SPANXB (SPANX family, member B)

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True   Likely   Speculative
Human Uniqueness Compared to "Great Apes": 
Likely Difference
Human Universality: 
Individual Universal (All Individuals Everywhere)
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Sperm protein associated with the nucleus, X-linked, family member B (SPANX-B) is a protein of unknown function that is expressed in human testis, sperm, and multiple types of cancers. SPANX-B has a human lineage specific 18-nucleotide exonic insertion and has undergone positive selection. The implications of these changes are not understood, but could have impacted human reproduction.


Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event. The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in 2017 as:

  • the Last Common Ancestor (LCA) of humans and old world monkeys was 25,000 - 30,000 thousand (25 - 30 million) years ago
  • the Last Common Ancestor (LCA) of humans and chimpanzees was 6,000 - 8,000 thousand (6 - 8 million) years ago
  • the emergence of the genus Homo was 2,000 thousand (2 million) years ago
  • the Last Common Ancestor (LCA) of humans and neanderthals was 500 thousand years ago
  • the common ancestor of modern humans was 100 - 300 thousand years ago

Definite Appearance (Lineage Separation Event): 
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Genetics Topic Attributes
Gene symbols follow the HUGO Gene Nomenclature Committee standard.
Type of Human-Specific Changes
Accelerated Evolution, Amino Acid Change


  1. The SPANX gene family of cancer/testis-specific antigens: rapid evolution and amplification in African great apes and hominids., Kouprina, Natalay, Mullokandov Michael, Rogozin Igor B., N Collins Keith, Solomon Greg, Otstot John, Risinger John I., Koonin Eugene V., J Barrett Carl, and Larionov Vladimir , Proc Natl Acad Sci U S A, 2004 Mar 2, Volume 101, Issue 9, p.3077-82, (2004)