 በእንስሳ እና በአካባቢያዊ ዝግመተ ለውጥ መካከል ቀጥተኛ መንስኤ እና ውጤት ግንኙነቶች ከባድ ክርክር ቢሆኑም ፣ እነዚህ ሁሉ ጥናቶች የመጀመሪያዎቹ እንስሳዎች ብቅ ካሉበት የኦክስጂን ጭማሪ ጋር ቀጥተኛ የሆነ መረጃ ባለመገኘታቸው ተቋርጠዋል።
While the direct cause-and-effect relationships between animal and environmental evolution remain topics of intense debate, all this research has been hampered by the lack of direct evidence for an oxygen increase coincident with the appearance of the earliest animals - until now.