Were the Neanderthals too few in number to have evolved? Does new hominid evidence point to special creation?
Factors Affecting Evolution
For terrestrial mammals, there are four important factors that determine whether a species will experience recognizable evolution in its morphology before it goes extinct. These are population size, population density, average adult body mass, and generation time.1 Morphology refers to the structure, shape, size, organization, and development of the bodies and organs of individuals comprising a species. Generation time refers to time between the birth of an individual within a species and when that individual would typically reproduce. Population density is the number of individuals per unit area. The probability of a mammal species going extinct before any significant change in morphology occurs rises as the population size drops, the population density drops, the average adult body size increases, and the generation time lengthens.
Conservation field studies on mammals reveal that of the four factors the most significant is the effective population size of the species, which is the total number of individuals within a species that are able to reproduce. However, if the effective population is so widely dispersed that subgroups within the species have no contact with one another, then the extinction-determining factor is the effective population of the largest subgroup.2
Low Neanderthal Population Size
Neanderthals lived across southern and central Europe and in southwestern Asia from ~400,000 until 40,200 years ago.3 Analysis of recovered Neanderthal DNA, fossils, and tools and artifacts attributed to Neanderthals independently yield estimates of Neanderthals’ maximum population sizes throughout their existence.4 These estimates range from 1,000 to 70,000 individuals.5
Estimates above 10,000 are based on the number of tools and artifacts discovered. These estimates, however, assume all the tools and artifacts were manufactured by Neanderthals. They also assume the sample size of recovered tools and artifacts is largely incomplete.
Most of the tools and artifacts have been found in or near caves. If Neanderthals lived in small, isolated groups and sought caves for shelter, the sample size of recovered tools and artifacts may be more complete than estimated. Also, many of the “tools and artifacts” may have been natural, not manufactured at all. Some may, in fact, have been made by modern humans. Therefore, the estimates based on tools and artifacts are overestimates.
Analysis of Neanderthal DNA shows pervasive inbreeding, Allee effects (diminished cooperative hunting and tool manufacture; random, large variations in sex ratios that make finding a mate difficult), and stochasticity (chance environmental catastrophes).6 Such inbreeding, Allee effects, and stochasticity indicate the total Neanderthal population rarely exceeded 10,000 individuals and never exceeded 15,000 individuals. Furthermore, it reveals that these individuals must have been divided into small, isolated, inbred groups that were widely separated from one another.7
A measure of the degree of inbreeding occurring among Neanderthals and Denisovans (a hominid that is thought to have diverged from Neanderthals) is their low level of heterozygosity. For both species only 2 of every 10,000 nucleotides differ between two copies of a chromosome. Such low heterozygosity implies effective population sizes (number of individuals capable of breeding) of no greater than 5,000 individuals.8
Evidence indicates Neanderthals’ effective population remained low throughout their ~360,000-year history. As shown by a team of 18 geneticists and anthropologists, “Patterns of mtDNA protein evolution are consistent with the notion that the effective population size of Neandertals was small and not only among late Neanderthals but over a longer period of their existence.”9
Neanderthal Habitat Range
Anthropologists have discovered Neanderthal fossils ranging from Britain to Gibraltar to Siberia and to Mesopotamia. Neanderthals’ habitat encompassed about 26 million square kilometers (10 million square miles), which translates to a population density of only 0.0002 individuals per square kilometer (0.0005 per square mile)! For comparison, the least densely populated independent nation today, Mongolia, has 2.07 humans per square kilometer (5.4 humans per square mile).
Implications of Low Long-Term Population Size
There is no reliable DNA data for hominid species predating Neanderthals and Denisovans. Nonetheless, the fossils and artifacts attributable to them indicate their effective population sizes were likely even smaller than they were for Neanderthals and Denisovans.
As noted, the probability for evolutionary change within a species is proportional to the species’ long-term effective population size and inversely proportional to the species’ average adult body mass and average generation time. With long-term effective population sizes less than 10,000, with body sizes in the tens of kilograms, and with generation times of several years, there is no natural possibility for premodern human or hominid species to experience any significant change (evolution) in their morphologies or genomes before going extinct. These outcomes are affirmed by the lack of any observable changes in the fossils of these species. For example, the oldest Neanderthal fossils look the same as the most recent. Likewise, the oldest Homo erectus fossils look the same as the most recent.
