Collaborative Research: Human Evolution, Rift Valley Environments and Orbitally Forced Climate Change

探索人类进化的过程超出了早期人类化石的发现和描述。为了理解导致直立行走、大大脑、工具制造和使用以及行为灵活性等关键人类特征的进化过程，有必要为这些创新开发一个背景。是什么环境力量塑造和指导了人类的进化？人类进化是早期原始人与其物理和生物环境相互作用的结果，有必要根据原始人的发现具体重建这些参数。然而，在陆地记录的相关尺度上记录古环境并发展进化与环境变化之间的因果关系仍然很困难。因此，人类进化的各个方面已经在海洋记录的环境数据的背景下得到了解释，海洋记录提供了大规模气候变化的详细记录。这种方法只有在全球或区域现象与当地人类生态系统的具体变化之间的联系能够得到证明的情况下才有效。本提案旨在通过研究一系列环境指标来直接解决这些问题，从而为东非大裂谷的一个有人类的序列开发一个高分辨率的古环境框架。这可以与全球气候变化联系起来。这项工作的重点是在肯尼亚巴林戈湖附近的裂谷内的一个断层块图根山暴露的200万至300万年前的沉积序列。这个序列显示了主要淡水湖系统的突然和重复循环，反映了波动的气候条件。在最近的研究中，该项目已经在这些短期振荡（每2.3万年一次）和米兰科维奇周期之间建立了明确的联系。米兰科维奇周期是由大气顶部接收到的太阳辐射的变化引起的，受地球轨道几何形状的变化控制。这些变化代表了地球气候系统的主要驱动力，包括冰期-间冰期旋回。包括三个原始人遗址在内的36个脊椎动物化石地点可以直接与这一序列联系起来，这为建立动物和植被对这些短期变化的反应模式提供了机会。这项研究是首次尝试开发多种环境和生态指标，这些指标可以直接与陆地裂谷背景下的米兰科维奇循环联系起来。这些数据将被用来深入了解过去600万年非洲人类生态系统对这些普遍存在的气候波动的进化反应。虽然这些数据与Baringo盆地的原始人类化石及其脊椎动物群落直接相关，但将当地生态变化与轨道强迫日照模式联系起来，为推断过去区域气候振荡对陆地生态系统的影响提供了前景。有了这些数据，我们可以开始制定高分辨率模型来解释气候与人类进化之间的相关性，并阐明环境变化在哺乳动物进化和人类进化中作为潜在驱动力的作用。这项研究将促进高度跨学科和合作的研究，对于发展进化和生态学之间多维联系的观点至关重要。这里概述的项目代表了一个理想的论坛，在这个论坛中，可以产生和整合跨越传统上不同学科的研究思想。这项研究将扩大机会，使肯尼亚国家博物馆的研究生和研究人员能够参与。

Exploring the course of human evolution extends beyond the discovery and description of the fossils of early humans. To understand the evolutionary processes that led to key human features such as upright walking, a large brain, tool manufacture and use, and behavioral flexibility, it is necessary to develop a context for these innovations. What were the environmental forces that shaped and directed human evolution? Human evolution is a consequence of the interactions of early hominids with their physical and biological surroundings and there is a need to specifically reconstruct these parameters in association with discoveries of hominids. Documenting paleoenvironments at a relevant scale in the terrestrial record and developing causal links between evolution and environmental change, however, remains difficult. As a result, aspects of human evolution have been interpreted in the context of environmental data from the marine record, which provide a detailed record of large scale climatic change. This approach is valid only if links between global or regional phenomena and specific shifts in local hominid ecosystems can be demonstrated.This proposal seeks to address directly these issues by examining a series of environmental indicators to develop a high-resolution paleoenvironmental framework for a hominid-bearing sequence in the East African Rift Valley. This can then be linked to global climate changes. The work has at its focus a 2-3 million year old sedimentary sequence exposed in the Tugen Hills, a fault block within the rift valley near Lake Baringo in Kenya. This sequence exhibits abrupt and repeated cycling of major freshwater lake systems reflecting fluctuating climatic conditions. In recent research, this project has established a clear link between these short term oscillations (every 23 thousand yrs) and Milankovitch cycles that result from variations in the solar radiation received at the top of the atmosphere, controlled by variations in the geometry of the earth''s orbit. These changes represent the major driving force in the earth climate system through time, including glacial-interglacial cycles. Thirty-six vertebrate fossil localities, including three hominid sites, can be linked directly to this sequence, providing an opportunity to establish patterns of response by animals and vegetation to these short term shifts. This research represents the first attempt to develop multiple environmental and ecological indicators that can be linked directly to Milankovitch cycling in a terrestrial rift valley context. These data will be used to generate insights into the evolutionary response of hominid ecosystems to these pervasive climatic oscillations over the last six million years in Africa. While these data relate directly to fossil hominids and their vertebrate communities in the Baringo Basin, linking local ecological shifts with orbitally-forced patterns of insolation affords the prospect of extrapolating the affects of climatic oscillations on terrestrial ecosystems regionally in the past. With these data, we can begin to formulate high-resolution models for interpreting correlations between climate and human evolution, and elucidate the role of environmental change as a potential driving force in mammalian evolution in general and human evolution in particular. This research will foster highly interdisciplinary and collaborative studies, essential in developing perspectives of the multi-dimensional links between evolution and ecology. The project outlined here represents an ideal forum in which to generate and integrate research ideas cutting across traditionally disparate academic disciplines. The study will broaden opportunities and enable the participation of graduate students as well as research personnel from the National Museums of Kenya.