Contrary to current understanding, the brains of human newborns aren’t significantly less developed compared to other primate species but appear so because so much brain development happens after birth.
Brains of newborns aren't underdeveloped compared to other primates | UCL News - UCL – University College London
Scientists are revising what was believed about the state of development of a human baby's brain at birth compared to that of a newborn Chimpanzee - but not in a way that brings any comfort to creationists.
This research compares the brain development of a human baby with that of other apes because the scientists have no doubt that humans are apes, so comparisons are scientifically valid.
It had been thought that a newborn human's brain was underdeveloped, or altricial, compared to the other apes, but this paper shows that to be a false impression caused by the fact the a human baby's brain grows more quickly and becomes more complex than that of our close relatives, however, the starting point is very similar to that of a chimpanzee.
The paper by researchers Aida Gómez-Roblesa and Christos Nicolaou of the Department of Anthropology, University College London (UCL) together with colleagues Jeroen B. Smaers of the Department of Anthropology, Stony Brook University, New York, USA and Chet C. Sherwood of the Center for the Advanced Study of Human Paleobiology, Department of Anthropology, The George Washington University, Washington, DC, USA, is published open access in Nature Ecology & Evolution.
The research and its significance are explained in a UCL News release:
The study, published in Nature Ecology & Evolution, found that humans are born with brains at a development level that’s typical for similar primate species, but the human brains grow so much larger and more complex than other species after birth, it gives the false impression that human newborns are underdeveloped, or “altricial.”
One way that scientists compare the brain development of different species is by measuring the size of their brains as newborns to their brain size as adults. Humans are born with a relatively smaller percentage of their adult brain size, compared to other primates, making it seem they’re born less developed. However, this new research shows that this measure is misleading as other measurements of human brain development show humans are largely in line with other species of primates such as chimpanzees, bonobos, gorillas and orangutans.This new work changes the overall understanding around the evolution of human brain development. Humans seem so much more helpless when they’re young compared to other primates not because their brains are comparatively underdeveloped but because they still have much further to go.
Dr Aida Gomez-Robles, lead author
Department of Anthropology and Genetics, Evolution & Environment
University College, London, UK.
The research challenges a prevailing understanding of evolutionary human brain development. Up to now, because of their helplessness and poor muscle control, it’s long been believed that humans are born with comparatively less developed brains than other primates. This was thought to be the result of an evolutionary compromise so babies’ heads could fit through their mother’s birth canal, which would require them to further develop outside of the womb.
Based on this understanding, scientists suggested that because humans emerged comparatively underdeveloped, their brains are more malleable in the earliest period of life and more easily affected by environmental stimuli as they grow. It was thought that this underdevelopment at birth encouraged greater brain plasticity, ultimately facilitating human intelligence.
Instead, the researchers found that while human brains do take longer than other species to grow to full capacity, it’s not because they come out significantly less developed at birth, but because their brains grow so much more later in life. The researchers added that their findings don’t negate the importance of brain plasticity in human evolution but make it unlikely that this enhanced plasticity resulted from being born less developed than other primates.
To understand the evolutionary development of human brains, the researchers analysed the brain development of 140 different mammal species including modern primates, rodents, carnivores, as well as the fossils of early humans and related ancestral hominins. They compared the length of foetal gestation in modern mammals, the relative size of newborn brains and bodies to their adult size, and the overall brain size of newborns and adults to understand the evolution of human brains.
They found that while there are major variations in brain development at birth between disparate mammal species, primates are relatively consistent with each other. Humans are not born at significantly lower levels of development than modern primates, nor their hominin ancestors. Similarly, human gestation period is not shorter than it would be expected when compared to other primates.
AbstractSo, absolutely no doubt there then that humans are apes and that the difference between humans and the other apes is due to evolution. And then there is the example of something else creationists are unfamiliar with and find incomprehensible - scientists changing their minds - in this case about a small detail of human development in comparison with the other apes.
Human newborns are considered altricial compared with other primates because they are relatively underdeveloped at birth. However, in a broader comparative context, other mammals are more altricial than humans. It has been proposed that altricial development evolved secondarily in humans due to obstetrical or metabolic constraints, and in association with increased brain plasticity. To explore this association, we used comparative data from 140 placental mammals to measure how altriciality evolved in humans and other species. We also estimated how changes in brain size and gestation length influenced the timing of neurodevelopment during hominin evolution. Based on our data, humans show the highest evolutionary rate to become more altricial (measured as the proportion of adult brain size at birth) across all placental mammals, but this results primarily from the pronounced postnatal enlargement of brain size rather than neonatal changes. In addition, we show that only a small number of neurodevelopmental events were shifted to the postnatal period during hominin evolution, and that they were primarily related to the myelination of certain brain pathways. These results indicate that the perception of human altriciality is mostly driven by postnatal changes, and they point to a possible association between the timing of myelination and human neuroplasticity.
Fig. 1: Phylogeny and brain and body proportion values.
a, Phylogeny highlighting the four best-represented orders of mammals studied in the different analyses (artiodactyls in dark orange, carnivorans in blue, primates in green, rodents in light orange, others in grey). b, Comparison of body proportions at birth (percentage of maternal body size at birth) across the four orders of mammals. c, Comparison of brain proportions at birth (percentage of adult brain size at birth) across the four orders of mammals. d, Mammalian phylogeny highlighting the clades whose species have a particularly large absolute adult brain size (perissodactyls in yellow, cetaceans in maroon, pinnipeds and bears in dark blue, hominids in dark green, elephants in purple). e, Comparison of body proportions at birth across the five groups of mammals with large brain sizes. f, Comparison of brain proportions at birth across the five groups of mammals with large brain sizes. Artio, artiodactyls (n = 26 species); Carn, carnivorans (n = 21 species); Prim, primates (n = 44 species); Rod, rodents (n = 24 species); Periss, perissodactyls (n = 5 species); Cet, cetaceans (n = 6 species); P&B, pinnipeds and bears (n = 8 species); Hom, hominids (n = 5 species); Eleph, elephants (n = 2 species). Raincloud plots show individual datapoints, probability density distributions and summary statistics in the box plots (median as the thick horizontal line, interquartile range within the box, minimum and maximum as the lower and upper whiskers, and outliers as black circles). Silhouettes are all from https://www.phylopic.org and are not to scale.
Fig. 2: Branch-specific evolutionary rates across the mammalian phylogeny.
a, Brain proportion at birth. b, Body proportion at birth. c, Adult brain size. d, Neonatal brain size. e, Gestation length. f, Comparison of the distribution of evolutionary rates for each trait across the mammalian phylogeny with the human rate (dark green dashed line). The layout of the plots in f is the same as in the general figure. For branch colours, yellow indicates fast rates to decrease the value of the trait under study, blue indicates high rates to increase the value of the traits and grey indicates low rates. Nodes are represented in white and tips are represented in black, with tip/node size proportional to the trait value within each phylogeny. Species names are colour-coded according to their order as in Fig. 1a, with humans highlighted in dark green. Silhouettes are all from https://www.phylopic.org.
Gómez-Robles, A., Nicolaou, C., Smaers, J.B. & Sherwood, C.C.
The evolution of human altriciality and brain development in comparative context.
Nat Ecol Evol (2023). https://doi.org/10.1038/s41559-023-02253-z
Copyright: © 2023 The authors.
Published by Springer Nature Ltd. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
All in all, another dreadful day for creationists and their childish cult.
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