that the Eurasians are closer to modern humans.

J Anat. 2008 Apr;212(4):394- 425.

Robson SL, Wood B.

Department of Anthropology, University of Utah, Salt Lake City, UT
84112, USA. robson@…

In this review we attempt to reconstruct the evolutionary history
of hominin life history from extant and fossil evidence. We utilize
demographic life history theory and distinguish life history
variables, traits such as weaning, age at sexual maturity, and life
span, from life history-related variables such as body mass, brain
growth, and dental development. The latter are either linked with, or
can be used to make inferences about, life history, thus providing an
opportunity for estimating life history parameters in fossil taxa.

We compare the life history variables of modern great apes and
identify traits that are likely to be shared by the last common
ancestor of Pan-Homo and those likely to be derived in hominins. All
great apes exhibit slow life histories and we infer this to be true
of the last common ancestor of Pan-Homo and the stem hominin.

Modern human life histories are even slower, exhibiting distinctively
long post-menopausal life spans and later ages at maturity, pointing
to a reduction in adult mortality since the Pan-Homo split. We
suggest that lower adult mortality, distinctively short interbirth
intervals, and early weaning characteristic of modern humans are
derived features resulting from cooperative breeding.

We evaluate the fidelity of three life history-related variables,
body mass, brain growth and dental development, with the life history
parameters of living great apes. We found that body mass is the best
predictor of great ape life history events.

Brain growth trajectories and dental development and eruption
are weakly related proxies and inferences from them should be made
with caution. We evaluate the evidence of life history-related
variables available for extinct species and find that prior to the
transitional hominins there is no evidence of any hominin taxon
possessing a body size, brain size or aspects of dental development
much different from what we assume to be the primitive life history
pattern for the Pan-Homo clade.

Data for life history-related variables among the transitional
hominin grade are consistent and none agrees with a modern human
pattern. Aside from mean body mass, adult brain size, crown and root
formation times, and the timing and sequence of dental eruption of
Homo erectus are inconsistent with that of modern humans.

Homo antecessor fossil material suggests a brain size similar to that
of Homo erectus s. s., and crown formation times that are not yet
modern, though there is some evidence of modern human-like timing of
tooth formation and eruption.

The body sizes, brain sizes, and dental development of Homo
heidelbergensis and Homo neanderthalensis are consistent with a
modern human life history but samples are too small to be certain
that they have life histories within the modern human range.

As more life history-related variable information for hominin species
accumulates we are discovering that they can also have distinctive
life histories that do not conform to any living model. At least one
extinct hominin subclade, Paranthropus, has a pattern of dental life
history-related variables that most likely set it apart from the life
histories of both modern humans and chimpanzees.