According to the Bible, the human species began with just two individuals, Adam and Eve. It is probable, however, that God created Eve with genetically diverse eggs. Therefore, inbreeding would not have been a problem for the first several generations of Adam and Eve’s offspring. Unlike the Neanderthals, Denisovans, and earlier hominid species, the human population multiplied quickly. Humanity’s long-term effective population grew into the millions and now into the billions. Hence, humans, at least so far, have escaped the extinction crises that plagued the preceding bipedal primate species.
Given that the hominid species predating modern humans were incapable of manifesting any significant natural evolution, the hypothesis that modern humans, Neanderthals, Denisovans, Homo erectus, and the other hominid species are descended from a common ancestor is no longer scientifically viable. They must all be the product of special creation.
J. P. Hilbers et al., “An Allometric Approach to Quantify the Extinction Vulnerability of Birds and Mammals,” Ecology 97, no. 3 (March 2016): 615–626, doi:10.1890/14-2019.1.Elise Eller, John Hawks, and John H. Relethford, “Local Extinction and Recolonization, Species Effective Population Size, and Modern Human Origins,” Human Biology 76, no. 5 (October 2004): 689–709, doi:10.1353/hub.2005.0006.Wil Roebroeks and Marie Soressi, “Neandertals Revised,” Proceedings of the National Academy of Sciences, USA 113, no. 23 (June 6, 2016): 6372–6379, doi:10.1073/pnas.1521269113.Kay Prüfer et al., “The Complete Genome Sequence of a Neanderthal from the Altai Mountains,” Nature 505, no. 7481 (January 2, 2014): 43–49, doi:10.1038/nature12886; Fabrizio Mafessoni and Kay Prüfer, “Better Support for a Small Effective Population Size of Neandertals and a Long Shared History of Neandertals and Denisovans,” Proceedings of the National Academy of Sciences, USA 114, no. 48 (November 28, 2017): E10256–E10257, doi:10.1073/pnas.1716918114; Jean-Pierre Bocquet-Appel and Anna Degioanni, “Neanderthal Demographic Estimates,” Current Anthropology 54, no. S8 (December 2013): S202–S213, doi:10.1086/673725.Bocquet-Appel and Degioanni, “Neanderthal Demographic Estimates”; Mafessoni and Prüfer, “Better Support for a Small Effective Population.”Krist Vaesen et al., “Inbreeding, Allee Effects and Stochasticity Might Be Sufficient to Account for Neanderthal Extinction,” PLoS One 14, no. 11 (November 27, 2019): id. e0225117, doi:10.1371/journal.pone.0225117; Prüfer et al., “The Complete Genome Sequence.”Mafessoni and Prüfer, “Better Support”; Krist Vaesen, Gerrit L. Dusseldorp, and Mark J. Brandt, “An Emerging Consensus in Palaeoanthropology: Demography was the Main Factor Responsible for the Disappearance of Neanderthals,” Scientific Reports 11, no. 1 (March 1, 2021): id. 4925, doi:10.1038/s41598-021-84410-7; Frederico Sánchez-Quinto and Carles Lalueza-Fox, “Almost 20 Years of Neanderthal Palaeogenetics: Adaptation, Admixture, Diversity, Demography and Extinction,” Philosophical Transactions of the Royal Society B: Biological Sciences 370, no. 1660 (January 19, 2015): id. 1660, doi:10.1098/rstb.2013.0374.Mafessoni and Prüfer, “Better Support.”Adrian W. Briggs et al., “Targeted Retrieval and Analysis of Five Neandertal mtDNA Genomes,” Science 325, no. 5938 (July 17, 2009): 318–321, doi:10.1126/science.1174462.
The post Neanderthal Population Size Nixes Evolution appeared first on Reasons to Believe.
Leave a Reply